Synthesis、Characterization And Catalyst Performance Of Hierarchical Molecular Sieves Based On MTO Reaction

Hierarchical molecular sieve——is a kind of new catalytic material greatly concerned by many such researchers. With high hydrothermal stability, selectivity, controllable acidity of traditional microporous molecular sieves and high specific surface area, high mass transfer capacity of mesoporous molecular sieves, it can be used widely in adsorption, separation, purification and catalysis reaction, etc.Nowadays, there are several synthesis methods to prepare these composite porous materials:■ Introducing mesopores into traditional microporous zeolites (to form larger size pore structure/meso-pore inside the zeolite crystal particles with micro-porous structure);■Inserting micro-structure with high hydrothermal stability into amorphous pore wall of mesoporous materials (to construct micropore secondary building units in original meso-structure);■Making smaller particles of traditional zeolite (to synthesize micro-porous-sized molecular sieves to construct uniformly distributed packing pore and secondary pore by interactions in a certain system);There are three methods applied in this paper:Method of Alkaline Solution Treatment which utilized inorganic alkali sodium hydroxide (NaOH), organic alkali tetrapropylammonium hydroxide (TPAOH) and inorganic-organic mixed alkali aqueous solution (TPAOH/NaOH) treating the microporous zeolite ZSM-5 (alkali solution soaking); Method of Mesoporous Silicon Source which adopted mesoporous silicon material as silicon source then through the traditional hydrothermal crystallization method and Soft Template Method which employed amphiphilic organosilane as soft template and the traditional quaternary ammonium hydroxide/alkaline template agent tetraethyl ammonium hydroxide (TEAOH) to prepare the hierarchical SAPO-34 molecular sieves. All these method above, to a certain extent, enriched and developed the porous materials research field.1. Alkaline Solution Treatment to prepare hierarchical ZSM-5 zeoliteUsed inorganic alkali sodium hydroxide (NaOH), organic alkali tetrapropylammonium hydroxide (TPAOH) and inorganic-organic mixed alkali aqueous solution (TPAOH/NaOH) treating the microporous zeolite ZSM-5 respectively and obtained hierarchical ZSM-5 zeolite under different conditions. The products were characterized by XRD, SEM, N2-adsorption and FTIR. The results showed that the products were definitely ZSM-5 zeolite with hierarchical framework and both the type and the concentration of alkali directly affected the prepared products’pore texture and acidity character.2. Method of Mesoporous Silicon Source to prepare hierarchical SAPO-34 molecular sievesUsed the mesoporous silicon material as silicon source and tetraethyl ammonium hydroxide as template through the traditional hydrothermal crystallization method to prepare hierarchical SAPO-34 molecular sieves. The products were characterized by XRD, SEM, N2-adsorption. The results showed that mesoporous silicon material as silicon source can synthesis SAPO-34 with large size, traditional microporosity structure and accumulation secondary pores. The SAPO-34 synthesized this way had the hierarchical pore feature.3. Soft Template Method to prepare hierarchical SAPO-34 molecular sievesAdopted amphiphilic organosilane as soft template in the traditional hydrothermal synthesis progress and obtained hierarchical SAPO-34 with special crystal morphology. The products were characterized by XRD, SEM, N2-adsorption, FTIR. The results stated that the products certainly had mesoporous structure but the crystal morphology didn’t have much significant difference synthesized by different chain length of amphiphilic organosilane.The catalytic activity of synthesized hierarchical ZSM-5 zeolite and SAPO-34 molecular sieves were assessed on methanol to olefin (MTO) reaction equipment which was self-building. The results displayed that synthesized hierarchical ZSM-5 zeolite was similar to the traditional ones such as high catalytic activity and reaction characteristics by the reason of existing of hierarchical pores structure, the selectivity to ethylene and propylene was higher than traditional molecular sieves. The results also showed that hierarchical SAPO-34 molecular sieves synthesized by mesoporous silicon materials as silicon source had higher selectivity to light olefin than traditional hydrothermal synthesis ones on MTO reaction. The SAPO-34 synthesized by amphiphilic organosilane as soft template didn’t show any advantage than traditional hydrothermal synthesis ones on MTO reaction right now.Method of Alkaline Solution Treatment to prepare hierarchical molecular sieves which can synthesize products repeatable, is simple and easy to carry out; So the Alkaline Solution Treatment method can certainly be extended. Method of Mesoporous Silicon Source provides a effective way of using mesoporous silicon as silicon source to synthesize hierarchical molecular sieves. It is also provide the foundation for industrialization and further development; Template Method is a new type method to broaden the research scope, extend the field of research and inspire new ideas of novel materials for future development.