Design, Synthesis Of Functionalized Mesoporous Materials And Catalytic Properties In Olefin Epoxidation

Inorganic porous materials, such as microporous molecular sieve, mesoporous materials and hierarchical porous materials, are widely used in the fields of lithium battery, electrochemical energy conversion and storage, medicine, catalysis, biology, etc. In recent years, they are found to be applied in some newly emerging fields of photoelectrocatalysis, biomedicine, etc. Mesoporous silica materials as supports have attracted great attentions in the catalytic application for their unique structure features, such as high total surface area, tunable pore diameter, narrow size distribution and good hydrothermal stability.The development of effective methods for selective oxidation of olefins has drawn much attention under the condition of increasing market demand of cycloolefins oxide over the past several years for the production of pharmaceuticals, pesticides, plant-protection agents and stabilizers. The development of sustainable oxidative procedures based on solid catalysts is, therefore, an object of extensive research with the aim of reducing the environmental impact of the epoxidation reaction.As a result, from the aspects of inorganic mesoporous materials, organic-inorganic mesoporous materials and hierarchical macro-mesoporous materials, this thesis introduces the tunable preparation of several kinds of inorganic mesoporous materials and organic-inorganic mesoporous materials, and their applications in epoxidation olefins. The main contents and results of this work are as following:1) A series of catalysts, including monometallic catalyst Ti-SBA-15-?36?, Mo-SBA-15-?180/28? and bimetallic catalyst Mo-Ti-SBA-15-?X?, were synthesized by the one-step method. The influence of Mo content in the bimetallic Mo-Ti-SBA-15-?X? on catalyst structure and catalytic property was investigated. The reasons for the differences' catalytic activity in the epoxidation olefin and their synergy mechanism were analyzed. The reaction conditions in the epoxidation cyclohexene reaction were studied. At the same time, the different olefins were taken into consideration. When the reaction condition?catalyst amount: 25 mg, cyclohexene: 2.5mmol, TBHP: 5mmol, 1,2-DCE: 10 m L, reaction temperature: 80 oC, reaction time: 8h? was used, the conversion of Ti-SBA-15-?36?, Mo-SBA-15-?180/28? and Mo-Ti-SBA-15-?180/28? was 41 %, 46 %, 98 %, respectively, and the selectivity was 98 %, 93 %, 98 %, correspondingly. The results showed that the optimum bimetallic catalyst Mo-Ti-SBA-15-?180/28? more catalytic activities than the monometallic catalyst Ti-SBA-15-?36?, Mo-SBA- 15-?180/28?. And the catalyst Mo-Ti-SBA-15-?180/28? has a wide application and good reusability.2) Two Mo??? tridentate Schiff base complexes supported onto modified mesoporous SBA-15 were designed and prepared using 3-chloropropyltriethoxysilane?CPTES? as a reactive surface modifier by a covalent grafting method, one of which involved the silylation with trimethylsilylation of Mo-FSAP-Cl-SBA-15 to remove the residual surface silanol groups. The supported materials were further characterized by XRD, SEM, TEM, nitrogen adsorption-desorption and FT-IR spectroscopy. And the spectroscopic data and nitrogen adsorption-desorption results confirmed the successful anchored with Mo??? tridentate Schiff base complexes. The SEM and TEM images indicated that the mesoporous structure were remained after the grafting procedure. The TGA, ICP-OES and EDS showed that the silylated catalyst has a more metallic active site than the non-silylated catalyst. The contact angle?CA? tests for silylated catalyst Mo-FSAP-CH3-Cl-SBA-15 and non-silylated catalyst Mo-FSAP-ClSBA-15 were carried out and the results showed that Mo-FSAP-CH3-Cl-SBA-15 has a better hydrophobicity. Both Mo-FSAP-CH3-Cl-SBA-15 and Mo-FSAP-Cl-SBA-15 were comparatively investigated in epoxidation of cyclohexene with TBHP as an oxidant. It was found that silylated catalyst showed higher active and selective to cyclohexene oxide than the non-silylated one. The superior catalytic activity for Mo-FSAP-CH3-Cl-SBA-15 was ascribed to the high content of Mo active sits and better surface hydrophobicity. The catalytic performance of the silylated materials showed that the material was efficient and selective catalysts for the heterogeneous oxidation of various olefins. The catalytic stability was