(679c) Generalized Trends of Hydride-Mediated C-H Bond Formation on TiO2-Supported Single Atom Catalysts

Single atom late transition metal catalysts, supported on reducible metal oxides, can show activity and remarkable selectivity in hydrogenation reactions. Our previous work has demonstrated that the metal atoms (i.e., Ag) are largely responsible for hydrogen activation facilitating metal oxide (i.e., TiO_­2­) reduction, while hydrogenation elementary steps occur on the partially reduced oxide¹. Although significant literature exists on hydrogenation mechanisms on extended metal clusters, elementary reaction mechanisms and the role of metal-oxide sites in hydrogenation remain an open area of research. Theoretical and experimental studies have identified and characterized spillover hydrogen on the surface of these catalysts, namely hydrides in oxygen vacancy defect sites which may be involved in C-H bond formation^1,2. We report a hydride-facilitated mechanism that guides our understanding of how C-H bonds form on reducible metal oxide-based catalysts.

We use density functional theory calculations to examine the co-adsorption of hydride species in oxygen vacancy sites, together with monoanionic ligands such as halides, alkyl, and phenyl-type groups. We demonstrate that C-H formation can proceed from this hydride co-adsorbed state, providing a kinetically feasible mechanism from a thermodynamically stable precursor. We introduce case studies of how hydride addition with negatively charged aromatic ligands such as benzoate to generalize how C-H bond formation may occur on TiO₂-supported single atom catalysts. Moreover, we investigate how the reduction of TiO₂ in the form of oxygen vacancies and Ce-atom doping can facilitate these hydride addition mechanisms. Finally, we propose generalized trends and rational design principles that link the electronic behavior of these metal oxide catalysts and their potential for favorable hydride-ligand bond formation to occur.

(1) Hu, J. et al., J. Phys. Chem. C 2022, 126 (17), 7482–7491.

(2) Liu, K. et al., Cell Rep. Phys. Sci. 2022, 3 (12), 101190.