(532cr) Density Functional Theory (DFT) for Selective Carboxylic Acid Hydrogenation on Ag, Cu-TiO2 Catalysts

Single atom catalysts have demonstrated selectivity for hydrogenating specific functionalities in molecules with multiple unsaturated moieties. Even metals traditionally dismissed as poor hydrogenation catalysts, such as Ag, can be active for hydrogen activation and spillover when deposited as single atoms on anatase TiO₂. However, many questions remain unanswered about how these single atom catalysts can facilitate selective hydrogenation, such as (1) the roles of single metal atoms and the extended oxide support in facilitating hydrogen activation and hydrogenation elementary reactions, and (2) why these elementary reactions (e.g., C-H or O-H bond formation) can be more selective in these single atom catalysts compared to traditional hydrogenation catalysts.

In our work, we provide mechanistic insight using density functional theory (DFT) on the selective hydrogenation of carboxylic acids derived from plastic waste on TiO₂ catalysts with Ag or Cu single atoms to facilitate H₂ activation. We examine how the redox behavior of these single atom catalysts can affect the electronic character of spillover H atoms and how they may favor the formation of one hydrogenation product over another. We investigate elementary pathways of benzoic acid hydrogenation and how the presence of oxygen vacancies and various states of adsorbed H may alter elementary energetics. Additionally, we study how the inclusion of Ce doped into the TiO₂ support alters the catalyst reducibility and the energetics of selective hydrogenation elementary mechanisms. Finally, we propose how our DFT results can be used to predict the behavior of similar candidates for selective hydrogenation reactions and support experimental results from ongoing collaborations.