Staff Scientist, Italian National Council of Research (1/1/2009 - 12/31/2011)
Postdoc, University of California Santa Barbara (4/1/2012 - 3/1/2015)
- Isolating the Electrocatalytic Activity of a Confined NiFe Motif within Zirconium Phosphate ADVANCED ENERGY MATERIALS 2021
- Operando Study of Thermal Oxidation of Monolayer MoS2 ADVANCED SCIENCE 2021
Tuning the electronic structure of Ag-Pd alloys to enhance performance for alkaline oxygen reduction.
2021; 12 (1): 620
Alloying is a powerful tool that can improve the electrocatalytic performance and viability of diverse electrochemical renewable energy technologies. Herein, we enhance the activity of Pd-based electrocatalysts via Ag-Pd alloying while simultaneously lowering precious metal content in a broad-range compositional study focusing on highly comparable Ag-Pd thin films synthesized systematically via electron-beam physical vapor co-deposition. Cyclic voltammetry in 0.1 M KOH shows enhancements across a wide range of alloys; even slight alloying with Ag (e.g. Ag0.1Pd0.9) leads to intrinsic activity enhancements up to 5-fold at 0.9 V vs. RHE compared to pure Pd. Based on density functional theory and x-ray absorption, we hypothesize that these enhancements arise mainly from ligand effects that optimize adsorbate-metal binding energies with enhanced Ag-Pd hybridization. This work shows the versatility of coupled experimental-theoretical methods in designing materials with specific and tunable properties and aids the development of highly active electrocatalysts with decreased precious-metal content.
View details for DOI 10.1038/s41467-021-20923-z
View details for PubMedID 33504815
- Understanding Selectivity in CO2 Hydrogenation to Methanol for MoP Nanoparticle Catalysts Using In Situ Techniques CATALYSTS 2021; 11 (1)
- Identifying and Tuning the In Situ Oxygen-Rich Surface of Molybdenum Nitride Electrocatalysts for Oxygen Reduction ACS APPLIED ENERGY MATERIALS 2020; 3 (12): 12433–46
- Acidic Oxygen Evolution Reaction Activity-Stability Relationships in Ru-Based Pyrochlores ACS CATALYSIS 2020; 10 (20): 12182–96
- Low-pressure methanol synthesis from CO2 over metal-promoted Ni-Ga intermetallic catalysts JOURNAL OF CO2 UTILIZATION 2020; 39
- Ni5Ga3 catalysts for CO2 reduction to methanol: Exploring the role of Ga surface oxidation/reduction on catalytic activity APPLIED CATALYSIS B-ENVIRONMENTAL 2020; 267
- Nitride or Oxynitride? Elucidating the Composition-Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction CHEMISTRY OF MATERIALS 2020; 32 (7): 2946–60
A versatile Johansson-type tender x-ray emission spectrometer
REVIEW OF SCIENTIFIC INSTRUMENTS
2020; 91 (3): 033101
We present a high energy resolution x-ray spectrometer for the tender x-ray regime (1.6-5.0 keV) that was designed and operated at Stanford Synchrotron Radiation Lightsource. The instrument is developed on a Rowland geometry (500 mm of radius) using cylindrically bent Johansson analyzers and a position sensitive detector. By placing the sample inside the Rowland circle, the spectrometer operates in an energy-dispersive mode with a subnatural line-width energy resolution (∼0.32 eV at 2400 eV), even when an extended incident x-ray beam is used across a wide range of diffraction angles (∼30° to 65°). The spectrometer is enclosed in a vacuum chamber, and a sample chamber with independent ambient conditions is introduced to enable a versatile and fast-access sample environment (e.g., solid/gas/liquid samples, in situ cells, and radioactive materials). The design, capabilities, and performance are presented and discussed.
View details for DOI 10.1063/1.5121853
View details for Web of Science ID 000519254000002
View details for PubMedID 32259983
Understanding the Origin of Highly Selective CO2 Electroreduction to CO on Ni, N-doped Carbon Catalysts.
