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

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.