Critical Role of Water and Oxygen Defects in C-O Scission during CO Reduction on ZnGeO(010).

Exploration of catalyst structure and environmental sensitivity for C-O bond scission is essential for improving the conversion efficiency because of the inertness of CO. We performed density functional theory calculations to understand the influence of the properties of adsorbed water and the reciprocal action with oxygen vacancy on the CO dissociation mechanism on ZnGeO(010). When a perfect surface was hydrated, the introduction of HO was predicted to promote the scission step by two modes based on its appearance, with the greatest enhancement from dissociative adsorbed HO. The dissociative HO lowers the barrier and reaction energy of CO dissociation through hydrogen bonding to preactivate the C-O bond and assisted scission via a COOH intermediate. The perfect surface with bidentate-binding HO was energetically more favorable for CO dissociation than the surface with monodentate-binding HO. Direct dissociation was energetically favored by the former, whereas monodentate HO facilitated the H-assisted pathway. The defective surface exhibited a higher reactivity for CO decomposition than the perfect surface because the generation of oxygen vacancies could disperse the product location. When the defective surface was hydrated, the reciprocal action for vacancy and surface HO on CO dissociation was related to the vacancy type. The presence of HO substantially decreased the reaction energy for the direct dissociation of CO on O- and O-defect surfaces, which converts the endoergic reaction to an exoergic reaction. However, the increased decomposition barrier made the step kinetically unfavorable and reduced the reaction rate. When HO was present on the O-defect surface, both the barrier and reaction energy for direct dissociation were invariable. This result indicated that the introduction of HO had little effect on the kinetics and thermodynamics. Moreover, the H-assisted pathway was suppressed on all hydrated defect surfaces. These results provide a theoretical perspective for the design of highly efficient catalysts.