(305e) Doping Metal Oxides to Improve Catalytic Performance for Chemoselective Hydrogenation Reactions

Chemoselective hydrogenation plays a key role in the upgrading of organic compounds from the waste streams of mixed plastics. Single atom late transition metal catalysts, supported on reducible metal oxides, exhibit remarkable activity and selectivity in hydrogenation reactions.² Single Ag atoms can activate hydrogen and facilitate the reduction of metal oxides (e.g., TiO₂).³ The reducible oxide can then facilitate hydrogenation of unsaturated moieties. Theoretical and experimental studies have identified the presence of spillover hydrogen on oxygen vacancy sites on the reduced oxide surfaces, present as hydrides.^3,4 These hydrides on the oxygen vacancy sites serve as crucial intermediates in C-H formation, offering a kinetically feasible pathway.⁵ To further enhance the catalytic performance of the oxide surfaces, we explore the modification of Lewis acid sites within oxide structures through transition metal cation doping.

Using density functional theory calculations, we explore how doping facilitates the reduction of oxide surfaces, providing active sites for hydrogenation reaction, and affects the subsequent formation of hydride species on the reduced sites. Doping influences 1) the co-adsorption of unsaturated hydrocarbon and hydride species, 2) activation barriers associated with the hydrogenation of unsaturated C-O or C-C bonds, as well as 3) selectivity as confirmed using microkinetic modeling methods. Starting from anatase TiO₂, we examine reducible metal oxides to investigate what geometric and ionic features are related to the catalytic performance. We identify generalized trends and establish rational design principles that link the electronic behavior of these metal oxide catalysts and their potential for facilitating hydride-ligand bond formation.

(1)Wei, J. et al., Catal. Sci. Technol. 2022, 13(5), 1258-1280.

(2)Zhang, L. et al., Chem. Rev. 2020, 120(2), 683-733.

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

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

(5)Zhou, Z. et al., ACS Catal. 2023, 13(14), 9588–9596