Preparation, Characterization And Catalytic Performance Of Tin-Based Mesoporous Materials

The tin-based catalysts are known to be effective catalysts for esterification, cyclication, addictive reaction and transesterification. However, most of the tin-based catalysts are homogeneous. Due to the problems of separation and reusing for homogeneous catalysts, the development of heterogeneous tin-based catalysts is very desirable. In this thesis, two types of tin-based heterogeneous catalysts, mesoporous stannosilicate molecular sieves with the MCM-48 structure (SnMCM-48) and organotin fUnctionalized mesoporous materials, were prepared and their catalytic performance in phenol hydroxylation and synthesis of dimethyl carbonate (DMC) from CO₂ and methanol were investigated. In which, direct synthesis of DMC from CO₂ and methanol, a process meeting the principles of Green Chemistry and Sustainable Society, is the research key. The main research contents in this thesis are as follows:1. SnMCM-48 have been synthesized by hydrothermal method and characterized by XRD, N₂ adsorption, UV-vis and FTIR. The results show that Sn in the synthesis gel can be incorporated into the tetrahedra lattice site of mesoporous MCM-48. The prepared SnMCM-48 exhibits good catalytic performance in phenol hydroxylation.2. SBA-15 functionzlized with (MeO)₂ClSi(CH₂)₃SnCl₃ was prepared by the post synthesis grafting and characterized by XRD, N2-adsorption, TEM, FTIR,～(29)Si MAS NMR,～(13)C CP MAS NMR and elemental analysis. The results show that (MeO)₂ClSi(CH₂)₃SnCl₃ is successfully grafted on SBA-15, the organotin loading can reach 1.05 mmol/g, and upon treatment of the functionalized material in methanol in the presence of Et₃N, the Cl group attached to Sn can be substituted by methoxy. The substituted material can be applied as heterogeneous catalyst for synthesis of DMC from methanol and CO₂, at 18MPa and 200℃, the turnover number of DMC can reach 3.57, higher than corresponding homogeneous catalyst. The prepared catalyst is stable in the employed reaction conditions and the activity changes little after six recycles.3. SBA-15 containing bridged organotin in the silicate framework were synthesized by condensation of TEOS and organotin (MeO)₂ClSi(CH₂)₃ -SnCl₃ in the presence of the triblock copolymer Pluronic Pl23 (EO₂₀PO₇₀EO₂₀). X-ray powder diffraction (XRD), N₂ adsorption and TEM results show that the ordering of the mesoporous material was dependent on the amount of organotin in the intial mixture and decrease with the increase of the amount of organotin. Solid-state nuclear magnetic resonance (NMR), FTIR and EDS show that (MeO)₂ClSi(CH₂)₃SnCl₃ can be hydrolysized and uniformly incorporated in the silica framework under the employed synthesis conditions. The prepared functionalized SBA-15 are active in synthesis of DMC from methanol and CO₂, and the activity can reach 1.83 TON.4. The effect of the methods of template removal on the preparation and catalytic performance of organtin functionalized MCM-41 was studied. Three different methods, calcination, solvent extraction and liquid-phase H₂O₂ oxidation were used to remove template from MCM-41. FTIR results show that the samples upon solvent extraction and liquid-phase oxidation remain much more silanol group than the sample upon calcination and in the identical grafting conditions, the grafting organotin amount on the sample upon solvent extraction is higher than on those upon H₂O₂ oxidation and calcination. The organotin grafted on MCM-41 treated by different methods of template method exhibit different catalytic activity in synthesis of DMC from CO₂ and methanol, in which organotin grafted on MCM-41 upon liquid-phase H₂O₂ oxidation has the highest activity with a TON of 4.52.5. Organotin functionalized MCM-48 was also prepared by post synthesis grafting and compared with the corresponding organotin functionalized MCM-41 and SBA-15. The results show that under the same grafting and catalytic reaction conditions, the prepared organotin functionalized MCM-48 has lower grafting organotin amount and catalytic activity in synthesis of DMC from methanol and CO₂ than the corresponding SBA-15.