Angewandte Chemie (International ed. in English)
Ni,N-doped carbon catalysts have shown promising catalytic performance for CO 2 electroreduction (CO 2 R) to CO; this activity has been attributed to the presence of nitrogen-coordinated, single metal atom active sites. However, experimentally confirming Ni-N bonding and correlating CO 2 reduction (CO 2 R) activity to these species has remained a fundamental challenge. We synthesized polyacrylonitrile-derived Ni, N-doped carbon electrocatalysts (Ni-PACN) with a range of pyrolysis temperatures and Ni loadings and correlated their electrochemical activity with extensive physiochemical characterization to rigorously address the origin of activity in these materials. We found that the CO- 2 R to CO partial current density increased with increased Ni content before plateauing at 2 wt% which suggests a dispersed Ni active site. These dispersed active sites were investigated by hard and soft x-ray spectroscopy, which revealed that pyrrolic nitrogen ligands selectively bind Ni atoms in a distorted square-planar geometry that strongly resembles the active sites of molecular metal-porphyrin catalysts.
View details for DOI 10.1002/anie.201912857
View details for PubMedID 31919948
Excited state charge distribution and bond expansion of ferrous complexes observed with femtosecond valence-to-core x-ray emission spectroscopy.
The Journal of chemical physics
2020; 152 (7): 074203
Valence-to-core x-ray emission spectroscopy (VtC XES) combines the sample flexibility and element specificity of hard x-rays with the chemical environment sensitivity of valence spectroscopy. We extend this technique to study geometric and electronic structural changes induced by photoexcitation in the femtosecond time domain via laser-pump, x-ray probe experiments using an x-ray free electron laser. The results of time-resolved VtC XES on a series of ferrous complexes [Fe(CN)2n(2, 2'-bipyridine)3-n]-2n+2, n = 1, 2, 3, are presented. Comparisons of spectra obtained from ground state density functional theory calculations reveal signatures of excited state bond length and oxidation state changes. An oxidation state change associated with a metal-to-ligand charge transfer state with a lifetime of less than 100 fs is observed, as well as bond length changes associated with metal-centered excited states with lifetimes of 13 ps and 250 ps.
View details for DOI 10.1063/1.5139441
View details for PubMedID 32087640
Precious Metal-Free Nickel Nitride Catalyst for the Oxygen Reduction Reaction.
ACS applied materials & interfaces
With promising activity and stability for the oxygen reduction reaction (ORR), transition metal nitrides are an interesting class of non-platinum group catalysts for polymer electrolyte membrane fuel cells. Here, we report an active thin-film nickel nitride catalyst synthesized through a reactive sputtering method. In rotating disk electrode testing in a 0.1 M HClO4 electrolyte, the crystalline nickel nitride film achieved high activity and selectivity to four-electron ORR. It also exhibited good stability during 10 and 40 h chronoamperometry measurements in acid and alkaline electrolyte, respectively. A combined experiment-theory approach, with detailed ex situ materials characterization and density functional theory calculations, provides insight into the structure of the catalyst and its surface during catalysis. Design strategies for activity and stability improvement through alloying and nanostructuring are discussed.
View details for DOI 10.1021/acsami.9b07116
View details for PubMedID 31310093
- Tungstenocene-grafted silica catalysts for the selective epoxidation of alkenes APPLIED CATALYSIS A-GENERAL 2019; 581: 133–42
A high-throughput energy-dispersive tender X-ray spectrometer for shot-to-shot sulfur measurements.
Journal of synchrotron radiation
2019; 26 (Pt 3): 629–34
An X-ray emission spectrometer that can detect the sulfur Kalpha emission lines with large throughput and a high energy resolution is presented. The instrument is based on a large d-spacing perfect Bragg analyzer that diffracts the sulfur Kalpha emission at close to backscattering angles. This facilitates the application of efficient concepts routinely employed in hard X-ray spectrometers towards the tender X-ray regime. The instrument described in this work is based on an energy-dispersive von Hamos geometry that is well suited for photon-in photon-out spectroscopy at X-ray free-electron laser and synchrotron sources. Comparison of its performance with previously used instrumentation is presented through measurements using sulfur-containing species performed at the LCLS. It is shown that the overall signal intensity is increased by a factor of 15. Implementation of this approach in the design of a tender X-ray spectroscopy endstation for LCLS-II is also discussed.
