Study Of CuAl₂O₄ Catalyst Promoted By CeO₂ For Methanol Synthesis From CO₂ Hydrogenation

CO2 is the most abundant and cheapest C1 resource on earth.In addition,a large amount of CO2 emissions has caused the greenhouse effect.To improve the environment and alleviate the energy crisis,technologies that can transform CO2 into high-added chemicals are urgently demanded.Catalytic conversion is a meaningful way to utilize CO2.Among many catalytic conversion products,methanol is a crucial raw feedstock for chemical deep processing and can be used as an excellent alternative candidate for gasoline.Therefore,the research on CO2 hydrogenation to methanol has attracted much attention.CO2 is an inert molecule in thermodynamics;thus the difficulty of this issue is to develop a catalyst with high activity and selectivity towards methanol.Among the present catalysts for C02 hydrogenation to methanol,copper-based catalysts have widely and extensively become a research hotspot due to their high catalytic performance and low cost,although the traditional copper-based catalysts have low methanol selectivity(about 60%)and their stability needs to be improved.Subsequently,uncovering more efficient catalysts for CO2 hydrogenation to methanol is urgent to be solved.In the meanwhile,spinel as a highly efficient and stable catalyst or carrier has been drawing increasing attention recently and applied spreadly.In the present work,a CeO2-promoted copper-alumina spinel catalyst with the excellent performance was exploited.This catalyst exerted high activity selectivity,and stability.Based on a series of characterization,the structure and catalytic performance of the catalysts were well correlated,providing a new type of catalyst and fundamental mechanism in understanding for CO2 hydrogenation to methanol.The catalytic results showed that the catalyst prepared by the hydrotheramal method had optimum CO2 hydrogenation performance than that prepared by the impregnation or the coprecipitation method.The methanol selectivity for the catalyst with different Ce content showed a trend of volcanic type variation.The optimal reaction conditions are as follows:reduction at 250 ?.reaction at T=220 ?,P=3.0 MPa,WHSV=3000 mL/(g·h),n(H2)/n(CO2)=3.0.Under these reaction conditions,5%Ce-CuAl2O4 exhibit the best catalytic activity:the CO2 conversion was 14.5%,the methanol towards methanol was 82.2%,and the selectivity of CO was only 16.3%.After 80 hours of continuous reaction stream,the methanol selectivity of 5%Ce-CuAl2O4 catalyst was still 67.1%,while that of CuAl2O4 catalyst decreased to 32.7%.Catalyst characterization results show that the precursor prepared by the hydrothermal method can be transformed into the stable spinel when the calcination temperature was raised to 800 ?.CeO2 acts as a mechanically isolating unit,which helps to disperse the active components and reduce the crystallinity of spinel.The interaction between Ce and Cu is conducive to the reduction of CuO,the adjustment of Cu0 and Cu+ ratio,and the change of adsorption of H2 and CO2 on the catalyst surface,which can promote the hydrogenation and the production of methanol.Also,the presence of CeO2 reduces the carbon deposition of the catalyst,thus enhancing the stability of the catalyst with regards to CuAl2O4,which is of research value.