Enhancement of CO2 hydrogenation to methanol over Cu-based catalysts mixed with hydrophobic additives†

Abstract

The hydrogenation of CO₂ by renewable power-generated hydrogen to methanol offers a promising pathway for achieving sustainable carbon recycling. However, the CO₂ hydrogenation process is restricted by the water by-product, requiring selective removal of water from the reaction system. In this study, simply physically mixing hydrophobic poly(divinylbenzene) with the Cu/Zn/Zr catalyst can rapidly remove water generated in the reaction system without altering the basic structure of the catalyst. By optimizing operation conditions, the CO₂ conversion of the catalyst can reach 23.45%, and the space–time yield of methanol can reach 245.4 mg_MeOH g_cat⁻¹ h⁻¹ under the conditions of 260 °C, 5 MPa, H₂/CO₂ = 3, GHSV of 6000 mL g_cat⁻¹ h⁻¹, and mass ratio of 3. Mechanistic investigation indicates that the poly(divinylbenzene) additive can accelerate the rapid diffusion of water from the catalyst surface through its hydrophobic water-conducting channels, thereby inhibiting the oxidation of copper active sites on the catalyst surface by water, which helps maintain high catalyst activity during CO₂ hydrogenation and ensures the smooth progression of the formate reaction pathway. Furthermore, molecular dynamics simulations demonstrate that water can continuously be removed from hydrophobic water-conducting channels. Such a physically mixed catalyst remains durable in the continuous test for 200 hours owing to the thermal stability of the poly(divinylbenzene) additive. By selecting more suitable hydrophobic additives, such as hydrophobic graphite, this strategy can be further extended to other CO₂ hydrogenation reactions.