Morphology And Acidity Control Of SAPO-34 Zeolite And Its Application In Conversion Of Syngas Into Lower Olefins

Catalytic conversion of syngas to light olefins is an important way for the conversion and utilization of non-oil-based resources,but the selective regulation of products has always been an important challenge in this field.Based on the research idea of direct synthesis of light olefins from syngas over bifunctional catalysts,this paper focuses on the SAPO-34 zeolite of bifunctional catalysts,and carries out the synthesis of nanosheet SAPO-34 zeolite and low acid SAPO-34 zeolite.The influences of synthesis methods and synthesis parameters on the structure,morphology and catalytic performance of zeolite were investigated,and the relationship between catalyst structure and catalytic performance was understood.Firstly,nanosheet SAPO-34 zeolite were synthesized by different methods.The results show that the Dry Gel Conversion can effectively reduce the size of the zeolite to the nanometer level(long 0.98 μm,thick 131 nm),and the Crystal Growth Inhibitor can further reduce the zeolite size and improve the catalytic performance.The size of the product can be precisely controlled by simply adjusting the amount of PEG,a kind of crystal growth inhibitor,and water during crystallization at high temperature,so the morphology of SAPO-34 zeolite can be controlled.PEG can also be used as a poreforming agent to introduce mesoporous for nanosheet SAPO-34 zeolite.The nanosheet SAPO-34 zeolite reduces the mass transfer resistance of reactants and products,reduces the formation rate of carbon deposition,and greatly reduces the deactivation rate of bifunctional catalysts.Among them,the conversion rate of SAPO-34-CGI(30 ml H2O)sample is 52.7%,the selectivity rate is 77.4%,and the deactivation rate is 0.03%.Furthermore,different synthesis methods were used to control the acidity of SAPO-34 zeolite.The results show that the acidity of zeolites can be reduced by HFMediated Method,but there are some SAPO-34-18 and SAPO-5 heterocrystals in the products,and the grain size is larger.Low acid nanosheet SAPO-34 zeolite with high purity can be synthesized by changing the Si feeding amount based on the Crystal Growth Inhibitor,and the proportion of Si elements in the skeleton is effectively controlled by simply adjusting the amount of Si,thus adjusting the acid amount of SAPO-34.Among them,the conversion of SAPO-34-CGI(0.0025Si)is 46.9%,the selectivity is 81.5%,and the deactivation rate is merely 0.01%.The reaserch show that the low acid nanosheet SAPO-34-CGI zeolite weakens the cyclization and hydrogenation ability of the intermediates,greatly improves the selectivity of light olefins,reduces the carbon deposition,and enhances the stability of the zeolite.