checked by recycling the solid catalysts for five times. The results presented higher catalytic stability in reuse.3) Schiff base complex was directly anchored onto 3-aminopropyl-modified SBA-15 and then coordinated with MoO₂?acac?2. At last, the Mo??? Schiff base mesoporous material was further modified by silylation with?CH3?3Si Cl and the catalyst Mo-CH3-SA-NH₂-SBA-15 was obtained. The synthesized SBA-15-grafted Mo??? complexes were characterized by using TGA, FT-IR, ICP-OES, etc. and confirmed that the Mo??? active species have been successfully grafted on the mesoporous material SBA-15 surface. The catalytic activity of the heterogenized organo catalyst can be further enhanced due to silylation of the residual Si-OH groups, which cause the higher content of Mo active sites and better surface hydrophobicity. The modified mesoporous materials remaining a uniform hexagonal mesoporous structure were verified by SEM, TEM and nitrogen adsorption-desorption analysis. The high surface area and narrow aperture distribution was also confirmed by nitrogen adsorption-desorption analysis. The catalytic mechanism of epoxidation was investigated and further verified with the effect using different solvent in the epoxidation reaction. The reusability of Mo-CH3-SA-NH₂-SBA-15 catalyst and the active metal probable leak from the catalyst were discussed. It was found that the solvent plays an important role and can also affect the conversion and selectivity of olefin epoxidation. Mo-CH3-SA-NH₂-SBA-15 catalyst can be recycled effectively and is significantly stable with little loss of active metal.4) A novel organic-inorganic mesoporous material with a type SBA-15 morphology and structure has successfully been synthesized by using co-condensation method with tetraethylorthosilicate?TEOS? and 3-chloropropyltrimethoxysilane?CPTES? as precursors for the framework of organic-inorganic mesoporous materials and P123 as a template. And then Schiff base ligand was anchored on the organic-inorganic mesoporous material and coordinated with MoO₂?acac?2. The structural properties of the prepared catalysts were characterized. The performances of epoxidation for the different olefins and reaction condition were investigated. The results showed that the organic-inorganic material Mo-SB-Cl-SiO₂ remains SBA-15-type structure. The BET specific surface areas, total pore volume and average pore diameter of the Mo-SB-Cl-SiO₂ was 486 m2/g, 0.44 cm3/g and 3.6 nm, respectively. The conversion of Mo-SB-Cl-SiO₂ was slightly lower than that for high active homogeneous Mo-SB catalyst. In comparison with Mo-SB-Cl-SBA-15, the Mo-SB-Cl-SiO₂ showed a higher conversion in epoxidation under the same condition. In the epoxidation of cyclohexene with Mo-SB-Cl-SiO₂ for 1 h, 85 % of conversion and over 99 % of selectivity was obtained. The catalytic activity remains constant after four runs and there was no active Mo metal detected in the reaction filtrate.5) Molybdenum-containing hierarchical macro-mesoporous silica Mo-MM-SBA-15-4-30 has been synthesized via dual-templating routes employing Pluronic P123 triblock copolymer and polymethylmethacrylate?PMMA? beads. The hierarchical porous structure and chemical state of Mo were investigated by various characterization techniques. Mo-MM-SBA-15-4-30 has a uniform hierarchical porous structure with interconnecting networks even after the loading of Mo O3 particles. TON was used to evaluate olefin epoxidation catalyzed by these Mo functionalized silica. It was found that the presence of Mo-MM-SBA-15-4-30 led to a significant enhancement of the reaction rate in the epoxidation of long chain ?-olefins compared to mesoporous materials Mo-M-SBA-15-0-30 because of the advantageous structure for the efficient contact of reactants with the catalytically active sites. The most important point in the construction of hierarchical macroporous structure is reducing the particle size of mesoporous silica accompanying with the shortening of the mesoporous channels. In this case, the diffusion distance of reactive species would shorten. The combined porous structure between macroporous and mesoporous is advantageous to the diffusion of relatively large compounds, which allowed a good accessibility to the Mo??? active sites. It is thus concluded that the Mo???-containing hierarchical macro-mesoporous hybrids are prospective catalysts used in epoxidation of long-chain linear ?-olefins.