Enhancing Stability of Cu/ZnO Catalysts in the CO2 Hydrogenation to Methanol by the Addition of MoO3 and ReO3 Promoters.

The catalytic hydrogenation of CO2 to methanol represents a promising route for carbon recycling and hydrogen storage. However, the stability of current catalysts remains one of the main technological challenges. In this work, we investigate the promotional effect of MoO3 and ReO3 on Cu/ZnO-based catalysts with metal loadings ranging from 0.06 to 3.5 wt%. Spectroscopic (XPS and in situ Raman) and kinetic studies reveal that the incorporation of ultra-low promoter amounts (0.06 wt%) enhances methanol productivity, whereas higher concentrations lead to partial blocking of the active copper sites. Rhenium promotes the stabilization of Cu+ species, while molybdenum establishes strong Cu-Mo interactions that modify the reducibility and surface composition of the catalyst. Remarkably, long-term stability tests (80 h, 240 °C, 20 bar and CO2/H2 = 3) demonstrate that Mo-promoted catalysts exhibit superior durability, reducing the deactivation constants by up to 82% compared to the un-promoted Cu/ZnO sample. This enhanced stability is attributed to the higher Cu-MoO3 interaction, enhanced Cu dispersion and high water affinity of Mo species, which trap water as Mo-OH bonds, preventing copper sintering under reaction conditions. These findings highlight the dual role of Re and Mo in tuning both activity and stability, emphasizing the crucial influence of Mo on the long-term performance of Cu-based catalysts for CO2 to methanol conversion.