Simon R Bare

All Publications

• Selective chemical looping combustion of acetylene in ethylene-rich streams. Science (New York, N.Y.) Jacob, M., Nguyen, H., Raj, R., Garcia-Barriocanal, J., Hong, J., Perez-Aguilar, J. E., Hoffman, A. S., Mkhoyan, K. A., Bare, S. R., Neurock, M., Bhan, A. 2025; 387 (6735): 744-749

  Abstract

  The requirement for C2H2 concentrations below 2 parts per million (ppm) in gas streams for C2H4 polymerization necessitates its semihydrogenation to C2H4. We demonstrate selective chemical looping combustion of C2H2 in C2H4-rich streams by Bi2O3 as an alternative catalytic pathway to reduce C2H2 concentration below 2 ppm. Bi2O3 combusts C2H2 with a first-order rate constant that is 3000 times greater than the rate constant for C2H4 combustion. In successive redox cycles, the lattice O of Bi2O3 can be fully replenished without discernible changes in local Bi coordination or C2H2 combustion selectivity. Heterolytic activation of C-H bonds across Bi-O sites and the higher acidity of C2H2 results in lower barriers for C2H2 activation than C2H4, enabling selective catalytic hydrocarbon combustion leveraging differences in molecular deprotonation energies.

  View details for DOI 10.1126/science.ads3181

  View details for PubMedID 39946462

• Quantifying the Site Heterogeneities of Non-Uniform Catalysts Using QuantEXAFS CHEMISTRYMETHODS Rana, R., Hong, J., Hoffman, A. S., Werghi, B., Bare, S. R., Kulkarni, A. R. 2024

  View details for DOI 10.1002/cmtd.202400020

  View details for Web of Science ID 001359781700001

• A US perspective on closing the carbon cycle to defossilize difficult-to-electrify segments of our economy. Nature reviews. Chemistry Shaw, W. J., Kidder, M. K., Bare, S. R., Delferro, M., Morris, J. R., Toma, F. M., Senanayake, S. D., Autrey, T., Biddinger, E. J., Boettcher, S., Bowden, M. E., Britt, P. F., Brown, R. C., Bullock, R. M., Chen, J. G., Daniel, C., Dorhout, P. K., Efroymson, R. A., Gaffney, K. J., Gagliardi, L., Harper, A. S., Heldebrant, D. J., Luca, O. R., Lyubovsky, M., Male, J. L., Miller, D. J., Prozorov, T., Rallo, R., Rana, R., Rioux, R. M., Sadow, A. D., Schaidle, J. A., Schulte, L. A., Tarpeh, W. A., Vlachos, D. G., Vogt, B. D., Weber, R. S., Yang, J. Y., Arenholz, E., Helms, B. A., Huang, W., Jordahl, J. L., Karakaya, C., Kian, K. C., Kothandaraman, J., Lercher, J., Liu, P., Malhotra, D., Mueller, K. T., O'Brien, C. P., Palomino, R. M., Qi, L., Rodriguez, J. A., Rousseau, R., Russell, J. C., Sarazen, M. L., Sholl, D. S., Smith, E. A., Stevens, M. B., Surendranath, Y., Tassone, C. J., Tran, B., Tumas, W., Walton, K. S. 2024

  Abstract

  Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets.

  View details for DOI 10.1038/s41570-024-00587-1

  View details for PubMedID 38693313

  View details for PubMedCentralID 9652356

• Recommendations to standardize reporting, execution, and interpretation of X-ray Absorption Spectroscopy measurements JOURNAL OF CATALYSIS Meyer, R. J., Bare, S. R., Canning, G. A., Chen, J. G., Chu, P. M., Hock, A. S., Hoffman, A. S., Karim, A. M., Kelly, S. D., Lei, Y., Stavitski, E., Wrasman, C. J. 2024; 432

  View details for DOI 10.1016/j.jcat.2024.115369

  View details for Web of Science ID 001225600700001

• Tracking Active Phase Behavior on Boron Nitride during the Oxidative Dehydrogenation of Propane Using Operando X-ray Raman Spectroscopy. Journal of the American Chemical Society Cendejas, M. C., Paredes Mellone, O. A., Kurumbail, U., Zhang, Z., Jansen, J. H., Ibrahim, F., Dong, S., Vinson, J., Alexandrova, A. N., Sokaras, D., Bare, S. R., Hermans, I. 2023

  Abstract

  Hexagonal boron nitride (hBN) is a highly selective catalyst for the oxidative dehydrogenation of propane (ODHP) to propylene. Using a variety of ex situ characterization techniques, the activity of the catalyst has been attributed to the formation of an amorphous boron oxyhydroxide surface layer. The ODHP reaction mechanism proceeds via a combination of surface mediated and gas phase propagated radical reactions with the relative importance of both depending on the surface-to-void-volume ratio. Here we demonstrate the unique capability of operando X-ray Raman spectroscopy (XRS) to investigate the oxyfunctionalization of the catalyst under reaction conditions (1 mm outer diameter reactor, 500 to 550 °C, P = 30 kPa C3H8, 15 kPa O2, 56 kPa He). We probe the effect of a water cofeed on the surface of the activated catalyst and find that water removes boron oxyhydroxide from the surface, resulting in a lower reaction rate when the surface reaction dominates and an enhanced reaction rate when the gas phase contribution dominates. Computational description of the surface transformations at an atomic-level combined with high precision XRS spectra simulations with the OCEAN code rationalize the experimental observations. This work establishes XRS as a powerful technique for the investigation of light element-containing catalysts under working conditions.

  View details for DOI 10.1021/jacs.3c08679

  View details for PubMedID 37931025

• CatMass: software for calculating optimal sample masses for X-ray absorption spectroscopy experiments involving complex sample compositions. Journal of synchrotron radiation Perez-Aguilar, J. E., Caine, A., Bare, S. R., Hoffman, A. S. 2023

  Abstract

  This paper presents software for calculating the optimal mass of samples with complex compositions (e.g. supported metal catalysts) for X-ray absorption spectroscopy (XAS) and scattering measurements. The ability to calculate the sample mass and other relevant parameters needed for an XAS measurement allows experimentalists to be better prepared in terms of detector selection, energy range of scan and overall time needed to complete the measurement, thus increasing efficiency. CatMass builds on existing sample mass calculators allowing users to determine the optimum sample preparation, collection geometry, usable energy range for a scan and approximate edge step of the absorption event. Visualization tools present the absorption calculation results in a format familiar to XAS experimentalists, with the added ability to save calculations and plots for future reference or recalculation. CatMass is a program broadly applicable in catalysis and is helpful for users with complex samples due to composition/stoichiometry or multiple competing elements.

  View details for DOI 10.1107/S160057752300615X

  View details for PubMedID 37594862

• Bridging the Gap between the X-ray Absorption Spectroscopy and the Computational Catalysis Communities in Heterogeneous Catalysis: A Perspective on the Current and Future Research Directions ACS CATALYSIS Rana, R., Vila, F. D., Kulkarni, A. R., Bare, S. R. 2022; 12 (22): 13813-13830

  View details for DOI 10.1021/acscatal.2c03863

  View details for Web of Science ID 000898440900001

• A Theory-Guided X-ray Absorption Spectroscopy Approach for Identifying Active Sites in Atomically Dispersed Transition-Metal Catalysts. Journal of the American Chemical Society Chen, Y., Rana, R., Sours, T., Vila, F. D., Cao, S., Blum, T., Hong, J., Hoffman, A. S., Fang, C., Huang, Z., Shang, C., Wang, C., Zeng, J., Chi, M., Kronawitter, C. X., Bare, S. R., Gates, B. C., Kulkarni, A. R. 2021

  Abstract

  Atomically dispersed supported metal catalysts offer new properties and the benefits of maximized metal accessibility and utilization. The characterization of these materials, however, remains challenging. Using atomically dispersed platinum supported on crystalline MgO (chosen for its well-defined bonding sites) as a prototypical example, we demonstrate how systematic density functional theory calculations for assessing all the potentially stable platinum sites, combined with automated analysis of extended X-ray absorption fine structure (EXAFS) spectra, leads to unbiased identification of isolated, surface-enveloped platinum cations as the catalytic species for CO oxidation. The catalyst has been characterized by atomic-resolution imaging and EXAFS and high-energy resolution fluorescence detection X-ray absorption near edge spectroscopy. The proposed platinum sites are in agreement with experiment. This theory-guided workflow leads to rigorously determined structural models and provides a more detailed picture of the structure of the catalytically active site than what is currently possible with conventional EXAFS analyses. As this approach is efficient and agnostic to the metal, support, and catalytic reaction, we posit that it will be of broad interest to the materials characterization and catalysis communities.

  View details for DOI 10.1021/jacs.1c07116

  View details for PubMedID 34806881

• Low-Temperature Restructuring of CeO2-Supported Ru Nanoparticles Determines Selectivity in CO2 Catalytic Reduction. Journal of the American Chemical Society Aitbekova, A. n., Wu, L. n., Wrasman, C. J., Boubnov, A. n., Hoffman, A. S., Goodman, E. D., Bare, S. R., Cargnello, M. n. 2018; 140 (42): 13736–45

  Abstract

  CO2 reduction to higher value products is a promising way to produce fuels and key chemical building blocks while reducing CO2 emissions. The reaction at atmospheric pressure mainly yields CH4 via methanation and CO via the reverse water-gas shift (RWGS) reaction. Describing catalyst features that control the selectivity of these two pathways is important to determine the formation of specific products. At the same time, identification of morphological changes occurring to catalysts under reaction conditions can be crucial to tune their catalytic performance. In this contribution we investigate the dependency of selectivity for CO2 reduction on the size of Ru nanoparticles (NPs) and on support. We find that even at rather low temperatures (210 °C), oxidative pretreatment induces redispersion of Ru NPs supported on CeO2 and leads to a complete switch in the performance of this material from a well-known selective methanation catalyst to an active and selective RWGS catalyst. By utilizing in situ X-ray absorption spectroscopy, we demonstrate that the low-temperature redispersion process occurs via decomposition of the metal oxide phase with size-dependent kinetics, producing stable single-site RuO x/CeO2 species strongly bound to the CeO2 support that are remarkably selective for CO production. These results show that reaction selectivity can be heavily dependent on catalyst structure and that structural changes of the catalyst can occur even at low temperatures and can go unseen in materials with less defined structures.

  View details for PubMedID 30252458

• Advanced EXAFS analysis techniques applied to theL-edges of the lanthanide oxides. Journal of applied crystallography Smerigan, A., Hoffman, A. S., Ostervold, L., Hong, J., Perez-Aguillar, J., Caine, A. C., Greenlee, L., Bare, S. R. 2024; 57 (Pt 6): 1913-1923

  Abstract

  The unique properties of the lanthanide (Ln) elements make them critical components of modern technologies, such as lasers, anti-corrosive films and catalysts. Thus, there is significant interest in establishing structure-property relationships for Ln-containing materials to advance these technologies. Extended X-ray absorption fine structure (EXAFS) is an excellent technique for this task considering its ability to determine the average local structure around the Ln atoms for both crystalline and amorphous materials. However, the limited availability of EXAFS reference spectra of the Ln oxides and challenges in the EXAFS analysis have hindered the application of this technique to these elements. The challenges include the limited k-range available for the analysis due to the superposition of L-edges on the EXAFS, multielectron excitations (MEEs) creating erroneous peaks in the EXAFS and the presence of inequivalent absorption sites. Herein, we removed MEEs to model the local atomic environment more accurately for light Ln oxides. Further, we investigated the use of cubic and non-cubic lattice expansion to minimize the fitting parameters needed and connect the fitting parameters to physically meaningful crystal parameters. The cubic expansion reduced the number of fitting parameters but resulted in a statistically worse fit. The non-cubic expansion resulted in a similar quality fit and showed non-isotropic expansion in the crystal lattice of Nd2O3. In total, the EXAFS spectra and the fits for the entire set of Ln oxides (excluding promethium) are included. The knowledge developed here can assist in the structural determination of a wide variety of Ln compounds and can further studies on their structure-property relationships.

  View details for DOI 10.1107/S1600576724010240

  View details for PubMedID 39628878

• Dynamic Behavior of Pt Multimetallic Alloys for Active and Stable Propane Dehydrogenation Catalysts. Journal of the American Chemical Society Werghi, B., Saini, S., Chung, P. H., Kumar, A., Ebrahim, A. M., Abels, K., Chi, M., Abild-Pedersen, F., Bare, S. R., Cargnello, M. 2024

  Abstract

  Improving the use of platinum in propane dehydrogenation catalysts is a crucial aspect to increasing the efficiency and sustainability of propylene production. A known and practiced strategy involves incorporating more abundant metals in supported platinum catalysts, increasing its activity and stability while decreasing the overall loading. Here, using colloidal techniques to control the size and composition of the active phase, we show that Pt/Cu alloy nanoparticles supported on alumina (Pt/Cu/Al2O3) displayed elevated rates for propane dehydrogenation at low temperature compared to a monometallic Pt/Al2O3 catalyst. We demonstrate that the enhanced catalytic activity is correlated with a higher surface Cu content and formation of a Pt-rich core and Cu-rich shell that isolates Pt sites and increases their intrinsic activity. However, rates declined on stream because of dynamic metal diffusion processes that led to a more uniform alloy structure. This transformation was only partially inhibited by adding excess hydrogen to the feed stream. Instead, cobalt was introduced to provide trimetallic Pt/Cu/Co catalysts with stabilized surface structure and stable activity and higher rates than the original Pt/Cu system. The structure-activity relationship insights in this work offer improved knowledge of propane dehydrogenation catalyst development featuring reduced Pt loadings and notable thermal stability for propylene production.

  View details for DOI 10.1021/jacs.4c09424

  View details for PubMedID 39475575

• Metal-support interactions in metal oxide-supported atomic, cluster, and nanoparticle catalysis CHEMICAL SOCIETY REVIEWS Leybo, D., Etim, U. J., Monai, M., Bare, S. R., Zhong, Z., Vogt, C. 2024; 53 (21): 10450-10490

  Abstract

  Supported metal catalysts are essential to a plethora of processes in the chemical industry. The overall performance of these catalysts depends strongly on the interaction of adsorbates at the atomic level, which can be manipulated and controlled by the different constituents of the active material (i.e., support and active metal). The description of catalyst activity and the relationship between active constituent and the support, or metal-support interactions (MSI), in heterogeneous (thermo)catalysts is a complex phenomenon with multivariate (dependent and independent) contributions that are difficult to disentangle, both experimentally and theoretically. So-called "strong metal-support interactions" have been reported for several decades and summarized in excellent review articles. However, in recent years, there has been a proliferation of new findings related to atomically dispersed metal sites, metal oxide defects, and, for example, the generation and evolution of MSI under reaction conditions, which has led to the designation of (sub)classifications of MSI deserving to be critically and systematically evaluated. These include dynamic restructuring under alternating redox and reaction conditions, adsorbate-induced MSI, and evidence of strong interactions in oxide-supported metal oxide catalysts. Here, we review recent literature on MSI in oxide-supported metal particles to provide an up-to-date understanding of the underlying physicochemical principles that dominate the observed effects in supported metal atomic, cluster, and nanoparticle catalysts. Critical evaluation of different subclassifications of MSI is provided, along with discussions on the formation mechanisms, theoretical and characterization advances, and tuning strategies to manipulate catalytic reaction performance. We also provide a perspective on the future of the field, and we discuss the analysis of different MSI effects on catalysis quantitatively.

  View details for DOI 10.1039/d4cs00527a

  View details for Web of Science ID 001324258700001

  View details for PubMedID 39356078

  View details for PubMedCentralID PMC11445804

• Synthesis of Amorphous and Various Phase-Pure Nanoparticles of Nickel Phosphide with Uniform Sizes via a Trioctylphosphine-Mediated Pathway. Inorganic chemistry Thompson, D., Hoffman, A. S., Mansley, Z., York, S., Wang, F., Zhu, Y., Bare, S. R., Chen, J. 2024

  Abstract

  Nickel phosphides are of particular interest because they are highly active and stable catalysts for petroleum/biorefinery and hydrogen production. Despite their significant catalytic potential, synthesizing various phase-pure nickel phosphide nanoparticles of uniform size remains a challenge. In this work, we develop a robust trioctylphosphine (TOP)-mediated route to make highly uniform phase-pure Ni12P5, Ni2P, and Ni5P4 nanoparticles. The synthetic route forms amorphous Ni70P30 nanoparticle intermediates. The reactions can be stopped at the amorphous stage when amorphous particles are desired. The amount of P incorporation can be controlled by varying the ratio of TOP to Ni(II). The mechanism for composition control involves the competition of the kinetics of two processes: the addition of the reduced Ni and the incorporation of P into Ni. Uniform Ni70P30 amorphous nanoparticles can be generated at a high TOP-to-Ni(II) ratio, where the P incorporation kinetics is made to dominate. Ni70P30 can later be transformed into phase-pure Ni12P5, Ni2P, and Ni5P4 nanocrystals of uniform size. The transformation can be controlled precisely by modulating the temperature. A UV-vis study coupled with theoretical modeling reveals Ni(0)-TOPx complexes along the synthetic path. This approach may be expanded to create other metal compounds, potentially enabling the synthesis of uniform nanoparticles of a greater variety.

  View details for DOI 10.1021/acs.inorgchem.4c03334

  View details for PubMedID 39328180

• Steam-Assisted Selective CO2 Hydrogenation to Ethanol over Ru-In Catalysts. Angewandte Chemie (International ed. in English) Zhou, C., Aitbekova, A., Liccardo, G., Oh, J., Stone, M., McShane, E. J., Werghi, B., Nathan, S., Song, C., Ciston, J., Bustillo, K., Hoffman, A. S., Hong, J., Perez-Aguilar, J., Bare, S., Cargnello, M. 2024: e202406761

  Abstract

  Multicomponent catalysts can be designed to synergistically combine reaction intermediates at interfacial active sites, but restructuring makes systematic control and understanding of such dynamics challenging. We here unveil how reducibility and mobility of indium oxide species in Ru-based catalysts crucially control the direct, selective conversion of CO2 to ethanol. When uncontrolled, reduced indium oxide species occupy the Ru surface, leading to deactivation. With the addition of steam as a mild oxidant and using porous polymer layers to control In mobility, Ru-In2O3 interface sites are stabilized, and ethanol can be produced with superior overall selectivity (70%, rest CO). Our work highlights how engineering of bifunctional active ensembles enables cooperativity and synergy at tailored interfaces, which unlocks unprecedented performance in heterogeneous catalysts.

  View details for DOI 10.1002/anie.202406761

  View details for PubMedID 38990707

• Understanding and Harnessing Nanoscale Immiscibility in Ru-In Alloys for Selective CO2 Hydrogenation. Journal of the American Chemical Society Zhou, C., Liccardo, G., Hoffman, A. S., Oh, J., Holmes, S. E., Vailionis, A., Bare, S. R., Cargnello, M. 2024

  Abstract

  Bimetallic alloys made from immiscible elements are characterized by their tendency to segregate on the macroscopic scale, but their behavior is known to change at the nanoscale. Here, we demonstrate that in the Ru-In system, In atoms preferentially decorate the surface of 6 nm Ru nanoparticles, forming Ru-In superficial immiscible alloys. This surface decoration dramatically affects the catalytic performance of the system, even at small atomic fractions of In added to Ru. The interfaces between Ru and In enabled unexplored methanol productivity from CO2 hydrogenation, which outperformed not only the individual constituents but also ordered RuIn3 intermetallic alloys. Our work highlights that the formation of superficial immiscible alloys could offer new insights into the understanding and design of heterogeneous catalysts.

  View details for DOI 10.1021/jacs.4c03652

  View details for PubMedID 38985019

• Revealing Structural Evolution of Nickel Phosphide-Iron Oxide Core-Shell Nanocatalysts in Alkaline Medium for the Oxygen Evolution Reaction. Chemistry of materials : a publication of the American Chemical Society Manso, R. H., Hong, J., Wang, W., Acharya, P., Hoffman, A. S., Tong, X., Wang, F., Greenlee, L. F., Zhu, Y., Bare, S. R., Chen, J. 2024; 36 (13): 6440-6453

  Abstract

  Metal phosphide-containing materials have emerged as a potential candidate of nonprecious metal-based catalysts for alkaline oxygen evolution reaction (OER). While it is known that metal phosphide undergoes structural evolution, considerable debate persists regarding the effects of dynamics on the surface activation and morphological stability of the catalysts. In this study, we synthesize NiP x -FeO x core-shell nanocatalysts with an amorphous NiP x core designed for enhanced OER activity. Using ex situ X-ray absorption spectroscopy, we elucidate the local structural changes as a function of the cyclic voltammetry cycles. Our studies suggest that the presence of corner-sharing octahedra in the FeO x shell improves structural rigidity through interlayer cross-linking, thereby inhibiting the diffusion of OH-/H2O. Thus, the FeO x shell preserves the amorphous NiP x core from rapid oxidation to Ni3(PO4)2 and Ni(OH)2. On the other hand, the incorporation of Ni from the core into the FeO x shell facilitates absorption of hydroxide ions for OER. As a result, Ni/Fe(OH) x at the surface oxidizes to the active γ-(oxy)hydroxide phase under the applied potentials, promoting OER. This intriguing synergistic behavior holds significance as such a synthetic route involving the FeO x shell can be extended to other systems, enabling manipulation of surface adsorption and diffusion of hydroxide ions. These findings also demonstrate that nanomaterials with core-shell morphologies can be tuned to leverage the strength of each metallic component for improved electrochemical activities.

