Study On Preparation Of Mesoporous Solid Superacid SO₄～(2-)/TiO₂ And Its Catalytic Performace

SO₄^2-/M_xO_y solid superacid has attracted much attention in superacid catalyst field for its excellences such as with no halogen, no corrosiveness and no pollution, high separation ability from the reactants, and high catalytic activity and stability in high temperature. At present, SO₄^2-/M_xO_y solid superacid hasn't been applied to industry for its preparation requires a complex process including many steps and many factors influencing on the performances of catalyst, as well as a short service life. To improve the catalytic activity and service life, common nanometer particle is replaced with a mesoporous catalytic materials with large porousity and specific surface area, which is used as supporter to prepare solid superacid. The mesoporous solid superacid not only has the advantages of untrafine oxides as supporters of solid superacid, but also favors the reaction of some big molecules and makes the best use of its inner surface to improve the catalytic activity and selectivity.In view of mesoporous material and solid superacid, mesoporous metatitanic acid with plentiful absorbed SO₄^2- was prepared via multi-step hydrolysis of industrial titanyl sulfate as raw material. Then the mesoporous solid superacid catalyst SO₄^2-/TiO₂ was obtained after washing and calcinations at different temperature and for different time. The prepared solid superacid catalyst SO₄^2-/TiO₂ was characterized by XRD, FT-IR, BET, XPS and Hammett indicator. The effects of sulfur content, calcination temperature and calcination time on the structure, the surface property and superacid center have been investigated. Using the reaction of synthesizing ethyl acetate as a probe, the catalytic activity of the mesoporous solid superacid SO₄^2-/TiO₂ prepared at different conditions were investigated. And the optimized preparation conditions were determined. The service life and regeneration of SO₄^2-/TiO₂ solid superacid were studied, and applications of SO₄^2-/TiO₂ solid superacid in energy resource and environment field were also primarily investigated.The results show that:(1) The new preparation method simplifies the traditional synthesis process of two-step of SO₄^2-/TiO₂ solid superacid. The low-angle XRD patterns and N₂ adsorption-desorption isotherms indicates that the prepared SO₄^2-/TiO₂ solid acid catalyst has mesoporous structure. And the calcination temperature plays an important role on mesoporous pore diameter distribution and pore structure. SO₄^2- can support pore structure and delays growth of crystal grain.(2) The tests of XPS and FT-IR argue that SO₄^2- is combined on surface of TiO₂ by chelating bidentate, and the synergistic action of the strong electronic inductive effect and the acid center produces the center of superacid.(3) The measurement of BET and Hammett indicator show that specific surface area and acid strength regularly vary with sulfur content, calcination temperature and calcination time. The catalyst SO₄^2-/TiO₂ has the highest acid strength of H₀<-14.52 and surface area of 151m²/g.(4) The mesoporous solid superacid SO₄^2-/TiO₂ behaves a excellent activity at the catalytic synthesis of ethyl acetate. The catalytic activity is closely related with acid strength and sulfur content in the catalyst. The catalyst calcined at 500℃with sulfur content of 2%(wt%) shows the highest catalytic activity.(5) The mesoporous solid acid catalyst SO₄^2-/TiO₂ will have a glorious application in the synthesis of biomasout and the catatytic decomposition of Hanlon-1211. But its stability should be improved.(6) The mesoporous solid superacid SO₄^2-/TiO₂ lost catalytic activity almost after constinous application in the synthesis of ethyl acetate for 4 times. The catalytic activity could not be recoverd by calcinations at high temperature and dipping H₂SO₄. Thus, these catalysts should be further studied and improved to prolong its service life and regenerable property.