Preparation Of Cu/ZnO/ZrO₂ Catalyst By Citric Acid Sol-gel Method And Study Of Its Catalytic Performanc

Since the industrial revolution,the use of large amounts of fossil energy has enabled society to develop rapidly,but it has also created problems such as the greenhouse effect and energy scarcity.The resource utilization of CO₂is an effective way to mitigate the greenhouse effect.Methanol is known as a clean energy source among organic fuels and is also widely used as a fuel substitute and as a basic chemical raw material.Therefore,CO₂hydrogenation to methanol has a broad application prospect and can effectively mitigate the greenhouse effect and energy crisis while realizing the carbon cycle.In this paper,a series of dry gels and the corresponding Cu-Zn-Zr catalysts were prepared by the sol-gel method and using copper nitrate,zinc nitrate,zirconium nitrate and citric acid as raw materials.The performance of the dry gels and catalysts were analyzed by characterization of TG-DTA,H₂-TPR,CO₂-TPD,FTIR,XRD,TEM and BET.In addition,the catalytic activity of CO₂hydrogenation to methanol was evaluated using a catalytic activity evaluation device,and the effects of the coordination mode of metal ions with carboxylate ions in citric acid and the number of citric acid ligands on the catalyst performance were investigated in depth.Different metal ions combine with the carboxylate in citric acid in different coordination modes and can interact with each other to change their coordination modes,so that the dry gel forms a three-dimensional structure.Therefore,the three-component catalyst has a large specific surface area and good copper dispersion,and also shows good catalytic performance for CO₂hydrogenation to methanol with a CO₂conversion of 11.9%.With the increase of citric acid coordination points,CuO-ZrO₂and Cu O-ZnO catalysts exhibited different catalytic properties.The increase in the number of coordination points in CuO-ZrO₂catalyst allows more Cu²⁺to be coordinated with the carboxylate in citric acid,and the catalyst has better specific surface area,pore capacity and copper dispersion,thus CuO-ZrO₂has better methanol selectivity of68.15%at 3 coordination points.However,when the number of coordination points is less,the dry gel forms a three-dimensional network structure with Cu²⁺as the core by interacting and uniting two different coordination modes of single tooth and double tooth,so that the metal ions are dispersed in the roasting process,which shows the smallest average grain size of Cu O and promotes the catalyst reduction process.When the number of coordination points is 1,the conversion of CO₂in CuO-ZrO₂is best at11.8%.And the appropriate number of coordination points in the Cu O-ZnO catalyst can promote the diversification of coordination modes in the dry gel,which is conducive to the formation of a network structure with Cu²⁺as the core and the effective dispersion of the metal oxides in the catalyst after roasting.When the coordination point is 2,the catalyst exhibits good catalytic properties.