The Preparation And Catalytic Performance Study Of ZSM-5 Zeolite Composite Catalysts

ZSM-5 is a class of porous materials with the typical MFI structure.Its morphology and structure are significant influenced by the synthesis conditions,which show a certain regularity.Thus,ZSM-5 is always widely used as industrial and laboratory catalysis.The internal pores of the ZSM-5 molecular sieves display their own respective characteristics in three dimensional,by that the ZSM-5 zeolites are applied to study for specific selectivity of reactant molecules.By post-processing,the application of modified zeolites is expanded.Among the modification methods,the introducing of organic or inorganic reactive species inside the molecular sieve has received increasing attentions.In this thesis,we conducted a fundamental study on the synthesis law of ZSM-5 molecular sieve and successfully controlled the crystal particle size in nanometer scale without mesoporous templating agent,and used the molecular sieve for catalytic cycloaddition reaction to investigate the effect of morphology on catalytic activity.Metallic palladium species were successfully introduced in hydrothermal synthesis by a one-step method and applied in Suzuki coupling reaction.The details of the study are as follows.Firstly,a suspension of siliceous crystalline species was prepared under relatively mild conditions（105°C）.The concentration of the crystalline precursors was changed by changing the ratio of H₂O in the solution,and three different crystalline suspensions were obtained.Coffin-shaped ZSM-5 molecular sieves with homogeneous morphology were obtained.The morphology,structure,and surface elemental properties of the catalysts were characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,and X-ray photoelectron spectroscopy（XPS）.The optimal reaction conditions for the catalytic cycloaddition reaction with nano-sized catalysts were explored.Among the conditions set,the highest conversion and yield were achieved when the CO₂pressure was 2 MPa,the temperature was 150°C,the reaction time was 8 h,and the catalyst dosage was 0.1 g.Under these reaction conditions,the effects of different morphological sizes on the catalytic reaction were compared,and the experimental results showed that the smaller the size of molecular sieve particles,the better the reaction effect.The synthesis step of the catalyst was improved,and ZSM-5 molecular sieves with a particle diameter of 200 nm were obtained by direct synthesis through a formulation similar to that used in the preparation of crystal seed precursors.Tetrapropylammonium hydroxide（TPAOH）was used as an organic template agent and its dosage was increased.In order to load the metallic palladium into the molecular sieve in one step,a palladium complex solution was prepared according to a configuration similar to that of tetraamminocopper and added to the precursor solution of the synthesized molecular sieve to obtain a catalyst with smaller particle size（80-90 nm）.The morphology,surface element distribution,crystal structure and the presence of metallic palladium were characterized by SEM,FESEM,XRD and XPS.The catalyst loaded with metallic palladium was applied to catalyze the Suzuki coupling reaction,and the reaction conditions were explored by varying the temperature,the amount of phenylboronic acid,and the amount of catalyst,and the substrate expansion experiments were carried out for phenylboronic acid and iodobenzene.The results show that the catalytic effect of ZSM-5 molecular sieve as a microporous material is directly related to the external surface area.Changing the synthesis conditions during preparation and appropriately reducing the size of a single catalyst particle to make its outer surface area larger can significantly increase the final yield.When loading metal palladium,compared to traditional post-treatment processes such as ion exchange,directly adding metal species to the precursor solution can more effectively immobilize it in the molecular sieve to catalyze the reaction.Nano ZSM-5 loaded with Pd without mesoporous templating agent not only simplifies the synthesis process,but is also beneficial to environmental protection,and is of great significance to industrial catalysis.