View details for DOI 10.1107/S1600577519002431
View details for PubMedID 31074425
- Development of Molybdenum Phosphide Catalysts for Higher Alcohol Synthesis from Syngas by Exploiting Support and Promoter Effects ENERGY TECHNOLOGY 2019; 7 (5)
- Revealing the Synergy between Oxide and Alloy Phases on the Performance of Bimetallic In-Pd Catalysts for CO2 Hydrogenation to Methanol ACS CATALYSIS 2019; 9 (4): 3399–3412
- Identification of the active complex for CO oxidation over single-atom Ir-on-MgAl2O4 catalysts NATURE CATALYSIS 2019; 2 (2): 149–56
Resolving structures of transition metal complex reaction intermediates with femtosecond EXAFS.
Physical chemistry chemical physics : PCCP
Femtosecond-resolved Extended X-ray Absorption Fine Structure (EXAFS) measurements of solvated transition metal complexes are successfully implemented at the X-ray Free Electron Laser LCLS. Benchmark experiments on [Fe(terpy)2]2+ in solution show a signal-to-noise ratio on the order of 500, comparable to typical 100 ps-resolution synchrotron measurements. In the few femtoseconds after photoexcitation, we observe the EXAFS fingerprints of a short-lived (∼100 fs) intermediate as well as those of a vibrationally hot long-lived (∼ns) excited state.
View details for DOI 10.1039/c9cp03483h
View details for PubMedID 31441480
Soft X-ray spectroscopy with transition-edge sensors at Stanford Synchrotron Radiation Lightsource beamline 10-1.
The Review of scientific instruments
2019; 90 (11): 113101
We present results obtained with a new soft X-ray spectrometer based on transition-edge sensors (TESs) composed of Mo/Cu bilayers coupled to bismuth absorbers. This spectrometer simultaneously provides excellent energy resolution, high detection efficiency, and broadband spectral coverage. The new spectrometer is optimized for incident X-ray energies below 2 keV. Each pixel serves as both a highly sensitive calorimeter and an X-ray absorber with near unity quantum efficiency. We have commissioned this 240-pixel TES spectrometer at the Stanford Synchrotron Radiation Lightsource beamline 10-1 (BL 10-1) and used it to probe the local electronic structure of sample materials with unprecedented sensitivity in the soft X-ray regime. As mounted, the TES spectrometer has a maximum detection solid angle of 2 × 10-3 sr. The energy resolution of all pixels combined is 1.5 eV full width at half maximum at 500 eV. We describe the performance of the TES spectrometer in terms of its energy resolution and count-rate capability and demonstrate its utility as a high throughput detector for synchrotron-based X-ray spectroscopy. Results from initial X-ray emission spectroscopy and resonant inelastic X-ray scattering experiments obtained with the spectrometer are presented.
View details for DOI 10.1063/1.5119155
View details for PubMedID 31779391
A Highly Active Molybdenum Phosphide Catalyst for Methanol Synthesis from CO and CO2
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
2018; 57 (46): 15045–50
Methanol is a major fuel and chemical feedstock currently produced from syngas, a CO/CO2 /H2 mixture. Herein we identify formate binding strength as a key parameter limiting the activity and stability of known catalysts for methanol synthesis in the presence of CO2 . We present a molybdenum phosphide catalyst for CO and CO2 reduction to methanol, which through a weaker interaction with formate, can improve the activity and stability of methanol synthesis catalysts in a wide range of CO/CO2 /H2 feeds.
