Flame Synthesis of Cu/ZnO–CeO ₂ Catalysts: Synergistic Metal–Support Interactions Promote CH ₃OH Selectivity in CO ₂ Hydrogenation

Abstract

The hydrogenation of CO ₂ to CH ₃OH is an important reaction for future renewable energy scenarios. Herein, we compare Cu/ZnO, Cu/CeO ₂, and Cu/ZnO–CeO ₂ catalysts prepared by flame spray pyrolysis. The Cu loading and support composition were varied to understand the role of Cu–ZnO and Cu–CeO ₂ interactions. CeO ₂ addition improves Cu dispersion with respect to ZnO, owing to stronger Cu–CeO ₂ interactions. The ternary Cu/ZnO–CeO ₂ catalysts displayed a substantially higher CH ₃OH selectivity than binary Cu/CeO ₂ and Cu/ZnO catalysts. The high CH ₃OH selectivity in comparison with a commercial Cu–ZnO catalyst is also confirmed for Cu/ZnO–CeO ₂ 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 CO ₂ hydrogenation over the Cu–Zn–Ce oxide catalysts. The higher CH ₃OH selectivity can be explained by synergistic Cu–CeO ₂ and Cu–ZnO interactions. Cu–ZnO interactions promote CO ₂ hydrogenation to CH ₃OH by Zn-decorated Cu active sites. Cu–CeO ₂ 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 CH ₃OH. These insights emphasize the potential of fine-tuning metal–support interactions to develop improved Cu-based catalysts for CO ₂ hydrogenation to CH ₃OH.