Research On Structural Regulation Of Zirconium-based Composite Metal Oxides And Catalytic CO₂ Hydrogenation To Methano

Catalytic CO₂ hydrogenation to methanol is an effective way to achieve the goal of carbon neutrality.Since CO₂ is very stable,a high temperature is more favorable for its activation.ZnO/ZrO₂ catalysts with high activity and stability at higher reaction temperatures have received much attention,but this catalytic system has not been clearly investigated for catalyst structural morphology as well as interfacial synergistic effects.The catalyst preparation method,structural morphology and the addition of promoters are all key factors affecting the catalytic performance.In this thesis,we focus on zirconium-based metal oxide catalysts,structurally modulating them to construct ZnO/ZrO₂ catalysts with special interfacial structures,and adding promoter to them to reveal the interfacial synergistic effects generated by structural modulation of catalysts through performance evaluation and various characterization methods,which is expected to provide new research ideas for optimal modification of zirconium-based loaded catalysts.Intending to reveal the conformational relationship between catalyst structural morphology and catalytic performance,the ZrO₂ supports with different morphologies were prepared by the solvothermal method and precipitation method,and the compounding method,ratio and calcination temperature of ZnO components and ZrO₂supports were optimized.The influence of catalyst structural morphology on its physicochemical properties was investigated by various characterization tools,and the process conditions were changed to further establish the conformational relationships.The results showed that ZrO₂-F in the form of hollow nano-framework structure could effectively inhibit the transformation of sub-stable phase t-ZrO₂ to m-ZrO₂ phase with high specific surface area and multi-level pore distribution.The impregnated ZnO formed a unique interfacial structure,which enhanced the metal oxide synergy,improved the hydrogen activation and generated more oxygen vacancies.In this reaction mechanism,the oxygen vacancy concentration was positively correlated with the methanol intermediate concentration.The ZnO/ZrO₂-F catalysts impregnated with20%ZnO and calcined at 500℃ showed the best catalyst performance under different process conditions.At reaction conditions:P=3 Mpa,T=320℃,V（H₂）:V（CO₂）=4:1and GHSV=24000 mL·g_cat^-1·h^-1,the CO₂ conversion of the ZnO/ZrO₂-F catalyst was6.2%,the methanol selectivity of 74.8%and the methanol space-time yield up to 324mg _MeOH·g_cat^-1·h^-1,which was 1.78 times higher than that of the irregularly aggregated particle form ZnO/ZrO₂-P and exhibited excellent stability.To improve the catalytic activity,the effects of the addition of promoters on the physicochemical properties of the catalysts as well as the interfacial synergistic effect were investigated based on the study of 20%ZnO/ZrO₂-F.The promoters,doping ratios and calcination temperatures were screened,respectively,and the conformational relationships of the ternary metal oxide catalysts were established by various characterization methods,and the effects of the process conditions on the catalytic performance were further investigated.The results showed that only the doping of Ga enhanced the catalytic performance of the ZnO/ZrO₂-F catalyst.The GaZnO_x/ZrO₂-F catalyst with Ga doping of 5%and calcination temperature of 500℃ has the largest specific surface area and pore capacity.The 5%GaZnO_x/ZrO₂-F catalyst with higher oxygen vacancy concentration can significantly enhance the adsorption activation of H₂ and CO₂ and promote the hydrogenation of HCOO*intermediates to CH₃O*.Under the same reaction conditions,the 5%GaZnO_x/ZrO₂-F catalyst showed CO₂ conversion of 7.2%,methanol selectivity of 81.0%,and methanol space-time yield of 410mg _{Me OH}·g_cat^-1·h^-1,which was 1.26 times higher than that of ZnO/ZrO₂-F,and exhibited excellent stability.