| The nano-sized zeolites synthesized by conventional methods suffer separation diffculty due to small particle size,and their powders are hard to be used directly in industrial prcesses unless molded into monolithic catalysts.Herein,this research was carried out with the purpose to prepare integrally structured MEL-type zeolites by in-situ hydrothermal synthesis.This thesis is composed of following three parts.The crystallization conditions and gel compositions of conventional TS-2nanoparticles were studied.TS-2 microspheres with the sizes of 5-20?m can be synthesized when the pH value is higher than 11.7 without the presence of alcohols.To investigate the mechanism,the crystallization process was traced in detail.It revealed that the primary crystals tended to cross-grow,forming the microsphere morphologies in the gels with a high pH value,whereas they were accumulated to form the nanoparticles easily in the weak base systems.In order to improve the catalytic performance of ammoximation of cyclohexanone,the TS-2 microspheres were chemically modified by the treatment in the solution of piperidine,NH4Cl and TBAOH,which resulted in more hydrophobic TS-2microspheres with hierarchical pores as a result of dissolution and recrystallization.The postsynthesized TS-2 microspheres could convert cyclohexanone to cyclohexanone oxime efficiently with an outstanding reusability.The integrally structured[Ti,Al]-ZSM-11 microspheres with hierarchical pores were successfully prepared through introducing Al source into the gels of TS-2 system.The effects of Si/Ti and Si/Al ratios on the microsphere formation were investigated.The resultant[Ti,Al]-ZSM-11,synthesized at Si/Al=132,showed a remarkable stability in methanol-to-olefins reaction,providing a single-run lifetime of 49 h?time till to a methanol conversion less than 90%?and a high propylene selectivity of 49.9%. |
PDF Full Text Request