Synthesis Of Heteroatom Aluminophosphate Molecular Sieve With AEL Topology By Solvent-free Method And Their Catalytic Application

Aluminophosphate molecular sieve（AlPO₄-n）is a kind of important porous inorganic crystal material,which has excellent performance in isomerization,alkylation,hydroxylation and other industrial catalysis in recent years.It has great research value due to the introduction of specific heteroatoms into the zeolite framwork can give certain properties,such as ion exchange performance and redox performance and so on.Among the many synthetic methods of heteroatom-substituted aluminophosphate molecular sieve,the solvent-free synthesis has attracted the great interest of zeolite researchers because of its high zeolite yield and low waste production,as well as the avoidance of high pressure safety issues and the cost of ionic liquids.A number of studies have also reported that the pretreatment of molecular sieve precursor and the addition of crystal seed can regulate the crystallinity,morphology and pore structure of zeolite crystals.In this work,several pretreatment methods were introduced into the solvent-free synthesis system of AEL-type heteroatom aluminophosphate molecular sieve were studied.The main research contents are as follows:FeAPO-11 molecular sieves with high crystallinity,specific morphology or pore structure were synthesized by introducing some additional synthetic variablesuch as low temperature pretreatment,mechanochemical pretreatment,seed crystals and hydrogen peroxide,based on the solvent-free synthesis of AEL-type molecular sieves reported in the literature.Their catalytic performances were investigated using phenol hydroxylation as a probe reaction.The resultant FeAPO-11 molecular sieves were characterized by XRD,SEM,N₂ physisorption and UV-Vis in detail.Moreover,the effects of Fe species content,distribution and surface area of the catalysts on the phenol hydroxylation reaction werefully explored.The synthetic results reveal that the introduction of low temperature pretreatment and hydrogen peroxide can significantly improve the crystallinity of FeAPO-11 zeolite,and FeAPO-11 molecular sieve with uniform morphology of nanocrystalline aggregates can be prepared under given reaction conditions.The catalytic results indicate that the introduction period of phenol hydroxylation reaction is mainly determined by the amount of oligonuclear iron in the forms of non-framework iron species in FeAPO-11 catalyst.Among the five selected catalysts under investigation,FeAPO-11-LHSB exhibited the best performance owing to its regular nanocrystallineaggregatesmorphologyandhighsurfacearea,giving33.6%dihydroxybenzene yield with a selectivity of 67.6%.In the same way,the introduction of silicon atom into the framework of AEL-type heteroatom aluminophosphate molecular sieve can make SAPO-11 possess proton exchange performance,so it has the potential application in acid catalytic reaction.SAPO-11 molecular sieves with AEL topology has been synthesized by introducing some additional synthetic variable such as microwave low temperature pretreatment and seed-assisted synthetic,founded on the system of solvent-free conditions.The resultant samples were characterized by XRD,SEM,BET,NH₃-TPD and FTIR in detail.Moreover,the effects of low temperature pretreatment and seed crystals on SAPO-11 molecular sieves were fully explored.Their catalytic performances were investigated using the alkylation of benzene with benzyl alcohol as a probe reaction.The results show that microwave low-temperature pretreatment can effectively improve the crystallinity of the samples synthesized by solvent-free synthesis,and the seed crystals can achieve the effect of controlling crystal morphology and improving the distribution of mesoporous pores.In typical samples,SP11-LSC₁ has the largest catalytic activity due to medium strong acid and large external surface area,which makes the conversion rate of benzyl alcohol reach 74.36%.