Crystalline phase effects of zirconia in Ag/ZrO2 catalysts: oxygen vacancy-mediated new pathways to promote carbon–oxygen bond hydrogenation

Abstract

The crystalline phase effect of zirconia provides a viable approach to investigate the interfacial sites of Ag/ZrO₂ catalysts in the hydrogenation of carbon–oxygen bonds. However, zirconia with different crystalline phases synthesised through general strategies faces the dilemma of ill-definition and huge structural differences, which present an insurmountable obstacle for the establishment of structure–activity relationships and the revelation of interfacial co-catalytic sites. This paper presents a novel synthetic strategy for the univariate modulation of zirconia crystalline phases. Compared with traditional strategies, the structure of zirconia synthesised by this strategy with different crystalline phases exhibits a high degree of similarity. Differently, the phase transition process endows monoclinic zirconia with a distinctive surface Zr³⁺–O_v site, which has been demonstrated to possess a robust adsorption capacity for carbon–oxygen bonds through in situ infrared spectroscopy and theoretical calculations. The coordination of surface Zr³⁺–O_v sites with silver sites capable of spilling hydrogen provides a novel interfacial co-catalytically active site-mediated reaction pathway for carbon–oxygen bond hydrogenation. The Ag/Zr–NH₄⁺ catalyst with this novel interfacial site exhibited excellent catalytic performance in the activity evaluation, with ethyl glycolate yields reaching 95.8%. The interfacial co-catalysis offers a novel reaction pathway and is anticipated to be applicable to other carbon–oxygen bonded hydrogenation systems.