Flame Synthesis of Cu/ZnO-CeO2 Catalysts: Synergistic Metal-Support Interactions Promote CH3OH Selectivity in CO2 Hydrogenation.

Abstract

The hydrogenation of CO2 to CH3OH is an important reaction for future renewable energy scenarios. Herein, we compare Cu/ZnO, Cu/CeO2, and Cu/ZnO–CeO2 catalysts prepared by flame spray pyrolysis. The Cu loading and support composition were varied to understand the role of Cu–ZnO and Cu–CeO2 interactions. CeO2 addition improves Cu dispersion with respect to ZnO, owing to stronger Cu–CeO2 interactions. The ternary Cu/ZnO–CeO2 catalysts displayed a substantially higher CH3OH selectivity than binary Cu/CeO2 and Cu/ZnO catalysts. The high CH3OH selectivity in comparison with a commercial Cu–ZnO catalyst is also confirmed for Cu/ZnO–CeO2 catalyst prepared with high Cu loading (∼40 wt %). In situ IR spectroscopy was used to probe metal–support interactions in the reduced catalysts and to gain insight into CO2 hydrogenation over the Cu–Zn–Ce oxide catalysts. The higher CH3OH selectivity can be explained by synergistic Cu–CeO2 and Cu–ZnO interactions. Cu–ZnO interactions promote CO2 hydrogenation to CH3OH by Zn-decorated Cu active sites. Cu–CeO2 interactions inhibit the reverse water–gas shift reaction due to a high formate coverage of Cu and a high rate of hydrogenation of the CO intermediate to CH3OH. These insights emphasize the potential of fine-tuning metal–support interactions to develop improved Cu-based catalysts for CO2 hydrogenation to CH3OH.