Plasma-Catalytic Methanol Synthesis from CO2 Hydrogenation over a Supported Cu Cluster Catalyst: Insights into the Reaction Mechanism

Plasma-catalytic CO2 hydrogenation for methanol production is gaining increasing interest, but our understanding of its reaction mechanism remains primitive. We present a combined experimental/computational study on plasma-catalytic CO2 hydrogenation to CH3OH over a size-selected Cu/γ-Al2O3 catalyst. Our experiments demonstrate a synergistic effect between the Cu/γ-Al2O3 catalyst and the CO2/H2 plasma, achieving a CO2 conversion of 10% at 4 wt % Cu loading and a CH3OH selectivity near 50%, further rising to 65% with H2O addition (for a H2O/CO2 ratio of 1). Furthermore, the energy consumption for CH3OH production was more than 20 times lower than with plasma only. We carried out density functional theory calculations over a Cu13/γ-Al2O3 model, which reveal that the interfacial sites of the Cu13 cluster and γ-Al2O3 support show a bifunctional effect: they do not only activate the CO2 molecules but also strongly adsorb key intermediates to promote their hydrogenation further. Reactive plasma species can regulate the catalyst surface reactions via the Eley–Rideal (E–R) mechanism, which accelerates the hydrogenation process and promotes the generation of the key intermediates. H2O can promote the CH3OH desorption by competitive adsorption over the Cu13/γ-Al2O3 surface. This study provides new insights into CO2 hydrogenation through plasma catalysis, and it provides inspiration for the conversion of some other small molecules (CH4, N2, CO, etc.) by plasma catalysis using supported-metal clusters.