Slurry methanol synthesis from CO2 hydrogenation over micro-spherical SiO2 support Cu/ZnO catalysts

The micro-spherical SiO2 support is prepared by the spray-drying method, and then a series of SiO2 supported Cu/ZnO-based catalysts with different percentage of Cu and ZnO are synthesized by ammonia-evaporation method. The Cu and ZnO loadings play a critical role on the physicochemical properties and catalytic performance of catalysts. The results show that Cu and Zn cations can be deposited into the pores of the micro-spherical SiO2 with well-distributed when the metal loadings are below 47.91 wt%. In addition, the specific surface area of catalysts increases with increasing loadings due to the formation of porous structure inside SiO2 support, while it decreases when the metal loading is above 47.91 wt%. According to XRD, XPS, XAES and CO adsorption in situ FTIR analysis, both Cu+ and Cu° species exist on the reduced surface of Cu/ZnO/SiO2 catalysts. The catalytic performance for slurry methanol synthesis from CO2 hydrogenation is examined. The Cu/ZnO/SiO2 catalyst exhibits an optimum catalytic activity when the metal loading reaches to 28.23 wt%. However, the CO2 conversion changes slightly with a further increase of metal loadings, because the pore of support is blocked and the reducibility of catalysts is decreased significantly with incorporation of excess metal compounds into SiO2. In addition, the methanol selectivity enhances with increasing metal loadings due to the decrease of the proportion of Cu+ species.