Synthesis, Structural Modification And Catalytic Properties Of MFI Zeolite Nanosheets

Due to the adjustable structure and morphology, high thermal stability and strong acidic，zeolites have been widely used in fields of oil processing，fine chemical, catalysis, adsorptionand separation. But they also have some structure limitations, such as the small pore size, thelong diffusion path length et.. Lamellar zeolite can not only shorten the diffusion path toimprove the mass transfer rate, but also can be obtained mesoporous by calcined or modifiedto reduce the diffusion resistance, thereby increasing the reaction rate of the catalytic reaction.So this paper synthesized MFI zeolite nanosheets, which have regular lamellar sheets andmulti-level pore structure. We also investigated the effect of silane dosage, reaction time to thepillaring process, and the catalytic properties of MFI zeolite nanosheets in catalytic reactions.In this paper, two types of quaternary ammonium surfactants were designed andsynthesized. One is gemini surfactants, the other is rigid bolaform tetra-head-groupquaternary ammonium surfactants. These two types surfactants were used as template agents，and their structure were characterized by1HNMR.MFI zeolite nanosheets were successful hydrothermal synthesized using geminisurfactants as template agents in this paper. The zeolite samples were characterized by acomplementary combination of X-ray diffraction, scanning electron microscopy, transmissionelectron microscopy etc. The effect of chain length of the templates to the as-synthesizedzeolites′structure and morphology was discussed. We also investigated the catalytic propertiesof MFI-C22-6-6in catalytic reactions. The results showed that: MFI-C22-6-6had uniformmorphology, regular lamellar structure, multi-level pore structure and strong thermal stability.Its BET surface area was467.94m2·g-1. Chain length of the template agents had a great impacton zeolites′structure. When the hydrophobic chain length was increased, the interlayerspacing increased; when the chain length between the coupling groups was too short, templateagents were decomposed so that no MFI zeolite nanosheets were synthesized. There was anoptimal head group chain length, while too long or too short, the distance between layerswould be short. Only the appropriate length could lead to a preferably zeolite. In thealdolization reaction of benzaldehyde and glycol, when the amount of MFI-C22-6-6was0.15g,the conversion of benzaldehyde was85%after refluxed for8h at78℃.The conversion ofphenol was27.83%after reacted4h at100℃in the Friedel-crafts alkylation reaction ofphenol and tert-butyl alcohol, when the amount of MFI-C22-6-6was0.15g. MFI-C22-6-6showed stronger catalytic performance on catalysis reactions compared to ordinary ZSM-5zeoliteunder the same conditions.MFI zeolite nanosheets were successful hydrothermal synthesized using rigid bolaformtetra-head-group quaternary ammonium surfactants as template agents in this paper. Theeffect of synthesis conditions, including synthesis mode,synthesis time, silica and aluminumsource, and chain length of the templates to the as-synthesized zeolites′structure andmorphology was discussed by a combination of XRD,SEM,TEM etc. We also investigated thecatalytic properties of MFI-C6-6-10-Oin catalytic reactions. The results showed that: Whenusing rigid bolaform tetra-head-group quaternary ammonium surfactant as a template agent,the best silicon source was TEOS, the best aluminum source was NaAlO2, and the bestreaction time was7days. MFI-C6-6-10-Ohad uniform morphology, regular lamellar structureand micro-mesoporous structure. Its BET surface area was445.83m2·g-1and its thermalstability was strong. Chain length of the template agents had a great impact on zeolites′structure. When the hydrophobic chain length was increased, the interlayer spacing increased.However, when it reached a certain length, there was no further increase of the layer spacing,because the hydrophobic chains would bend. There was an optimal head group chain length,while too long or too short, the distance between layers would be short. Only the appropriatelength can lead to a preferably zeolite. In the aldolization reaction, the conversion ofbenzaldehyde was85%after refluxed for8h at78℃.The conversion of phenol was29.75%after reacted4h at100℃in the Friedel-crafts alkylation reaction. MFI-C6-6-10-Oshowedstronger catalytic performance on catalysis reactions compared to ordinary ZSM-5zeoliteunder the same conditions.In this paper, zeolite MFI-C22-6-6was pillared by TEOS. The effect of silane reagentdosage, reaction time in pillaring process was inspected by characterization of XRD, SEM,TEM, etc. The results showed that: The MFI-C22-6-6zeolite could be pillared by TEOS. Thebest ratio of zeolite: TEOS was1:3, and the best pillared time was12h. We got MFI zeolitewith larger BET surface area, pore size, and more ordered lamellar structure after pillared byTEOS. It not only solved the problem of calcination collapse of the lamellar zeolite, but alsois expected to be applied to petrochemical reactions.