Preparation Of Titania Nanotubes And Their Selective Hydrodesulfurization Performance

It is a significant way to produce high quality and low sulfur gasoline byselective hydrodesulfurization, which can not only reduce the sulfur content in FCCgasoline but also reduce olefins saturation. In order to develop new selectivehydridesulfurization catalyst, the effects of preparation conditions of TiO₂nanotubes（NT） and the selective hydrodesulfurization performance of TiO₂nanotubessupported CoMo are investigated. The main conclusions are as follows:First, titanate nanotubes were prepared by hydrothermal processing, and theaffects of concentration of acid, reaction temperature, NaOH/Ti molar ratio andcalcination temperature on the microstructure and crystal composition of TiO₂nanotubes were investigated, and characterized by SEM、HRTEM、XRD、BET. Theresults showed that, when pickling concentration below0.1mol/L nanotubes structruecan be kept, and their structure was destroyed when concentration was0.5mol/L;with the increase of acid concentration, the product composition transformedgradually from Na_x-2H_xTi₂O₅H₂O to anatase. Only membrane-like material and a fewnanotubes were obtained when reaction temperature was90℃; the length of thenanotubes grew gradually as the reaction temperature increased from110℃to190℃.The surface area and pore volume could be increased by suitable concentration of acidand reaction temperature. The morphology of nanotubes were better when theNaOH/Ti molar ratio was24⁴0. With the increase of calcination temperature, thenanotubes gradually agglomerated into particles, meanwhile the surface area and porevolume reduced.Second, the affects of pickling-modify and calcination-modify on supports ofCoMo/NT catalyst and their selective hydrodesulfurization performance wereinvestigated, and the physical and chemical properties of catalyst were characterizedby HRTEM, XRD, BET, NH3-TPD, Py-IR and XPS. Hydrodesulfurization（HDS）activity in low-temperature section and hydrogenation of olefins（HYD） activity inwhole temperature section were increasing as pickling concentration increased. Whenthe concentration of acid was0.01mol/L, the performance of catalyst at260℃wasbest with thiophene conversion of81.7%and the selective factor of9.9; the physical and chemical properties characterization results indicate that, as acid concentrationincreased, L and B acid sites of catalysts were increasing, and surface sulfided degreeof catalysts reduced. HDS and HYD activity of catalysts were reducing as calcinationtemperature increased; the weak acid sites were the activity center of HDS and HYD;calcination of the support can adjust the number of weak acid sites, the higher thecalcination temperature, the fewer the number of weak acid, and the correspondingcatalytic activity getting lower. In the same reaction conditions, the HDS activity ofTiO2nanotubes catalyst slightly lower than the Al₂O₃catalyst, but the selectivityfactor is much higher than the Al₂O₃and P25catalyst.