CO(2) Activation and Hydrogenation on Cu-ZnO/Al(2)O(3) Nanorod Catalysts: An In Situ FTIR Study

CuZnO/Al(2)O(3) is the industrial catalyst used for methanol synthesis from syngas (CO + H(2)) and is also promising for the hydrogenation of CO(2) to methanol. In this work, we synthesized Al(2)O(3) nanorods (n-Al(2)O(3)) and impregnated them with the CuZnO component. The catalysts were evaluated for the hydrogenation of CO(2) to methanol in a fixed-bed reactor. The support and the catalysts were characterized, including via in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The study of the CO(2) adsorption, activation, and hydrogenation using in situ DRIFT spectroscopy revealed the different roles of the catalyst components. CO(2) mainly adsorbed on the n-Al(2)O(3) support, forming carbonate species. Cu was found to facilitate H(2) dissociation and further reacted with the adsorbed carbonates on the n-Al(2)O(3) support, transforming them to formate or additional intermediates. Like the n-Al(2)O(3) support, the ZnO component contributed to improving the CO(2) adsorption, facilitating the formation of more carbonate species on the catalyst surface and enhancing the efficiency of the CO(2) activation and hydrogenation into methanol. The synergistic interaction between Cu and ZnO was found to be essential to increase the space–time yield (STY) of methanol but not to improve the selectivity. The 3% CuZnO/n-Al(2)O(3) displayed improved catalytic performance compared to 3% Cu/n-Al(2)O(3), reaching a CO(2) conversion rate of 19.8% and methanol STY rate of 1.31 mmolg(cat)(−1)h(−1) at 300 °C. This study provides fundamental and new insights into the distinctive roles of the different components of commercial methanol synthesis catalysts.