Synthesis And Catalytic Performance Of *BEA,MFI Type Zeolite

Zeolite is a kind of crystallized material with uniform channel and cavity.By changing the composition of zeolite,the zeolite can show different solid acidity leading to different catalytic performance.Recently,the high silica zeolite shows great catalytic performance of FT synthesis and MTH process.Combining the function of zeolite and oxide,the bifunctional catalysts could convert syngas into hydrocarbon with high selectivity,such as the high selectivity of aromatics over OX/ZSM-5.However,the difference of performance over ZSM-5 between the MTA and FTA attracted the attention of researcher.Though some hypothesis had been assumed,elucidation of this issue required much more systematic studies,considering the complex reaction environment.Because the framework of zeolite had great effects on the products selectivity of FT,the study of application of zeolite with different framework in FT synthesis was also necessary.Based on such situation,we investigated the catalytic performance of FT synthesis over*BEA and MFI-type zeolite.Besides,aiming to solve the problem during the preparation and application of high silica Beta zeolite,we developed new strategy to prepare the high-silica Beta and Ti-Beta inspired by interzeolite transformation method,where the Beta zeolite could be prepared quickly with nanosized crystal and low content of defects.In the first part,the ZnAlOx/ZSM-5 bifunctional catalysts were used to catalyze the conversion of syngas to research the production of aromatics.Owing to the high aromatic selectivity arising from ZSM-5,the catalytic performance of MTA over ZSM-5 was investigated under different reaction condition.And the results suggested that CH₃COOH promoted the selectivity to aromatics during the conversion of methanol.Thus,we supposed that the CO and methanol could convert into CH₃COOH partly leading to the high selectivity of aromatics.Then,the in-situ FT-IR spectrum of CO hydrogenation over ZnAlOx and ZnAlOx/ZSM-5 showed the band the CH₃COOH suggesting the generation of CH₃COOH.And the discovery of cyclopentenone illustrated that the CH₃COOH took part in the FTA process.In the second part,though the high silica Beta showed the great MTP performance,the catalytic performance of FT synthesis over composite catalyst prepared by coupling the ZnAlOx and high silica Beta was investigated.Different from the Al-rich Beta,the high silica Beta performed the high selectivity to light olefin.During the conversion of syngas,hydrogen transfer had great influence on the product distribution.Under the optimal reaction condition,the selectivity to light olefin achieved to 87%.However,the lifetime of ZnAlOx/Beta was only 5 h,which was related to the high content of defects in the framework of high silica Beta.In the third part,aiming to reduce the content of defects and the crystal size,a new strategy was developed to synthesize the high-silica Beta with a relative short synthetic period.With the assistance of NH₄F and TEAOH,the dealuminated MOR was converted into high silica Beta at an extremely low content of H₂O with low content of defects and nanosized crystal size.The investigation about the crystallization mechanism suggested the dissolution of MOR zeolite and crystallization of Beta occurred simultaneously.Compared to the Beta-F prepared by conventional fluoride method,Beta-PS prepared by post-treatment,Beta-T prepared by interzeolite transformation from MOR zeolite exhibited more excellent catalytic performance,owing to the nanosized crystal size and low content of defects.In the fourth part,inspired by the interzeolite transformation,the dealuminated Beta served as silica source to prepare the Ti-Beta via reconstruction method.During the preparation,the Beta and TBOT was dissolved in TEAOH solution firstly.Then,the NH₄F was added in the synthesis gel to start the crystallization process.The comparison between the Beta-Re(prepared by reconstruction method),Beta-F(prepared by hydrothermal method in fluoride medium),Beta-OH(prepared by alkaline hydrothermal method),Beta-PS(prepared by post-synthesis)suggested that the high hydrophobic and nanosized crystal size were beneficial for the epoxidation of cyclohexene.