Study On The Ionothermal Synthesis Of Nano-and Hierarchical Porous Aluminophosphate Molecular Sieves

Molecular sieves are a kind of important inorganic microporous materials,which have regular microporous channels.However,the small single microporous channels are not conducive to the diffusion between reactants and products.In order to improve the structural defects of single microporous molecular sieves,many researchers pay more attention to the research of hierarchical porous molecular sieves.In this thesis,the synthesis of hierarchical porous aluminum phosphate molecular sieves in ion-thermal system is studied.The results show that the nanostructured and hierarchical porous aluminum phosphate molecular sieves are an effective way to improve the limitation of micropore diffusion,which is beneficial to material transport and maintain the high selectivity of molecular sieves.AlPO₄-LTA nanosized aluminum phosphate zeolites were prepared in an open system with 1-butyl-3-methyl-imidazolium bromide as reaction medium and 4-methylammonium hydroxide as co-guiding agent at 120℃for 10 minutes.The effects of parameters such as TMAOH/Al,HF/Al and heating methods on the synthesis were investigated.The optimized results show that appropriate HF/Al and high TMAOH/Al ratio accelerate the crystal growth,and the AlPO₄-LTA molecular sieve with good crystallinity,small particle size（about 130 nm）and large BET specific surface area（867m²/g）can be obtained.It is shown that the formation of the products takes place through a non-classical crystallization mechanism:the original worm-like amorphous material first aggregates into loosely assembled balls,and then the crystallinity of the balls gradually increases while keeping the particle size constant.The nano-AlPO₄-LTA molecular sieve is expected to be applied in molecular sieve membranes.In the system of deep eutectic mixture consisting of diethylamine hydrochloride and ethylene glycol,a spherical aggregate SAPO-11 lamellar molecular sieve was synthesized by adding additional small organic amines in the eutectic system composed of diethylamine hydrochloride and ethylene glycol.Combined with powder X-ray diffraction,nitrogen physical adsorption and scanning electron microscopy,it was proved that the prepared product has high crystallinity,large specific surface area and moderate weak acidity.By changing the ratio of diethylamine hydrochloride and ethylene glycol system and the crystallization conditions,the influence of the content and types of organic amines on the morphology of the molecular sieve was investigated,and the growth process of the synthesized molecular sieve was analyzed.The results show that the initial raw materials are aggregated into clusters in the system,and gradually evolve into thick flake aggregates under the action of 1-methylimidazole,which gradually differentiate into paper-like flakes and assemble into spherical aggregates with prolonged crystallization time.By changing the type of organic amines,it was found that the addition of 1-methylimidazole selectively adsorbed on the（001）crystal plane and inhibited its overgrowth in this dimension.The final prepared spherical aggregate SAPO-11 lamellar molecular sieve has good weak acidity,can better improve the diffusion path,and has good performance in the isomerization catalytic reaction.Hierarchical porous SAPO-41 was prepared in the diethylamine DEAC-EG system by changing the synthesis parameters.After investigation,it was found that the pure phase hierarchical porous SAPO-41 molecular sieve could be crystallized at 160℃.By increasing the temperature and extending the crystallization time,it was found that the crystallization process from SAPO-41 to SAPO-11 occurred in the aggregate formed by nanocrystalline assembly.Both of the two molecular sieves have multi-pore structure and the same structural density,indicating that SAPO-11 and SAPO-41 prepared by this system have more stable thermodynamics.At the same time,the effects of crystallization process at different temperatures on the morphology and structure of SAPO-41 were investigated,and it was found that the SAPO-41 synthesized at low temperature had larger specific surface area and smaller particle size.