Identifying the Activity Origin of Silver Catalysts Induced by Interfacial Electron Localization for Regioselective C – O Bond Hydrogenation

Abstract

Deciphering intrinsic reactive sites of metal–oxide catalysts and activity origin remains a challenge. Given that the extreme complexity of heterogeneous catalysis catalytically active sites, the activity origin, and reaction mechanism generally present a so-called 'black box'. Herein, Ag/ZrO 2 –x achieves outstanding hydrogenation activity for selective scission of C–O bond per mass Ag, as illustrated by the preliminary hydrogenation of dimethyl oxalate to methyl glycolate. The in-depth characterization revealed that the Ag δ+ –O v –Zr 3+ (O v refers to as oxygen vacancy) structure could be engineered owing to the higher affinity of Ag for the partially reduced ZrO 2 surface and heteroatom junctions (in preference to the inert support). Furthermore, the local environment of different crystallite phases induced tunable (electronic) metal–support interactions (EMSIs), resulting in the enhanced catalytic activity and ultra-stability for C–O bond hydrogenation. XPS, methyl acetate-TPD, and in situ DRIFTS results unveiled the activity origin of silver–oxide systems, where the location of active metal sites for distinct functionalities over superficial and interfacial phases was validated. More importantly, time-resolved DRIFTS confirmed the crucial interfacial sites of Ag–ZrO 2 –x for regioselective C–O bond adsorption and activation. Further, the distinct active sites over Ag–ZrO 2 –x may release the shifted hydrogenation mechanisms, i.e. , conventional Langmuir–Hinshelwood on Ag/SiO 2 versus quasi Mars–Van Krevelen process (Ag–ZrO 2 –x ), presenting the new pathway for regioselective C–O bond hydrogenation. The coordinated EMSIs were proposed as the activity origin caused by the synergistic catalysis of the interfacial/superficial sites. These findings rationalize the underlying understanding of the EMSI and highlight the instructive role for perceiving the structure-performance relationships, guiding the catalyst design involved scale-up industrial applications.

Keywords: Activity origin, Silver particles, Interfacial synergy, Electronic metal-support interaction, C-O bond hydrogenation