Preparation,Characterization And Catalytic Properties Of Supported Nobel Metal MFI Zeolite With Core Shell Structure

In recent years,a considerable attention has been focused on supported noble metal catalysts due to their high catalytic activity and selectivity.MFI zeolites with uniform porosity,high crystallinity,structural diversity,and large surface areas,have been extensively studied as a ideal suppor for supported noble metal catalysts.Based on the structural features of the MFI zeolite,encapsulation of noble metal clusters within MFI zeolite was achieved by two different ways in this thesis:to prepare the composite composed of metal nanoparticles encapsulated in the MFI zeolites.I)Pd nanoparticles were encapsulated inside the S-1 zeolite by silane grafting and recrystallization?denoted Pd@S-1?.Then the core-shell structure catalyst Pd@S-1@ZSM-5 was synthesized by epitaxial growth processes in the surface of Pd@S-1.II)Nobel metal clusters?Pd,Pt?were encapsulated within nanosized silicalite-1 zeolite under direct hyrothermal conditions using ligand-stabilized metal precursors.And the catalystic performances of prepared catalysts were studied.The main results are as fllows:1)Synthesis of MFI zeolitesS-1 and ZSM-5zeolites were synthetized during hydrothermal conditions,and different morphology zeolite could be obtained by changing the synthesis conditions.S-1 zeolites were synthetized with different template agents,the results showed the S-1 zeolites have uniform integral hexagonal crystal structures using tetrapropylammonium bromide?TPABr?as template.In addition,mineralizers have great effect for synthesis of ZSM-5.ZSM-5 with rod-shaped congeries morphology could be synthesized using NaOH as mineralizers.2)Synthesis of core-shell structure Pd@S-1@ZSM-5 catalystFirst,silicalite-1 was modified with 3-aminopropyltrimethoxysilane?APTMS?,which has a large abundance of NH₂ that can anchor Pd²⁺groups ions.Second,the composite was etched with TPAOH and recrystallized upon hydrothermal treatment,all the Pd²⁺ions were reduced to Pd nanopaticles.Finally,ZSM-5 crystals were crystallized in the surface of Pd@S-1 by epitaxial growth processes.?denoted Pd@S-1@ZSM-5?3)Catalytic performance and sulfur tolerant property of Pd@S-1@ZSM-5in hydrogenation of naphthaleneThe Pd@S-1@ZSM-5 catalyst has high catalytic activity in hydrogenation of naphthalene and of decahydronaphthalene.In addition,the sulfur-tolerant property of the catalyst was tested using benzothiophene as sulfur source.When500 ppm of benzothiophene was added to the naphthalene feedstock,the conversion of naphthalene retained 95%of the originated activity with Pd@S-1@ZSM-5 catalyst,while the conversion was reduced by 82%with Pd/S-1.The results indicated that the Pd@S-1@ZSM-5 catalyst showed very excellent sulfur resistance in naphthalene hydrogenation.4)Preparation,characterization and catalytic performances of M@S-1-inEncapsulation of noble metal clusters?Pt,Pd?within silicalite-1?S-1?zeolite was achieved by direct hydrothermal synthesis using ligand-stabilized metals precursors and characterized by XRD,N₂ adsorption,SEM and TEM.The prepared M@S-1 catalysts exhibited excellent catalytic performances in hydrogenation of cinnamaldehyde compared with the catalysts prepared by impregnation method.