Hydrogenation of CO2 to methanol utilizing the hydrogen from renewable energy sources offers a promising way to reduce CO2 emissions through the CO2 utilization as a carbon source. However, it is a challenge to convert CO2 to methanol with high activity and high methanol selectivity. Herein, we report a class of metal-oxide solid-solution catalysts: MaZrOx (Ma = Cd, Ga), which show a methanol selectivity up to 80% with the CO2 single pass conversion reaching 4.3%-12.4% under the reaction conditions of H2/CO2 = 3/1, 24※000 h-1, 5 MPa. Structural and electronic characterizations combined with denisty functional theory calculations suggest that the Ma and Zr components in MaZrOx (Ma = Cd, Ga) solid-solution catalysts show a strong synergetic effect, which enhances the H2 heterolytic dissociation and results in high activity and high methanol selectivity. The solid-solution catalyst with dual metal oxide components offers an approach for the selective hydrogenation of CO2 to chemicals.@en

Although methanol synthesis via CO hydrogenation has been industrialized, CO2 hydrogenation to methanol still confronts great obstacles of low methanol selectivity and poor stability, particularly for supported metal catalysts under industrial conditions. We report a binary metal oxide, ZnO-ZrO2 solid solution catalyst, which can achieve methanol selectivity of up to 86 to 91% with CO2 single-pass conversion of more than 10% under reaction conditions of 5.0 MPa, 24,000 ml/(g hour), H2/CO2 = 3:1 to 4:1, 320° to 315°C. Experimental and theoretical results indicate that the synergetic effect between Zn and Zr sites results in the excellent performance. The ZnO-ZrO2 solid solution catalyst shows high stability for at least 500 hours on stream and is also resistant to sintering at higher temperatures. Moreover, no deactivation is observed in the presence of 50 ppm SO2 or H2S in the reaction stream.@en

The role of formate species for CO2 hydrogenation is still under debate. Although formate has been frequently observed and commonly proposed as the possible intermediate, there is no definite evidence for the reaction of formate species for methanol production. Here, formate formation and conversion over the ZnZrOx solid solution catalyst are investigated by in situ/operando diffuse reflectance infrared Fourier transform spectroscopy-mass spectroscopy (DRIFTS-MS) coupled with density functional theory (DFT) calculations. Spectroscopic results show that bidentate carbonate formed from CO2 adsorption is hydrogenated to formate on Zn-O-Zr sites (asymmetric sites), where the Zn site is responsible for H2 activation and the Zr site is beneficial for the stabilization of reaction intermediates. The asymmetric Zn-O-Zr sites with adjacent and inequivalent features on the ZnZrOx catalyst promote not only formate formation but also its transformation. Both theoretical and experimental results demonstrate that the origin of the excellent performance of the ZnZrOx catalyst for methanol formation is associated with the H2 heterolytic cleavage promoted by the asymmetric Zn and Zr sites.@en