  View details for DOI 10.1021/acs.chemmater.4c00379

  View details for PubMedID 39005533

  View details for PubMedCentralID PMC11238331

• Revealing Structural Evolution of Nickel Phosphide-Iron Oxide Core-Shell Nanocatalysts in Alkaline Medium for the Oxygen Evolution Reaction CHEMISTRY OF MATERIALS Manso, R. H., Hong, J., Wang, W., Acharya, P., Hoffman, A. S., Tong, X., Wang, F., Greenlee, L. F., Zhu, Y., Bare, S. R., Chen, J. 2024

  View details for DOI 10.1021/acs.chemmater.4c00379

  View details for Web of Science ID 001253461600001

• Site requirements for inhibition-free CO oxidation over silica-supported bimetallic PdCu alloys CATALYSIS SCIENCE & TECHNOLOGY Kristy, S., Svadlenak, S., Hoffmann, A. S., Bare, S. R., Goulas, K. A. 2024; 14 (14): 3956-3965

  View details for DOI 10.1039/d4cy00255e

  View details for Web of Science ID 001250827500001

• Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations. Chemical science Chen, Y., Rana, R., Zhang, Y., Hoffman, A. S., Huang, Z., Yang, B., Vila, F. D., Perez-Aguilar, J. E., Hong, J., Li, X., Zeng, J., Chi, M., Kronawitter, C. X., Wang, H., Bare, S. R., Kulkarni, A. R., Gates, B. C. 2024; 15 (17): 6454-6464

  Abstract

  Supported noble metal catalysts, ubiquitous in chemical technology, often undergo dynamic transformations between reduced and oxidized states-which influence the metal nuclearities, oxidation states, and catalytic properties. In this investigation, we report the results of in situ X-ray absorption spectroscopy, scanning transmission electron microscopy, and other physical characterization techniques, bolstered by density functional theory, to elucidate the structural transformations of a set of MgO-supported palladium catalysts under oxidative treatment conditions. As the calcination temperature increased, the as-synthesized supported metallic palladium nanoparticles underwent oxidation to form palladium oxides (at approximately 400 °C), which, at approximately 500 °C, were oxidatively fragmented to form mixtures of atomically dispersed palladium cations. The data indicate two distinct types of atomically dispersed species: palladium cations located at MgO steps and those embedded in the first subsurface layer of MgO. The former exhibit significantly higher (>500 times) catalytic activity for ethylene hydrogenation than the latter. The results pave the way for designing highly active and stable supported palladium hydrogenation catalysts with optimized metal utilization.

  View details for DOI 10.1039/d4sc00035h

  View details for PubMedID 38699272

  View details for PubMedCentralID PMC11062082

• A Versatile Electrochemical Cell for <i>Operando</i> XAS CHEMCATCHEM Ostervold, L., Hoffman, A. S., Thompson, D., Bare, S. R., Clark, E. 2024

  View details for DOI 10.1002/cctc.202400072

  View details for Web of Science ID 001216684600001

• Dynamic structural evolution of MgO-supported palladium catalysts: from metal to metal oxide nanoparticles to surface then subsurface atomically dispersed cations CHEMICAL SCIENCE Chen, Y., Rana, R., Zhang, Y., Hoffman, A. S., Huang, Z., Yang, B., Vila, F. D., Perez-Aguilar, J. E., Hong, J., Li, X., Zeng, J., Chi, M., Kronawitter, C. X., Wang, H., Bare, S. R., Kulkarni, A. R., Gates, B. C. 2024

  View details for DOI 10.1039/d4sc00035h

  View details for Web of Science ID 001196673200001

• Reduction of Cofed Carbon Dioxide Modifies the Local Coordination Environment of Zeolite-Supported, Atomically Dispersed Chromium to Promote Ethane Dehydrogenation. Journal of the American Chemical Society Zhou, W., Felvey, N., Guo, J., Hoffman, A. S., Bare, S. R., Kulkarni, A. R., Runnebaum, R. C., Kronawitter, C. X. 2024

  Abstract

  The reduction of CO2 is known to promote increased alkene yields from alkane dehydrogenations when the reactions are cocatalyzed. The mechanism of this promotion is not understood in the context of catalyst active-site environments because CO2 is amphoteric, and even general aspects of the chemistry, including the significance of competing side reactions, differ significantly across catalysts. Atomically dispersed chromium cations stabilized in highly siliceous MFI zeolite are shown here to enable the study of the role of parallel CO2 reduction during ethylene-selective ethane dehydrogenation. Based on infrared spectroscopy and X-ray absorption spectroscopy data interpreted through calculations using density functional theory (DFT), the synthesized catalyst contains atomically dispersed Cr cations stabilized by silanol nests in micropores. Reactor studies show that cofeeding CO2 increases stable ethylene-selective ethane dehydrogenation rates over a wide range of partial pressures. Operando X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine-structure (EXAFS) spectra indicate that during reaction at 650 °C the Cr cations maintain a nominal 2+ charge and a total Cr-O coordination number of approximately 2. However, CO2 reduction induces a change, correlated with the CO2 partial pressure, in the population of two distinct Cr-O scattering paths. This indicates that the promotional effect of parallel CO2 reduction can be attributed to a subtle change in Cr-O bond lengths in the local coordination environment of the active site. These insights are made possible by simultaneously fitting multiple EXAFS spectra recorded in different reaction conditions; this novel procedure is expected to be generally applicable for interpreting operando catalysis EXAFS data.

  View details for DOI 10.1021/jacs.4c00995

  View details for PubMedID 38551239

• Acetylene ligands stabilize atomically dispersed supported rhodium complexes under harsh conditions CHEMICAL ENGINEERING JOURNAL Zhao, Y., Kurtoglu-Oztulum, S. F., Hoffman, A. S., Hong, J., Perez-Aguilar, J., Bare, S. R., Uzun, A. 2024; 485

  View details for DOI 10.1016/j.cej.2024.149738

  View details for Web of Science ID 001194062900001

• Dynamic Behavior of Platinum Atoms and Clusters in the Native Oxide Layer of Aluminum Nanocrystals. ACS nano Robatjazi, H., Battsengel, T., Finzel, J., Tieu, P., Xu, M., Hoffman, A. S., Qi, J., Bare, S. R., Pan, X., Chmelka, B. F., Halas, N. J., Christopher, P. 2024

  Abstract

  Strong metal-support interactions (SMSIs) are well-known in the field of heterogeneous catalysis to induce the encapsulation of platinum (Pt) group metals by oxide supports through high temperature H2 reduction. However, demonstrations of SMSI overlayers have largely been limited to reducible oxides, such as TiO2 and Nb2O5. Here, we show that the amorphous native surface oxide of plasmonic aluminum nanocrystals (AlNCs) exhibits SMSI-induced encapsulation of Pt following reduction in H2 in a Pt structure dependent manner. Reductive treatment in H2 at 300 °C induces the formation of an AlOx SMSI overlayer on Pt clusters, leaving Pt single-atom sites (Ptiso) exposed available for catalysis. The remaining exposed Ptiso species possess a more uniform local coordination environment than has been observed on other forms of Al2O3, suggesting that the AlOx native oxide of AlNCs presents well-defined anchoring sites for individual Pt atoms. This observation extends our understanding of SMSIs by providing evidence that H2-induced encapsulation can occur for a wider variety of materials and should stimulate expanded studies of this effect to include nonreducible oxides with oxygen defects and the presence of disorder. It also suggests that the single-atom sites created in this manner, when combined with the plasmonic properties of the Al nanocrystal core, may allow for site-specific single-atom plasmonic photocatalysis, providing dynamic control over the light-driven reactivity in these systems.

  View details for DOI 10.1021/acsnano.3c12869

  View details for PubMedID 38350032

• Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts (Retraction of Vol 2, Pg 2259, 2022) JACS AU Zichittella, G., Ebrahim, A. M., Zhu, J., Brenner, A. E., Drake, G., Beckham, G. T., Bare, S. R., Rorrer, J. E., Roman-Leshkov, Y. 2024; 4 (2): 865

  Abstract

  [This retracts the article DOI: 10.1021/jacsau.2c00402.].

  View details for DOI 10.1021/jacsau.4c00090

  View details for Web of Science ID 001177401200001

  View details for PubMedID 38425905

  View details for PubMedCentralID PMC10900197

• Impact of Local Structure in Supported CaO Catalysts for Soft-Oxidant-Assisted Methane Coupling Assessed through Ca K-Edge X-ray Absorption Spectroscopy JOURNAL OF PHYSICAL CHEMISTRY C Filardi, L. R., Vila, F. D., Hong, J., Hoffman, A. S., Perez-Aguilar, J. E., Bare, S. R., Runnebaum, R. C., Kronawitter, C. X. 2024; 128 (3): 1165-1176

  Abstract

  Soft-oxidant-assisted methane coupling has emerged as a promising pathway to upgrade methane from natural gas sources to high-value commodity chemicals, such as ethylene, at selectivities higher than those associated with oxidative (O2) methane coupling (OCM). To date, few studies have reported investigations into the electronic structure and the microscopic physical structure of catalytic active sites present in the binary metal oxide catalyst systems that are known to be effective for this reaction. Correlating the catalyst activity to specific active site structures and electronic properties is an essential aspect of catalyst design. Here, we used X-ray absorption spectroscopy at the Ca K-edge to ascertain the most probable local environment of Ca in the ZnO-supported Ca oxide catalysts. These catalysts are shown here to be active for N2O-assisted methane coupling (N2O-OCM) and have previously been reported to be active for CO2-assisted methane coupling (CO2-OCM). X-ray absorption near edge structure features at multiple Ca loadings are interpreted through simulated spectra derived from ab initio full multiple scattering calculations. These simulations included consideration of CaO structures organized in multiple spatial arrangements-linear, planar, and cubic-with separate analyses of Ca atoms in the surfaces and bulk of the three-dimensional structures. The morphology of the oxide clusters was found to influence the various regions of the X-ray absorption spectrum differently. Experiment and theory show that for low-Ca-loading catalysts (≤1 mol %), which contain sites particularly active for methane coupling, Ca primarily exists in an oxidized state that is consistent with the coordination environment of Ca ions in one- and two-dimensional clusters. In addition to their unique nanoscale structures, the spectra also indicate that these clusters have varying degrees of undercoordinated surface Ca atoms that could further influence their catalytic activities. The local Ca structure was correlated to methane coupling activity from N2O-OCM and previously reported CO2-OCM reactor studies. This study provides a unique perspective on the relationship between the catalyst physical and electronic structure and active sites for soft-oxidant-assisted methane coupling, which can be used to inform future catalyst development.

  View details for DOI 10.1021/acs.jpcc.3c06527

  View details for Web of Science ID 001151539000001

  View details for PubMedID 38293693

  View details for PubMedCentralID PMC10823472

• Understanding the Control of Speciation of Molybdenum Oxides in MFI-Type Zeolites CHEMISTRY OF MATERIALS Hiennadi, E. J., Molajafari, F., Rana, R., Hoffman, A. S., Bare, S. R., Howe, J. D., Khatib, S. J. 2023; 35 (23): 9907-9923

  View details for DOI 10.1021/acs.chemmater.3c01545

  View details for Web of Science ID 001142893200001

• Significant Roles of Surface Hydrides in Enhancing the Performance of Cu/BaTiO_2.8H_0.2 Catalyst for CO₂ Hydrogenation to Methanol ANGEWANDTE CHEMIE-INTERNATIONAL EDITION He, Y., Li, Y., Lei, M., Polo-Garzon, F., Perez-Aguilar, J., Bare, S. R., Formo, E., Kim, H., Daemen, L., Cheng, Y., Hong, K., Chi, M., Jiang, D., Wu, Z. 2023: e202313389

  Abstract

  Tuning the anionic site of catalyst supports can impact reaction pathways by creating active sites on the support or influencing metal-support interactions when using supported metal nanoparticles. This study focuses on CO2 hydrogenation over supported Cu nanoparticles, revealing a 3-fold increase in methanol yield when replacing oxygen anions with hydrides in the perovskite support (Cu/BaTiO2.8 H0.2 yields ~146 mg/h/gCu vs. Cu/BaTiO3 yields ~50 mg/h/gCu). The contrast suggests that significant roles are played by the support hydrides in the reaction. Temperature programmed reaction and isotopic labelling studies indicate that BaTiO2.8 H0.2 surface hydride species follow a Mars van Krevelen mechanism in CO2 hydrogenation, promoting methanol production. High-pressure steady-state isotopic transient kinetic analysis (SSITKA) studies suggest that Cu/BaTiO2.8 H0.2 possesses both a higher density and more active and selective sites for methanol production compared to Cu/BaTiO3 . An operando high-pressure diffuse reflectance infrared spectroscopy (DRIFTS)-SSITKA study shows that formate species are the major surface intermediates over both catalysts, and the subsequent hydrogenation steps of formate are likely rate-limiting. However, the catalytic reactivity of Cu/BaTiO2.8 H0.2 towards the formate species is much higher than Cu/BaTiO3 , likely due to the altered electronic structure of interface Cu sites by the hydrides in the support as validated by density functional theory (DFT) calculations.

  View details for DOI 10.1002/anie.202313389

  View details for Web of Science ID 001103744000001

  View details for PubMedID 37906130

• Ceria Incorporation in Sinter-Resistant Platinum-Based Catalysts ACS CATALYSIS Stone, M. L., Cendejas, M. C., Persson, A., Liccardo, G., Smith, J., Kumar, A., Zhou, C., Gardner, E., Aitbekova, A., Bustillo, K. C., Chi, M., Bare, S. R., Cargnello, M. 2023; 13 (22): 14853-14863

  View details for DOI 10.1021/acscatal.3c02766

  View details for Web of Science ID 001141207100001

• Spectroscopic determination of metal redox and segregation effects during CO and CO/NO oxidation over silica-supported Pd and PdCu catalysts APPLIED CATALYSIS B-ENVIRONMENT AND ENERGY Kristy, S., Svadlenak, S., Hoffman, A. S., Bare, S. R., Goulas, K. A. 2024; 342

  View details for DOI 10.1016/j.apcatb.2023.123329

  View details for Web of Science ID 001109529600001

• Cation Incorporation into Copper Oxide Lattice at Highly Oxidizing Potentials. ACS applied materials & interfaces Ostervold, L., Smerigan, A., Liu, M. J., Filardi, L. R., Vila, F. D., Perez-Aguilar, J. E., Hong, J., Tarpeh, W. A., Hoffman, A. S., Greenlee, L. F., Clark, E. L., Janik, M. J., Bare, S. R. 2023

  Abstract

  Electrolyte cations can have significant effects on the kinetics and selectivity of electrocatalytic reactions. We show an atypical mechanism through which electrolyte cations can impact electrocatalyst performance─direct incorporation of the cation into the oxide electrocatalyst lattice. We investigate the transformations of copper electrodes in alkaline electrochemistry through operando X-ray absorption spectroscopy in KOH and Ba(OH)2 electrolytes. In KOH electrolytes, both the near-edge structure and extended fine-structure agree with previous studies; however, the X-ray absorption spectra vary greatly in Ba(OH)2 electrolytes. Through a combination of electronic structure modeling, near-edge simulation, and postreaction characterization, we propose that Ba2+ cations are directly incorporated into the lattice and form an ordered BaCuO2 phase at potentials more oxidizing than 200 mV vs the normal hydrogen electrode (NHE). BaCuO2 formation is followed by further oxidation to a bulk Cu3+-like BaxCuyOz phase at 900 mV vs NHE. Additionally, during reduction in Ba(OH)2 electrolyte, we find both Cu-O bonds and Cu-Ba scattering persist at potentials as low as -400 mV vs NHE. To our knowledge, this is the first evidence for direct oxidative incorporation of an electrolyte cation into the bulk lattice to form a mixed oxide electrode. The oxidative incorporation of electrolyte cations to form mixed oxides could open a new route for the in situ formation of active and selective oxidation electrocatalysts.

  View details for DOI 10.1021/acsami.3c10296

  View details for PubMedID 37756387

• Elucidating the role of Fe-Mo interactions in the metal oxide precursors for Fe promoted Mo/ZSM-5 catalysts in non-oxidative methane dehydroaromatization CHEMICAL ENGINEERING JOURNAL Hossain, M., Dhillon, G., Liu, L., Sridhar, A., Hiennadi, E. J., Hong, J., Bare, S. R., Xin, H., Ericson, T., Cozzolino, A., Khatib, S. J. 2023; 475

  View details for DOI 10.1016/j.cej.2023.146096

  View details for Web of Science ID 001084295700001

• Aqueous Structure of Lanthanide-EDTA Coordination Complexes Determined by a Combined DFT/EXAFS Approach INORGANIC CHEMISTRY Smerigan, A., Biswas, S., Vila, F. D., Hong, J., Perez-Aguilar, J., Hoffman, A. S., Greenlee, L., Getman, R. B., Bare, S. R. 2023; 62 (36): 14523-14532

  Abstract

  Sustainable production of rare earth elements (REEs) is critical for technologies needed for climate change mitigation, including wind turbines and electric vehicles. However, separation technologies currently used in REE production have large environmental footprints, necessitating more sustainable strategies. Aqueous, affinity-based separations are examples of such strategies. To make these technologies feasible, it is imperative to connect aqueous ligand structure to ligand selectivity for individual REEs. As a step toward this goal, we analyzed the extended X-ray absorption fine structure (EXAFS) of four lanthanides (La, Ce, Pr, and Nd) complexed by a common REE chelator, ethylenediaminetetraacetic acid (EDTA) to determine the aqueous-phase structure. Reference structures from density functional theory (DFT) were used to help fit the EXAFS spectra. We found that all four Ln-EDTA coordination complexes formed 9-coordinate structures with 6 coordinating atoms from EDTA (4 carboxyl oxygen atoms and 2 nitrogen atoms) and 3 oxygen atoms from water molecules. All EXAFS fits were of high quality (R-factor < 0.02) and showed decreasing average first-shell coordination distance across the series (2.62-2.57 Å from La-Nd), in agreement with DFT (2.65-2.56 Å from La-Nd). The insights determined herein will be useful in the development of ligands for sustainable rare earth elements (REE) separation technologies.

  View details for DOI 10.1021/acs.inorgchem.3c01334

  View details for Web of Science ID 001188440200001

  View details for PubMedID 37624729

• Size-Dependent Dispersion of Rhodium Clusters into Isolated Single Atoms at LowTemperature and the Consequences for CO Oxidation Activity. Angewandte Chemie (International ed. in English) Albrahim, M., Shrotri, A., Unocic, R., Hoffman, A., Bare, S., Karim, A. M. 2023: e202308002

  Abstract

  Understanding the dynamic structural evolution of supported metal clusters under reaction conditions is crucial to develop structure reactivity relations. Here, we followed the structure of different size Rh clusters supported on Al2O3using in situ/operando spectroscopy and ex situ aberration-corrected electron microscopy. We report a dynamic evolution of rhodium clusters into thermally stable isolated single atoms upon exposure to oxygen and during CO oxidation. Rh clusters partially disperse into single atoms at room temperatureand the extent of dispersion increases as the Rh size decreases and as the reaction temperature increases. A strong correlation is found between the extent of dispersion and the CO oxidation kinetics. More importantly, dispersing Rh clusters into single atoms increases the activity at room temperature by more than two orders of magnitude due to the much lower activation energy on single atoms (40 vs. 130 kJ/mol). This work demonstrates that the structure and reactivity of small Rh clusters are very sensitive to the reaction environment.