View details for PubMedID 30134041
- A Strong Support Effect in Selective Propane Dehydrogenation Catalyzed by Ga(i-Bu)(3) Grafted onto gamma-Alumina and Silica ACS CATALYSIS 2018; 8 (8): 7566–77
- Systematic Structure Property Relationship Studies in Palladium Catalyzed Methane Complete Combustion ACS CATALYSIS 2017; 7 (11): 7810–21
High-Energy-Resolution X-ray Absorption Spectroscopy for Identification of Reactive Surface Species on Supported Single-Site Iridium Catalysts
CHEMISTRY-A EUROPEAN JOURNAL
2017; 23 (59): 14760–68
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
- Effects of Gold Substrates on the Intrinsic and Extrinsic Activity of High-Loading Nickel-Based Oxyhydroxide Oxygen Evolution Catalysts ACS CATALYSIS 2017; 7 (8): 5399–5409
- Uniform Pt/Pd Bimetallic Nanocrystals Demonstrate Platinum Effect on Palladium Methane Combustion Activity and Stability ACS CATALYSIS 2017; 7 (7): 4372–80
Ligand Exchange-Mediated Activation and Stabilization of a Re-Based Olefin Metathesis Catalyst by Chlorinated Alumina
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
2016; 138 (39): 12935–47
Extensive chlorination of γ-Al2O3 results in the formation of highly Lewis acidic surface domains depleted in surface hydroxyl groups. Adsorption of methyltrioxorhenium (MTO) onto these chlorinated domains serves to activate it as a low temperature, heterogeneous olefin metathesis catalyst and confers both high activity and high stability. Characterization of the catalyst reveals that the immobilized MTO undergoes partial ligand exchange with the surface, whereby some Re sites acquire a chloride ligand from the modified alumina while donating an oxo ligand to the support. More specifically, Re LIII-edge EXAFS and DFT calculations support facile ligand exchange between MTO and Cl-Al2O3 to generate [CH3ReO2Cl+] fragments that interact with a bridging oxygen of the support via a Lewis acid-base interaction. According to IR and solid-state NMR, the methyl group remains intact, and does not evolve spontaneously to a stable methylene tautomer. Nevertheless, the chloride-promoted metathesis catalyst is far more active and productive than MTO/γ-Al2O3, easily achieving a TON of 100 000 for propene metathesis in a flow reactor at 10 °C (compared to TON < 5000 for the nonchlorinated catalyst). Increased activity is a consequence of both a larger fraction of active sites and a higher intrinsic activity for the new sites. Increased stability is tentatively attributed to a stronger interaction between MTO and chlorinated surface regions, as well as extensive depletion of the Brønsted acidic surface hydroxyl population. The reformulated catalyst represents a major advance for Re-based metathesis catalysts, whose widespread use has thus far been severely hampered by their instability.
View details for DOI 10.1021/jacs.6b06953
View details for Web of Science ID 000384952100037
View details for PubMedID 27574817
- Tuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution Reaction ELECTROCHIMICA ACTA 2016; 193: 240-245
- Selective Grafting of Ga(i-Bu)(3) on the Silanols of Mesoporous H-ZSM-5 by Surface Organometallic Chemistry JOURNAL OF PHYSICAL CHEMISTRY C 2015; 119 (47): 26611–19
- Hydrogen storage over metal-doped activated carbon INTERNATIONAL JOURNAL OF HYDROGEN ENERGY 2015; 40 (24): 7609–16
Silica supported copper and cobalt oxide catalysts for methanol decomposition: Effect of preparation procedure
BULGARIAN CHEMICAL COMMUNICATIONS
2015; 47 (1): 283–90
View details for Web of Science ID 000367650000043
- CoTiOx Catalysts for the Oxygen Evolution Reaction JOURNAL OF THE ELECTROCHEMICAL SOCIETY 2015; 162 (12): H841-H846
- Control of copper particles deposition in mesoporous SBA-15 silica by modified CVD method INORGANICA CHIMICA ACTA 2014; 423: 145–51
- Evidence of Facilitated Electron Transfer on Hydrogenated Self-Doped TiO2 Nanocrystals CHEMELECTROCHEM 2014; 1 (8): 1415–21
- Tailored copper nanoparticles in ordered mesoporous KIT-6 silica: Preparation and application as catalysts in integrated system for NO removal with products of methanol decomposition APPLIED CATALYSIS A-GENERAL 2013; 464: 243–52
- Niobium metallocenes deposited onto mesoporous silica via dry impregnation as catalysts for selective epoxidation of alkenes JOURNAL OF CATALYSIS 2013; 298: 77–83
