Synthesis, Characterizations And Catalytic Properties Of Mesoporous Metallosilicates And Interlayer Expanded Zeolites

The dissertation has been carried out to increase the accessibility of the catalyticactive sites in the framework of zeolite and then to improve the diffusion properties ofzeolite so as to broaden the scope of its utility.The researches are composed of twotopics,one of which is the synthesis of mesoporous metallosilicates and the other isthe interlayer expansion of zeolitic lamellar precursors by post-silylation.Firstly,mesoporous TS-1 were hydrothermally synthesized with the aid ofamphiphilic organosilane and the effects of various parameters on the structural andtextural properties of the resultant materials were investigated.The physicochemicalproperties of the samples were characterized by various techniques and their catalyticperformance was investigated by the epoxidation of hexene and cyclohexene withhydrogen peroxide.The content of organosilane added was essential for the formationof uniform mesopore in TS-1,and it greatly influenced the crystallinity.The basicityof the synthesis system also was of importance as high basicity did not contribute tothe formation of uniform mesopore.By optimizing the synthesis conditions,highlycrystallized TS-1 with uniform mesopores of 3.7 nm diameter was successfullysynthesized.The mesoporous TS-1 preserved tetrahedrally coordinated Ti ions in theframework,but it was featured with more hydrophobic surface and less defect sites incomparison to conventional TS-1.Mesoporous TS-1 showed a higher conversion forthe epoxidation of cyclohexene owing to an easier access of bulky molecules to thecatalytic active sites,while showing similar activity for the epoxidation of hexene incomparison to conventional TS-1.Besides,mesoporous TS-1's higher hydrophobicitymade its epoxide selectivity two times as much as that of conventional TS-1.Under similar approach,mesoporous Zr-MFI with different Zr contents werehydrothermally synthesized with the aid of amphiphilic organosilane.Theirphysicochemical properties were characterized by various techniques,and theircatalytic performance was investigated for Meerwein-Ponndorf-Verley (MPV)reduction of cyclohexanone with 2-propanol.The mesoporous Zr-MFI preserved theproperties of conventional Zr-MFI such as high crystallinity and incorporation oftetrahedral Zr ions in framework,and was further featured with mesoporosity of 3.5nm diameter,enlarged external surface area,more Lewis acid sites and less defectsites.Compared with conventional Zr-MFI,the mesoporous Zr-MFI showed drastically improved activity for the MPV reduction of cyclohexanone,which waspredominantly attributed to the contribution of the mesopores supplying an easieraccessibility to the catalytic active sites for bulky molecules.Moreover,themesoporous Zr-MFI was a stable and reusable catalyst.Then,interlayer expanded MCM-22 was prepared by a new postsynthesismethod,that is swelling the precursor of zeolite MCM-22 (MCM-22 (P)) under roomtemperature firstly and then silylating the swollen materials with ClMe₂Si-SiMe₂Cl,ClMe₂Si-O-SiMe₂Cl,ClMe₂Si-CH₂-CH₂-SiMe₂Cl and OHMe₂Si-benzene-SiMe₂OHin nitric acid solution.The effects of postsynthesis conditions such as theconcentration of nitric acid solution and the amount of silylation agent on thestructure of final samples were investigated in details.The resultant samples preparedunder the most optimized conditions preserved highly crystallized MWW intralayerstructure and had much larger interlayer space of 2.0 (?) in comparison to that ofMCM-22 (Si) prepared by silylation of MCM-22 (P) directly with monomeric Sisource (Me₂Si (OEt)₂) as reported before.That is to say,the new postsynthesis methodis more effective for the synthesis of interlayer expanded MCM-22 with largerinterlayer space.Finally,FER with expanded interlayer pore windows was synthesized bysilylating the precursor of FER zeolite (PREFER) with ClMe₂Si-SiMe₂Cl,ClMe₂Si-O-SiMe₂Cl,ClMe₂Si-CH₂-CH₂-SiMe₂Cl and OHMe₂Si-benzene-SiMe₂OHin nitric acid solution.The effects of postsynthesis conditions such as theconcentration of nitric acid solution and the amount of silylation agent on thestructure of final samples were investigated.The structure of the resultant materialswere compared with the sample prepared with monomeric Si source (Me₂Si (OEt)₂)under the same conditions.Results evidenced that by optimizing the postsynthesiscondition,samples with larger interlayer space with comparison to that of FER (Si)can be synthesized with newly chosen silylation agent.Besides,the interlayer space ofFER can be modified by varying the silylation agent,which is helpful for its use incatalytic process involving substrates with different molecular dimensions.