  View details for DOI 10.1002/anie.202308002

  View details for PubMedID 37488071

• Temporal Ni K-Edge X-ray Absorption Spectroscopy Study Reveals the Kinetics of the Ni Redox Behavior of the Iron-Nickel Oxide Bimetallic OER Catalyst JOURNAL OF PHYSICAL CHEMISTRY C Acharya, P., Hong, J., Manso, R., Hoffman, A. S., Kekedy-Nagy, L., Chen, J., Bare, S. R., Greenlee, L. F. 2023

  View details for DOI 10.1021/acs.jpcc.3c03480

  View details for Web of Science ID 001008590900001

• CO Oxidation on Ir-1/TiO2: Resolving Ligand Dynamics and Elementary Reaction Steps ACS CATALYSIS Thompson, C. B., Liu, L., Leshchev, D. S., Hoffman, A. S., Hong, J., Bare, S. R., Unocic, R. R., Stavitski, E., Xin, H., Karim, A. M. 2023; 13 (12): 7802-7811

  View details for DOI 10.1021/acscatal.3c01433

  View details for Web of Science ID 001010999700001

• Observations of Ethylene-for-CO Ligand Exchanges on a Zeolite-Supported Single-Site Rh Catalyst by X-ray Absorption Spectroscopy. The journal of physical chemistry letters Hoffman, A. S., Muller, O., Hong, J., Canning, G. A., Fang, C., Perez-Aguilar, J. E., Gates, B. C., Bare, S. R. 2023: 4591-4599

  Abstract

  Quick-scanning X-ray absorption fine structure (QXAFS) measurements were used to characterize the exchanges of ethylene and CO ligands in a zeolite HY-supported single-site Rh complex at a sampling rate of 1.0 Hz. The two ligands were reversibly exchanged on the rhodium, with quantitative results determined for the C2H4-for-CO exchange that are consistent with a first-order process. The apparent rate constant for the exchange decreased with increasing temperature. Fourier-transform infrared spectra characterizing the C2H4 sorbed in the zeolite showed that the amount decreased with increasing temperature, consistent with the decrease in the exchange rate with increasing temperature. The results, illustrating the dynamics of ligand exchanges on a single-site supported metal catalyst, demonstrate the broad emerging applicability of the QXAFS technique for characterizing the dynamics of reactive intermediates on catalysts.

  View details for DOI 10.1021/acs.jpclett.3c00349

  View details for PubMedID 37166100

• Memory-dictated dynamics of single-atom Pt on CeO2 for CO oxidation. Nature communications Zhang, Z., Tian, J., Lu, Y., Yang, S., Jiang, D., Huang, W., Li, Y., Hong, J., Hoffman, A. S., Bare, S. R., Engelhard, M. H., Datye, A. K., Wang, Y. 2023; 14 (1): 2664

  Abstract

  Single atoms of platinum group metals on CeO2 represent a potential approach to lower precious metal requirements for automobile exhaust treatment catalysts. Here we show the dynamic evolution of two types of single-atom Pt (Pt1) on CeO2, i.e., adsorbed Pt1 in Pt/CeO2 and square planar Pt1 in PtATCeO2, fabricated at 500°C and by atom-trapping method at 800°C, respectively. Adsorbed Pt1 in Pt/CeO2 is mobile with the in situ formation of few-atom Pt clusters during CO oxidation, contributing to high reactivity with near-zero reaction order in CO. In contrast, square planar Pt1 in PtATCeO2 is strongly anchored to the support during CO oxidation leading to relatively low reactivity with a positive reaction order in CO. Reduction of both Pt/CeO2 and PtATCeO2 in CO transforms Pt1 to Pt nanoparticles. However, both catalysts retain the memory of their initial Pt1 state after reoxidative treatments, which illustrates the importance of the initial single-atom structure in practical applications.

  View details for DOI 10.1038/s41467-023-37776-3

  View details for PubMedID 37160890

• Dynamic Evolution of Palladium Single Atoms on Anatase Titania Support Determines the Reverse Water-Gas Shift Activity. Journal of the American Chemical Society Chen, L., Allec, S. I., Nguyen, M., Kovarik, L., Hoffman, A. S., Hong, J., Meira, D., Shi, H., Bare, S. R., Glezakou, V., Rousseau, R., Szanyi, J. 2023

  Abstract

  Research interest in single-atom catalysts (SACs) has been continuously increasing. However, the lack of understanding of the dynamic behaviors of SACs during applications hinders catalyst development and mechanistic understanding. Herein, we report on the evolution of active sites over Pd/TiO2-anatase SAC (Pd1/TiO2) in the reverse water-gas shift (rWGS) reaction. Combining kinetics, in situ characterization, and theory, we show that at T ≥ 350 °C, the reduction of TiO2 by H2 alters the coordination environment of Pd, creating Pd sites with partially cleaved Pd-O interfacial bonds and a unique electronic structure that exhibit high intrinsic rWGS activity through the carboxyl pathway. The activation by H2 is accompanied by the partial sintering of single Pd atoms (Pd1) into disordered, flat, 1 nm diameter clusters (Pdn). The highly active Pd sites in the new coordination environment under H2 are eliminated by oxidation, which, when performed at a high temperature, also redisperses Pdn and facilitates the reduction of TiO2. In contrast, Pd1 sinters into crystalline, 5 nm particles (PdNP) during CO treatment, deactivating Pd1/TiO2. During the rWGS reaction, the two Pd evolution pathways coexist. The activation by H2 dominates, leading to the increasing rate with time-on-stream, and steady-state Pd active sites similar to the ones formed under H2. This work demonstrates how the coordination environment and nuclearity of metal sites on a SAC evolve during catalysis and pretreatments and how their activity is modulated by these behaviors. These insights on SAC dynamics and the structure-function relationship are valuable to mechanistic understanding and catalyst design.

  View details for DOI 10.1021/jacs.3c02326

  View details for PubMedID 37145876

• Limits of Detection for EXAFS Characterization of Heterogeneous Single-Atom Catalysts ACS CATALYSIS Finzel, J., Gutierrez, K., Hoffman, A. S., Resasco, J., Christopher, P., Bare, S. R. 2023; 13 (9): 6462-6473

  View details for DOI 10.1021/acscatal.3c01116

  View details for Web of Science ID 000983579400001

• Rigorous Oxidation State Assignments for Supported Ga-Containing Catalysts Using Theory-Informed X-ray Absorption Spectroscopy Signatures from Well-Defined Ga(I) and Ga(III) Compounds ACS CATALYSIS Li, L., Chalmers, J. A., Bare, S. R., Scott, S. L., Vila, F. D. 2023: 6549-6561

  View details for DOI 10.1021/acscatal.3c01021

  View details for Web of Science ID 000984925100001

• Genesis of Active Pt/CeO2 Catalyst for Dry Reforming of Methane by Reduction and Aggregation of Isolated Platinum Atoms into Clusters. Small (Weinheim an der Bergstrasse, Germany) Das, S., Anjum, U., Lim, K. H., He, Q., Hoffman, A. S., Bare, S. R., Kozlov, S. M., Gates, B. C., Kawi, S. 2023: e2207272

  Abstract

  Atomically dispersed metal catalysts offer the advantages of efficient metal utilization and high selectivities for reactions of technological importance. Such catalysts have been suggested to be strong candidates for dry reforming of methane (DRM), offering prospects of high selectivity for synthesis gas without coke formation, which requires ensembles of metal sites and is a challenge to overcome in DRM catalysis. However, investigations of the structures of isolated metal sites on metal oxide supports under DRM conditions are lacking, and the catalytically active sites remain undetermined. Data characterizing the DRM reaction-driven structural evolution of a cerium oxide-supported catalyst, initially incorporating atomically dispersed platinum, and the corresponding changes in catalyst performance are reported. X-ray absorption and infrared spectra show that the reduction and agglomeration of isolated cationic platinum atoms to form small platinum clusters/nanoparticles are necessary for DRM activity. Density functional theory calculations of the energy barriers for methane dissociation on atomically dispersed platinum and on platinum clusters support these observations. The results emphasize the need for in-operando experiments to assess the active sites in such catalysts. The inferences about the catalytically active species are suggested to pertain to a broad class of catalytic conversions involving the rate-limiting dissociation of light alkanes.

  View details for DOI 10.1002/smll.202207272

  View details for PubMedID 36942900

• Elemental zoning enhances mass transport in zeolite catalysts for methanol to hydrocarbons NATURE CATALYSIS Le, T. T., Qin, W., Agarwal, A., Nikolopoulos, N., Fu, D., Patton, M. D., Weiland, C., Bare, S. R., Palmer, J. C., Weckhuysen, B. M., Rimer, J. D. 2023; 6 (3): 254-+

  View details for DOI 10.1038/s41929-023-00927-2

  View details for Web of Science ID 000952914300002

• Dynamic Tracking of NiFe Smart Catalysts using In Situ X-Ray Absorption Spectroscopy for the Dry Methane Reforming Reaction ACS CATALYSIS Shah, S., Hong, J., Cruz, L., Wasantwisut, S., Bare, S. R., Gilliard-AbdulAziz, K. 2023

  View details for DOI 10.1021/acscatal.2c05572

  View details for Web of Science ID 000947923900001

• Selective Catalytic Behavior Induced by Crystal-Phase Transformation in Well-Defined Bimetallic Pt-Sn Nanocrystals. Small (Weinheim an der Bergstrasse, Germany) Werghi, B., Wu, L., Ebrahim, A. M., Chi, M., Ni, H., Cargnello, M., Bare, S. R. 2023: e2207956

  Abstract

  The Pt-Sn bimetallic system is a much studied and commercially used catalyst for propane dehydrogenation. The traditionally prepared catalyst, however, suffers from inhomogeneity and phase separation of the active Pt-Sn phase. Colloidal chemistry offers a route for the synthesis of Pt-Sn bimetallic nanoparticles (NPs) in a systematic, well-defined, tailored fashion over conventional methods. Here, the successful synthesis of well-defined ≈2 nm Pt, PtSn, and Pt3 Sn nanocrystals with distinct crystallographic phases is reported; hexagonal close packing (hcp) PtSn and fcc Pt3 Sn show different activity and stability depending on the hydrogen-rich or poor environment in the feed. Moreover, face centred cubic (fcc) Pt3 Sn/Al2 O3 , which exhibited the highest stability compared to hcp PtSn, shows a unique phase transformation from an fcc phase to an L12 -ordered superlattice. Contrary to PtSn, H2 cofeeding has no effect on the Pt3 Sn deactivation rate. The results reveal structural dependency of the probe reaction, propane dehydrogenation, and provide a fundamental understanding of the structure-performance relationship on emerging bimetallic systems.

  View details for DOI 10.1002/smll.202207956

  View details for PubMedID 36807838

• Structure and Site Evolution of Framework Ni Species in MIL-127 MOFs for Propylene Oligomerization Catalysis. Journal of the American Chemical Society Yeh, B., Chheda, S., Prinslow, S. D., Hoffman, A. S., Hong, J., Perez-Aguilar, J. E., Bare, S. R., Lu, C. C., Gagliardi, L., Bhan, A. 2023

  Abstract

  A mixed-valence oxotrimer metal-organic framework (MOF), Ni-MIL-127, with a fully coordinated nickel atom and two iron atoms in the inorganic node, generates a missing linker defect upon thermal treatment in helium (>473 K) to engender an open coordination site on nickel which catalyzes propylene oligomerization devoid of any cocatalysts or initiators. This catalyst is stable for 20 h on stream at 500 kPa and 473 K, unprecedented for this chemistry. The number of missing linkers on synthesized and activated Ni-MIL-127 MOFs is quantified using temperature-programmed oxidation, 1H nuclear magnetic resonance spectroscopy, and X-ray absorption spectroscopy to be 0.7 missing linkers per nickel; thus, a majority of Ni species in the MOF framework catalyze propylene oligomerization. In situ NO titrations under reaction conditions enumerate 62% of the nickel atoms as catalytically relevant to validate the defect density upon thermal treatment. Propylene oligomerization rates on Ni-MIL-127 measured at steady state have activation energies of 55-67 kJ mol-1 from 448 to 493 K and are first-order in propylene pressures from 5 to 550 kPa. Density functional theory calculations on cluster models of Ni-MIL-127 are employed to validate the plausibility of the missing linker defect and the Cossee-Arlman mechanism for propylene oligomerization through comparisons between apparent activation energies from steady-state kinetics and computation. This study illustrates how MOF precatalysts engender defective Ni species which exhibit reactivity and stability characteristics that are distinct and can be engineered to improve catalytic activity for olefin oligomerization.

  View details for DOI 10.1021/jacs.2c10551

  View details for PubMedID 36724435

• Nano-sized Metallic Nickel Clusters Stabilized on Dealuminated beta-Zeolite: A Highly Active and Stable Ethylene Hydrogenation Catalyst JOURNAL OF PHYSICAL CHEMISTRY C Meloni, M., Hong, J., Hoffman, A. S., Holton, S., Kulkarni, A., Bare, S. R., Runnebaum, R. C. 2022

  View details for DOI 10.1021/acs.jpcc.2c05504AJ

  View details for Web of Science ID 000895698500001

• Templated encapsulation of platinum-based catalysts promotes high-temperature stability to 1,100°C. Nature materials Aitbekova, A., Zhou, C., Stone, M. L., Lezama-Pacheco, J. S., Yang, A., Hoffman, A. S., Goodman, E. D., Huber, P., Stebbins, J. F., Bustillo, K. C., Ercius, P., Ciston, J., Bare, S. R., Plessow, P. N., Cargnello, M. 2022

  Abstract

  Stable catalysts are essential to address energy and environmental challenges, especially for applications in harsh environments (for example, high temperature, oxidizing atmosphere and steam). In such conditions, supported metal catalysts deactivate due to sintering-a process where initially small nanoparticles grow into larger ones with reduced active surface area-but strategies to stabilize them can lead to decreased performance. Here we report stable catalysts prepared through the encapsulation of platinum nanoparticles inside an alumina framework, which was formed by depositing an alumina precursor within a separately prepared porous organic framework impregnated with platinum nanoparticles. These catalysts do not sinter at 800°C in the presence of oxygen and steam, conditions in which conventional catalysts sinter to a large extent, while showing similar reaction rates. Extending this approach to Pd-Pt bimetallic catalysts led to the small particle size being maintained at temperatures as high as 1,100°C in air and 10% steam. This strategy can be broadly applied to other metal and metal oxides for applications where sintering is a major cause of material deactivation.

  View details for DOI 10.1038/s41563-022-01376-1

  View details for PubMedID 36280703

• Hydrogenolysis of Polyethylene and Polypropylene into Propane over Cobalt-Based Catalysts (Retracted Article) JACS AU Zichittella, G., Ebrahim, A. M., Zhu, J., Brenner, A. E., Drake, G., Beckham, G. T., Bare, S. R., Rorrer, J. E., Roman-Leshkov, Y. 2022; 2 (10): 2259-2268

  Abstract

  The development of technologies to recycle polyethylene (PE) and polypropylene (PP), globally the two most produced polymers, is critical to increase plastic circularity. Here, we show that 5 wt % cobalt supported on ZSM-5 zeolite catalyzes the solvent-free hydrogenolysis of PE and PP into propane with weight-based selectivity in the gas phase over 80 wt % after 20 h at 523 K and 40 bar H2. This catalyst significantly reduces the formation of undesired CH4 (≤5 wt %), a product which is favored when using bulk cobalt oxide or cobalt nanoparticles supported on other carriers (selectivity ≤95 wt %). The superior performance of Co/ZSM-5 is attributed to the stabilization of dispersed oxidic cobalt nanoparticles by the zeolite support, preventing further reduction to metallic species that appear to catalyze CH4 generation. While ZSM-5 is also active for propane formation at 523 K, the presence of Co promotes stability and selectivity. After optimizing the metal loading, it was demonstrated that 10 wt % Co/ZSM-5 can selectively catalyze the hydrogenolysis of low-density PE (LDPE), mixtures of LDPE and PP, as well as postconsumer PE, showcasing the effectiveness of this technology to upcycle realistic plastic waste. Cobalt supported on zeolites FAU, MOR, and BEA were also effective catalysts for C2-C4 hydrocarbon formation and revealed that the framework topology provides a handle to tune gas-phase selectivity.

  View details for DOI 10.1021/jacsau.2c00402

  View details for Web of Science ID 000868951000001

  View details for PubMedID 36311830

  View details for PubMedCentralID PMC9597591

• Surface Fe clusters promote syngas reaction to oxygenates on Rh catalysts modified by atomic layer deposition JOURNAL OF CATALYSIS Nathan, S. S., Asundi, A. S., Hoffman, A. S., Hong, J., Zhou, C., Vila, F. D., Cargnello, M., Bare, S. R., Bent, S. F. 2022; 414: 125-136

  View details for DOI 10.1016/j.jcat.2022.08.026

  View details for Web of Science ID 000861104600001

• Dehydrogenation of Propane and n-Butane Catalyzed by Isolated PtZn4 Sites Supported on Self-Pillared Zeolite Pentasil Nanosheets ACS CATALYSIS Qi, L., Zhang, Y., Babucci, M., Chen, C., Lu, P., Li, J., Dun, C., Hoffman, A. S., Urban, J. J., Tsapatsis, M., Bare, S. R., Han, Y., Gates, B. C., Bell, A. T. 2022; 12 (18): 11177-11189

  View details for DOI 10.1021/acscatal.2c01631

  View details for Web of Science ID 000893509000001

• Extension of Rietveld Refinement for Benchtop Powder XRD Analysis of Ultrasmall Supported Nanoparticles CHEMISTRY OF MATERIALS Lipp, J., Banerjee, R., Patwary, M., Patra, N., Dong, A., Girgsdies, F., Bare, S. R., Regalbuto, J. R. 2022

  View details for DOI 10.1021/acs.chemmater.2c00101

  View details for Web of Science ID 000858968600001

• Interconversion of Atomically Dispersed Platinum Cations and Platinum Clusters in Zeolite ZSM-5 and Formation of Platinum gem-Dicarbonyls. Journal of the American Chemical Society Felvey, N., Guo, J., Rana, R., Xu, L., Bare, S. R., Gates, B. C., Katz, A., Kulkarni, A. R., Runnebaum, R. C., Kronawitter, C. X. 2022

  Abstract

  Catalysts composed of platinum dispersed on zeolite supports are widely applied in industry, and coking and sintering of platinum during operation under reactive conditions require their oxidative regeneration, with the platinum cycling between clusters and cations. The intermediate platinum species have remained only incompletely understood. Here, we report an experimental and theoretical investigation of the structure, bonding, and local environment of cationic platinum species in zeolite ZSM-5, which are key intermediates in this cycling. Upon exposure of platinum clusters to O2 at 700 °C, oxidative fragmentation occurs, and Pt2+ ions are stabilized at six-membered rings in the zeolite that contain paired aluminum sites. When exposed to CO under mild conditions, these Pt2+ ions form highly uniform platinum gem-dicarbonyls, which can be converted in H2 to Ptdelta+ monocarbonyls. This conversion, which weakens the platinum-zeolite bonding, is a first step toward platinum migration and aggregation into clusters. X-ray absorption and infrared spectra provide evidence of the reductive and oxidative transformations in various gas environments. The chemistry is general, as shown by the observation of platinum gem-dicarbonyls in several commercially used zeolites (ZSM-5, Beta, mordenite, and Y).

  View details for DOI 10.1021/jacs.2c05386

  View details for PubMedID 35854402

• Iridium pair sites anchored to Zr6O8 nodes of the metal-organic framework UiO-66 catalyze ethylene hydrogenation JOURNAL OF CATALYSIS Babucci, M., Conley, E. T., Hoffman, A. S., Bare, S. R., Gates, B. C. 2022; 411: 177-186

  View details for DOI 10.1016/j.jcat.2022.04.003

  View details for Web of Science ID 000810197500001

• Atomically Dispersed Platinum in Surface and Subsurface Sites on MgO Have Contrasting Catalytic Properties for CO Oxidation. The journal of physical chemistry letters Chen, Y., Rana, R., Huang, Z., Vila, F. D., Sours, T., Perez-Aguilar, J. E., Zhao, X., Hong, J., Hoffman, A. S., Li, X., Shang, C., Blum, T., Zeng, J., Chi, M., Salmeron, M., Kronawitter, C. X., Bare, S. R., Kulkarni, A. R., Gates, B. C. 2022: 3896-3903

  Abstract

  Atomically dispersed metals on metal oxide supports are a rapidly growing class of catalysts. Developing an understanding of where and how the metals are bonded to the supports is challenging because support surfaces are heterogeneous, and most reports lack a detailed consideration of these points. Herein, we report two atomically dispersed CO oxidation catalysts having markedly different metal-support interactions: platinum in the first layer of crystalline MgO powder and platinum in the second layer of this support. Structural models have been determined on the basis of data and computations, including those determined by extended X-ray absorption fine structure and X-ray absorption near edge structure spectroscopies, infrared spectroscopy of adsorbed CO, and scanning transmission electron microscopy. The data demonstrate the transformation of surface to subsurface platinum as the temperature of sample calcination increased. Catalyst performance data demonstrate the lower activity but greater stability of the subsurface platinum than of the surface platinum.

