Study On Synthesis Of Micro/Mesoporous Composite Molecular Sieve Of β/MCM-41

The composite molecular sieve with the pore advantage of the mesoporous material, the high acidity and high hydrothermal stability of microporous material has comprehensively applicational prospects in the fields such as petrochemical industry, adsorption separation, macromolecule shape selective catalysis, and so on.Firstly, the Al-MCM-41 mesoporous molecular sieve was synthesized by the dynamic method under low temperature with C₁₆ H₃₃ (CH₃) ₃NBr as structural template, and was characterized by XRD and FTIR and N physical adsorption/desorption. The effects of crystallization temperature, crystallization time, the value of pH and the ratio of H₂O/SiO₂ on the crystallization and the structure of MCM-41 were investigated by XRD, and while the synthesis conditions were optimized as well. The results suggested that the MCM-41 mesoporous molecular sieve can be synthesized under the conditions of crystallization temperature from 35℃to 40℃, crystallization time from 16h to 28h , the value of pH from 9．5 to 10．5 and the ratio of H₂O and silica from 100 to 200． The compositeβ/MCM-41 which was synthesized by stepwise crystallization method was characterized by XRD, IR, N₂ physical adsorption/desorption, SEM and so on. The results suggested that the composite had mesoporous and microporous structures with a mean diameter of about 100nm. The ratio of mesoporous and microporous structures in the compositeβ/MCM-41 can be adjusted during the synthesis progress. The composite molecular sieve with well-ordered mesoporous structure can be synthesized under the conditions as follows: the crystallization time from 16h to 36h, the ratio of surfactant and silica from 0．10 to 0．25 and the ratio of sodium and silica being 0．09 during the second synthesis progress. The research results of the catalytic properties in the alkylation of benzene with propylene showed that the activity of composite material was better than that of a physical mixture of MCM-41 andβzeolite. Moreover, the results of the hydrothermal treatment also showed that the hydrothermal stability of the mesoporous phase in the composite material was greatly improved.The compositeβ/MCM-41 with high hydrothermal stability was synthesized by the way of crystallization of mesopore walls with MCM-41 as silica-alumina sources and was characterized by XRD, FTIR, N₂ adsorption /desorption, SEM, DTG and so on. The effect of crystallization conditions on the structure was also investigated. The results showed that the obtained samples had mesoporous and microporous structures and the hydrothermal stability of the mesoporous phase in the composite molecular sieve was greatly improved. Moreover, the adding of crystal seed can shorten induction period, accelerate crystallization and decrease crystallization time greatly.