Preparation Of Mn₂O₃-ZnO/SAPO-34 Bifunctional Catalyst And Study On CO₂ Hydrogenation To Olefins

Focusing on the bifunctional tandem catalysts of CO₂ hydrogenation to lower olefins with methanol as an intermediate product,so this paper proposes compositing Mn₂O₃-Zn O/SAPO-34 as bifunctional tandem catalysts used for the hydrogenation of CO₂ to lower olefins,which is to achieve high conversion and thermal stability of oxides in the tandem reaction process and carries out the preparation,characterization,and catalytic performance evaluation of Mn₂O₃-Zn O bimetallic oxide composite SAPO-34molecular sieve.First,prepared and analyzed the effects of Mn₂O₃-Zn O bimetallic oxide preparation conditions on the catalytic performance of Mn₂O₃-Zn O/SAPO-34 bifunctional tandem catalysts in conditions of different Mn₂O₃-Zn O mass ratios,different precipitants,different precursor concentrations and different preparation methods etc.The result shows that the best preparation conditions of Mn₂O₃-Zn O bimetallic oxide are 20wt%Mn₂O₃,coprecipitation method,ammonium carbonate as precipitator,and a precursor concentration of 0.2 mol/L.The mesoporous Mn₂O₃-Zn O bimetallic oxide having weak alkaline,with specific surface area of 35.6 m²/g and pore volume of 0.28 cm³/g.Then,the effects of mass ratio of Mn₂O₃-Zn O oxide and molecular sieve,reaction temperatures,reaction pressures,reaction space velocity,tandem distances between Mn₂O₃-Zn O oxide and molecular sieve,and time of ball milling on the catalytic performance of the system were investigated.The result shows that the appropriate mass ratio of Mn₂O₃-Zn O and SPAO-34,should be 3 to 1,the reaction temperature should be 380?,the reaction pressure should be 3 MPa,and the reaction space velocity should be 3600 m L/g_cat/h.For lower olefins,the yield was largely influenced by the tandem spacing,the mechanical and physical mix way of ball milling and the time of ball milling for 15 min showed the best catalytic properties.The CO₂ conversion was29.8%and the by-product CO selective was 55.1%.The lower olefins selectivity and single pass yield are 10.7%,80.2%,respectively.We researched the structure-activity relationship between structure and catalytic performance of catalysts through analyzing the crystal structural a mixed phase of zinc-manganese spinel and wurtzite,the surface of bimetallic oxides is rich in zinc,and the oxygen vacancy concentration is 21.9%,The average pore diameter is 4.11 nm.By mean of in situ Drifts to reveal the reaction mechanism of catalytic conversion of CO₂to methanol should follow the path that formate is as intermediates,and the methanol is then transferred to the molecular sieve to generate lower olefins through MTO reaction.