First-principles study of water activation on Cu-ZnO catalysts

Abstract Although many water-related catalytic reactions on Cu-ZnO catalysts, such as methanol steam reforming and water gas shift, have been extensively investigated, little is known about water dissociation on Cu-ZnO catalysts. To reveal the active center for water dissociation on Cu-ZnO catalysts, we performed density functional theory calculations on various domains of Cu-ZnO catalysts, including Cu surfaces, supported ZnO films, and Cu-ZnO interfaces. It is found that water dissociation is hindered by a relatively large energy barrier on both the planar and the stepped Cu surfaces. On supported ZnO films, the barrier of water dissociation is significantly lowered compared with the Cu surfaces and the reaction is essentially thermo-neutral, thus the dissociation reaction will easily reach a state of dynamic equilibrium and dissociative and molecular water can coexist on the film. At the Cu-ZnO interface, water dissociation is exothermic and proceeds essentially without an energy barrier. The enhanced activity of the Cu-ZnO interface is due to the strong adsorption of both the H atom and hydroxyl group, and the step-like structure at the interface. The low energy barrier of hydroxyl diffusion and water-assisted hydrogen diffusion on ZnO films allows water dissociation to occur continuously at the interface. This work highlights the unique role of the Cu-ZnO interface in water dissociation on Cu-ZnO catalysts.