Heterolytic Hydrogen Activation: Understanding Support Effects in Water-Gas Shift, Hydrodeoxygenation, and CO Oxidation Catalysis

Identifying the role of oxide supports in transition-metal catalysis is critical toward our understanding of heterogeneous catalysis. The water-gas shift (WGS) reaction is a prototypical example where the oxide support dictates catalytic activity, yet the cause for this remains uncertain. Herein, we show that a single descriptor-the equilibrium constant for hydroxyl formation-relates the WGS turnover frequency across disparate oxide supports. The dissimilar equilibrium constant, or oxophilicity, between early and late transition metals exemplifies the utility of metal-support interfacial sites to circumvent adsorption-energy scaling restrictions, thereby providing bifunctional gains for the WGS reaction class. In relation, the equilibrium constant for hydroxyl formation is equivalent to the equilibrium constant for the formal heterolytic dissociation of hydrogen and therefore reflects the ability of the metal-support interface to participate in hydrogen heterolysis. The ubiquitous coexistence, yet divergent chemical reactivity of homo- and heterolytically activated hydrogen, renders the identity of the oxide support central toward our understanding of hydrogenation catalysis.