Fabrication And Regulation Of Active Sites Over Ni/SAPO-11 Catalyst For Hydroisomerization Of Light Alkanes

Hydroisomerization of light alkanes is an important technology for optimizing the composition of gasoline pools in China.,and the key lies in the development of high-efficiency and low-cost catalysts.As a typical bifunctional catalyst,the isomerization activity of the Ni/SAPO-11 catalyst is not only related to the properties of the metal sites and acid sites,but also related to the synergy between metal and acid sites.Therefore,fabricating the metal and acid sites of the bifunctional catalysts to achieve good synergy is the key to obtaining a high-efficiency isomerization catalyst.Based on this,the thesis takes Ni/SAPO-11catalyst as the research object,optimizes its isomerization performance by adjusting the metal location and acid properties of the catalyst,and clarifies the influence of the metal location on the synergistic relationship between the metal and the acid sites,which in order to provides a theoretical basis for the development of high-efficiency nickel-based isomerization catalysts.The pore-blocking effect of the SAPO-11 zeolite template was used to control the metal location,and the catalyst isomerization activity of n-hexane under different metal positions was investigated.The results show that increasing the number of metal sites on the external surface can reduce the blockage of the pores so that the acid sites in the pores could be more exposed,which leads to the specific surface of the catalyst micropores and the total acid content are increased.The difference in metal location will influence the synergy between the metal and acid sites.Increasing the amount of the metal sites on the external surface can improve the synergy relationship between the metal and acid sites.Appropriately increasing the distance between the metal site and the acid site can effectively promote the intermediate diffusion between active sites and inhibit the（s,p）βcracking reaction occurring in the micropores,improving the yield of iso-hexane In addition,the difference in metal location will affect the number synergy between metal and acid sites.When Ni species locate on the external surface of the catalyst,1 metallic nickel and 5 acid sites could achieve the best match in quantity;when Ni species locate on the external surface and in the pores of catalyst,a single metallic nickel site is able to balance ca.2.5 acid sites.Once the metal Ni species is excessive,the excessive Ni species would block the pores of SAPO-11,reduce the exposure of acid sites in the pores and increase the size of nickel species,leading to aggravate the hydrogenolysis reaction.Therefore,the conversion of n-hexane and the selectivity of i-C₆decrease.Without changing the metal loading,the acid properties of the Ni/SAPO-11 catalyst can be adjusted by changing the amount of silicon introduced,introducing surfactants with different chain lengths,and changing the type of template agent.The results show that increasing the amount of Si introduced can increase the concentration of active silicon species in the initial gel,but excessive introduction of silicon will cause the content of"silicon island"structure（Si（4Si））to increase and the amount of molecular sieve acid to decrease.When the amount of silicon introduced SiO₂/Al₂O₃ is 0.6,the catalyst has the highest total acid content and the best isomerization performance.The introduction of surfactants can not only promote the isomorphous substitution of Si atoms and increase the acid content of the catalyst,but also affect the growth of SAPO-11 zeolite[002]crystal planes to change the morphology of the catalyst.The increase in acid content leads to the conversion of n-hexane in the catalyst while the selectivity of cracked products soared.The difference in the type of template will affect the relative content of Si atom SMIII substitution to affect the acid properties of the catalyst.The Ni/SAPO-11 catalyst synthesized with diethylamine（DEA）as the template has the highest"silicon island"structure content and the lowest total acid content,lower total acid content leads to a significant decrease in the isomerization activity of n-hexane.In summary,the key to obtaining a high-efficiency hydro-isomerization catalyst is to control the metal sites and acid sites of the Ni/SAPO-11 catalyst.