- Nickel Catalysts Supported Over TiO2, SiO2 and ZrO2 for the Steam Reforming of Glycerol CHEMCATCHEM 2013; 5 (1): 294–306
Cluster-derived Ir-Sn/SiO2 catalysts for the catalytic dehydrogenation of propane: a spectroscopic study
2013; 42 (35): 12714–24
Ir-Sn bimetallic silica-based materials have been prepared via deposition of the molecular organometallic clusters (NEt4)2[Ir4(CO)10(SnCl3)2] and NEt4[Ir6(CO)15(SnCl3)] or via deposition of Sn organometallic precursor Sn(n-C4H9)4 onto pre-formed Ir metal particles. These solids possess promising properties, in terms of selectivity, as catalysts for propane dehydrogenation to propene. Detailed CO-adsorption DRIFTS, XANES and EXAFS characterization studies have been performed on these systems in order to compare the structural and electronic evolution of systems in relation to the nature of the Ir-Sn bonds present in the precursor compounds and to propose a structural model of the Ir-Sn species present at the silica surface of the final catalyst.
View details for DOI 10.1039/c3dt51144h
View details for Web of Science ID 000323114600023
View details for PubMedID 23752740
- Epoxidation with hydrogen peroxide of unsaturated fatty acid methyl esters over Nb(V)-silica catalysts EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY 2013; 115 (1): 86–93
Niobium-silica catalysts for the selective epoxidation of cyclic alkenes: the generation of the active site by grafting niobocene dichloride
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2013; 15 (32): 13354–62
Niobium-containing silica materials obtained by deposition via liquid-phase grafting or dry impregnation of niobocene(iv) dichloride are active and selective catalysts in the epoxidation of alkenes in the presence of aqueous hydrogen peroxide. The generation of the catalytically-active Nb species was followed step-by-step, and investigated using a combined DR-UV-Vis, NIR, Raman, XRD, XANES and EXAFS analyses. At the end of the grafting procedure, the nature of the surface active species can be described as an oxo-Nb(v) site, tripodally grafted onto the silica surface in close proximity to other Nb(v) centres. The liquid-phase methodology provides a better dispersion of the metal sites onto the siliceous support than the dry-impregnation approach. The niobium-silica catalysts were then tested in the epoxidation of cyclohexene and 1-methylcyclohexene, as model substrates.
View details for DOI 10.1039/c3cp51570b
View details for Web of Science ID 000322401600013
View details for PubMedID 23873523
- Bimetallic heterogeneous catalysts for hydrogen production CATALYSIS TODAY 2012; 197 (1): 190–205
Effect of Nitrogen-Containing Impurities on the Activity of Perovskitic Catalysts for the Catalytic Combustion of Methane
2012; 51 (21): 11680–87
LaMnO(3), either pure or doped with 10 mol % Sr, has been prepared by flame pyrolysis in nanostructured form. Such catalysts have been tested for the catalytic flameless combustion of methane, achieving very high catalytic activity. The resistance toward poisoning by some model N-containing impurities has been checked in order to assess the possibility of operating the flameless catalytic combustion with biogas, possibly contaminated by S- or N-based compounds. This would be a significant improvement from the environmental point of view because the application of catalytic combustion to gas turbines would couple improved energy conversion efficiency and negligible noxious emissions, while the use of biogas would open the way to energy production from a renewable source by means of very efficient technologies. A different behavior has been observed for the two catalysts; namely, the undoped sample was more or less heavily poisoned, whereas the Sr-doped sample showed slightly increasing activity upon dosage of N-containing compounds. A possible reaction mechanism has been suggested, based on the initial oxidation of the organic backbone, with the formation of NO. The latter may adsorb more or less strongly depending on the availability of surface oxygen vacancies (i.e., depending on doping). Decomposition of NO may leave additional activated oxygen species on the surface, available for low-temperature methane oxidation and so improving the catalytic performance.
