Insights into Bimetallic Oxide Synergy during Carbon Dioxide Hydrogenation to Methanol and Dimethyl Ether over GaZrOx Oxide Catalysts

Hydrogenation of CO2 to methanol and dimethyl ether (DME) is one strategy to tackle the global climate change and meet the portable fuel demand simultaneously. The bimetallic oxide synergy is known to boost the yields of methanol and DME from CO2 hydrogenation. However, the origin of this synergy is still unclear. We synthesized a series of GaZrOx catalysts by the evaporation-induced self-assembly method. The GaZrOx (27%) catalyst displays superior activity than admixtures of the (Ga2O3 + ZrO2) oxides. We propose that the Zr3+-OV-Ga-O species (OV represents the oxygen vacancy) on the GaZrOx catalyst is the active site. Our results demonstrate that the synergistic effect stems from neighboring Ga-O sites and Zr3+-OV sites, as revealed by complementary X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, in situ diffuse reflectance infrared Fourier transform spectroscopy, electron paramagnetic resonance spectroscopy, and solid-state NMR spectroscopy results. We demonstrate that H2 is dissociated on polarized Ga-O sites to produce Ga-H and -OH species, while CO2 is trapped by the oxygen vacancies and activated by electron transfer from the Zr3+ ions. The whole picture of the CO2 hydrogenation reaction mechanism on the GaZrOx catalyst is presented. The atomic- and electronic-levels understanding of the active sites and the origin of the synergistic effect open up a new avenue for the rational design of highly active catalysts for CO2 hydrogenation. © 2021 American Chemical Society.