Study On The Preparation Of SAPO-34/CZA Composite Catalyst And Its Catalytic Performance In The CO₂ Hydrogenation To Light Carbon Olefins

The process of CO₂ hydrogenation to light carbon olefins has attracted much attention due to its environmental protection,energy saving,economy and so on the multiple significance,It is not only beneficial to the utilization of greenhouse gas CO₂,but also to reduce the dependence of light carbon olefin production on oil resources.Since the reaction follows the Fischer Tropsch reaction path has much insufficient such as reaction conditions relatively harsh,reaction heat is not easy to transfer,improving product selectivity is limited and so on,researchers have proposed different path of CO₂ hydrogenation to methanol and methanol to olefins by catalytic cracking reaction.In this paper,starting from the design of new structure catalyst,the composite catalysts with coating structure were prepared by co-precipitation method,the structural properties and catalytic performance of the catalysts were compared with other methods,at the same time,the preparation conditions was optimizationed of the cladding phase CZA catalyst,also studied the preparation conditions and process parameters on the structural properties and catalytic performance of the composite catalyst prepared by co-precipitation method.Preparation of influencing factors of CZA catalyst prepared by co-precipitation method were investigated.These obtained products were characterized by XRD,SEM,BET and CO₂-TPD techniques to investigate their crystalline phase,morphology,pore structure and surface alkalinity.The results indicated that molar ratio of Cu/Zn,The content of aluminum and the addition of the state,system pH value and calcination temperature posed significant impact on the structure properties of CZA catalyst.CZA catalyst has large specific surface area and pore volume?90.09m2·g-1 and 0.4231 cm3·g-1?,pore size concentration?8-20nm?,alkaline mainly in medium strong alkali and surface active component dispersivity was better when the molar ratio of Cu/Zn was 2,aluminum molar content of 10% and adding in the form of aluminum salt,pH value of 7,calcination temperature of 400?.The composite catalysts with the main components of CZA and SAPO-34 molecular sieves were synthesized by co-precipitation method,microwave hydrothermal coating method and physical blending method.SAPO-34/CZA composite catalyst possess coated structure prepared by co-precipitation method,effects of mass ratio,pH value,the addition of aluminum on structure properties and catalytic performance of SAPO-34/CZA composite catalyst were investigated.These obtained composite catalysts were characterized by XRD,FT-IR,SEM,BET,NH₃-TPD and CO₂-TPD techniques to investigate their crystalline phase,skeletal structure,morphology,pore structure and surface acidity and alkalinity,and the catalytic performance was investigated in the hydrogenation of CO₂ to light carbon olefins.The results indicated that structure properties and catalytic performance of the composite catalysts were quite different with different preparation methods;mass ratio,pH value and the addition of aluminum has great influence on structure properties and catalytic performance of SAPO-34/CZA composite catalyst.SAPO-34/CZA composite catalyst not only possess coated structure,but also has multi-level pore distribution?microporous specific surface area of 53.15 m2·g-1,mesoporous specific surface area of 59.84 m2·g-1?,suitable weak acid sites?0.00976 mmol·g-1?,rich alkaline sites?weak alkali of 0.00566 mmol·g-1?medium strong alkali of 0.02114 mmol·g-1?prepared by co-precipitation method with mass ratio of 1:1,pH value of 7 and adding in the form of aluminum salt.The CO₂ conversion and light olefins selectivity were reached to 64.80% and 49.68%,respectively.The process conditions of SAPO-34/CZA composite catalyst for hydrogenation of CO₂ to light carbon olefins were optimized,effects of reaction temperature,reaction pressure and volume space velocity on the conversion of CO₂ and selectivity of olefins were investigated.The results indicated that the optimum reaction conditions of CO₂ hydrogenation to light carbon olefins were reduction temperature of 285?,reaction temperature of 325?,the reaction pressure of 3.0MPa,V?H₂?/V?CO₂?of 3.0 and space velocity of 3500mL·g-1·h-1.