Stanford Advisors

Current Research and Scholarly Interests

Development of machine-learning models from high-throughput catalysis simulations.

All Publications

  • Hydrolysis of Acetamide on Low-Index CeO2 Surfaces: Ceria as a Deamidation and General De-esterification Catalyst ACS CATALYSIS Bhasker-Ranganath, S., Xu, Y. 2022; 12 (16): 10222-10234


    Using DFT calculations and acetamide as the main example, we show that ceria is a potential catalyst for the hydrolysis of amide and similar bonds. The overall reaction is endergonic in the gas phase, yielding acetic acid and ammonia, but is slightly exergonic in the aqueous phase, which facilitates ionization of the products (CH3COO- and NH4 +). Neighboring Ce and O sites on the CeO2(111), (110), and (100) facets are conducive to the formation of an activated metastable tetrahedral intermediate (TI) complex, followed by C-N bond scission. With van der Waals and solvation effects taken into account, the overall reaction energetics is found to be most favorable on the (111) facet as desorption of acetic acid is much more uphill energetically on (110) and (100). We further suggest that the Ce-O-Ce sites on ceria surfaces can activate X(=Y)-Z type bonds in amides, amidines, and carboxylate and phosphate esters, among many others that we term "generalized esters". A Brønsted-Evans-Polanyi relationship is identified correlating the stability of the transition and final states of the X-Z generalized ester bond scission. A simple descriptor (ΣΔχ) based on the electronegativity of the atoms that constitute the bond (X, Y, Z) versus those of the catalytic site (O, Ce, Ce) captures the trend in the stability of the transition state of generalized ester bond scission and suggests a direction for modifying ceria for targeting specific organic substrates.

    View details for DOI 10.1021/acscatal.2c02514

    View details for Web of Science ID 000844147600001

    View details for PubMedID 36033367

    View details for PubMedCentralID PMC9397537

  • Elucidating the Mechanism of Ambient-Temperature Aldol Condensation of Acetaldehyde on Ceria ACS CATALYSIS Bhasker-Ranganath, S., Rahman, M., Zhao, C., Calaza, F., Wu, Z., Xu, Y. 2021; 11 (14): 8621-8634


    Using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations, we conclusively demonstrate that acetaldehyde (AcH) undergoes aldol condensation when flown over ceria octahedral nanoparticles, and the reaction is desorption-limited at ambient temperature. trans-Crotonaldehyde (CrH) is the predominant product whose coverage builds up on the catalyst with time on stream. The proposed mechanism on CeO2(111) proceeds via AcH enolization (i.e., α C-H bond scission), C-C coupling, and further enolization and dehydroxylation of the aldol adduct, 3-hydroxybutanal, to yield trans-CrH. The mechanism with its DFT-calculated parameters is consistent with reactivity at ambient temperature and with the kinetic behavior of the aldol condensation of AcH reported on other oxides. The slightly less stable cis-CrH can be produced by the same mechanism depending on how the enolate and AcH are positioned with respect to each other in C-C coupling. All vibrational modes in DRIFTS are identified with AcH or trans-CrH, except for a feature at 1620 cm-1 that is more intense relative to the other bands on the partially reduced ceria sample than on the oxidized sample. It is identified to be the C=C stretch mode of CH3CHOHCHCHO adsorbed on an oxygen vacancy. It constitutes a deep energy minimum, rendering oxygen vacancies an inactive site for CrH formation under given conditions.

    View details for DOI 10.1021/acscatal.1c01216

    View details for Web of Science ID 000674927200023

    View details for PubMedID 34306815

    View details for PubMedCentralID PMC8294007

  • Theoretical analysis of the adsorption of phosphoric acid and model phosphate monoesters on CeO2 (111) SURFACE SCIENCE Bhasker-Ranganath, S., Zhao, C., Xu, Y. 2021; 705
  • Adsorption structure of adenine on cerium oxide APPLIED SURFACE SCIENCE Bercha, S., Bhasker-Ranganath, S., Zheng, X., Beranova, K., Vorokhta, M., Acres, R. G., Skala, T., Matolin, V., Prince, K. C., Xu, Y., Tsud, N. 2020; 530
  • Computational insights into the molecular mechanisms for chromium passivation of stainless-steel surfaces MATERIALS TODAY CHEMISTRY Bhasker-Ranganath, S., Wick, C. D., Ramachandran, B. R. 2020; 17
  • Role of Metal-Lithium Oxide Interfaces in the Extra Lithium Capacity of Metal Oxide Lithium-Ion Battery Anode Materials JOURNAL OF THE ELECTROCHEMICAL SOCIETY Ranganath, S., Hassan, A. S., Ramachandran, B., Wick, C. D. 2016; 163 (10): A2172-A2178