Combined Role of Ce Promotion and TiO2 Support Improves CO2 Hydrogenation to Methanol on Cu Catalysts: Interplay Between Structure and Kinetics

Ce promotion increases the rate of methanol formation by two orders of magnitude compared to Cu/TiO2 and Cu/SiO2 catalysts. The promotion proceeds via the generation of a new active site in which Ce3+ intervenes at the interface with Cu, without significant influence of the support identity. For higher promoter concentrations (Ce/ (Cu + Ce) greater than 0.3), additional active sites are not further generated due to the saturation of the space around copper clusters. TiO2-supported samples presented higher methanol selectivity (ca. 80% at 220 degrees C and 8 bar) compared to the ones supported on SiO2 (ca. 20%), due to an inhibition of the r-WGSR related to the strong metal support interaction between Cu and TiO2, which blocks surface sites responsible for CO production. Operando - DRIFTS further verified that the mechanism for methanol formation is the same between both families of catalysts and that it likely proceeds via the generation of formates at the Cu - Ce interface.