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Identifying the activity origin of silver catalysts induced by interfacial electron localization for regioselective CO bond hydrogenation

Jinglin Zou,Xinping Duan,Xu Liu,Lele Huang,Xiaoying Liu,Jiachang Zuo,Weizhou Jiao,Haiqiang Lin,Linmin Ye,Youzhu Yuan

Deciphering intrinsic reactive sites of metal–oxide catalysts, where the outer surface and/or interfaces coupled with oxygen species in the vicinity of nanoparticles concurrently work, remains a challenge. Given the extreme complexity of heterogeneous catalysis ( e.g. , metal catalysts for preliminary hydrogenation process), catalytically active sites, the activity origin, and reaction mechanism generally present a so-called 'black box'. Herein, Ag/ZrO 2−x achieves a higher intrinsic hydrogenation rate for selective scission of C O bond per mass Ag than the reference Ag/SiO 2 catalyst, 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+ (Ag δ+ –O–Zr 4+ , 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, such as SiO 2 and Al 2 O 3 ). Furthermore, the local environment of different crystallite phases (tetragonal or monoclinic ZrO 2 ) induced tunable (electronic) metal–support interactions (EMSIs), resulting in 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. The mediated O v was verified to stabilize the thermodynamically unstable metallic (Ag 0 ) and charged silver species (Ag + or Ag n δ+ ). 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 altered reaction mechanisms, i.e. , conventional Langmuir–Hinshelwood (LH) on Ag/SiO 2 versus quasi Mars–Van Krevelen process (Ag–ZrO 2−x ), which presents the new pathway for regioselective C O bond hydrogenation. The coordinated EMSIs were proposed as the origin of the catalytic activity 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 and the activity origin in heterogeneous catalysts, thus moving away from the 'black-box' cognition.