Oxide catalysts are increasingly employed for hydrogenation reactions,among which ZnCrOx is a major catalyst for the oxide-zeolite(OXZEO)process and for the hydrogenation of C1 molecules in general.Owing to the comple...Oxide catalysts are increasingly employed for hydrogenation reactions,among which ZnCrOx is a major catalyst for the oxide-zeolite(OXZEO)process and for the hydrogenation of C1 molecules in general.Owing to the complex nature of ternary oxides,the surface and catalytic properties of ZnCr_(2)O_(4) spinel have remained controversial for CO hydrogenation.Combining in-situ Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy,we examined the adsorption and reaction of CO/H_(2) on the ZnCr_(2)O_(4) catalysts,which were pre-treated under oxidative or reductive conditions.The reduced ZnCr_(2)O_(4) catalyst was found to expose more surface sites for CO adsorption/reaction than the oxidized ZnCr_(2)O_(4) catalyst.Exposing the reduced ZnCr_(2)O_(4) to H_(2) at room temperature led to the formation of surface hydride species,which would transform into hydroxyl species at elevated temperatures.The reduced ZnCr_(2)O_(4) surface exhibited much stronger interaction with CO and H_(2) than ZnO and Cr_(2)O_(3).Exposing the reduced ZnCr_(2)O_(4) to the CO and H_(2)(1:1)mixture gas led to the hydrogenation of CO.However,CO was oxidized by the hydroxyl species via the water-gas-shift reaction,whereas the hydrogenation of CO could only be achieved by surface hydride species on the reduced ZnCr_(2)O_(4) to formyl or formate species at 373-473 K.Our study has thus shed light on the active species that control elementary reaction process of CO hydrogenation on complex oxide surfaces.展开更多
文摘Oxide catalysts are increasingly employed for hydrogenation reactions,among which ZnCrOx is a major catalyst for the oxide-zeolite(OXZEO)process and for the hydrogenation of C1 molecules in general.Owing to the complex nature of ternary oxides,the surface and catalytic properties of ZnCr_(2)O_(4) spinel have remained controversial for CO hydrogenation.Combining in-situ Fourier-transformed infrared spectroscopy and X-ray photoelectron spectroscopy,we examined the adsorption and reaction of CO/H_(2) on the ZnCr_(2)O_(4) catalysts,which were pre-treated under oxidative or reductive conditions.The reduced ZnCr_(2)O_(4) catalyst was found to expose more surface sites for CO adsorption/reaction than the oxidized ZnCr_(2)O_(4) catalyst.Exposing the reduced ZnCr_(2)O_(4) to H_(2) at room temperature led to the formation of surface hydride species,which would transform into hydroxyl species at elevated temperatures.The reduced ZnCr_(2)O_(4) surface exhibited much stronger interaction with CO and H_(2) than ZnO and Cr_(2)O_(3).Exposing the reduced ZnCr_(2)O_(4) to the CO and H_(2)(1:1)mixture gas led to the hydrogenation of CO.However,CO was oxidized by the hydroxyl species via the water-gas-shift reaction,whereas the hydrogenation of CO could only be achieved by surface hydride species on the reduced ZnCr_(2)O_(4) to formyl or formate species at 373-473 K.Our study has thus shed light on the active species that control elementary reaction process of CO hydrogenation on complex oxide surfaces.