View details for DOI 10.1021/ic3015892
View details for Web of Science ID 000313220200055
View details for PubMedID 23039114
- Size controlled copper nanoparticles hosted in mesoporous silica matrix: Preparation and characterization APPLIED CATALYSIS B-ENVIRONMENTAL 2012; 126: 161–71
H2 Production by Renewables Photoreforming on Pt-Au/TiO2 Catalysts Activated by Reduction
2012; 5 (9): 1800–1811
Bimetallic Pt-Au nanoparticles supported on reduced anatase nanocrystals represent a new class of promising photocatalysts with high activity in hydrogen production by photoreforming of aqueous solution of renewable feedstock, such as ethanol and glycerol. The catalysts are easily obtained by metal impregnation of commercial TiO₂, followed by a reductive treatment. Remarkably, deeper catalyst pre-reduction results in enhanced photoactivity. When ethanol is used as sacrificial agent, under both UV-A or simulated sunlight irradiation, H₂ is the most abundant product in the gas stream whereas, in the case of glycerol, significant amounts of CO₂ have also been detected, indicating a more efficient oxidation of the organic sacrificial agent. The presence of bimetallic Pt-Au nanoparticles and of Ti³⁺ sites/O²⁻ vacancies in the bulk structure of titania are two key parameters to maximize light absorption and feedstock activation, finally resulting in good photocatalytic performances.
View details for DOI 10.1002/cssc.201200085
View details for Web of Science ID 000308407900020
View details for PubMedID 22696301
- Influence of reaction parameters on the activity of ruthenium based catalysts for glycerol steam reforming APPLIED CATALYSIS B-ENVIRONMENTAL 2012; 121: 40–49
- Optimization of the preparation procedure of cobalt modified silicas as catalysts in methanol decomposition APPLIED CATALYSIS A-GENERAL 2012; 417: 209–19
- Selective butadiene hydrogenation by Pd nanoparticles deposed onto nano-sized oxide supports by CVD of Pd-hexafluoroacetylacetonate INORGANICA CHIMICA ACTA 2012; 380: 216–22
- Glycerol steam reforming for hydrogen production: Design of Ni supported catalysts APPLIED CATALYSIS B-ENVIRONMENTAL 2012; 111: 225–32
- Bimetallic Au-Pt/TiO2 photocatalysts active under UV-A and simulated sunlight for H-2 production from ethanol GREEN CHEMISTRY 2012; 14 (2): 330–33
- Structure and catalytic activity of hosted in mesoporous silicas copper species: Effect of preparation procedure and support pore topology APPLIED CATALYSIS A-GENERAL 2011; 406 (1-2): 13–21
- Single-site and nanosized Fe-Co electrocatalysts for oxygen reduction: Synthesis, characterization and catalytic performance JOURNAL OF POWER SOURCES 2011; 196 (5): 2519–29
- Hydrogen Production by Glycerol Steam Reforming with Ru-based Catalysts: A Study on Sn Doping CHEMICAL VAPOR DEPOSITION 2010; 16 (10-12): 305–10
- Tailored supported metal nanoparticles by CVD: an easy and efficient scale-up by a rotary bed OMCVD device JOURNAL OF MATERIALS CHEMISTRY 2009; 19 (47): 9030–37
- Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)(2) APPLIED CATALYSIS A-GENERAL 2008; 346 (1-2): 126–33
- Catalytic dehydrogenation of propane over cluster-derived Ir-Sn/SiO2 catalysts CATALYSIS LETTERS 2006; 112 (1-2): 89–95