Influence of Cu/Al Ratio on the Performance of Carbon-Supported Cu/ZnO/Al2O3 Catalysts for CO2 Hydrogenation to Methanol

Abstract

CO2 hydrogenation to methanol was conducted using a set of activated carbon-supported Cu/ZnO/Al2O3 catalysts (CCZA) prepared by an incipient wetness impregnation approach. The effect of the Cu/Al ratio on the physicochemical properties of the catalysts, as well as their catalytic performance, were investigated. As Cu/Al ratio increased, the metallic Cu surface area displayed a reducing trend from 6.88 to 4.18 m2∙gcat−1, while the CO2 adsorption capacity exhibited an increasing trend. Meanwhile, aluminum content will have an important effect on the catalysts’ reducibility and, thus, on their catalytic performance. The CCZA-2.7-de catalyst demonstrated the highest selectivity to methanol at 83.75% due to the excellent distribution and synergistic effect of copper and zinc. Although the CO2 conversion of CCZA-2.2-de and CCZA-3.5-de exceeded 10%, the CH3OH selectivity was less than 60%, which may be attributed to the larger particle sizes of ZnO and poor interactions in Cu–Zn. The present study offers a novel approach to increase the number of active sites, optimize the activated carbon-aided Cu/ZnO/Al2O3 catalyst’s composition, and finally elucidate the mechanism for CO2 hydrogenation to methanol.