Unraveling the Role of H2O on Cu-Based Catalyst in CO2 Hydrogenation to Methanol

CO2 hydrogenation to methanol has been extensively studied over Cu-based catalysts. H2O is an inevitable by-product during this reaction process. The essential role of H2O in determining the catalytic performance remains controversial. Herein, three kinds of common Cu-based catalysts (Cu/ZnO, Cu/Al2O3, Cu/SiO2) were selected to investigate the effect of H2O on the reaction performance over the range of 190 degrees C-290 degrees C in detail. Of all catalysts tested, it was noted that adding H2O showed substantially different effects on the methanol selectivity compared with the normal reaction. The representative Cu/SiO2 catalyst was further selected to investigate the role of H2O through a series of characterizations including BET, XRD, TEM, H-2-TPR and XPS, etc. Moreover, in situ FT-IR experiment was further conducted to understand the effect of H2O on the reaction pathways. The results indicated that H2O played the significant role on regulating the methanol selectivity by inhibiting and promoting the transformation from monodentate carbonate to bidentate formate over all the Cu-based catalysts at low (190-230 degrees C) and high (230-290 degrees C) temperature ranges, respectively. This preliminary study offers directions for the optimization of experimental conditions for the H2O involving reactions and provides referable experience for the further exploration and utilization of H2O effects on related fields as well. [GRAPHICS] .