Effect of promoter on physicochemical properties and catalytic performance of ZnO/ZrO2
CO2 hydrogenation to methanol is an effective way to achieve the goal of carbon neutrality.Although the reported ZnO/ZrO2 catalysts have high activity and stability,their catalytic performance are expected to be further improved.A series of Ma-ZnOx/ZrO2 catalysts with different elements doping were prepared by the impregnation method,and it was found by evaluation that only Ga promoted the catalytic CO2 hydrogenation to methanol by ZnO/ZrO2 catalyst.Among them,5%Ga-ZnOx/ZrO2 catalyst showed excellent catalytic performance.At the reaction conditions:P=3 MPa,T=320℃,V(H2)∶V(CO2)= 4∶1 and gas weight hourly space velocity(WHSV)=24 000 mL/(g∙h),the CO2 conversion of 5%Ga-ZnOx/ZrO2 catalyst was 7.2%,the methanol selectivity was 81.0%and the methanol space-time yield was up to 410 mg/(g∙h),which was 1.26 times higher than that of the ZnO/ZrO2.And there was no significant decay in the catalytic performance within 100 h of reac-tion.X-ray photoelectron spectrometry(XPS)and electron paramagnetic resonance(EPR)characterization showed that dop-ing with the appropriate amount of Ga promoter could promote the formation of oxygen vacancies in the catalyst.H2 tempera-ture programmed reduction(H2-TPR),temperature-programmed desorption of the preabsorbed CO2/H2(CO2/H2-TPD)re-sults showed that the doping of the Ga promoter enhanced the activity of the active sites of the ZnO/ZrO2 catalyst,and the Ga-ZnOx/ZrO2 catalyst exhibited a stronger capacity for the adsorption and activation of CO2 and H2.The in situ diffuse re-flectance infrared Fourier transform spectroscopy(in situ DRIFTS)results showed that the synthesis of methanol by each catalyst followed the formate-methoxy pathway,and the incorporation of Ga promoter facilitated the formation of methanol intermediates and was favorable for the conversion of HCOO* species to CH3O* species,thus improving the methanol yield.
CO2 hydrogenationmethanolZnO/ZrO2Ga promoteroxygen vacancy
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