(704c) Investigating the Stability of Single Metal Atoms (Silver/Copper) Supported on Titania (TiO2) Under Redox Conditions Using DFT

Single-atom catalysts (SACs) supported on metal oxide have emerged as promising candidates for driving hydrodeoxygenation reactions in catalytic processes, showcasing remarkable activity and selectivity (Toyao et al., 2017). However, their stability poses a significant challenge due to aggregation processes leading to catalyst deactivation under typical operating conditions. To address this challenge, we undertook a comprehensive computational inquiry aimed at elucidating the thermodynamic and kinetic stability of single-atom catalysts, delving into the intricate interplay between the redox characteristics of the reaction environment and the mobility of SACs. Focusing on the utilization of titania-supported Silver/Copper single atoms due to their promising capabilities in hydrogen dissociation and spillover, our study illustrates how the existence of atomic hydrogen, whether positioned atop the single atom or on the surface, resulting in the formation of metal hydrides and hydroxyl groups respectively, as well as the generation of oxygen vacancies, significantly impacts the aggregation behavior of SACs.

Utilizing ab initio thermodynamics, this study investigates the stability of various phases (AgO/TiO2, Ag/TiO2, AgH/TiO2, Ag/Hydroxylated TiO2, AgH/Hydroxylated TiO2, and Ag/Reduced TiO2) amidst transitions in reaction atmospheres from oxidizing to reducing conditions through incremental increases in hydrogen partial pressure. Employing density functional theory, we systematically examine adsorption preferences and surface diffusion patterns across different phases. Surface potential energy plots tailored to each case study offer insights into the thermodynamic and kinetic mobility of known species. Notably, our analysis reveals a distinct volcano effect concerning the energy barrier, correlating with the degree of reduction in the reaction environment.

_{Toyao, T., Siddiki, S. M. A. H., Touchy, A. S., Onodera, W., Kon, K., Morita, Y., Kamachi, T., Yoshizawa, K., & Shimizu, K. (2017). TiO 2 ‐Supported Re as a General and Chemoselective Heterogeneous Catalyst for Hydrogenation of Carboxylic Acids to Alcohols. Chemistry – A European Journal, 23(5), 1001–1006. https://doi.org/10.1002/chem.201604762}