Surface Zn-enriched Cu/Zn/Al catalysts synthesized by mechanochemical milling with precursor size control for CO2 hydrogenation to methanol

To address the trade-off between CO 2 conversion and methanol selectivity inherent in Cu-ZnO based catalysts and mitigate the drawbacks of wet chemical synthesis methods, in this study, Cu/ZnO/Al 2 O 3 catalysts with high methanol selectivity were developed for CO 2 hydrotreating to methanol using a mechanochemical method suitable for industrial scale preparation. Combining CuO and ZnO precursors of different sizes (micronscale or nanoscale), four catalyst variants were prepared by a mechanochemical method combining ball milling and auto-combustion of citric acid, which compared with commercial catalyst prepared by co-precipitation method. Characterizations of the catalysts structure and element distribution indicate that due to the different thermal decomposition kinetics of copper citrate and zinc citrate during the calcination process, the surface Zn content of the ball milling catalysts significantly increase, thereby promoting the formation of the Cu-ZnO x interface. Among them, the catalyst of plain CuO + nano ZnO shows the best performance (0.4 g MeOH •g cat -1 •h −1 ). Although its CO 2 conversion is lower than that of commercial catalyst, it has better methanol selectivity and produced higher methanol space–time yield which remained stable during the 30 h stability test. In addition, H 2 -TPR and CO 2 -TPD experimental results show that although mechanical mixing resulted in ball milling catalysts with large copper grains, more oxygen vacancies and moderately strong basic sites enhanced Cu-ZnO synergism, inhibited the reverse water–gas shift (RWGS) reaction, and facilitated methanol synthesis.