  View details for DOI 10.1021/acs.jpclett.2c00667

  View details for PubMedID 35471032

• Catalytic Performance and Near-Surface X-ray Characterization of Titanium Hydride Electrodes for the Electrochemical Nitrate Reduction Reaction. Journal of the American Chemical Society Liu, M. J., Guo, J., Hoffman, A. S., Stenlid, J. H., Tang, M. T., Corson, E. R., Stone, K. H., Abild-Pedersen, F., Bare, S. R., Tarpeh, W. A. 2022

  Abstract

  The electrochemical nitrate reduction reaction (NO3RR) on titanium introduces significant surface reconstruction and forms titanium hydride (TiHx, 0 < x ≤ 2). With ex situ grazing-incidence X-ray diffraction (GIXRD) and X-ray absorption spectroscopy (XAS), we demonstrated near-surface TiH2 enrichment with increasing NO3RR applied potential and duration. This quantitative relationship facilitated electrochemical treatment of Ti to form TiH2/Ti electrodes for use in NO3RR, thereby decoupling hydride formation from NO3RR performance. A wide range of NO3RR activity and selectivity on TiH2/Ti electrodes between -0.4 and -1.0 VRHE was observed and analyzed with density functional theory (DFT) calculations on TiH2(111). This work underscores the importance of relating NO3RR performance with near-surface electrode structure to advance catalyst design and operation.

  View details for DOI 10.1021/jacs.2c01274

  View details for PubMedID 35315649

• Steering CO2 hydrogenation toward C-C coupling to hydrocarbons using porous organic polymer/metal interfaces. Proceedings of the National Academy of Sciences of the United States of America Zhou, C., Asundi, A. S., Goodman, E. D., Hong, J., Werghi, B., Hoffman, A. S., Nathan, S. S., Bent, S. F., Bare, S. R., Cargnello, M. 2022; 119 (7)

  Abstract

  The conversion of CO2 into fuels and chemicals is an attractive option for mitigating CO2 emissions. Controlling the selectivity of this process is beneficial to produce desirable liquid fuels, but C-C coupling is a limiting step in the reaction that requires high pressures. Here, we propose a strategy to favor C-C coupling on a supported Ru/TiO2 catalyst by encapsulating it within the polymer layers of an imine-based porous organic polymer that controls its selectivity. Such polymer confinement modifies the CO2 hydrogenation behavior of the Ru surface, significantly enhancing the C2+ production turnover frequency by 10-fold. We demonstrate that the polymer layers affect the adsorption of reactants and intermediates while being stable under the demanding reaction conditions. Our findings highlight the promising opportunity of using polymer/metal interfaces for the rational engineering of active sites and as a general tool for controlling selective transformations in supported catalyst systems.

  View details for DOI 10.1073/pnas.2114768119

  View details for PubMedID 35135880

• Fe Coordination Environment, Fe-Incorporated Ni(OH)(2) Phase, and Metallic Core Are Key Structural Components to Active and Stable Nanoparticle Catalysts for the Oxygen Evolution Reaction ACS CATALYSIS Acharya, P., Manso, R. H., Hoffman, A. S., Bakovic, S., Kekedy-Nagy, L., Bare, S. R., Chen, J., Greenlee, L. F. 2022

  View details for DOI 10.1021/acscatal.1c04881

  View details for Web of Science ID 000746965900001

• CO oxidation on MgAl2O4 supported Ir-n: activation of lattice oxygen in the subnanometer regime and emergence of nuclearity-activity volcano JOURNAL OF MATERIALS CHEMISTRY A Lu, Y., Thompson, C., Kuo, C., Zhang, X., Hoffman, A. S., Boubnov, A., Bare, S. R., Kovarik, L., Xin, H., Karim, A. M. 2022

  View details for DOI 10.1039/d1ta09740g

  View details for Web of Science ID 000748367400001

• Reactivity of Pd-MO2 encapsulated catalytic systems for CO oxidation CATALYSIS SCIENCE & TECHNOLOGY Paz Herrera, L., Freitas, L., Hong, J., Hoffman, A. S., Bare, S. R., Nikolla, E., Medlin, J. 2022

  View details for DOI 10.1039/d1cy01916c

  View details for Web of Science ID 000749672000001

• Colloidal Platinum-Copper Nanocrystal Alloy Catalysts Surpass Platinum in Low-Temperature Propene Combustion. Journal of the American Chemical Society Tahsini, N., Yang, A. C., Streibel, V., Werghi, B., Goodman, E. D., Aitbekova, A., Bare, S. R., Li, Y., Abild-Pedersen, F., Cargnello, M. 2022

  Abstract

  Low-temperature removal of noxious environmental emissions plays a critical role in minimizing the harmful effects of hydrocarbon fuels. Emission-control catalysts typically consist of large quantities of rare, noble metals (e.g., platinum and palladium), which are expensive and environmentally damaging metals to extract. Alloying with cheaper base metals offers the potential to boost catalytic activity while optimizing the use of noble metals. In this work, we show that PtxCu100-x catalysts prepared from colloidal nanocrystals are more active than the corresponding Pt catalysts for complete propene oxidation. By carefully controlling their composition while maintaining nanocrystal size, alloys with dilute Cu concentrations (15-30% atomic fraction) demonstrate promoted activity compared to pure Pt. Complete propene oxidation was observed at temperatures as low as 150 °C in the presence of steam, and five to ten times higher turnover frequencies were found compared to monometallic Pt catalysts. Through DFT studies and structural and catalytic characterization, the remarkable activity of dilute PtxCu100-x alloys was related to the tuning of the electronic structure of Pt to reach optimal binding energies of C* and O* intermediates. This work provides a general approach toward investigation of structure-property relationships of alloyed catalysts with efficient and optimized use of noble metals.

  View details for DOI 10.1021/jacs.1c10248

  View details for PubMedID 35050603

• First-Principles Approach to Extracting Chemical Information from X-ray Absorption Near-Edge Spectra of Ga-Containing Materials JOURNAL OF PHYSICAL CHEMISTRY C Groden, K., Vila, F. D., Li, L., Bare, S. R., Scott, S. L., McEwen, J. 2021; 125 (51): 27901-27908

  View details for DOI 10.1021/acs.jpcc.1c07728

  View details for Web of Science ID 000756016500002

• Dynamic Surface Reconstruction Unifies the Electrocatalytic Oxygen Evolution Performance of Nonstoichiometric Mixed Metal Oxides. JACS Au Samira, S., Hong, J., Camayang, J. C., Sun, K., Hoffman, A. S., Bare, S. R., Nikolla, E. 1800; 1 (12): 2224-2241

  Abstract

  Compositionally versatile, nonstoichiometric, mixed ionic-electronic conducting metal oxides of the form A n+1B n O3n+1 (n = 1 ; A = rare-earth-/alkaline-earth-metal cation; B = transition-metal (TM) cation) remain a highly attractive class of electrocatalysts for catalyzing the energy-intensive oxygen evolution reaction (OER). The current design strategies for describing their OER activities are largely derived assuming a static, unchanged view of their surfaces, despite reports of dynamic structural changes to 3d TM-based perovskites during OER. Herein, through variations in the A- and B-site compositions of A n+1B n O3n+1 oxides (n = 1 (A2BO4) or n = (ABO3); A = La, Sr, Ca; B = Mn, Fe, Co, Ni), we show that, in the absence of electrolyte impurities, surface restructuring is universally the source of high OER activity in these oxides and is dependent on the initial oxide composition. Oxide surface restructuring is induced by irreversible A-site cation dissolution, resulting in in situ formation of a TM oxyhydroxide shell on top of the parent oxide core that serves as the active surface for OER. The rate of surface restructuring is found to depend on (i) composition of A-site cations, with alkaline-earth-metal cations dominating lanthanide cation dissolution, (ii) oxide crystal phase, with n = 1 A2BO4 oxides exhibiting higher rates of A-site dissolution in comparison to n = ABO3 perovskites, (iii) lattice strain in the oxide induced by mixed rare-earth- and alkaline-earth-metal cations in the A-site, and (iv) oxide reducibility. Among the in situ generated 3d TM oxyhydroxide structures from A n+1B n O3n+1 oxides, Co-based structures are characterized by superior OER activity and stability, even in comparison to as-synthesized Co-oxyhydroxide, pointing to the generation of high active surface area structures through oxide restructuring. These insights are critical toward the development of revised design criteria to include surface dynamics for effectively describing the OER activity of nonstoichiometric mixed-metal oxides.

  View details for DOI 10.1021/jacsau.1c00359

  View details for PubMedID 34977894

• Mechanistic and Electronic Insights into a Working NiAu Single-Atom Alloy Ethanol Dehydrogenation Catalyst. Journal of the American Chemical Society Giannakakis, G., Kress, P., Duanmu, K., Ngan, H. T., Yan, G., Hoffman, A. S., Qi, Z., Trimpalis, A., Annamalai, L., Ouyang, M., Liu, J., Eagan, N., Biener, J., Sokaras, D., Flytzani-Stephanopoulos, M., Bare, S. R., Sautet, P., Sykes, E. C. 1800

  Abstract

  Elucidation of reaction mechanisms and the geometric and electronic structure of the active sites themselves is a challenging, yet essential task in the design of new heterogeneous catalysts. Such investigations are best implemented via a multipronged approach that comprises ambient pressure catalysis, surface science, and theory. Herein, we employ this strategy to understand the workings of NiAu single-atom alloy (SAA) catalysts for the selective nonoxidative dehydrogenation of ethanol to acetaldehyde and hydrogen. The atomic dispersion of Ni is paramount for selective ethanol to acetaldehyde conversion, and we show that even the presence of small Ni ensembles in the Au surface results in the formation of undesirable byproducts via C-C scission. Spectroscopic, kinetic, and theoretical investigations of the reaction mechanism reveal that both C-H and O-H bond cleavage steps are kinetically relevant and single Ni atoms are confirmed as the active sites. X-ray absorption spectroscopy studies allow us to follow the charge of the Ni atoms in the Au host before, under, and after a reaction cycle. Specifically, in the pristine state the Ni atoms carry a partial positive charge that increases upon coordination to the electronegative oxygen in ethanol and decreases upon desorption. This type of oxidation state cycling during reaction is similar to the behavior of single-site homogeneous catalysts. Given the unique electronic structure of many single-site catalysts, such a combined approach in which the atomic-scale catalyst structure and charge state of the single atom dopant can be monitored as a function of its reactive environment is a key step toward developing structure-function relationships that inform the design of new catalysts.

  View details for DOI 10.1021/jacs.1c09274

  View details for PubMedID 34908398

• Propane Dehydrogenation Catalyzed by Isolated Pt Atoms in =SiOZn-OH Nests in Dealuminated Zeolite Beta. Journal of the American Chemical Society Qi, L., Babucci, M., Zhang, Y., Lund, A., Liu, L., Li, J., Chen, Y., Hoffman, A. S., Bare, S. R., Han, Y., Gates, B. C., Bell, A. T. 2021

  Abstract

  Atomically dispersed noble metal catalysts have drawn wide attention as candidates to replace supported metal clusters and metal nanoparticles. Atomic dispersion can offer unique chemical properties as well as maximum utilization of the expensive metals. Addition of a second metal has been found to help reduce the size of Pt ensembles in bimetallic clusters; however, the stabilization of isolated Pt atoms in small nests of nonprecious metal atoms remains challenging. We now report a novel strategy for the design, synthesis, and characterization of a zeolite-supported propane dehydrogenation catalyst that incorporates predominantly isolated Pt atoms stably bonded within nests of Zn atoms located within the nanoscale pores of dealuminated zeolite Beta. The catalyst is stable in long-term operation and exhibits high activity and high selectivity to propene. Atomic resolution images, bolstered by X-ray absorption spectra, demonstrate predominantly atomic dispersion of the Pt in the nests and, with complementary infrared and nuclear magnetic resonance spectra, determine a structural model of the nested Pt.

  View details for DOI 10.1021/jacs.1c10261

  View details for PubMedID 34881868

• Identifying higher oxygenate synthesis sites in Cu catalysts promoted and stabilized by atomic layer deposited Fe2O3 JOURNAL OF CATALYSIS Asundi, A. S., Nathan, S. S., Hong, J., Hoffman, A. S., Pennel, M., Bare, S. R., Bent, S. F. 2021; 404: 210-223

  View details for DOI 10.1016/j.jcat.2021.09.015

  View details for Web of Science ID 000710707800012

• Lanthanum induced lattice strain improves hydrogen sulfide capacities of copper oxide adsorbents AICHE JOURNAL Canning, G. A., Azzam, S. A., Hoffman, A. S., Boubnov, A., Alshafei, F. H., Ghosh, R., Ko, B., Datye, A., Bare, S. R., Simonetti, D. A. 2021

  View details for DOI 10.1002/aic.17484

  View details for Web of Science ID 000709421200001

• Monolayer Support Control and Precise Colloidal Nanocrystals Demonstrate Metal-Support Interactions in Heterogeneous Catalysts. Advanced materials (Deerfield Beach, Fla.) Goodman, E. D., Asundi, A. S., Hoffman, A. S., Bustillo, K. C., Stebbins, J. F., Bare, S. R., Bent, S. F., Cargnello, M. 2021: e2104533

  Abstract

  Electronic and geometric interactions between active and support phases are critical in determining the activity of heterogeneous catalysts, but metal-support interactions are challenging to study. Here, it is demonstrated how the combination of the monolayer-controlled formation using atomic layer deposition (ALD) and colloidal nanocrystal synthesis methods leads to catalysts with sub-nanometer precision of active and support phases, thus allowing for the study of the metal-support interactions in detail. The use of this approach in developing a fundamental understanding of support effects in Pd-catalyzed methane combustion is demonstrated. Uniform Pd nanocrystals are deposited onto Al2 O3 /SiO2 spherical supports prepared with control over morphology and Al2 O3 layer thicknesses ranging from sub-monolayer to a 4nm thick uniform coating. Dramatic changes in catalytic activity depending on the coverage and structure of Al2 O3 situated at the Pd/Al2 O3 interface are observed, with even a single monolayer of alumina contributing an order of magnitude increase in reaction rate. By building the Pd/Al2 O3 interface up layer-by-layer and using uniform Pd nanocrystals, this work demonstrates the importance of controlled and tunable materials in determining metal-support interactions and catalyst activity.

  View details for DOI 10.1002/adma.202104533

  View details for PubMedID 34535919

• Insights and comparison of structure-property relationships in propane and propene catalytic combustion on Pd- and Pt-based catalysts JOURNAL OF CATALYSIS Yang, A., Streibel, V., Choksi, T. S., Aljama, H., Werghi, B., Bare, S. R., Sanchez-Carrera, R. S., Schaefer, A., Li, Y., Abild-Pedersen, F., Cargnello, M. 2021; 401: 89-101

  View details for DOI 10.1016/j.jcat.2021.06.018

  View details for Web of Science ID 000691545800010

• Characterization of a Metal-Organic Framework Zr6O8 Node-Supported Atomically Dispersed Iridium Catalyst for Ethylene Hydrogenation by X-ray Absorption Near-Edge Structure and Infrared Spectroscopies JOURNAL OF PHYSICAL CHEMISTRY C Babucci, M., Hoffman, A. S., Bare, S. R., Gates, B. C. 2021; 125 (31): 16995-17007

  View details for DOI 10.1021/acs.jpcc.1c03563

  View details for Web of Science ID 000685650400012

• Tailoring the Local Environment of Platinumin Single-Atom Pt1/CeO2 Catalysts for Robust Low-Temperature CO Oxidation. Angewandte Chemie (International ed. in English) Jiang, D., Yao, Y., Li, T., Wan, G., Pereira-Hernandez, X. I., Lu, Y., Tian, J., Khivantsev, K., Engelhard, M. H., Sun, C., Garcia-Vargas, C. E., Hoffman, A. S., Bare, S. R., Datye, A. K., Hu, L., Wang, Y. 2021

  Abstract

  Single-atom Pt 1 /CeO 2 catalyst by atom trapping (AT, 800 o C in air) shows excellent thermal stability, however, it is inactive for CO oxidation at low temperatures due to over-stabilization of Pt 2+ in a highly symmetric square-planar Pt 1 O 4 coordination. Reductive activation forming Pt nanoparticles (NPs) results in enhanced activity, however, NPs are easily oxidized leading to drastic activity loss. Here we show that tailoring the local environment of isolated Pt 2+ via thermal-shock (TS) synthesis leads to a highly active and thermally stable Pt 1 /CeO 2 catalyst. Ultrafast shockwaves (> 1200 o C) in an inert atmosphere induce surface reconstruction of CeO 2 , generating Pt single atoms in an asymmetric Pt 1 O 4 configuration. Originating from this unique coordination, Pt 1 delta+ in a partially reduced state dynamically evolved during CO oxidation, resulting in an exceptional low-temperature performance. The CO oxidation reactivity on the Pt 1 /CeO 2 _TS catalyst is retained under oxidizing conditions.

  View details for DOI 10.1002/anie.202108585

  View details for PubMedID 34346155

• Beyond Radical Rebound: Methane Oxidation to Methanol Catalyzed by Iron Species in Metal-Organic Framework Nodes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Simons, M. C., Prinslow, S. D., Babucci, M., Hoffman, A. S., Hong, J., Vitillo, J. G., Bare, S. R., Gates, B. C., Lu, C. C., Gagliardi, L., Bhan, A. 2021; 143 (31): 12165-12174

  Abstract

  Recent work has exploited the ability of metal-organic frameworks (MOFs) to isolate Fe sites that mimic the structures of sites in enzymes that catalyze selective oxidations at low temperatures, opening new pathways for the valorization of underutilized feedstocks such as methane. Questions remain as to whether the radical-rebound mechanism commonly invoked in enzymatic and homogeneous systems also applies in these rigid-framework materials, in which resisting the overoxidation of desired products is a major challenge. We demonstrate that MOFs bearing Fe(II) sites within Fe3-μ3-oxo nodes active for conversion of CH4 + N2O mixtures (368-408 K) require steps beyond the radical-rebound mechanism to protect the desired CH3OH product. Infrared spectra and density functional theory show that CH3OH(g) is stabilized as Fe(III)-OCH3 groups on the MOF via hydrogen atom transfer with Fe(III)-OH groups, eliminating water. Consequently, upon addition of a protonic zeolite in inter- and intrapellet mixtures with the MOF, we observed increases in CH3OH selectivity with increasing ratio and proximity of zeolitic H+ to MOF-based Fe(II) sites, as methanol is protected within the zeolite. We infer from the data that CH3OH(g) is formed via the radical-rebound mechanism on Fe(II) sites but that subsequent transport and dehydration steps are required to protect CH3OH(g) from overoxidation. The results demonstrate that the radical-rebound mechanism commonly invoked in this chemistry is insufficient to explain the reactivity of these systems, that the selectivity-controlling steps involve both chemical and physical rate phenomena, as well as offering a strategy to mitigate overoxidation in these and similar systems.

  View details for DOI 10.1021/jacs.1c04766

  View details for Web of Science ID 000684581100033

  View details for PubMedID 34314584

• Unlocking the Catalytic Potential of TiO2-Supported Pt Single Atoms for the Reverse Water-Gas Shift Reaction by Altering Their Chemical Environment JACS AU Chen, L., Unocic, R. R., Hoffman, A. S., Hong, J., Braga, A. H., Bao, Z., Bare, S. R., Szanyi, J. 2021; 1 (7): 977-986

  View details for DOI 10.1021/jacsau.1c00111

  View details for Web of Science ID 000678387300010

• Unlocking the Catalytic Potential of TiO2-Supported Pt Single Atoms for the Reverse Water-Gas Shift Reaction by Altering Their Chemical Environment. JACS Au Chen, L., Unocic, R. R., Hoffman, A. S., Hong, J., Braga, A. H., Bao, Z., Bare, S. R., Szanyi, J. 2021; 1 (7): 977-986

  Abstract

  Single-atom catalysts (SACs) often exhibit dynamic responses to the reaction and pretreatment environment that affect their activity. The lack of understanding of these behaviors hinders the development of effective, stable SACs, and makes their investigations rather difficult. Here we report a reduction-oxidation cycle that induces nearly 5-fold activity enhancement on Pt/TiO2 SACs for the reverse water-gas shift (rWGS) reaction. We combine microscopy (STEM) and spectroscopy (XAS and IR) studies with kinetic measurements, to convincingly show that the low activity on the fresh SAC is a result of limited accessibility of Pt single atoms (Pt1) due to high Pt-O coordination. The reduction step mobilizes Pt1, forming small, amorphous, and unstable Pt aggregates. The reoxidation step redisperses Pt into Pt1, but in a new, less O-coordinated chemical environment that makes the single metal atoms more accessible and, consequently, more active. After the cycle, the SAC exhibits superior rWGS activity to nonatomically dispersed Pt/TiO2. During the rWGS, the activated Pt1 experience slow deactivation, but can be reactivated by mild oxidation. This work demonstrates a clear picture of how the structural evolution of Pt/TiO2 SACs leads to ultimate catalytic efficiency, offering desired understanding on the rarely explored dynamic chemical environment of supported single metal atoms and its catalytic consequences.

