Effects of co-doping of Co and Zr on performances of In-based catalysts for carbon dioxide hydrogenation to methanol
CO2 hydrogenation to methanol is one of promising route for CO2 utilization.In-based catalysts has high methanol selectivity but low CO2 conversion rate for CO2 hydrogenation to methanol.In order to investigate the effects of doping different proportions of Co and Zr on the performances of In-based catalysts,In-based catalysts doped with different n(Zr)∶n(Co)were synthesized by co-precipitation method while keeping the same mole fraction of In in the precursor.The catalysts were characterized by low-temperature Ar physical adsorption,X-ray diffraction(XRD),high resolution transmission electron microscope(HRTEM),X-ray photoelectron spectroscopy(XPS)and H2 temperature-programmed reduction(H2-TPR).The catalytic performances of each catalyst were tested under the conditions of temperature from 240 ℃ to 300 ℃,pressure of 3.0 MPa and gas space velocity of 7200 mL/(h·g).The results show that the catalysts with Co and Zr at the same time has a higher CO2 conversion rate and methanol time-space yield than the catalysts with Co or Zr alone in a certain n(Zr)∶n(Co)range.n(Zr)∶n(Co)will produce different degrees of metal-to-metal interactions,which will affect the specific surface area,particle size and reduction performance of the catalysts.When the doped n(Zr)∶n(Co)is 1∶3,the catalyst has the best methanol synthesis ability and the methanol time-space yield is up to 178 mg/(g·h).The CO2 conversion rate decreases in the order:Zr5Co15In,Zr2.5Co17.5In,Zr7.5Co12.5In,Co20In,Zr10Co10In,Zr20In and In100,which is consistent with the trend of oxygen vacancy ratio.The Zr5Co15In catalyst has a smaller particle size with a larger specific surface area,which can expose more active sites,and has higher reducibility and stronger intermetallic interactions.The CO2 conversion rate of Zr5Co15In can reach 13.63％,which is 19.9％higher than Co20In and 64.7％higher than Zr20In.
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