The role of Al doping in Pd/ZnO catalyst for CO2 hydrogenation to methanol

Conversion of CO2 into methanol is a promising strategy to solve the urgent energy and environment problems, but the efficiency of this reaction is still limited due to the difficulty in CO2 activation. Here, we report a strategic Al doping in Pd/ZnO catalysts for enhancing methanol synthesis via CO2 hydrogenation. When the loading amount of Al is below 3.93 wt.%, CO2 conversion and CH3OH yield increase as Al content increases. The best catalytic performance is observed over Pd/ZnO catalysts with 3.93 wt.% Al, where the CO2 conversion and CH3OH yield are increased to 2.5 times and 1.7 times that of Pd/ZnO, respectively. Combined with a variety of experimental characterizations and density functional theory calculations, the enhanced performance is attributed to the Al doping in ZnO which can facilitate the adsorption and activation of CO2, and thus improving the catalytic performance of Pd/ZnO catalysts. Further increasing the loading amount of Al to higher than 3.93 wt.%, the CO2 conversion and CH3OH yield decrease, which can be attributed to the formation of ZnAl2O4 spinel and amorphous Al2O3 on the surface of ZnO.