| Composite zeolites combine the two zeolites effectively,achieve its’mutual syneries by taking advantage of the pore characteristics of single zeolite,and good performance was obtained in catalytic reaction.EU-1 has higher catalytic selectivity in methanol aromatization reaction as a result of it’s special pore structure.However,MOR and EU-1 zeolites are similar in pore structure.So in this paper,using MOR zeolite secondary structural unit as precursor,MOR/EU-1 composite zeolites with embedded structure was synthesized by the nano-assembly method.Samples were characterized by a series of methods.The results showed that:the morphology was that most of the outer surface of mercerized zeolite was evenly covered by irregular EU-1 zeolite,growing in layers along the MOR zeolite,the morphology of EU-1 zeolite transformed from elliptic to irregular hexagonal,embedded on the outer side of nanowires of MOR zeolite.The composite zeolites are mainly composed of microporous composite materials and have high thermal stability.By analyzing the synthesis process,the optimal conditions are obtained:The mole ratio of of sodium oxide to silicon dioxide was 0.15,The molar ratio of the templating agent to the silica was 0.09～0.11.Suitable crystallization time were two days.By probing into crystallization dynamics analysis,the crystallization nucleation activation energy En was 83.51k J/mol and the apparent growth activation energy Eg was40.11k J/mol.In methanol aromatization reaction,the distribution of p-xylene in products reached 73.12%,the selectivity to p-xylene product was higher.Composite zeolites can also improve the acid position and morphology of single zeolite.Therefore,in this paper,we try to use the 12-element ring channel of L zeolite to make up for the defect of ZSM-5 zeolite that restricts the entry of larger zeolites,,the ZSM-5 and L zeolites were compounded together to improve the microscopic properties and pore structure of zeolites and further the acid position of the composite zeolites was optimized.In this paper,the nanowire Mosaic structure ZSM-5/L composite zeolites were rapidly synthesized by a two-step crystallization method that pretreated ZSM-5 with tetrapropylammonium hydroxide to a seed crystal.The properties of the composite zeolites were characterized by various characterization methods and the factors affecting the synthesis of composite zeolites were also investigated.And through the modification of iron elements and further study of acid properties,which provided further theoretical ground for methanol aromatization reaction.The results showed that:the ellipsoidal L zeolite was embedded in the ZSM-5 zeolite around the nanowire,the composite zeolites have multi-stage pore structure composed of micropores and mesopores and high thermal stability.The pretreatment of the seed crystal affects the electric charge of the synthetic sol and the morphology of the zeolite.When the mass fraction of ZSM-5 in the synthetic sample is less than 2 wt%,the gel has more negative charges,forming ellipsoidal L molecular sieve readily.When the mass fraction of ZSM-5 in the synthetic sample is greater than 2 wt%,the zeta potential fluctuates between-39.822 m V and-42.352 m V,the morphology of ZSM-5 zeolite changes from strip to nanowire.The cation ratio affects the change of the L-type zeolites morphology,When the cationic ratio is less than0.6,it is not conducive to the formation of L-type zeolite.When the cationic ratio is greater than 0.6,in other words,when K+is more than Na+,the formation ofα-calcium nepheline cages in L-type zeolite is facilitated.The morphology of the composite zeolites changed after the modification of iron.NH3-TPD indicates that both strong and weak acid ratios of composite materials are less than 1,which improves the acid properties of the composite zeolites.It may be beneficial to the aromatization reaction of methanol. |
