Insights Into Bimetallic Oxide Synergy During CO₂ Hydrogenation To Methanol And Dimethyl Ether Over GaZrO_x Oxide Catalysts

The conversion of carbon dioxide（CO₂）into value-added products has emerged as an attractive solution to tackle the global climate change caused by anthropogenic CO₂ emissions.Methanol and dimethyl ether（DME）are not only crucial platform molecules that can be further converted into fuels and valuable chemicals but also used as hydrogen storage compounds.Therefore,hydrogenation of CO₂ into methanol and DME using“green H₂”is also significant in the context of portable fuel sources.Bimetallic oxide catalysts have attracted much attention due to their excellent catalytic performance for CO₂ hydrogenation to methanol.However,the in-depth understanding is still limited toward the relationship between structure and catalytic activity,which is significant for enhancing the activation of CO₂ and H₂.Based on the above reasons,we synthesized a series of GaZrO_x catalysts by the evaporation-induced self-assembly（EISA）method and investigated the structure of active sites on the GaZrO_x catalyst.The GaZrO_x（27%）catalyst displays superior activity than admixtures of the（Ga₂O₃+Zr O₂）oxides.Besides,we proposed the synergistic effect originates from two adjacent sites of Ga-O and Zr³⁺-O_v,which is revealed by complementary techniques such as X-ray Photoelectron Spectroscopy（XPS）,Time of Flight Secondary Ion MassSpectrometry（ToF-SIMS）,in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy（In situ DRIFTS）,Electron Paramagnetic Resonance（EPR）,and solid-state Nuclear Magnetic Resonance（ssNMR）.Based on this understanding,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.Our results suggest that the Zr³⁺-O_v-Ga-O species（O_v represents oxygen vacancy）on the GaZrO_x catalyst is the active site.The whole picture of the CO₂ hydrogenation reaction mechanism on the GaZrO_xcatalyst is presented.The atomic-and electronic-level 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.