Effect of the Synthesis Method on Physicochemical Properties and Performance of Cu/ZnO/Nb2O5 Catalysts for CO2 Hydrogenation to Methanol

In the present work, we investigated the influence of the synthesis method of Nb-promoted Cu/Zn materials on their physicochemical and catalytic properties. Cu/ZnO/Nb2O5 was prepared by coprecipitation (CP), deposition–precipitation (DP), wet impregnation (WI), and incipient wetness impregnation (IW) methods. The physicochemical properties of these materials were investigated by XRF, XRD, N2 physisorption, SEM, TEM, TEM–EDS, H2-TPR, N2O passivation, and CO2-TPD. According to the results, it was found that when Nb was coprecipitated with copper and zinc (Cu/Zn/Nb–CP) there was the formation of a material with smaller particles, larger specific surface area, larger metallic copper area, and higher basicity than those of the other investigated materials. In the CO2 hydrogenation at 200 °C, this catalyst exhibited the best performance in terms of activity (XCO2 = 5.2%) and selectivity to methanol (SMeOH = 70.2%). Further characterization, via in situ DRIFTS, revealed that the formation of methanol over Cu/Zn/Nb–CP occurs via "RWGS + CO-Hydro" and "formate" pathways.