  View details for DOI 10.1021/jacsau.1c00111

  View details for PubMedID 34467344

  View details for PubMedCentralID PMC8395703

• Understanding Degradation Mechanisms in SrIrO3 Oxygen Evolution Electrocatalysts: Chemical and Structural Microscopy at the Nanoscale ADVANCED FUNCTIONAL MATERIALS Ben-Naim, M., Liu, Y., Stevens, M., Lee, K., Wette, M. R., Boubnov, A., Trofimov, A. A., Ievlev, A. V., Belianinov, A., Davis, R. C., Clemens, B. M., Bare, S. R., Hikita, Y., Hwang, H. Y., Higgins, D. C., Sinclair, R., Jaramillo, T. F. 2021

  View details for DOI 10.1002/adfm.202101542

  View details for Web of Science ID 000662722100001

• Catalytic CO Oxidation on MgAl2O4-Supported Iridium Single Atoms: Ligand Configuration and Site Geometry JOURNAL OF PHYSICAL CHEMISTRY C Wang, J., Lu, Y., Liu, L., Yu, L., Yang, C., Delferro, M., Hoffman, A. S., Bare, S. R., Karim, A. M., Xin, H. 2021; 125 (21): 11380-11390

  View details for DOI 10.1021/acs.jpcc.1c02287

  View details for Web of Science ID 000661114000009

• Reduction and Agglomeration of Supported Metal Clusters Induced by High-Flux X-ray Absorption Spectroscopy Measurements JOURNAL OF PHYSICAL CHEMISTRY C Albrahim, M., Thompson, C., Leshchev, D., Shrotri, A., Unocic, R. R., Hong, J., Hoffman, A. S., Meloni, M. J., Runnebaum, R. C., Bare, S. R., Stavitski, E., Karim, A. M. 2021; 125 (20): 11048-11057

  View details for DOI 10.1021/acs.jpcc.1c01823

  View details for Web of Science ID 000657357100025

• Directing reaction pathways via in situ control of active site geometries in PdAu single-atom alloy catalysts. Nature communications Ouyang, M., Papanikolaou, K. G., Boubnov, A., Hoffman, A. S., Giannakakis, G., Bare, S. R., Stamatakis, M., Flytzani-Stephanopoulos, M., Sykes, E. C. 2021; 12 (1): 1549

  Abstract

  The atomic scale structure of the active sites in heterogeneous catalysts is central to their reactivity and selectivity. Therefore, understanding active site stability and evolution under different reaction conditions is key to the design of efficient and robust catalysts. Herein we describe theoretical calculations which predict that carbon monoxide can be used to stabilize different active site geometries in bimetallic alloys and then demonstrate experimentally that the same PdAu bimetallic catalyst can be transitioned between a single-atom alloy and a Pd cluster phase. Each state of the catalyst exhibits distinct selectivity for the dehydrogenation of ethanol reaction with the single-atom alloy phase exhibiting high selectivity to acetaldehyde and hydrogen versus a range of products from Pd clusters. First-principles based Monte Carlo calculations explain the origin of this active site ensemble size tuning effect, and this work serves as a demonstration of what should be a general phenomenon that enables in situ control over catalyst selectivity.

  View details for DOI 10.1038/s41467-021-21555-z

  View details for PubMedID 33750788

• On the Cobalt Carbide Formation in a Co/TiO2 Fischer-Tropsch Synthesis Catalyst as Studied by High-Pressure, Long-Term Operando X-ray Absorption and Diffraction. ACS catalysis van Ravenhorst, I. K., Hoffman, A. S., Vogt, C., Boubnov, A., Patra, N., Oord, R., Akatay, C., Meirer, F., Bare, S. R., Weckhuysen, B. M. 2021; 11 (5): 2956–67

  Abstract

  Operando X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) were performed on a Co/TiO2 Fischer-Tropsch synthesis (FTS) catalyst at 16 bar for (at least) 48 h time-on-stream in both a synchrotron facility and a laboratory-based X-ray diffractometer. Cobalt carbide formation was observed earlier during FTS with operando XAS than with XRD. This apparent discrepancy is due to the higher sensitivity of XAS to a short-range order. Interestingly, in both cases, the product formation does not noticeably change when cobalt carbide formation is detected. This suggests that cobalt carbide formation is not a major deactivation mechanism, as is often suggested for FTS. Moreover, no cobalt oxide formation was detected by XAS or XRD. In other words, one of the classical proposals invoked to explain Co/TiO2 catalyst deactivation could not be supported by our operando X-ray characterization data obtained at close to industrially relevant reaction conditions. Furthermore, a bimodal cobalt particle distribution was observed by high-angle annular dark-field scanning transmission electron microscopy and energy-dispersive X-ray analysis, while product formation remained relatively stable. The bimodal distribution is most probably due to the mobility and migration of the cobalt nanoparticles during FTS conditions.

  View details for DOI 10.1021/acscatal.0c04695

  View details for PubMedID 33815895

• Operando high-pressure investigation of size-controlled CuZn catalysts for the methanol synthesis reaction. Nature communications Divins, N. J., Kordus, D., Timoshenko, J., Sinev, I., Zegkinoglou, I., Bergmann, A., Chee, S. W., Widrinna, S., Karslioglu, O., Mistry, H., Lopez Luna, M., Zhong, J. Q., Hoffman, A. S., Boubnov, A., Boscoboinik, J. A., Heggen, M., Dunin-Borkowski, R. E., Bare, S. R., Cuenya, B. R. 2021; 12 (1): 1435

  Abstract

  Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu0.7Zn0.3 nanoparticles supported on ZnO/Al2O3, gamma-Al2O3 and SiO2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al2O3 and CuZn/SiO2, but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO2. Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO2. In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity.

  View details for DOI 10.1038/s41467-021-21604-7

  View details for PubMedID 33664267

• Impurity Control in Catalyst Design: The Role of Sodium in Promoting and Stabilizing Co and Co2C for Syngas Conversion CHEMCATCHEM Asundi, A. S., Hoffman, A. S., Nathan, S. S., Boubnov, A., Bare, S. R., Bent, S. F. 2021

  View details for DOI 10.1002/cctc.202001703

  View details for Web of Science ID 000604330400001

• Understanding Support Effects of ZnO-Promoted Co Catalysts for Syngas Conversion to Alcohols Using Atomic Layer Deposition CHEMCATCHEM Nathan, S. S., Asundi, A. S., Singh, J. A., Hoffman, A. S., Boubnov, A., Hong, J., Bare, S. R., Bent, S. F. 2020

  View details for DOI 10.1002/cctc.202001630

  View details for Web of Science ID 000595223800001

• Enhanced alcohol production over binary Mo/Co carbide catalysts in syngas conversion JOURNAL OF CATALYSIS Asundi, A. S., Hoffman, A. S., Chi, M., Nathan, S. S., Boubnov, A., Hong, J., Bare, S. R., Bent, S. F. 2020; 391: 446–58

  View details for DOI 10.1016/j.jcat.2020.09.003

  View details for Web of Science ID 000590678200005

• Effect of Si/Al ratio of ZSM-5 support on structure and activity of Mo species in methane dehydroaromatization FUEL Rahman, M., Infantes-Molina, A., Hoffman, A. S., Bare, S. R., Emerson, K. L., Khatib, S. J. 2020; 278

  View details for DOI 10.1016/j.fuel.2020.118290

  View details for Web of Science ID 000560684500006

• Insight into restructuring of Pd-Au nanoparticles using EXAFS Boubnov, A., Timoshenko, J., Wrasman, C. J., Hoffman, A. S., Cargnello, M., Frenkel, A. I., Bare, S. R. PERGAMON-ELSEVIER SCIENCE LTD. 2020

  View details for DOI 10.1016/j.radphyschem.2019.04.054

  View details for Web of Science ID 000543372500029

• Insights into Copper Sulfide Formation from Cu and S K edge XAS and DFT studies. Inorganic chemistry Azzam, S. A., Boubnov, A., Hoffman, A. S., Lopez-Ausens, T., Chiang, N., Canning, G., Sautet, P., Bare, S. R., Simonetti, D. A. 2020

  Abstract

  An understanding of the fundamentals of the reaction between CuO with trace amounts of H2S to form CuS products is critical for the optimal utilization of this process in sulfur removal applications. Unfortunately, CuS is a complex material, featuring various Cu2-xS compounds (with 0 ≤ x ≤ 1), distorted crystal phases, and varying electronic structures and coordination environments of Cu and S ions. In this work, we combine ex situ and in situ X-ray absorption spectroscopy (XAS) at S and Cu K edges, fixed bed sorption experiments, DFT simulations, and other characterization techniques to speciate the CuS products formed at different temperatures (298-383 K) and from CuO sorbents with different crystallite sizes (2.8-40 nm). The results of our analysis identify the formation of a distorted CuS layer at the surface of CuO crystals with disulfide groups with shorter Cu-S bonds and higher delocalization of the positive charge of the Cu center into (S1-)2. This distorted CuS layer dominates the XAS signal at lower temperatures (298-323 K) and at the initial stages of sulfidation at higher temperatures (353 and 383 K) where conversion is low (<40%). First-principles atomistic simulations confirm the thermodynamic favorability of the formation of surface (S1-)2 on both CuO (111) and (111) surfaces, providing further support for our experimental observations. Furthermore, these simulations reveal that the presence of disulfide bonds stabilized surface hydroxyl groups, leading to lower Gibbs Free Energies of their surface migration.

  View details for DOI 10.1021/acs.inorgchem.0c02232

  View details for PubMedID 33001646

• Supported Metal Pair-Site Catalysts ACS CATALYSIS Guan, E., Ciston, J., Bare, S. R., Runnebaum, R. C., Katz, A., Kulkarni, A., Kronawitter, C. X., Gates, B. C. 2020; 10 (16): 9065–85

  View details for DOI 10.1021/acscatal.0c02000

  View details for Web of Science ID 000563749900009

• Selective Methanol Carbonylation to Acetic Acid on Heterogeneous Atomically Dispersed ReO4/SiO2 Catalysts JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Qi, J., Finzel, J., Robatjazi, H., Xu, M., Hoffman, A. S., Bare, S. R., Pan, X., Christopher, P. 2020; 142 (33): 14178–89

  Abstract

  Methanol carbonylation to acetic acid (AA) is a large-scale commodity chemical production process that requires homogeneous liquid-phase organometallic catalysts with corrosive halide-based cocatalysts to achieve high selectivity and activity. Here, we demonstrate a heterogeneous catalyst based on atomically dispersed rhenium (ReO4) active sites on an inert support (SiO2) for the halide-free, gas phase carbonylation of methanol to AA. Atomically dispersed ReO4 species and nanometer sized ReO x clusters were deposited on a high surface area (700 m2/g) inert SiO2 using triethanolamine as a dispersion promoter and characterized using aberration corrected scanning transmission electron microscopy (AC-STEM), UV-vis spectroscopy, and X-ray absorption spectroscopy (XAS). Reactivity measurements at atmospheric pressure with 30 mbar of methanol and CO (1:1 molar ratio) showed that bulk Re2O7 and ReO x clusters on SiO2 (formed at >10 wt %) were selective for dimethyl ether formation, while atomically dispersed ReO4 on SiO2 (formed at <10 wt %) exhibited stable (for 60 h) > 93% selectivity to AA with single pass conversion >60%. Kinetic analysis, in situ FTIR, and in situ XAS measurements suggest that the AA formation mechanism involves methanol activation on ReO4, followed by CO insertion into the terminal methyl species. Further, the introduction of ∼0.2 wt % of atomically dispersed Rh to 10 wt % atomically dispersed ReO4 on SiO2 resulted in >96% selectivity toward AA production at volumetric reaction rates comparable to homogeneous processes. This work introduces a new class of promising heterogeneous catalysts based on atomically dispersed ReO4 on inert supports for alcohol carbonylation.

  View details for DOI 10.1021/jacs.0c05026

  View details for Web of Science ID 000563079000022

  View details for PubMedID 32689793

• Pretreatment Effects on the Surface Chemistry of Small Oxygenates on Molybdenum Trioxide ACS CATALYSIS Najmi, S., Rasmussen, M., Innocenti, G., Chang, C., Stavitski, E., Bare, S. R., Medford, A. J., Medlin, J., Sievers, C. 2020; 10 (15): 8187–8200

  View details for DOI 10.1021/acscatal.0c01992

  View details for Web of Science ID 000562075000016

• Environmentally benign synthesis of a PGM-free catalyst for low temperature CO oxidation APPLIED CATALYSIS B-ENVIRONMENTAL Riley, C., Canning, G., De La Riva, A., Zhou, S., Peterson, E., Boubnov, A., Hoffman, A., Minh Tran, Bare, S. R., Lin, S., Guo, H., Datye, A. 2020; 264

  View details for DOI 10.1016/j.apcatb.2019.118547

  View details for Web of Science ID 000515195200065

• Tunable Catalytic Performance of Palladium Nanoparticles for H2O2 Direct Synthesis via Surface-Bound Ligands ACS CATALYSIS e Freitas, L. L., Puertolas, B., Zhang, J., Wang, B., Hoffman, A. S., Bare, S. R., Perez-Ramirez, J., Medlin, J., Nikolla, E. 2020; 10 (9): 5202–7

  View details for DOI 10.1021/acscatal.0c01517

  View details for Web of Science ID 000530090800038

• Revealing the structure of a catalytic combustion active-site ensemble combining uniform nanocrystal catalysts and theory insights. Proceedings of the National Academy of Sciences of the United States of America Yang, A. C., Choksi, T. n., Streibel, V. n., Aljama, H. n., Wrasman, C. J., Roling, L. T., Goodman, E. D., Thomas, D. n., Bare, S. R., Sánchez-Carrera, R. S., Schäfer, A. n., Li, Y. n., Abild-Pedersen, F. n., Cargnello, M. n. 2020

  Abstract

  Supported metal catalysts are extensively used in industrial and environmental applications. To improve their performance, it is crucial to identify the most active sites. This identification is, however, made challenging by the presence of a large number of potential surface structures that complicate such an assignment. Often, the active site is formed by an ensemble of atoms, thus introducing further complications in its identification. Being able to produce uniform structures and identify the ones that are responsible for the catalyst performance is a crucial goal. In this work, we utilize a combination of uniform Pd/Pt nanocrystal catalysts and theory to reveal the catalytic active-site ensemble in highly active propene combustion materials. Using colloidal chemistry to exquisitely control nanoparticle size, we find that intrinsic rates for propene combustion in the presence of water increase monotonically with particle size on Pt-rich catalysts, suggesting that the reaction is structure dependent. We also reveal that water has a near-zero or mildly positive reaction rate order over Pd/Pt catalysts. Theory insights allow us to determine that the interaction of water with extended terraces present in large particles leads to the formation of step sites on metallic surfaces. These specific step-edge sites are responsible for the efficient combustion of propene at low temperature. This work reveals an elusive geometric ensemble, thus clearly identifying the active site in alkene combustion catalysts. These insights demonstrate how the combination of uniform catalysts and theory can provide a much deeper understanding of active-site geometry for many applications.

  View details for DOI 10.1073/pnas.2002342117

  View details for PubMedID 32554500

• Uniformity Is Key in Defining Structure-Function Relationships for Atomically Dispersed Metal Catalysts: The Case of Pt/CeO2. Journal of the American Chemical Society Resasco, J., DeRita, L., Dai, S., Chada, J. P., Xu, M., Yan, X., Finzel, J., Hanukovich, S., Hoffman, A. S., Graham, G. W., Bare, S. R., Pan, X., Christopher, P. 2019

  Abstract

  Catalysts consisting of atomically dispersed Pt (Ptiso) species on CeO2 supports have received recent interest due to their potential for efficient metal utilization in catalytic convertors. However, discrepancies exist between the behavior (reducibility, interaction strength with adsorbates) of high surface area Ptiso/CeO2 systems and of well-defined surface science and computational model systems, suggesting differences in Pt local coordination in the two classes of materials. Here, we reconcile these differences by demonstrating that high surface area Ptiso/CeO2 synthesized at low Pt loadings (<0.1% weight) exhibit resistance to reduction and sintering up to 500 °C in 0.05 bar H2 and minimal interactions with CO-properties previously seen only for model system studies. Alternatively, Pt loadings >0.1 weight % produce a distribution of sub-nanometer Pt structures, which are difficult to distinguish using common characterization techniques, and exhibit strong interactions with CO and weak resistance to sintering, even in 0.05 bar H2 at 50 °C-properties previously seen for high surface area materials. This work demonstrates that low metal loadings can be used to selectively populate the most thermodynamically stable adsorption sites on high surface area supports with atomically dispersed metals. Further, the site uniformity afforded by this synthetic approach is critical for the development of relationships between atomic scale local coordination and functional properties. Comparisons to recent studies of Ptiso/TiO2 suggest a general compromise between the stability of atomically dispersed metal catalysts and their ability to interact with and activate molecular species.

  View details for DOI 10.1021/jacs.9b09156

  View details for PubMedID 31815460

• Structure, Dynamics, and Reactivity for Light Alkane Oxidation of Fe(II) Sites Situated in the Nodes of a Metal-Organic Framework JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Simons, M. C., Vitillo, J. G., Babucci, M., Hoffman, A. S., Boubnov, A., Beauvais, M. L., Chen, Z., Cramer, C. J., Chapman, K. W., Bare, S. R., Gates, B. C., Lu, C. C., Gagliardi, L., Bhan, A. 2019; 141 (45): 18142-18151

  Abstract

  Metal organic frameworks (MOFs), with their crystalline, porous structures, can be synthesized to incorporate a wide range of catalytically active metals in tailored surroundings. These materials have potential as catalysts for conversion of light alkanes, feedstocks available in large quantities from shale gas that are changing the economics of manufacturing commodity chemicals. Mononuclear high-spin (S = 2) Fe(II) sites situated in the nodes of the MOF MIL-100(Fe) convert propane via dehydrogenation, hydroxylation, and overoxidation pathways in reactions with the atomic oxidant N2O. Pair distribution function analysis, N2 adsorption isotherms, X-ray diffraction patterns, and infrared and Raman spectra confirm the single-phase crystallinity and stability of MIL-100(Fe) under reaction conditions (523 K in vacuo, 378-408 K C3H8 + N2O). Density functional theory (DFT) calculations illustrate a reaction mechanism for the formation of 2-propanol, propylene, and 1-propanol involving the oxidation of Fe(II) to Fe(III) via a high-spin Fe(IV)═O intermediate. The speciation of Fe(II) and Fe(III) in the nodes and their dynamic interchange was characterized by in situ X-ray absorption spectroscopy and ex situ Mössbauer spectroscopy. The catalytic relevance of Fe(II) sites and the number of such sites were determined using in situ chemical titrations with NO. N2 and C3H6 production rates were found to be first-order in N2O partial pressure and zero-order in C3H8 partial pressure, consistent with DFT calculations that predict the reaction of Fe(II) with N2O to be rate determining. DFT calculations using a broken symmetry method show that Fe-trimer nodes affecting reaction contain antiferromagnetically coupled iron species, and  highlight the importance of stabilizing high-spin (S = 2) Fe(II) species for effecting alkane oxidation at low temperatures (<408 K).

  View details for DOI 10.1021/jacs.9b08686

  View details for Web of Science ID 000498281600027

  View details for PubMedID 31670511

• Palladium oxidation leads to methane combustion activity: Effects of particle size and alloying with platinum. The Journal of chemical physics Goodman, E. D., Ye, A. A., Aitbekova, A., Mueller, O., Riscoe, A. R., Nguyen Taylor, T., Hoffman, A. S., Boubnov, A., Bustillo, K. C., Nachtegaal, M., Bare, S. R., Cargnello, M. 2019; 151 (15): 154703

  Abstract

  Pd- and Pt-based catalysts are highly studied materials due to their widespread use in emissions control catalysis. However, claims continue to vary regarding the active phase and oxidation state of the metals. Different conclusions have likely been reached due to the heterogeneous nature of such materials containing various metal nanoparticle sizes and compositions, which may each possess unique redox features. In this work, using uniform nanocrystal catalysts, we study the effect of particle size and alloying on redox properties of Pd-based catalysts and show their contribution to methane combustion activity using operando quick extended x-ray absorption fine structure measurements. Results demonstrate that for all studied Pd sizes (3 nm-16 nm), Pd oxidation directly precedes CH4 combustion to CO2, suggesting Pd oxidation as a prerequisite step to methane combustion, and an oxidation pretreatment shows equal or better catalysis than a reduction pretreatment. Results are then extended to uniform alloyed PtxPd1-x nanoparticles, where oxidative pretreatments are shown to enhance low-temperature combustion. In these uniform alloys, we observe a composition-dependent effect with Pt-rich alloys showing the maximum difference between oxidative and reductive pretreatments. In Pt-rich alloys, we initially observe that the presence of Pt maintains Pd in a lower-activity reduced state. However, with time on stream, PdO eventually segregates under oxidizing combustion conditions, leading to a slowly increasing activity. Overall, across particle sizes and alloy compositions, we relate increased catalytic activity to Pd oxidation, thus shedding light on previous contrasting results related to the methane combustion activity of these catalysts.

