Stabilizing Cu⁺ in Cu/SiO₂ Catalysts with a Shattuckite-Like Structure Boosts CO₂ Hydrogenation into Methanol

Abstract

Cu-based catalysts are widely employed for CO or CO2 hydrogenation into methanol. However, their catalytic performance highly depends on supports, and the real evolution of Cu species is still covered by active components. Herein, we supply a Cu/SiO2 catalyst prepared by flame spray pyrolysis (FSP), showing catalytic performance comparable to that of the active Cu/ZrO2 catalyst for methanol synthesis from CO2. It reaches 79% selectivity at a CO2 conversion of 5.2%, which is an outstanding selectivity among previously reported Cu/SiO2 catalysts, considering they are generally treated as nearly inert catalysts. In situ X-ray absorption spectroscopy (XAS) analysis shows that 5 times more Cu+ species in the FSP-Cu/SiO2 are stabilized in comparison to those in the traditional ammonia evaporation (AE) made catalyst even after reduction at 350 °C. A unique shattuckite-like precursor with a slightly distorted Cu–O–Si texture structure formed in the FSP-made catalyst is responsible for the enriched Cu+ species. Variations of intermediate formation and methanol production are found to have a good relationship with the amount of Cu+ species. According to the results of high-pressure in situ DRIFTS, we attribute this to the promotional effect of Cu+ on the stabilization of CO* intermediates, which inhibits CO desorption and facilitates further hydrogenation to CH3OH via the RWGS + CO-Hydro pathway. These results bring insights into the Cu reduction behavior and the function of Cu+ species during methanol production on Cu-based catalysts without the assistance of active supports.