Controllable Synthesis Of Highly Stable And Strongly Acidic Nano BEA

Zeolite molecular sieve materials have been widely used in catalysis,adsorption and ion exchange due to their excellent pore structure,high hydrothermal stability,strong acidity,large specific surface area and shape selectivity.However,due to the microporous nature of zeolites,they are limited in transporting large reactant molecules,resulting in reduced catalyst life.In order to solve this problem,the pore structure was improved and multistage pore zeolite was synthesized.In recent years,many methods have been developed for the synthesis of multiporous molecular sieves,among which the preparation of nano-molecular sieves and the improvement of mesoporous structure between nanoparticles are also ways to create multiporous structure.In this paper,zeolite Beta is taken as the research object.Under the strategy of highly efficient seed induction,the hydrolysis rate of inorganic source and the speed of prefabrication and construction unit are slowed down.Based on the process of efficient crystallization assembly,zeolite Beta with high crystallinity and strong acidic multi-pore structure is obtained.The specific research contents are as follows:（1）In the concentrated sol system,in the case of no additional organic structure guide agent（OSDAs）,under the seed induction strategy,hydrothermal synthesis of high crystallinity with BEA structure of zeolite Beta.The physicochemical properties of the synthesized zeolite are affected by the composition of the initial inorganic source,and the products with Si/Al ratio of 40-50 are the best.The products with Si/Al ratio of 50 show high nano properties,high crystallinity,a large number of intergranular mesoporous structures and strong Bronsted acid properties.The catalytic degradation reaction of low density polyethylene showed good catalytic activity.In terms of skeleton construction,Raman and XRD results show that during the crystallization process of zeolite Beta,a large number of six-membered ring（6-MRs）and eight-membered ring（8-MRs）structures are generated by continuous hydrolysis and rearrangement of internal inorganic sources during long-term slow induction.When the number of sixmembered ring（6-MRs）structures is accumulated to a certain amount,bonds and links are generated between 6-mrs.The 4-membered ring（4-MRs）and 5-mrs structures were formed.The 8-MRs dissociation provided partial inorganic source for subsequent skeleton construction,and the zeolite Beta skeleton was constructed.The nanozeolite Beta was assembled within 2 hours,and the final Beta zeolite synthesized had high crystallinity and good nano properties.（2）Al-SBA-15 molecular sieve with highly ordered mesoscopic structure was synthesized using non-ionic triblock copolymer（P123）as template and used as initial inorganic source.By adjusting the depolymerization process of silicon and aluminum species in al-SBA-15 pore wall by using seed assisted strategy.The whole al-SBA-15 particles were transformed into zeolite Beta with multiporosity.It was found that the pore structure of the synthesized Al-SBA-15 mesoporous molecular sieve was highly ordered.After heat treatment at 400°C,the micelle of P123 surfactant could not be completely removed,resulting in a carbon-rich structure,which was evenly dispersed in the mesoporous interior with granular morphology.These carbon-rich species interacted with the mesoporous pore wall and restricted the growth of zeolite Beta.Before conversion,al-SBA-15 molecular sieve was washed with ethanol solution and pretreated with ethanol steam to form polar groups on the inner surface of the pore.The results show that the former produces more polar groups and improves the effect of crystal seed.The primary particles of the synthesized zeolite are very close,the content of pore structure between particles is low,and the properties of multistage pores are relatively poor,but the crystallinity is high.The latter form a relatively small number of polar groups,weaken the interaction between al-SBA-15 surface and Beta crystals,strengthen the growth of single Beta crystals,weaken the curing effect,and improve the mesoporous properties of nano-particle aggregates.In addition to high crystallinity,the synthesized zeolite Beta also has excellent multi-pore properties.