  View details for DOI 10.1063/1.5126219

  View details for PubMedID 31640349

• Transition state and product diffusion control by polymer-nanocrystal hybrid catalysts NATURE CATALYSIS Riscoe, A. R., Wrasman, C. J., Herzing, A. A., Hoffman, A. S., Menon, A., Boubnov, A., Vargas, M., Bare, S. R., Cargnello, M. 2019; 2 (10): 852–63

  View details for DOI 10.1038/s41929-019-0322-7

  View details for Web of Science ID 000489769600009

• A versatile approach for quantification of surface site fractions using reaction kinetics: The case of CO oxidation on supported Ir single atoms and nanoparticles JOURNAL OF CATALYSIS Lu, Y., Kuo, C., Kovarik, L., Hoffman, A. S., Boubnov, A., Driscoll, D. M., Morris, J. R., Bare, S. R., Karim, A. M. 2019; 378: 121–30

  View details for DOI 10.1016/j.jcat.2019.08.023

  View details for Web of Science ID 000494887100014

• Engineering of Ruthenium-Iron Oxide Colloidal Heterostructures Leads to Improved Yields in CO2 Hydrogenation to Hydrocarbons. Angewandte Chemie (International ed. in English) Cargnello, M., Aitbekova, A., Goodman, E., Wu, L., Boubnov, A., Hoffman, A., Genc, A., Cheng, H., Casalena, L., Bare, S. 2019

  Abstract

  Catalytic CO2 reduction to fuels and chemicals is one of the major pursuits in reducing greenhouse gas emissions. One such popular approach utilizes the reverse water-gas shift reaction, followed by Fischer-Tropsch synthesis, and iron is a well-known candidate for this process. Some attempts have been made to modify and improve its reactivity, but resuted in limited success. In this work, using ruthenium-iron oxide colloidal heterodimers we demonstrate that close contact between the two phases promotes the reduction of iron oxide via a proximal hydrogen spillover effect, leading to the formation of ruthenium-iron core-shell structures active for the reaction at significantly lower temperatures than in bare iron catalysts. Furthermore, by engineering the iron oxide shell thickness, we achieve a fourfold increase in hydrocarbon yield compared to the heterodimers. In general, our work shows how rational design of colloidal heterostructures can result in materials with significantly improved catalytic performance in CO2 conversion processes.

  View details for DOI 10.1002/anie.201910579

  View details for PubMedID 31545533

• Catalyst deactivation via decomposition into single atoms and the role of metal loading NATURE CATALYSIS Goodman, E. D., Johnston-Peck, A. C., Dietze, E. M., Wrasman, C. J., Hoffman, A. S., Abild-Pedersen, F., Bare, S. R., Plessow, P. N., Cargnello, M. 2019; 2 (9): 748–55

  View details for DOI 10.1038/s41929-019-0328-1

  View details for Web of Science ID 000486144700006

• Synergistic selective oxidation of alcohols using dilute Pd/Au alloys on oxide supports Wrasman, C., Hoffman, A., Bare, S., Cargnello, M. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000525055502212

• Highly tunable platform for biomimetic catalysis from nanocrystal-polymer composites Cargnello, M., Riscoe, A., Wrasman, C., Herzing, A., Bare, S. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000525055504093

• Ruthenium-iron oxide colloidal heterodimers unravel promotion mechanism in iron-catalyzed CO2 hydrogenation to hydrocarbons Aitbekova, A., Goodman, E., Boubnov, A., Hoffman, A., Bare, S., Cargnello, M. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000525055502216

• Single-atom species determine the deactivation of supported catalysts Cargnello, M., Goodman, E., Abild-Pedersen, F., Bare, S. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000525055502294

• Low temperature restructuring of CeO2 supported Ru nanoparticles determines selectivity in CO2 catalytic reduction Aitbekova, A., Wu, L., Wrasman, C., Boubnov, A., Hoffman, A., Bare, S., Cargnello, M. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000525055502277

• Increasing the catalytic stability by optimizing the formation of zeolite-supported Mo carbide species ex situ for methane dehydroaromatization JOURNAL OF CATALYSIS Rahman, M., Infantes-Molina, A., Boubnov, A., Bare, S. R., Stavitski, E., Sridhar, A., Khatib, S. J. 2019; 375: 314–28

  View details for DOI 10.1016/j.jcat.2019.06.002

  View details for Web of Science ID 000486104500033

• Dynamic Reorganization and Confinement of Ti<SUP>IV</SUP> Active Sites Controls Olefin Epoxidation Catalysis on Two-Dimensional Zeotypes JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Grosso-Giordano, N. A., Hoffman, A. S., Boubnov, A., Small, D. W., Bare, S. R., Zones, S. I., Katz, A. 2019; 141 (17): 7090-7106

  Abstract

  The effect of dynamic reorganization and confinement of isolated TiIV catalytic centers supported on silicates is investigated for olefin epoxidation. Active sites consist of grafted single-site calix[4]arene-TiIV centers or their calcined counterparts. Their location is synthetically controlled to be either unconfined at terminal T-atom positions (denoted as type-(i)) or within confining 12-MR pockets (denoted as type-(ii); diameter ∼7 Å, volume ∼185 Å3) composed of hemispherical cavities on the external surface of zeotypes with *-SVY topology. Electronic structure calculations (density functional theory) indicate that active sites consist of cooperative assemblies of TiIV centers and silanols. When active sites are located at unconfined type-(i) environments, the rate constants for cyclohexene epoxidation (323 K, 0.05 mM TiIV, 160 mM cyclohexene, 24 mM tert-butyl hydroperoxide) are 9 ± 2 M-2 s-1; whereas within confining type-(ii) 12-MR pockets, there is a ∼5-fold enhancement to 48 ± 8 M-2 s-1. When a mixture of both environments is initially present in the catalyst resting state, the rate constants reflect confining environments exclusively (40 ± 11 M-2 s-1), indicating that dynamic reorganization processes lead to the preferential location of active sites within 12-MR pockets. While activation enthalpies are Δ H‡app = 43 ± 1 kJ mol-1 irrespective of active site location, confining environments exhibit diminished entropic barriers (Δ S‡app = -68 J mol-1 K-1 for unconfined type-(i) vs -56 J mol-1 K-1 for confining type-(ii)), indicating that confinement leads to more facile association of reactants at active sites to form transition state structures (volume ∼ 225 Å3). These results open new opportunities for controlling reactivity on surfaces through partial confinement on shallow external-surface pockets, which are accessible to molecules that are too bulky to benefit from traditional confinement within micropores.

  View details for DOI 10.1021/jacs.9b02160

  View details for Web of Science ID 000466987900041

  View details for PubMedID 30955340

• Structural evolution of atomically dispersed Pt catalysts dictates reactivity. Nature materials DeRita, L., Resasco, J., Dai, S., Boubnov, A., Thang, H. V., Hoffman, A. S., Ro, I., Graham, G. W., Bare, S. R., Pacchioni, G., Pan, X., Christopher, P. 2019

  Abstract

  The use of oxide-supported isolated Pt-group metal atoms as catalytic active sites is of interest due to their unique reactivity and efficient metal utilization. However, relationships between the structure of these active sites, their dynamic response to environments and catalytic functionality have proved difficult to experimentally establish. Here, sinter-resistant catalysts where Pt was deposited uniformly as isolated atoms in well-defined locations on anatase TiO2 nanoparticle supports were used to develop such relationships. Through a combination of in situ atomic-resolution microscopy- and spectroscopy-based characterization supported by first-principles calculations it was demonstrated that isolated Pt species can adopt a range of local coordination environments and oxidation states, which evolve in response to varied environmental conditions. The variation in local coordination showed a strong influence on the chemical reactivity and could be exploited to control the catalytic performance.

  View details for DOI 10.1038/s41563-019-0349-9

  View details for PubMedID 31011216

• Density-dependent deactivation mechanism in supported catalysts by high-temperature decomposition of particles into single atoms Goodman, E., Johnston-Peck, A., Dietze, E., Wrasman, C., Hoffman, A., Abild-Pedersen, F., Bare, S., Plessow, P., Cargnello, M. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478860502379

• Uncovering the details of methane combustion on palladium catalysts using well-defined nanocrystal precursors Cargnello, M., Huang, W., Goodman, E., Willis, J., Yang, A., Abild-Pedersen, F., Johnston-Peck, A., Bare, S. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478860502176

• Controlling catalytic activity and selectivity for partial hydrogenation by tuning the environment around active sites in iridium complexes bonded to supports CHEMICAL SCIENCE Babucci, M., Fang, C., Perez-Aguilar, J. E., Hoffman, A. S., Boubnov, A., Guan, E., Bare, S. R., Gates, B. C., Uzun, A. 2019; 10 (9): 2623-2632

  Abstract

  Single-site Ir(CO)2 complexes bonded to high-surface-area metal oxide supports, SiO2, TiO2, Fe2O3, CeO2, MgO, and La2O3, were synthesized by chemisorption of Ir(CO)2(acac) (acac = acetylacetonate) followed by coating with each of the following ionic liquids (ILs): 1-n-butyl-3-methylimidazolium tetrafluoroborate, [BMIM][BF4], 1-n-butyl-3-methylimidazolium acetate, [BMIM][Ac], and 1-(3-cyanopropyl)-3-methylimidazolium dicyanamide, [CPMIM][DCA]. Extended X-ray absorption fine structure spectroscopy showed that site-isolated iridium was bonded to oxygen atoms of the support. Electron densities on the iridium enveloped by each IL sheath/support combination were characterized by carbonyl infrared spectroscopy of the iridium gem-dicarbonyls and by X-ray absorption near-edge structure data. The electron-donor/acceptor tendencies of both the support and IL determine the activity and selectivity of the catalysts for the hydrogenation of 1,3-butadiene, with electron-rich iridium being selective for partial hydrogenation. The results resolve the effects of the IL and support as ligands; for example, the effect of the IL becomes dominant when the support has a weak electron-donor character. The combined effects of supports and ILs as ligands offer broad opportunities for tuning catalytic properties of supported metal catalysts.

  View details for DOI 10.1039/c8sc05287e

  View details for Web of Science ID 000459929800004

  View details for PubMedID 30996978

  View details for PubMedCentralID PMC6419936

• Identification of the active complex for CO oxidation over single-atom Ir-on-MgAl2O4 catalysts NATURE CATALYSIS Lu, Y., Wang, J., Yu, L., Kovarik, L., Zhang, X., Hoffman, A. S., Gallo, A., Bare, S. R., Sokaras, D., Kroll, T., Dagle, V., Xin, H., Karim, A. M. 2019; 2 (2): 149–56

  View details for DOI 10.1038/s41929-018-0192-4

  View details for Web of Science ID 000458554800010

• Role of Co2C in ZnO-promoted Co Catalysts for Alcohol Synthesis from Syngas CHEMCATCHEM Singh, J. A., Hoffman, A. S., Schumann, J., Boubnov, A., Asundi, A. S., Nathan, S. S., Norskov, J., Bare, S. R., Bent, S. F. 2019; 11 (2): 799–809

  View details for DOI 10.1002/cctc.201801724

  View details for Web of Science ID 000459734900021

• Probing the Location and Speciation of Elements in Zeolites with Correlated Atom Probe Tomography and Scanning Transmission X-Ray Microscopy CHEMCATCHEM Schmidt, J. E., Ye, X., van Ravenhors, I. K., Oord, R., Shapiro, D. A., Yu, Y., Bare, S. R., Meirer, F., Poplawsky, J. D., Weckhuysen, B. M. 2019; 11 (1): 488-494

  Abstract

  Characterizing materials at nanoscale resolution to provide new insights into structure property performance relationships continues to be a challenging research target due to the inherently low signal from small sample volumes, and is even more difficult for nonconductive materials, such as zeolites. Herein, we present the characterization of a single Cu-exchanged zeolite crystal, namely Cu-SSZ-13, used for NOX reduction in automotive emissions, that was subject to a simulated 135,000-mile aging. By correlating Atom Probe Tomography (APT), a single atom microscopy method, and Scanning Transmission X-ray Microscopy (STXM), which produces high spatial resolution X-ray Absorption Near Edge Spectroscopy (XANES) maps, we show that a spatially non-uniform proportion of the Al was removed from the zeolite framework. The techniques reveal that this degradation is heterogeneous at length scales from micrometers to tens of nanometers, providing complementary insight into the long-term deactivation of this catalyst system.

  View details for DOI 10.1002/cctc.201801378

  View details for Web of Science ID 000457144200041

  View details for PubMedID 31123533

  View details for PubMedCentralID PMC6519228

• Probing Atomic Distributions in Mono- and Bimetallic Nanoparticles by Supervised Machine Learning NANO LETTERS Timoshenko, J., Wrasman, C. J., Luneau, M., Shirman, T., Cargnello, M., Bare, S. R., Aizenberg, J., Friend, C. M., Frenkel, A. I. 2019; 19 (1): 520–29

  Abstract

  Properties of mono- and bimetallic metal nanoparticles (NPs) may depend strongly on their compositional, structural (or geometrical) attributes and their atomic dynamics, all of which can be efficiently described by a partial radial distribution function (PRDF) of metal atoms. For NPs that are several nanometers in size, finite size effects may play a role in determining crystalline order, interatomic distances and particle shape. Bimetallic NPs may also have different compositional distributions than bulk materials. These factors all render the determination of PRDFs challenging. Here extended X-ray absorption fine structure (EXAFS) spectroscopy, molecular dynamics simulations and supervised machine learning (artificial neural-network) method are combined to extract PRDFs directly from experimental data. By applying this method to several systems of Pt and PdAu NPs, we demonstrate the finite size effects on the nearest neighbor distributions, bond dynamics and alloying motifs in mono- and bimetallic particles and establish the generality of this approach.

  View details for PubMedID 30501196

• Supported Catalyst Deactivation by Decomposition into Single Atoms Is Suppressed by Increasing Metal Loading. Nature catalysis Goodman, E. D., Johnston-Peck, A. C., Dietze, E. M., Wrasman, C. J., Hoffman, A. S., Abild-Pedersen, F., Bare, S. R., Plessow, P. N., Cargnello, M. 2019; 2

  Abstract

  In the high-temperature environments needed to perform catalytic processes, supported precious metal catalysts severely lose their activity over time. Even brief exposure to high temperatures can lead to significant losses in activity, which forces manufacturers to use large amounts of noble metals to ensure effective catalyst function for a required lifetime. Generally, loss of catalytic activity is attributed to nanoparticle sintering, or processes by which larger particles grow at the expense of smaller ones. Here, by independently controlling particle size and particle loading using colloidal nanocrystals, we reveal the opposite process as a novel deactivation mechanism: nanoparticles rapidly lose activity by high-temperature nanoparticle decomposition into inactive single atoms. This deactivation route is remarkably fast, leading to severe loss of activity in as little as ten minutes. Importantly, this deactivation pathway is strongly dependent on particle density and concentration of support defect sites. A quantitative statistical model explains how for certain reactions, higher particle densities can lead to more stable catalysts.

  View details for DOI 10.1038/s41929-019-0328-1

  View details for PubMedID 32118197

  View details for PubMedCentralID PMC7047889

• Understanding Structure-Property Relationships of MoO3-Promoted Rh Catalysts for Syngas Conversion to Alcohols. Journal of the American Chemical Society Asundi, A. S., Hoffman, A. S., Bothra, P. n., Boubnov, A. n., Vila, F. D., Yang, N. n., Singh, J. A., Zeng, L. n., Raiford, J. A., Abild-Pedersen, F. n., Bare, S. R., Bent, S. F. 2019

  Abstract

  Rh-based catalysts have shown promise for the direct conversion of syngas to higher oxygenates. Although improvements in higher oxygenate yield have been achieved by combining Rh with metal oxide promoters, details of the structure of the promoted catalyst and the role of the promoter in enhancing catalytic performance are not well understood. In this work, we show that MoO3-promoted Rh nanoparticles form a novel catalyst structure in which Mo substitutes into the Rh surface, leading to both a 66-fold increase in turnover frequency and an enhancement in oxygenate yield. By applying a combination of atomically controlled synthesis, in situ characterization, and theoretical calculations, we gain an understanding of the promoter-Rh interactions that govern catalytic performance for MoO3-promoted Rh. We use atomic layer deposition to modify Rh nanoparticles with monolayer-precise amounts of MoO3, with a high degree of control over the structure of the catalyst. Through in situ X-ray absorption spectroscopy, we find that the atomic structure of the catalytic surface under reaction conditions consists of Mo-OH species substituted into the surface of the Rh nanoparticles. Using density functional theory calculations, we identify two roles of MoO3: first, the presence of Mo-OH in the catalyst surface enhances CO dissociation and also stabilizes a methanol synthesis pathway not present in the unpromoted catalyst; and second, hydrogen spillover from Mo-OH sites to adsorbed species on the Rh surface enhances hydrogenation rates of reaction intermediates.

  View details for DOI 10.1021/jacs.9b07460

  View details for PubMedID 31724857

• In situ observation of phase changes of a silica-supported cobalt catalyst for the Fischer-Tropsch process by the development of a synchrotron-compatible insitu/operando powder X-ray diffraction cell. Journal of synchrotron radiation Hoffman, A. S., Singh, J. A., Bent, S. F., Bare, S. R. 2018; 25 (Pt 6): 1673–82

  Abstract

  In situ characterization of catalysts gives direct insight into the working state of the material. Here, the design and performance characteristics of a universal insitu synchrotron-compatible X-ray diffraction cell capable of operation at high temperature and high pressure, 1373 K, and 35 bar, respectively, are reported. Its performance is demonstrated by characterizing a cobalt-based catalyst used in a prototypical high-pressure catalytic reaction, the Fischer-Tropsch synthesis, using X-ray diffraction. Cobalt nanoparticles supported on silica were studied insitu during Fischer-Tropsch catalysis using syngas, H2 and CO, at 723 K and 20 bar. Post reaction, the Co nanoparticles were carburized at elevated pressure, demonstrating an increased rate of carburization compared with atmospheric studies.

  View details for PubMedID 30407177

• Synthesis of Colloidal Pd/Au Dilute Alloy Nanocrystals and Their Potential for Selective Catalytic Oxidations. Journal of the American Chemical Society Wrasman, C. J., Boubnov, A., Riscoe, A. R., Hoffman, A. S., Bare, S. R., Cargnello, M. 2018

  Abstract

  Selective oxidations are crucial for the creation of valuable chemical building blocks but often require expensive and unstable stoichiometric oxidants such as hydroperoxides and peracids. To date, many catalysts that contain a single type of active site have not been able to attain the desired level of selectivity for partially oxidized products over total combustion. However, catalysts containing multiple types of active sites have proven to be successful for selective reactions. One category of such catalysts is bimetallic alloys, in which catalytic activity and selectivity can be tuned by modifying the surface composition. Traditional catalyst synthesis methods using impregnation struggle to create catalysts with sufficient control over surface chemistry to accurately tune the ensemble size of the desired active sites. Here we describe the synthesis of colloidal nanocrystals of dilute alloys of palladium and gold. We show that when supported on titania (TiO2), tuning the composition of the Pd/Au nanocrystal surface provides a synergistic effect in the selective oxidation of 2-propanol to acetone in the presence of H2 and O2. In particular, we show that certain Pd/Au surface ratios exhibit activity and selectivity far superior to Pd or Au individually. Through precise structural characterization we demonstrate that isolated atoms of Pd exist in the most active catalysts. The synergy between isolated Pd atoms and Au allows for the formation of reactive oxidizing species, likely hydroperoxide groups, responsible for selective oxidation while limiting oxygen dissociation and, thus, complete combustion. This work opens the way to more efficient utilization of scarce noble metals and new options for catalyzed selective oxidations.

