One-pot Synthesis And Catalytic Performance Of Single Crystalline Hierarchical Sn-MFI Zeolite

As a porous material,zeolites have been widely used in petrochemical,fine chemical,biomedical and other fields due to order pore,large specific surface,acid tunability and chemical stability.However,the further application of zeolites is hindered due to the diffusion limitations from relatively smaller micropores.Therefore,post-treatment synthesis or in-situ synthesis of hierarchical pore zeolites is an effective strategy to solve this problem.Nevertheless,post-treatment synthetic routes require selective dealuminization/desilication with strong acid/alkali,which will cause environmental pollution and equipment corrosion.Moreover,the stability of hierarchical pore zeolites obtained by this method is decreased due to the increase of defects or hydroxyl groups,which may be avoided through in-situ synthesis.But in-situ synthesis approach usually requires mesoporous template,which not only increases the cost but also generates more energy consumption.For current problems,this thesis adopt in-situ synthesis to synthesize high-stability hierarchical pore zeolites from the perspective of regulating the nucleation and growth of zeolite without any mesoporous template agent.In this paper,the transition metal Sn was innovatively used as the regulatory factor,regulating the nucleation and growth process to synthesis single crystal hierarchical pore Sn-MFI Zeolite（SCHP Sn-MFI zeolite）with intra-crystalline mesopores（5～10 nm）and intercrystalline pore structures.The hierarchical pore material shows excellent hydrothermal stability and thermal stability,and its skeleton structure and crystallinity change little after being treated at 700℃pure water vapor and 1000℃air atmosphere respectively.The single crystal property of this material were observed by transmission electron microscopy（TEM）and scanning transmission electron microscopy（STEM）,which indicated that the single crystal hierarchical pore Sn-MFI zeolite（SCHP Sn-MFI zeolite）was synthesized for the first time by one-pot metal-changing method.The nucleation and growth of zeolite were investigated by changing Sn content,crystallization temperature and time,finding that SCHP Sn-MFI zeolite was attributed to the formation of"protozeolite-like nanoparticles"after the gel was separated by Sn.These"protozeolite-like nanoparticles"aggregate with each other and grew limited under the control of Sn.2-amantadanone Baeyer-Villiger oxidation reaction showed Sn-MFI series zeolites had higher catalytic activity than Si-MFI.Interestingly,when the metal content changes from 1%to 3%,the conversion rate changes little until 5%,the conversion increases to 80.0%.This is due not only to the fact that 5%Sn-MFI has more Lewis acids,but also to the accessibility of Lewis acids.UV-Vis results show that the Lewis acid of the material is derived from the Sn ^IVspecies in the skeleton,and the hierarchical pore structure makes the Lewis acid in 5%Sn-MFI more accessible.UV-Vis results show that Lewis acid is derived from the Sn ^IV species in the skeleton and the hierarchical pore structure makes the Lewis acid in 5%Sn-MFI more accessible.5%Sn-MFI was also applied to the oxidation reaction after hydrothermal treatment,the conversion of reactants almost did not change and the catalytic activity was well maintained.In addition,we also found that Sn heteroatomic zeolite also exhibit excellent propane dehydrogenation performance and potential non-noble metal propane dehydrogenation catalysts.The excellent stability and unique pore structure make this SCHP Sn-MFI zeolite show great potential in the catalysis.The strategy of synthesizing SCHP Sn-MFI zeolite through metal induction breaks the limitation of mesoporous template and further promotes the development of hierarchical pore zeolite.