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.