  View details for PubMedID 30220200

• Understanding and tuning catalytic materials using well-defined nanocrystal precursors Cargnello, M., Willis, J., Goodman, E., Wrasman, C., Yang, A., Abild-Pedersen, F., Bare, S. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447600002371

• Synergistic effect in colloidal Pd/Au single atom alloy nanocrystals for selective oxidations Wrasman, C., Riscoe, A., Hoffman, A., Boubnov, A., Bare, S., Cargnello, M. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447600002071

• Well-defined nanocrystals catalysts as active phases and premier materials for spectroscopic studies of catalyst restructuring Cargnello, M., Goodman, E., Aitbekova, A., Wrasman, C., Riscoe, A., Yang, A., Abild-Pedersen, F., Bare, S. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447600002061

• Highly tunable platform for biomimetic catalysts from nanocrystal-amorphous polymer composites Cargnello, M., Riscoe, A., Wrasman, C., Aitbekova, A., Goodman, E., Herzing, A., Bare, S. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447600002012

• Uniform Pt/Pd bimetallic nanocrystals demonstrate platinum effect on palladium methane combustion activity and stability Goodman, E., Dai, S., Yang, A., Wrasman, C., Gallo, A., Bare, S., Hoffman, A., Jaramillo, T., Graham, G., Pan, X., Cargnello, M. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000435537702178

• Biomimetic oxidation catalyst from polymer-nanocrystal composite material Riscoe, A., Wrasman, C., Hoffman, A., Menon, A., Boubnov, A., Goodman, E., Bare, S., Cargnello, M. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000435537702408

• Direct observation of the kinetics of gas–solid reactions using in situ kinetic and spectroscopic techniques Reaction Chemistry & Engineering Hoffman, A. S., Azzam, S., Zhang, K., Xu, Y., Liu, Y., Bare, S. R., Simonetti, D. A. 2018; 3: 668-675

  View details for DOI 10.1039/C8RE00020D

• High-Energy-Resolution X-ray Absorption Spectroscopy for Identification of Reactive Surface Species on Supported Single-Site Iridium Catalysts CHEMISTRY-A EUROPEAN JOURNAL Hoffman, A. S., Sokaras, D., Zhang, S., Debefve, L. M., Fang, C., Gallo, A., Kroll, T., Dixon, D. A., Bare, S. R., Gates, B. C. 2017; 23 (59): 14760–68

  Abstract

  We report high-energy-resolution X-ray absorption spectroscopy detection of ethylene and CO ligands adsorbed on catalytically active iridium centers isolated on zeolite HY and on MgO supports. The data are supported by density functional theory and FEFF X-ray absorption near-edge modelling, together with infrared (IR) spectra. The results demonstrate that high-energy-resolution X-ray absorption spectra near the iridium LIII (2p3/2 ) edge provide clearly ascribable, distinctive signatures of the ethylene and CO ligands and illustrate effects of supports and other ligands. This X-ray absorption technique is markedly more sensitive than conventional IR spectroscopy for characterizing surface intermediates, and it is applicable to samples having low metal loadings and in reactive atmospheres and is expected to have an increasing role in catalysis research by facilitating the determination of mechanisms of solid-catalyzed reactions through identification of reaction intermediates in working catalysts.

  View details for PubMedID 28749554

• Tuning the Selectivity of Single-Site Supported Metal Catalysts with Ionic Liquids ACS CATALYSIS Babucci, M., Fang, C., Hoffman, A. S., Bare, S. R., Gates, B. C., Uzun, A. 2017; 7 (10): 6969–72

  View details for DOI 10.1021/acscatal.7b02429

  View details for Web of Science ID 000412795700061

• Understanding and controlling the activity and stability of Pd/Pt oxide catalysts for methane activation Cargnello, M., Goodman, E., Yang, A., Dai, S., Wrasman, C., Bare, S., Hoffman, A., Graham, G., Pan, X. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000429525601603

• Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability ACS CATALYSIS Goodman, E. D., Dai, S., Yang, A., Wrasman, C. J., Gallo, A., Bare, S. R., Hoffman, A. S., Jaramillo, T. F., Graham, G. W., Pan, X., Cargnello, M. 2017; 7 (7): 4372–80

  View details for DOI 10.1021/acscatal.7b00393

  View details for Web of Science ID 000405360800018

• Characterization of Coke on a Pt-Re/gamma-Al2O3 Re-Forming Catalyst: Experimental and Theoretical Study ACS CATALYSIS Bare, S. R., Vila, F. D., Charochak, M. E., Prabhakar, S., Bradley, W. J., Jaye, C., Fischer, D. A., Hayashi, S. T., Bradley, S. A., Rehr, J. J. 2017; 7 (2): 1452–61

  View details for DOI 10.1021/acscatal.6b02785

  View details for Web of Science ID 000393539200061

• Transmission and fluorescence X-ray absorption spectroscopy cell/flow reactor for powder samples under vacuum or in reactive atmospheres (vol 97, 073108, 2016) REVIEW OF SCIENTIFIC INSTRUMENTS Hoffman, A. S., Debefve, L. M., Bendjeriou-Sedjerari, A., Ould-Chikh, S., Bare, S. R., Basset, J., Gates, B. C. 2016; 87 (12): 129901

  View details for DOI 10.1063/1.4971181

  View details for Web of Science ID 000392096800081

  View details for PubMedID 28040947

• Coke Formation in a Zeolite Crystal During the Methanol-to-Hydrocarbons Reaction as Studied with Atom Probe Tomography Schmidt, J. E., Poplawsky, J. D., Mazumder, B., Attila, O., Fu, D., de Winter, D., Meirer, F., Bare, S. R., Weckhuysen, B. M. WILEY-V C H VERLAG GMBH. 2016: 11173–77

  Abstract

  Understanding the formation of carbon deposits in zeolites is vital to developing new, superior materials for various applications, including oil and gas conversion processes. Herein, atom probe tomography (APT) has been used to spatially resolve the 3D compositional changes at the sub-nm length scale in a single zeolite ZSM-5 crystal, which has been partially deactivated by the methanol-to-hydrocarbons reaction using (13) C-labeled methanol. The results reveal the formation of coke in agglomerates that span length scales from tens of nanometers to atomic clusters with a median size of 30-60 (13) C atoms. These clusters correlate with local increases in Brønsted acid site density, demonstrating that the formation of the first deactivating coke precursor molecules occurs in nanoscopic regions enriched in aluminum. This nanoscale correlation underscores the importance of carefully engineering materials to suppress detrimental coke formation.

  View details for DOI 10.1002/anie.201606099

  View details for Web of Science ID 000383642300038

  View details for PubMedID 27485276

• Transmission and fluorescence X-ray absorption spectroscopy cell/flow reactor for powder samples under vacuum or in reactive atmospheres REVIEW OF SCIENTIFIC INSTRUMENTS Hoffman, A. S., Debefve, L. M., Bendjeriou-Sedjerari, A., Ouldchikh, S., Bare, S. R., Basset, J., Gates, B. C. 2016; 87 (7): 073108

  Abstract

  X-ray absorption spectroscopy is an element-specific technique for probing the local atomic-scale environment around an absorber atom. It is widely used to investigate the structures of liquids and solids, being especially valuable for characterization of solid-supported catalysts. Reported cell designs are limited in capabilities-to fluorescence or transmission and to static or flowing atmospheres, or to vacuum. Our goal was to design a robust and widely applicable cell for catalyst characterizations under all these conditions-to allow tracking of changes during genesis and during operation, both under vacuum and in reactive atmospheres. Herein, we report the design of such a cell and a demonstration of its operation both with a sample under dynamic vacuum and in the presence of gases flowing at temperatures up to 300 °C, showing data obtained with both fluorescence and transmission detection. The cell allows more flexibility in catalyst characterization than any reported.

  View details for DOI 10.1063/1.4958824

  View details for Web of Science ID 000382448600011

  View details for PubMedID 27475549

• Surface analysis of zeolites: An XPS, variable kinetic energy XPS, and low energy ion scattering study SURFACE SCIENCE Bare, S. R., Knop-Gericke, A., Teschner, D., Haevacker, M., Blume, R., Rocha, T., Schloegl, R., Chan, A. Y., Blackwell, N., Charochak, M. E., ter Veen, R., Brongersma, H. H. 2016; 648: 376–82

  View details for DOI 10.1016/j.susc.2015.10.048

  View details for Web of Science ID 000374198600054

• Aberration-Corrected Transmission Electron Microscopy and InSitu XAFS Structural Characterization of Pt/-Al2O3 Nanoparticles CHEMCATCHEM Sinkler, W., Sanchez, S. I., Bradley, S. A., Wen, J., Mishra, B., Kelly, S. D., Bare, S. R. 2015; 7 (22): 3779–87

  View details for DOI 10.1002/cctc.201500784

  View details for Web of Science ID 000365116400021

• Expanding Beyond the Micropore: Active-Site Engineering in Hierarchical Architectures for Beckmann Rearrangement ACS Catalysis Newland, S. H., Sinkler, W., Mezza, T., Bare, S. R., Carravetta, M., Haies, I. M., Levy, A., Keenan, S., Raja, R. 2015; 5 (11): 6587–93

  View details for DOI 10.1021/acscatal.5b01595

  View details for Web of Science ID 000364441300040

• Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Potter, M. E., Paterson, A. J., Mishra, B., Kelly, S. D., Bare, S. R., Cora, F., Levy, A. B., Raja, R. 2015; 137 (26): 8534-8540

  Abstract

  A combined electronic structure computational and X-ray absorption spectroscopy study was used to investigate the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Probing the nature of the molecular species at the atomic level has led to the identification of a unique Co-O-Ti bond, which serves as the loci for the superior performance of the bimetallic catalyst, when compared with its analogous monometallic counterpart. The structural and spectroscopic features associated with this active site have been characterized and contrasted, with a view to affording structure-property relationships, in the wider context of designing sustainable catalytic oxidations with porous solids.

  View details for DOI 10.1021/jacs.5b03734

  View details for Web of Science ID 000357964400039

  View details for PubMedID 26076192

• Determining the location and nearest neighbours of aluminium in zeolites with atom probe tomography NATURE COMMUNICATIONS Perea, D. E., Arslan, I., Liu, J., Ristanovic, Z., Kovarik, L., Arey, B. W., Lercher, J. A., Bare, S. R., Weckhuysen, B. M. 2015; 6

  Abstract

  Zeolite catalysis is determined by a combination of pore architecture and Brønsted acidity. As Brønsted acid sites are formed by the substitution of AlO4 for SiO4 tetrahedra, it is of utmost importance to have information on the number as well as the location and neighbouring sites of framework aluminium. Unfortunately, such detailed information has not yet been obtained, mainly due to the lack of suitable characterization methods. Here we report, using the powerful atomic-scale analysis technique known as atom probe tomography, the quantitative spatial distribution of individual aluminium atoms, including their three-dimensional extent of segregation. Using a nearest-neighbour statistical analysis, we precisely determine the short-range distribution of aluminium over the different T-sites and determine the most probable Al-Al neighbouring distance within parent and steamed ZSM-5 crystals, as well as assess the long-range redistribution of aluminium upon zeolite steaming.

  View details for DOI 10.1038/ncomms8589

  View details for Web of Science ID 000358855900002

  View details for PubMedID 26133270

  View details for PubMedCentralID PMC4506508

• Characterization of a Fluidized Catalytic Cracking Catalyst on Ensemble and Individual Particle Level by X-ray Micro-and Nanotomography, Micro-X-ray Fluorescence, and Micro-X-ray Diffraction CHEMCATCHEM Bare, S. R., Charochak, M. E., Kelly, S. D., Lai, B., Wang, J., Chen-Wiegart, Y. 2014; 6 (5): 1427–37

  View details for DOI 10.1002/cctc.201300974

  View details for Web of Science ID 000335926400037

• Pressure-Dependent Effect of Hydrogen Adsorption on Structural and Electronic Properties of Pt/gamma-Al2O3 Nanoparticles CHEMCATCHEM Mistry, H., Behafarid, F., Bare, S. R., Roldan Cuenya, B. 2014; 6 (1): 348–52

  View details for DOI 10.1002/cctc.201300783

  View details for Web of Science ID 000330636800044

• Science and Technology of Framework Metal-Containing Zeotype Catalysts ADVANCES IN CATALYSIS, VOL 57 Nemeth, L., Bare, S. R., Jentoft, F. C. 2014; 57: 1-97

  View details for DOI 10.1016/B978-0-12-800127-1.00001-1

  View details for Web of Science ID 000348699600003

• Interplay between nanoscale reactivity and bulk performance of H-ZSM-5 catalysts during the methanol-to-hydrocarbons reaction JOURNAL OF CATALYSIS Aramburo, L. R., Teketel, S., Svelle, S., Bare, S. R., Arstad, B., Zandbergen, H. W., Olsbye, U., de Groot, F. F., Weckhuysen, B. M. 2013; 307: 185–93

  View details for DOI 10.1016/j.jcat.2013.07.009

  View details for Web of Science ID 000327903900021

• Operando Effects on the Structure and Dynamics of PtnSnm/gamma-Al2O3 from Ab Initio Molecular Dynamics and X-ray Absorption Spectra JOURNAL OF PHYSICAL CHEMISTRY C Vila, F. D., Rehr, J. J., Kelly, S. D., Bares, S. R. 2013; 117 (24): 12446–57

  View details for DOI 10.1021/jp403931z

  View details for Web of Science ID 000320911100007

• Operando IV CATALYSIS TODAY Sievers, C., Bare, S. R., Stavitski, E. 2013; 205: 1-2

  View details for DOI 10.1016/j.cattod.2013.01.003

  View details for Web of Science ID 000316791700001

• EXAFS Model of 2-Dimensional Platinum Clusters Kelly, S. D., Charochak, M. E., Blackwell, N., Bare, S. R., Wu, Z. Y. IOP PUBLISHING LTD. 2013

  View details for DOI 10.1088/1742-6596/430/1/012061

  View details for Web of Science ID 000320464300061

• Electronic properties and charge transfer phenomena in Pt nanoparticles on gamma-Al2O3: size, shape, support, and adsorbate effects PHYSICAL CHEMISTRY CHEMICAL PHYSICS Behafarid, F., Ono, L. K., Mostafa, S., Croy, J. R., Shafai, G., Hong, S., Rahman, T. S., Bare, S. R., Roldan Cuenya, B. 2012; 14 (33): 11766–79

  Abstract

  This study presents a systematic detailed experimental and theoretical investigation of the electronic properties of size-controlled free and γ-Al(2)O(3)-supported Pt nanoparticles (NPs) and their evolution with decreasing NP size and adsorbate (H(2)) coverage. A combination of in situ X-ray absorption near-edge structure (XANES) and density functional theory (DFT) calculations revealed changes in the electronic characteristics of the NPs due to size, shape, NP-adsorbate (H(2)) and NP-support interactions. A correlation between the NP size, number of surface atoms and coordination of such atoms, and the maximum hydrogen coverage stabilized at a given temperature is established, with H/Pt ratios exceeding the 1 : 1 ratio previously reported for bulk Pt surfaces.

  View details for DOI 10.1039/c2cp41928a

  View details for Web of Science ID 000307017800023

  View details for PubMedID 22828479

• Controlled one-step synthesis of hierarchically structured macroscopic silica spheres MICROPOROUS AND MESOPOROUS MATERIALS Scholz, S., Bare, S. R., Kelly, S. D., Lercher, J. A. 2011; 146 (1-3): 18–27

  View details for DOI 10.1016/j.micromeso.2011.04.036

  View details for Web of Science ID 000295769400004

• Density functional theory study of the effect of subsurface H, C, and Ag on C2H2 hydrogenation on Pd(1 1 1) CATALYSIS TODAY Tiruppathi, P., Low, J. J., Chan, A. Y., Bare, S. R., Meyer, R. J. 2011; 165 (1): 106–11

  View details for DOI 10.1016/j.cattod.2011.02.029

  View details for Web of Science ID 000289789800015

• Experimental (XAS, STEM, TPR, and XPS) and Theoretical (DFT) Characterization of Supported Rhenium Catalysts JOURNAL OF PHYSICAL CHEMISTRY C Bare, S. R., Kelly, S. D., Vila, F. D., Boldingh, E., Karapetrova, E., Kas, J., Mickelson, G. E., Modica, F. S., Yang, N., Rehr, J. J. 2011; 115 (13): 5740–55

  View details for DOI 10.1021/jp1105218

  View details for Web of Science ID 000288885900068

• Simultaneous XAFS measurements of multiple samples JOURNAL OF SYNCHROTRON RADIATION Ravel, B., Scorzato, C., Siddons, D. P., Kelly, S. D., Bare, S. R. 2010; 17: 380–85

  Abstract

  A four-channel ionization chamber has been designed, constructed and tested. This ionization chamber allows X-ray absorption spectra to be collected in transmission from up to four samples simultaneously. This results in spectra that are free of systematic uncertainty in relative energy alignment introduced by scan-to-scan stability of the monochromator or of numerical uncertainty associated with a post-processing alignment algorithm, allowing, in a single shot, an absolute measure of edge shift between four samples of different valence. As four samples can be measured in parallel, the time expended over the course of an experiment to cycle the measurement environment between its rest state and the measurement condition is substantially reduced. The ionization chamber is simple in design and could be implemented at virtually any XAFS beamline with a horizontal fan of radiation such as that provided by a bend magnet or wiggler.

  View details for DOI 10.1107/S0909049510006230

  View details for Web of Science ID 000276785600012

  View details for PubMedID 20400837

• Characterizing industrial catalysts using in situ XAFS under identical conditions PHYSICAL CHEMISTRY CHEMICAL PHYSICS Bare, S. R., Kelly, S. D., Ravel, B., Greenlay, N., King, L., Mickelson, G. E. 2010; 12 (27): 7702–11

  Abstract

  In situ X-ray absorption spectroscopy (XAS) in catalysis research has traditionally been conducted by making one measurement at a time on a single sample. In an industrial research environment this is especially limiting as sample throughput (productivity) and turnaround time (direct project relevance) are critical issues in the use of XAS in a fast-moving technology delivery project. In order to address these issues we have developed and implemented a four-channel ionization chamber combined with two different in situ cells that allows XAS data to be collected simultaneously from four samples, or four regions, in transmission geometry without any sample or detector movement. In the development of this new capability it was realized that there are other benefits from this simultaneous detection in addition to increased productivity. Namely, (i) the use of EXAFS to determine the structure of a catalyst in situ axially at four different positions down a catalyst bed; (ii) the ability to collect up to four XAFS spectra simultaneously and thereby avoid any scan-to-scan uncertainties, and (iii) the added confidence in the ability to discriminate small differences in similarly prepared catalysts which is typical in the development of a commercial catalyst. Specific illustrations of each of these applications are shown. The methodology is simple to implement and could be used on any XAFS beamline with a horizontal fan of radiation, such as at a typical bending magnet or wiggler source beamline.

  View details for DOI 10.1039/b926621f

  View details for Web of Science ID 000279514500045

  View details for PubMedID 20505854

• Morphology-dependent zeolite intergrowth structures leading to distinct internal and outer-surface molecular diffusion barriers NATURE MATERIALS Karwacki, L., Kox, M. F., de Winter, D., Drury, M. R., Meeldijk, J. D., Stavitski, E., Schmidt, W., Mertens, M., Cubillas, P., John, N., Chan, A., Kahn, N., Bare, S. R., Anderson, M., Kornatowski, J., Weckhuysen, B. M. 2009; 8 (12): 959-965

  Abstract

  Zeolites play a crucial part in acid-base heterogeneous catalysis. Fundamental insight into their internal architecture is of great importance for understanding their structure-function relationships. Here, we report on a new approach correlating confocal fluorescence microscopy with focused ion beam-electron backscatter diffraction, transmission electron microscopy lamelling and diffraction, atomic force microscopy and X-ray photoelectron spectroscopy to study a wide range of coffin-shaped MFI-type zeolite crystals differing in their morphology and chemical composition. This powerful combination demonstrates a unified view on the morphology-dependent MFI-type intergrowth structures and provides evidence for the presence and nature of internal and outer-surface barriers for molecular diffusion. It has been found that internal-surface barriers originate not only from a 90 degrees mismatch in structure and pore alignment but also from small angle differences of 0.5 degrees-2 degrees for particular crystal morphologies. Furthermore, outer-surface barriers seem to be composed of a silicalite outer crust with a thickness varying from 10 to 200 nm.

