Selective Production of Oxygenates from Carbon Dioxide Hydrogenation over a Mesoporous-Silica-Supported Copper-Gallium Nanocomposite Catalyst

The hydrogenation of CO₂ to oxygenates (methanol and dimethyl ether; DME) was investigated over bifunctional supported Cu catalysts promoted with Ga. The supported Cu-Ga nanocomposite catalysts were characterized by using XRD, TEM with energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and H₂ temperature-programmed reduction. In comparison with Cu-SBA-15-based catalysts, the Ga-promoted catalyst prepared by the urea deposition method (Cu-Ga/SBA-15-UDP) was more active and selective for CO₂ hydrogenation to oxygenates. The use of Ga as the promoter led to increased acidic sites, which was confirmed by using NH₃ temperature-programmed deposition and IR spectroscopy with pyridine and 2,6-lutidine as probe molecules. The favorable effect of Ga on the CO₂ conversion and selectivity to oxygenates may come from the strong interaction of Ga with silica, which is responsible for the enhanced metal surface area, the formation of the nanocomposite, and the metal dispersion. Notably, the incorporation of Ga into Cu/SiO₂ led to a several-fold higher rate for methanol formation (13.12 μmol g_Cu ⁻¹ s⁻¹) with a reasonable rate for DME formation (2.15 μmol g_Cu ⁻¹ s⁻¹) compared to Cu/SiO₂ catalysts.