| The catalytic transformation of synthesis gas into high-value chemicals is a key process for the conversion and utilization of carbon-based energy and resources.The products include hydrocarbons such as diesel,olefins,aromatic hydrocarbons,as well as organic oxygen-containing compounds such as methanol,ethanol,and higher alcohols.This thesis aims to directly synthesize lower olefins from synthesis gas with high selectivity.Based on the design of multi-functional catalyst system,we prepared metal oxides/zeolite by by post-treatment with different acidic and alkaline solutions on S APO-34 zeolite to improve the selectivity of lower olefins and the stability of the catalyst for syngas conversion.Through the development of the multifunctional catalyst combination and the optimization on the reaction conditions,ethylene is synthesized from syngas with high selectivity by precise control on C-C couplingThis thesis examines the effect of post-treating SAPO-34 zeolite with different acidic and alkaline solutions on catalytic performances of syngas conversion over Zn O-ZrO2/SAPO-34 catalyst.The results show that the crystallinity of the SAPO-34 zeolite treated with TEAOH was maintained,and a large number of mesopores appear on the surface of the zeolite.As compared to ZnO-ZrO2/SAPO-34 catalyst without treatment,the conversion of CO increased to 30.7%and the selectivity of C2-4=reached 80.9%.after treatment on SAPO-34 zeolite with 0.2 M TEAOH.We speculate that due to the removal of part of the silicon on the surface of the zeolite,the acidity of the zeolite is reduced,and the olefins hydrogenation is also weakened,thus the selectivity of lower olefins is improved.Moreover,the introduction of mesopore in SAPO-34 zeolite reduces the gas diffusion resistance during the reaction process and the intermediate product residence time,the conversion of CO increased through pulling the reaction equilibrium,and the catalyst stability is also greatly extended because the carbon deposition is significantly reduced.Subsequently,the kinetics of the conversion of synthesis gas to olefins was studied.The reaction was carried out in an internal circulation non-gradient reactor.The side reaction was reduced as much as possible by increasing the weight of catalyst,and the effect of internal and external diffusion was eliminated by changing the particle size of catalyst and gas space velocity of reactants.The data of the effect of reaction temperature and pressure on catalytic activity were obtained.It is convenient for the follow-up kinetic equation calculation.This paper further focuses on the production of ethylene direct from syngas.A combination of multi-functional catalysts was designed to efficiently integrate the four reactions of synthesis gas to methanol,methanol carbonylation to acetic acid,acetic acid hydrogenation to ethanol and ethanol dehydration to ethylene in the way of relay catalysis achieving high-selective conversion of syngas into ethanol has been realized.Through the development of the catalyst and the optimization of the reaction conditions,the formation of intermediate products of methanol,acetic acid,and ethanol in the four-step relay catalytic system is precisely controlled,achieving highselective conversion of syngas into ethanol.Cu-ZnO | H-MOR-DA-12MR | PtSn/SiC | H-MOR-DA-12MR catalyst combination is used in the synthesis gas conversion to ethylene,in which the CO conversion exceeds 14%,and the selectivity of ethylene is～83%,and the performances are stable during 100 h test.By this strategy,we successfully obtain a high selectivity of ethylene from synthesis gas over multi-functional catalysts system. |
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