  View details for DOI 10.1038/NMAT2530

  View details for Web of Science ID 000272066800015

  View details for PubMedID 19767739

• Structural characterization of Ni-W hydrocracking catalysts using in situ EXAFS and HRTEM JOURNAL OF CATALYSIS Kelly, S. D., Yang, N., Mickelson, G. E., Greenlay, N., Karapetrova, E., Sinkler, W., Bare, S. R. 2009; 263 (1): 16-33

  View details for DOI 10.1016/j.jcat.2009.01.019

  View details for Web of Science ID 000265000800003

• Manganese oxide catalyzed methane partial oxidation in trifluoroacetic acid: Catalysis and kinetic analysis CATALYSIS TODAY Chen, W., Kocal, J. A., Brandvold, T. A., Bricker, M. L., Bare, S. R., Broach, R. W., Greenlay, N., Popp, K., Walenga, J. T., Yang, S. S., Low, J. J. 2009; 140 (3-4): 157-161

  View details for DOI 10.1016/j.cattod.2008.10.011

  View details for Web of Science ID 000263448000007

• Characterization of Catalysts in Reactive Atmospheres by X-ray Absorption Spectroscopy ADVANCES IN CATALYSIS, VOL 52 Bare, S. R., Ressler, T., Gates, B. C., Knozinger, H. 2009; 52: 339-465

  View details for DOI 10.1016/S0360-0564(08)00006-0

  View details for Web of Science ID 000264678800006

• Alumina-supported trirhenium clusters: Stable high-temperature catalysts for methylcyclohexane conversion JOURNAL OF PHYSICAL CHEMISTRY C Lobo-Lapidus, R. J., McCall, M. J., Lanuza, M., Tonnesen, S., Bare, S. R., Gates, B. C. 2008; 112 (9): 3383-3391

  View details for DOI 10.1021/jp709957t

  View details for Web of Science ID 000253512400035

• Oxidative desulfurization of sulfur compounds: Oxidation of thiophene and derivatives with hydrogen peroxide using Ti-Beta catalyst Nemeth, L., Bare, S. R., Rathbun, W., Gatter, M., Low, J., Gedeon, A., Massiani, P., Babonneau, F. ELSEVIER SCIENCE BV. 2008: 1017-1020

  View details for Web of Science ID 000283742800060

• Design and operation of a high pressure reaction cell for in situ X-ray absorption spectroscopy Bare, S. R., Yang, N., Kelly, S. D., Mickelson, G. E., Modica, F. S. ELSEVIER SCIENCE BV. 2007: 18-26

  View details for DOI 10.1016/j.cattod.2006.10.007

  View details for Web of Science ID 000249098700003

• In situ XAS of Ni-W hydrocracking catalysts Yang, N., Mickelson, G. E., Greenlay, N., Kelly, S. D., Bare, S. R., Hedman, B., Painetta, P. AMER INST PHYSICS. 2007: 663-+

  View details for Web of Science ID 000245805900198

• Design and operation of an in situ high pressure reaction cell for x-ray absorption spectroscopy Bare, S. R., Yang, N., Kelly, S. D., Mickelson, G. E., Modica, F. S., Hedman, B., Painetta, P. AMER INST PHYSICS. 2007: 622-+

  View details for Web of Science ID 000245805900185

• Directed-sorting method for synthesis of bead-based combinatorial libraries of heterogeneous catalysts JOURNAL OF COMBINATORIAL CHEMISTRY Ramnarayanan, R., Chan, B. C., Salvitti, M. A., Mallouk, T. E., Falih, F. M., Davis, J., Galloway, D. B., Bare, Willis, R. R. 2006; 8 (2): 199-212

  Abstract

  The synthesis and analysis of inorganic material combinatorial libraries by a directed-sorting, split-pool bead method was demonstrated. Directed-sorting, split-pool, metal-loaded libraries were synthesized by adsorbing metal salts (H2PtCl6, SnCl2, CuCl2, and NiCl2) and metal standards (Pt, Cu, Ni in HCl) onto 2-mg porous gamma-alumina beads in 96- or 384-well plates. A matrix algorithm for the synthesis of bead libraries treated each bead as a member of a row or column of a given matrix. Computer simulations and manual tracking of the sorting process were used to assess library diversity. The bead compositions were analyzed by energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy, electron probe microanalysis, inductively coupled plasma atomic emission spectroscopy, and inductively coupled plasma mass spectroscopy. The metal-loaded beads were analyzed by laser-activated membrane introduction mass spectroscopy (LAMIMS) for catalytic activity using methylcyclohexane dehydrogenation to toluene as a probe reaction. The catalytic activity of individual beads that showed minimal (approximately 20% of that of Pt on alumina) to high conversion could be determined semiquantitatively by LAMIMS. This method, therefore, provides an alternative to screening using microreactors for reactors that employ catalysts in the form of beads. The directed-sorting method offers the potential for synthesis of focused libraries of inorganic materials through relatively simple benchtop split-pool chemistry.

  View details for DOI 10.1021/cc050137r

  View details for Web of Science ID 000236217300012

  View details for PubMedID 16529515

• Simple flow through reaction cells for <i>in situ</i> transmission and fluorescence x-ray-absorption spectroscopy of heterogeneous catalysts REVIEW OF SCIENTIFIC INSTRUMENTS Bare, Mickelson, G. E., Modica, F. S., Ringwelski, A. Z., Yang, N. 2006; 77 (2)

  View details for DOI 10.1063/1.2168685

  View details for Web of Science ID 000235664200006

• Uniform catalytic site in Sn-β-zeolite determined using X-ray absorption fine structure JOURNAL OF THE AMERICAN CHEMICAL SOCIETY Bare, Kelly, S. D., Sinkler, W., Low, J. J., Modica, F. S., Valencia, S., Corma, A., Nemeth, L. T. 2005; 127 (37): 12924-12932

  Abstract

  The Sn silicate zeolite, Sn-beta, has been shown to be an efficient, selective heterogeneous catalyst for Baeyer-Villiger oxidations. Using primarily a multishell fit to extended X-ray absorption fine structure (EXAFS) data, we show that the Sn does not randomly insert into the beta-zeolite structure but rather occupies identical, specific, crystallographic sites. These sites are the T5/T6 sites in the six-membered rings. Moreover, the Sn is substituted in pairs on opposite sides of these six-membered rings. We believe that it is the specific, uniform crystallographic location of the Sn in the beta crystal structure that leads to sites with uniform catalytic activity, and consequently to the high chemical selectivity demonstrated for this catalyst. This manifests itself in the almost enzyme-like selectivity of this catalyst in Baeyer-Villiger oxidations. This uniform site distribution of the Sn suggests that there is likely a symbiotic relationship between the structure-directing agent in the zeolite synthesis and the Sn heteroatoms during the framework formation.

  View details for DOI 10.1021/ja052543k

  View details for Web of Science ID 000231928800048

  View details for PubMedID 16159286

• Split-pool method for synthesis of solid-state material combinatorial libraries JOURNAL OF COMBINATORIAL CHEMISTRY Sun, Y. P., Chan, B. C., Ramnarayanan, R., Leventry, W. M., Mallouk, T. E., Bare, Willis, R. R. 2002; 4 (6): 569-575

  Abstract

  The synthesis and analysis of inorganic material combinatorial libraries by the split-pool bead method were demonstrated at the proof-of-concept level. Millimeter-size spherical beads of porous gamma-alumina, a commonly used support material for heterogeneous catalysts, were modified with Al(13)O(4)(OH)(24)(H(2)O)(12)(7+) cations in order to promote irreversible adsorption of the anionic fluorescent dyes Cascade Blue, Lucifer Yellow, and Sulforhodamine 101. The compositions of individual beads were easily determined through three split-pool cycles using a conventional fluorescence plate reader. Small split-pool material libraries were made by adsorbing noble metal salts (H(2)PtCl(6), H(2)IrCl(6), and RhCl(3)) into the beads. Analysis of these beads by micro-X-ray fluorescence showed that quantitative adsorption of metal salts without cross-contamination of beads could be achieved at levels (0.3 wt % metal loading) relevant to heterogeneous catalysis. The method offers the potential for synthesis of rather large libraries of inorganic materials through relatively simple benchtop split-pool chemistry.

  View details for DOI 10.1021/cc020021k

  View details for Web of Science ID 000179254700007

  View details for PubMedID 12425601

• In-situ XANES of carbon-supported Pt-Ru anode electrocatalyst for reformate-air polymer electrolyte fuel cells JOURNAL OF PHYSICAL CHEMISTRY B Viswanathan, R., Hou, G. Y., Liu, R. X., Bare, Modica, F., Mickelson, G., Segre, C. U., Leyarovska, N., Smotkin, E. S. 2002; 106 (13): 3458-3465

  View details for DOI 10.1021/jp0139787

  View details for Web of Science ID 000174792600018

• Sensitivity of Pt x-ray absorption near edge structure to the morphology of small Pt clusters JOURNAL OF CHEMICAL PHYSICS Ankudinov, A. L., Rehr, J. J., Low, J. J., Bare 2002; 116 (5): 1911-1919

  View details for DOI 10.1063/1.1432688

  View details for Web of Science ID 000173418600018

• Effect of hydrogen adsorption on the x-ray absorption spectra of small Pt clusters PHYSICAL REVIEW LETTERS Ankudinov, A. L., Rehr, J. J., Low, J., Bare 2001; 86 (8): 1642-1645

  Abstract

  Hydrogen adsorption on Pt(6)H(n) clusters leads to striking changes in the Pt L(2,3) x-ray absorption spectra. These effects are interpreted using a self-consistent real space Green's function approach. Calculations show that they are due largely to changes in the atomic background contribution to x-ray absorption (i.e., atomic x-ray absorption fine structure) and to reduced Pt-Pt scattering at the edge, while Pt-H multiple scattering is relatively weak. The origin of both effects is traced to the change in the local Pt potential due to Pt-H bonding.

  View details for DOI 10.1103/PhysRevLett.86.1642

  View details for Web of Science ID 000167010000062

  View details for PubMedID 11290213

• Hybridization peaks in Pt-Cl XANES CHEMICAL PHYSICS LETTERS Ankudinov, A. L., Rehr, J. J., Bare 2000; 316 (5-6): 495-500

  View details for DOI 10.1016/S0009-2614(99)01358-5

  View details for Web of Science ID 000084960000026

• Structural characteristics and reactivity/reducibility properties of dispersed and bilayered V₂O₅/TiO₂/SiO₂ catalysts JOURNAL OF PHYSICAL CHEMISTRY B Gao, X. T., Bare, Fierro, J. L., Wachs, I. E. 1999; 103 (4): 618-629

  View details for DOI 10.1021/jp983357m

  View details for Web of Science ID 000079043100005

• In situ spectroscopic investigation of molecular structures of highly dispersed vanadium oxide on silica under various conditions JOURNAL OF PHYSICAL CHEMISTRY B Gao, X. T., Bare, Weckhuysen, B. M., Wachs, I. E. 1998; 102 (52): 10842-10852

  View details for DOI 10.1021/jp9826367

  View details for Web of Science ID 000077837200025

• An in situ x-ray absorption spectroscopic cell for high temperature gas-flow measurements REVIEW OF SCIENTIFIC INSTRUMENTS Meitzner, G., Bare, Parker, D., Woo, H., Fischer, D. A. 1998; 69 (7): 2618-2621

  View details for DOI 10.1063/1.1148988

  View details for Web of Science ID 000075279200005

• Synthesis, bonding, and reactions of π-bonded allyl groups on Cu(100);: Allyl radical ejection (vol 14, pg 1419, 1998) LANGMUIR Gurevich, A. B., Teplyakov, A. V., Yang, M. X., Bent, B. E., Holbrook, M. T., Bare 1998; 14 (7): 1943

  View details for DOI 10.1021/la980265f

  View details for Web of Science ID 000072914700067

• The desorption of propylene oxide from oxygen atom and hydroxyl covered Ag(110) SURFACE SCIENCE Ranney, J. T., Gland, J. L., Bare 1998; 401 (1): 1-11

  View details for DOI 10.1016/S0039-6028(97)00880-7

  View details for Web of Science ID 000073427300007

• Surface structure of highly dispersed MoO₃ on MgO using in situ Mo L₃-edge XANES Bare AMER CHEMICAL SOC. 1998: 1500-1504

  View details for DOI 10.1021/la9707134

  View details for Web of Science ID 000072683500033

• Supported VPO catalysts for selective oxidation of butane .2. Characterization of VPO/SiO2 catalysts JOURNAL OF PHYSICAL CHEMISTRY B Birkeland, K. E., Babitz, S. M., Bethke, G. K., Kung, H. H., Coulston, G. W., Bare 1997; 101 (35): 6895-6902

  View details for DOI 10.1021/jp962571c

  View details for Web of Science ID A1997XT95400017

• The reaction of propylene with ordered and disordered oxygen atoms adsorbed on the Ag(110) surface SURFACE SCIENCE Ranney, J. T., Bare 1997; 382 (1-3): 266-274

  View details for DOI 10.1016/S0039-6028(97)00184-2

  View details for Web of Science ID A1997XQ14100040

• Chemistry of chloroethylenes on Cu(100): Bonding and reactions SURFACE SCIENCE Yang, M. X., Kash, P. W., Sun, D. H., Flynn, G. W., Bent, B. E., Holbrook, M. T., Bare, Fischer, D. A., Gland, J. L. 1997; 380 (2-3): 151-164

  View details for DOI 10.1016/S0039-6028(96)01002-3

  View details for Web of Science ID A1997XF84300009

• Oxidation of cyclopropane with coadsorbed oxygen on Pt(111) SURFACE SCIENCE Franz, A. J., Ranney, J. T., Gland, J. L., Bare 1997; 374 (1-3): 162-168

  View details for DOI 10.1016/S0039-6028(96)01229-0

  View details for Web of Science ID A1997WN42500017

• Degradation of multiply-chlorinated hydrocarbons on Cu(100) LANGMUIR Yang, M. X., Sarkar, S., Bent, B. E., Bare, Holbrook, M. T. 1997; 13 (2): 229-242

  View details for DOI 10.1021/la960404y

  View details for Web of Science ID A1997WD91600020

• Generation and reaction of vinyl groups on a Cu(100) surface JOURNAL OF PHYSICAL CHEMISTRY Yang, M. X., Eng, J., Kash, P. W., Flynn, G. W., Bent, B. E., Holbrook, M. T., Bare, Gland, J. L., Fischer, D. A. 1996; 100 (30): 12431-12439

  View details for DOI 10.1021/jp952386j

  View details for Web of Science ID A1996UY93800045

• GENERATION OF ATOMIC OXYGEN ON AG(111) AND AG(110) USING NO2 - A TPD, LEED, HREELS, XPS AND NRA STUDY SURFACE SCIENCE BARE, GRIFFITHS, K., LENNARD, W. N., TANG, H. T. 1995; 342 (1-3): 185-198

  View details for DOI 10.1016/0039-6028(95)00670-2

  View details for Web of Science ID A1995TH88600026

• SURFACE-STRUCTURES OF SUPPORTED MOLYBDENUM OXIDE CATALYSTS - CHARACTERIZATION BY RAMAN AND MO L(3)-EDGE XANES JOURNAL OF PHYSICAL CHEMISTRY HU, H. C., WACHS, I. E., BARE 1995; 99 (27): 10897-10910

  View details for DOI 10.1021/j100027a034

  View details for Web of Science ID A1995RH22100034

• LOCAL SITE SYMMETRY OF DISPERSED MOLYBDENUM OXIDE CATALYSTS - XANES AT THE MO L2,3-EDGES JOURNAL OF PHYSICAL CHEMISTRY BARE, MITCHELL, G. E., MAJ, J. J., VRIELAND, G. E., GLAND, J. L. 1993; 97 (22): 6048-6053

  View details for DOI 10.1021/j100124a043

  View details for Web of Science ID A1993LE95100043

• COMPARISON OF ETHYLENE-OXIDE AND PROPYLENE-OXIDE CHEMISORBED ON CLEAN AND OXYGEN PRECOVERED AG(110) BARE AMER INST PHYSICS. 1992: 2336-2342

  View details for DOI 10.1116/1.577940

  View details for Web of Science ID A1992JE68300033

• THE INFLUENCE OF ORIENTATION ON THE H-D EXCHANGE-REACTIONS IN CHEMISORBED AROMATICS - BENZENE AND PYRIDINE ADSORBED ON PT[110] SURFACE SCIENCE SURMAN, M., BARE, HOFMANN, P., KING, D. A. 1987; 179 (2-3): 243-253

  View details for DOI 10.1016/0039-6028(87)90056-2

  View details for Web of Science ID A1987F803200004

• AMMONIA-SYNTHESIS OVER IRON SINGLE-CRYSTAL CATALYSTS - THE EFFECTS OF ALUMINA AND POTASSIUM JOURNAL OF PHYSICAL CHEMISTRY BARE, STRONGIN, D. R., SOMORJAI, G. A. 1986; 90 (20): 4726-4729

  View details for DOI 10.1021/j100411a003

  View details for Web of Science ID A1986E226400004

• REACTION OF METHANOL ON SI(111)-7X7 SURFACE SCIENCE STROSCIO, J. A., BARE, HO, W. 1985; 154 (1): 35-51

  View details for DOI 10.1016/0039-6028(85)90350-4

  View details for Web of Science ID A1985AJQ4200007

• OBSERVATION OF STRUCTURE-INDUCED SURFACE VIBRATIONAL RESONANCES ON METAL-SURFACES PHYSICAL REVIEW LETTERS STROSCIO, J. A., PERSSON, M., BARE, HO, W. 1985; 54 (13): 1428-1431

  View details for DOI 10.1103/PhysRevLett.54.1428

  View details for Web of Science ID A1985AED8200024

  View details for PubMedID 10031029

• THE EFFECTS OF PREADSORBED OXYGEN ON THE ADSORPTION AND DECOMPOSITION OF METHANOL ON NI(110) SURFACE SCIENCE BARE, STROSCIO, J. A., HO, W. 1985; 155 (2-3): L281-L291

  View details for DOI 10.1016/0039-6028(85)90003-2

  View details for Web of Science ID A1985ALF4900003

• CHARACTERIZATION OF THE ADSORPTION AND DECOMPOSITION OF METHANOL ON NI(110) SURFACE SCIENCE BARE, STROSCIO, J. A., HO, W. 1985; 150 (2): 399-418

  View details for DOI 10.1016/0039-6028(85)90655-7

  View details for Web of Science ID A1985ADW0900010

• ISOLATION OF A FORMATE INTERMEDIATE IN THE DECOMPOSITION OF METHANOL ON NI(110)-(2X1)O BARE, STROSCIO, J. A., HO, W. AMER INST PHYSICS. 1985: 1647-1648

  View details for DOI 10.1116/1.573029

  View details for Web of Science ID A1985AKX5100174

• VIBRATIONAL STUDIES OF THE SURFACE PHASES OF CO ON PT(110) AT 300-K SURFACE SCIENCE BARE, HOFMANN, P., KING, D. A. 1984; 144 (2-3): 347-369

  View details for DOI 10.1016/0039-6028(84)90106-7

  View details for Web of Science ID A1984TK99900007

• THE CHEMISORPTION AND DECOMPOSITION OF ETHYLENE AND ACETYLENE ON NI(110) SURFACE SCIENCE STROSCIO, J. A., BARE, HO, W. 1984; 148 (2-3): 499-525

  View details for DOI 10.1016/0039-6028(84)90596-X

  View details for Web of Science ID A1984AAH4200029

• DIRECT CHARACTERIZATION OF A CATALYTIC SURFACE-REACTION STEP - BENZENE-DEUTERIUM EXCHANGE ON PT(110) SURFACE SCIENCE SURMAN, M., BARE, HOFMANN, P., KING, D. A. 1983; 126 (1-3): 349-358

  View details for DOI 10.1016/0039-6028(83)90728-8

  View details for Web of Science ID A1983QN29900041

• SPATIAL INTENSITY DISTRIBUTIONS FROM ELECTRON-IMPACT SCATTERING-MODES - W(100)(1X1)H JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA BARE, HOFMANN, P., SURMAN, M., KING, D. A. 1983; 29 (JAN): 265-272

  View details for DOI 10.1016/0368-2048(83)80073-5

  View details for Web of Science ID A1983QJ06900041

• SURFACE PHASE-TRANSITIONS IN CO CHEMISORPTION ON PT(110) SURFACE SCIENCE HOFMANN, P., BARE, KING, D. A. 1982; 117 (1-3): 245-256

  View details for DOI 10.1016/0039-6028(82)90505-2

  View details for Web of Science ID A1982NW83800028

• TILTED CO CHEMISORBED ON PT (110) VACUUM BARE, HOFMANN, P., KING, D. A. 1981; 31 (10-1): 463-465

  View details for DOI 10.1016/0042-207X(81)90037-3

  View details for Web of Science ID A1981MY77000018

• ANGLE-RESOLVED THERMAL-DESORPTION OF N-2 FROM W(310) AND W(110) VACUUM COSSER, R. C., BARE, FRANCIS, S. M., KING, D. A. 1981; 31 (10-1): 503-506

  View details for DOI 10.1016/0042-207X(81)90048-8

  View details for Web of Science ID A1981MY77000029