Studies On Preparation, Characterization And Catalytic Oxidation Performance Of Titanium, Cobalt And Manganese-modified Mesostructured Molecular Sieves

4-tert-Butylbenzaldehyde is a valued intermediate for the production of medicines,dyes and flavour and fragrance compounds, whose synthesis processes are urgentlyneeded to be improved in order to realize environment-friendly green chemicalprocesses. The chemical modification methods for mesoporous sieves, such asframework substitution, surface grafting, impregnation, etc., make it possible to realizeshape catalytic oxidation for bulky molecule over transition metal-modified mesoporousmaterials in mild reaction condition. Titanium, cobalt and manganese-modifiedmesoporous molecular sieves are excellent catalytic materials for selective oxidation ofhydrocarbons. The efforts have been made in this thesis to prepare titanium, cobalt andmanganese-modified HMS(Hexagonal Mesoporous Silica) to develop new catalystswith high activity, high selectivity and high stability in synthesis of 4-tert-butyl-benzaldehyde in liquid phase oxidations with being friendly to environment. The maincontents are as follows:In the first part, preparation and catalytic performance of titanium-modifiedmesoporous molecular sieves were studied. Firstly, the influence of synthesis conditionof H₂O/EtOH(v/v) on catalytic performance of Ti-grafted HMS was investigated. HMSis mesoporous silica-based molecular sieve with 3D wormhole structure, smallerdomain size with shorter channels, and larger textural mesoporosity compared withMCM-41 with 1D hexagonal framework structure. These features of HMS providebetter transport channels for reactants to access the active centers and better diffusionchannels for products to remove out. In order to prepare HMS with textural mesoporousproperties, we chose H₂O/EtOH(v/v) of 1, 2, 5 and 9 in synthesis of HMS. Grafted-TiHMS prepared using HMS whose molar composition of the reaction mixture was1.0TEOS:0.25DDA:5.0 EtOH:81.0H₂O and H₂O/EtOH(v/v) was equal to 5 as supportgave larger textural mesoporosity and higher catalytic activity. Secondly, the influenceof loading-Ti amount on Ti(â…£) coordination environment and catalytic performance ofTi-grafted HMS was studied. A series of grafted-Ti HMS with 2.8～6.8% Ti loading were prepared. When containing-Ti amount was over 6.8 mol%, Ti(â…£) atom wasobviously reduced and catalytic performance was lower. Thirdly, the influence of HMSpretreatment methods of calcination (Methodâ… ), ethanol-extraction followed bycalcination (Methodâ…¡) and ethanol-extraction followed by hydrolysis (Methodâ…¢) onTi(â…£) coordination environment and catalytic performance of Ti-grafted HMS wasdiscussed. Methodâ…¡and Methodâ…¢favored Ti(â…£) atom in coordination environmentin HMS and improvement of catalytic activities. Finally, grafted-Ti MCM-41 materialswere synthesized and their catalytic performances were investigated. Ti(â…£)-modifiedderivatives of mesostructured HMS and MCM-41 silica with 3D wormhole and 1Dhexagonal framework structures, were synthesized through the grafting of titanocenedichloride to the framework walls, followed by calcination. They were examined ascatalysts for the oxidation of 4-tert-butyltoluene to 4-tert-butylbenzaldehyde usingtert-butylhydroperoxide (TBHP) and aqueous hydrogen peroxide as oxidizing agents inacetonitrile solution in mild reaction condition.In the second part, preparation and catalytic performance of HMS impregnated bycobalt, potassium and manganese were studied. Different impregnation precursors leadto active species with different structural characteristics which cause difference incatalytic performances. Firstly, active species and catalytic performances of Co-HMSprepared by incipient-wetness impregnation using cobalt acetate, cobalt nitrate asprecursors and calcined at 550℃were discussed. Tetrahedral divalent cobalt wasdominant species using cobalt acetate as precursor, and CO₃O₄ and CoO were dominantspecies using cobalt nitrate as precursor in their corresponding samples. The catalyticperformances of Co-HMS(N) was better than Co-HMS(A), and tetrahedral divalentcobalt in Co-HMS(A) was instable in the reaction. Secondly, the influence of theassistance of potassium in HMS on catalytic performance was studied. Tetrahedraldivalent cobalt was dominant species in the samples of Co-K-HMS impregnated usingcobalt acetate and potassium acetate as precursors. Adding proper potassium amount inCo-HMS resulted in improving catalytic activity. Tetrahedral divalent cobalt inCo-K-HMS was more stable than that in Co-HMS(A). Finally, the influence of theassistance of manganese in Co-HMS on catalytic performance was investigated. Co₃O₄ and Mn₃O₄ were dominant species in Co-Mn-HMS prepared by impregnation usingcobalt nitrate and manganese acetate as precursors. Proper Mn-loading content inCo-HMS facilitated to improve catalytic activity. The catalytic performances of Co, Kand Mn-supported HMS were tested in the oxidation of 4-tert-butyltoluene to4-tert-butylbenzaldehyde using dioxygen as oxidizing agent in acetonitrile solution inatmosphere pressure.Ti, Co and Mn-modified mesoporous molecular sieves mentioned above werecharacterized by powder X-ray diffraction (XRD), nitrogen adsorption-desorptionisotherms, diffuse reflectance UV visible spectroscopies (UV-VIS), Fourier transforminfrared spectroscopies (FT-IR), thermogravimetric and differential thermal analysis(TG-DTA) and ²⁹ Si magic angle spinning neclear magnetic resonanice (²⁹ Si MASNMR) spectra. The relationship between their physical properties and catalyticperformances were investigated.