(700b) Chemoselective Hydrogenation of Aromatic Carboxylic Acids on TiO2-Supported Single Atom Catalysts

Pyrolysis processes, such as those using mixed PET plastic waste as feedstocks, have been found to form aromatic carboxylic acids such as benzoic acid as prevalent products¹. The further catalytic hydrogenation of benzoic acid into aromatic products such as benzaldehyde, benzyl alcohol, and toluene is largely desired due to their versatility as commodity chemicals and intermediates. Single-atom late transition metal catalysts supported on reducible metal oxides such as anatase TiO₂ are promising candidates due to their performance in similar types of reactions. However, compared to well-studied hydrogenation processes on extended late transition metals, mechanisms of C-H bond formation directly on reducible metal oxide support sites remain an open area of research.

Density functional theory calculations are used to elucidate plausible chemoselective C-H bond formation mechanisms on anatase TiO₂. A microkinetic model was constructed using computed reaction energies and activation barriers to predict the performance of TiO₂-supported catalysts under reaction conditions. We demonstrate that competing hydrogenation mechanisms and electronic effects from the support largely dictate the relative selectivity of hydrogenation products. We also show that favorable mechanisms of C-H bond formation are consistently mediated by hydrides present on reduced surface sites. Finally, we use our microkinetic model to predict which elementary mechanisms are rate-determining and we propose rational design principles from our results that can maximize the performance of similar systems.

(1) Diaz-Silvarrey, L.S. et al., Journal of Analytical and Applied Pyrolysis, 134 (2018) 621-631.