The Study On Preparation Of Bimetallic Oxide/SAPO-34 Tandem Catalysts And The Hydrogenation Of CO₂

A one-step reaction route with high CO₂conversion rate and high lower olefins selectivity has been developed based on the thermocatalytic conversion process of CO₂hydrogenation.For CO₂hydrogenation to methanol and methanol dehydration to lower olefins,different reaction temperature and pressure are existing.To make the two catalytic processes reach the balance,the development of methanol catalysts can be suitable for high temperature is an important direction.Due to the thermodynamic stability of CO₂molecules,the tandem reaction is mainly limited to the reaction of hydrogenation of CO₂to methanol.At the same time,the combination of oxides and molecular sieves and intimacy play important roles in the product distribution and catalytic activity of the tandem catalysts.Therefore,in order to solve the above problems,the microfluidic continuous coprecipitation method was proposed to construct the catalytic system of Al₂O₃-ZnO and Al₂O₃-CeO₂bimetallic oxides.The structure-activity relationship of catalytic hydrogenation of CO₂to methanol was established,and the influence of intimacy of oxide and molecular sieve on the product distribution was studied.The effects of the catalytic systems of Me_xO_1-x-ZnO on the hydrogenation of CO₂to methanol were investigated by microfluidic continuous co-precipitation method,and the optimal catalytic system of Al₂O₃-ZnO was obtained.Then,the effects of different preparation methods on the structural properties of Al₂O₃-ZnO mixed crystal phase（spinel structure and solid solution structure）catalyst were studied.The effects of preparation process conditions（flow rate,aging temperature and aging time）on the catalytic hydrogenation of CO₂to methanol by Al₂O₃-ZnO were systematically investigated.The catalytic system of Al₂O₃-ZnO/SAPO-34 was studied by mass ratio,combination mode,milling time and reaction conditions（reaction temperature,reaction pressure and space velocity）.XRD,XRF,DRUV-Vis,SEM,TEM and CO₂/NH₃-TPD were used to reveal the relationship between structural properties and catalytic performance of the catalysts.The results showed that under the conditions of flow rate of（25,25）m L/min,aging temperature of 75℃and aging time of 2 h,the40%Al₂O₃-ZnO-MR bimetalline oxide prepared by microfluidic method showed the best catalytic performance at 320℃and 3 MP for the hydrogenation of CO₂to methanol.The Al₂O₃-ZnO/SAPO-34 tandem catalyst with ball-milling time of 25 min has the best kinetics effect,and shows a better performance of inhibiting reverse water gas.Under the reaction temperature of 380℃,reaction pressure of 3 MPa and volume space velocity of 3600 m L/g^-1·h^-1,the CO₂conversion rate is 28.7%,the selectivity of lower olefins is 86.5%,and the selectivity of by-product CO is 39.7%.According to the excellent performance of Al₂O₃-ZnO catalytic system in the hydrogenation of CO₂,the catalytic hydrogenation of CO₂to methanol by Al₂O₃metal oxide catalytic system was studied.The influence of different Al₂O₃-Me_xO_1-xcatalytic systems on the hydrogenation of CO₂to methanol were investigated by the microfluidic continuous co-precipitation method,and the optimal Al₂O₃-CeO₂catalytic system was obtained.The effects of different preparation methods on the structural properties of Al₂O₃-CeO₂solid solution structural catalyst were studied.The effects of Al₂O₃-CeO₂preparation process conditions（flow rate,aging temperature and aging time）on the catalytic hydrogenation of CO₂to methanol by Al₂O₃-CeO₂were systematically investigated.The Al₂O₃-CeO₂/SAPO-34 tandem catalyst was studied by mass ratio,combination mode,milling time and reaction conditions（reaction temperature,reaction pressure and space velocity）.XRD,XRF,DRUV-Vis,SEM,TEM and CO₂/NH₃-TPD were used to reveal the relationship between structural properties and catalytic performance of the catalysts.The results show that the 20%Al₂O₃-CeO₂-MR bimetalline oxide prepared by microfluidic method has the best catalytic performance under the conditions of flow rate of（25,25）m L/min,aging temperature of 75℃and aging time of 2 h.The hydrogenation of CO₂to methanol at320℃and 3 MP has the best catalytic performance.The Al₂O₃-CeO₂/SAPO-34catalyst with ball-milling time of 15 min has the best kinetics effect and shows a good performance of inhibiting reverse water gas.Under the reaction temperature of 380℃,reaction pressure of 3 MPa and volume space velocity of 3600 m L/g^-1·h^-1,the CO₂conversion rate is 22.6%,the selectivity of lower olefins is 84.6%,and the selectivity of by-product CO is 35.4%.