CO2 Hydrogenation to Methanol on Core-Shell-Structured SiO2-Encapsulated Cu-ZnO-In2O3 Nanoparticles.

Abstract

Since Cu-ZnO-based catalysts for CO₂ hydrogenation to methanol are generally suffered from thermal aggregations of Cu nanoparticles under an excess water environment, SiO₂-encapsulated Cu-ZnO-based nanoparticles with multicore-shell structures were applied in this study. The synergistic effects of In₂O₃ on the Cu-ZnO surfaces and protective SiO₂ overlayers were verified to explain the positive contributions of In₂O₃ with decreased CO selectivity and an increased methanol selectivity above 80%, which were attributed to the prohibited competitive reverse water-gas shift reaction activity and less aggregation nature of active metal (oxides) by SiO₂ shells. The increased oxygen vacant sites from partially reduced In₂O₃, ZnO and Cuⁿ⁺ phases and larger surface area of metallic Cu⁰ surfaces on the Cu-ZnO-In₂O₃@SiO₂ were responsible for an enhanced CO₂ conversion (25.3%) and methanol selectivity (80.1%) by easily activating CO₂ dissociation and suppressing RWGS reaction. To verify overall reaction mechanisms on the In₂O₃ metal oxide-substituted Cu nanoparticles, Gibbs free energy diagrams for formyl, formate, and carboxyl intermediates pathways were compared by Density functional theory calculations, which revealed that the most favorable pathway for CO₂ hydrogenation to CH₃OH was CHO₂H^* intermediate-based formyl pathway on In₂O₃-substituted Cu(111) surfaces by decreasing CO selectivity due to the suppressed RWGS reaction activity.