Effect of the Zn/Ce ratio in Cu/ZnO–CeO2 catalysts on CO2 hydrogenation for methanol synthesis

Abstract

The hydrogenation of carbon dioxide to methanol is perceived as an effective way to mitigate global warming and drive fossil-fuel companies towards sustainable energy sources. In this study, a series of Cu/ZnO–CeO₂ catalysts were prepared by a co-precipitation method, and the effect of the CeO₂ content on the catalytic performance of the Cu/ZnO–CeO₂ catalysts for the hydrogenation of CO₂ to CH₃OH was analysed. The physicochemical properties of the catalysts were investigated using XRD, H₂-TPR, CO₂-TPD, BET, XPS, TEM, and DRIFTS. The CZC-3 catalyst (CZC stands for Cu/ZnO–CeO₂ catalyst and 3 indicates a 30% CeO₂ content) had the best catalytic activity at 280 °C in a 3 MPa CO₂/H₂ (1/3) atmosphere, exhibiting a CO₂ conversion rate of 15.6% and a methanol yield of 10.06%. More dispersed CuO species and oxygen vacancies were detected on the CZC-3 catalyst, leading to good activation of H₂ and CO₂, respectively. In situ DRIFTS results for the catalysts showed that the hydrogenation of CO₂ to methanol over Cu/ZnO–CeO₂ catalysts occurs via the formate pathway. The CeO₂-rich Cu/ZnO–CeO₂ catalyst facilitated the conversion of formate to CH₃OH, and the presence of a large number of intermediate species on the surface of the CZC-3 catalyst greatly contributed to its catalytic performance for CO₂ hydrogenation.