Preparation Of Catalyst With Fumed SiO₂ And TiCl₄ For The Gas-phase Epoxidation Of Propylene And H₂O₂

The gas-phase epoxidation of propylene with H₂O₂ over TS-1 zeolite is expected to able to overcome the problems faced by the well-known liquid-phase epoxidation process（HPPO）owing to the use of large volume of methanol solvent.The purpose of this thesis is to search for a new way to synthesize TS-1 zeolite with low-cost and high performance.Main research works and results are as follows.First,investigations were carried out to prepare Ti/SiO₂ amorphous intermediate from fumed SiO₂ and TiCl4 raw materials via chemical vapor deposition（CVD）.Attentions were paid to the influences of the specific area of fumed SiO₂ and the conditions of the CVD.Results show that,the amorphous Ti/SiO₂ intermediate prepared has tetra-coordinated Ti species which would show an UV absorption band around 230 ? 235 nm.A water rinsed amorphous Ti/SiO₂ intermediate obtained by the TiCl4 CVD at 400 ℃（5 h）on a fumed SiO₂ with a specific area of 380 m2/g,showed 5.04% propylene conversion,53.17% propylene oxide（PO）selectivity and 21.70% H₂O₂ utility in the gas-phase epoxidation.Its catalytic performance was comparable to the traditional micrometer TS-1 zeolite synthesized via hydrothermal synthesis.On this basis,the amorphous Ti/SiO₂ intermediate was subjected to hydrothermal crystallization treatment using low-concentration tetra-propylammonium hydroxide（TPAOH）solutions.The effects of crystallization time and tempalte dosage（TPA+/SiO₂）etc.were investigated.Results show that,TS-1 zeolite can be obtained with the amorphous Ti/SiO₂ intermediate via a convenient hydrothermal synthesis at the conditions of 170℃,TPA+/SiO₂=0.045?0.06,liquid to solid ratio =5:1¹0:1and crystallization time = 48 h?72 h.This TS-1zeolite would show a UV absorption band around 230 nm and irregular lumpish shapes（primary crystals were expected to have nanometer sizes）.The TS-1 zeolite obtained at the condition of TPA+/SiO₂= 0.045,showed 17.09% propylene conversion,40.72% propylene oxide（PO）selectivity and 71.16% H₂O₂ utility in the gas-phase epoxidation,indicating high activity and high H₂O₂ utility merits.Finally,the hydrothermally prepared TS-1 was subjected to further modification treatment with a TPAOH solution containing alkali metal ions.Results indicate that the modification can significantly increase PO selectivity of the TS-1zeolite obtained with the amorphous Ti/SiO₂ intermediate.