Preparation of Nickel Catalyst Supported on Ultra Fine Titania Particles

采用四异丙醇钛（TTIP）气相分解法制备了超细二氧化钛颗粒。颗粒的平均直径和比表面积与制备条件密切相关，即高温、高TTIP浓度和在反应器中停留时间长导致颗粒尺寸大、比表面积小。二氧化钛颗粒的最小尺寸约为15 nm，与氮吸附法测得的比表面积值基本吻合。结果表明，表面面积视为外表面积，颗粒不存在微孔。采用浸渍法和气相沉积法制备了负载在超细颗粒上的镍催化剂。在镍催化剂上进行了苯的气相加氢反应。在镍含量相同的情况下，催化剂的加氢活性与超细二氧化钛的表面积成正比。结果表明，镍在大表面积的二氧化钛上分散良好。CVD法制备的催化剂镍含量虽然低于浸渍催化剂，但前者的翻转频率大于后者。结果表明，CVD法制备高分散镍催化剂是可行的。在间歇式反应器中，常压下进行了油酸甲酯的加氢反应。将浸渍法制备的镍催化剂和CVD法制备的镍催化剂分散在油酸甲酯溶液中，并向溶液中供给恒流量氢气。考察了催化剂对硬脂酸甲酯的催化活性和选择性。CVD法制备的催化剂的选择性高于浸渍法制备的催化剂。然而，在大孔体积氧化铝负载催化剂上进行反应，对硬脂酸甲酯的选择性显著降低。此外，氧化铝负载催化剂的催化失活比CVD法制备的二氧化钛负载催化剂的失活要大。认为在氧化铝微孔中镍活性位点进一步分解会降低选择性。CVD法制备的超细二氧化钛颗粒可作为催化剂载体，具有较大的反应热

The preparation of ultra fine titania particles was carried out by the decomposition of titanium tetraisopropoxide(TTIP) in gas phase. The mean diameter and surface area of the particles were strongly dependent upon the preparation conditions, that is, high temperature, high TTIP concentration and long residence time in a reactor resulted in large particle size and small surface area. The smallest size of titania particle was around 15 nm and it was almost coincided the value calculated from the surface area, measured from nitrogen adsorption method. The result indicated that the surface area was regarded as outer surface area and the particles did not have a micro pore.The nickel catalyst supported on the ultra fine particles was prepared with impregnation method and CVD method. Furthermore, the gas phase hydrogenation of benzene was carried out over the nickel catalysts. The hydrogenation activity was proportional to the surface area of the ultra fine titania, even though the catalys … More t had the same nickel contents. The result suggested that nickel was well dispersed on the titania with large surface area. Although the nickel content of the catalyst prepared by CVD method was lower than that of impregnated ca talyst, the turn over frequency of the former was larger than that of the latter. This result implied that nickel catalyst with high dispersion could be prepared by a CVD method.The hydrogenation of methyl oleate was carried out in a batch reactor at an atmospheric pressure. The nickel catalysts prepared by the impregnation method and CVD method were dispersed in the solution contained methyl oleate, and hydrogen with constant flow rate was supplied in the solution. The catalytic activity and selectivity to methyl stearate were examined over the catalysts. The selectivity over the catalyst prepared by CVD method was higher than that over the catalyst prepared from impregnation method. However, the reaction was carried out over the catalyst supported on alumina with large pore volume, the selectivity to methyl stearate significantly decreased. Furthermore, the catalytic deactivation of alumina supported catalyst was larger than that supported on the titania prepared from the CVD method. It was considered that the further decomposition over nickel active sites in the micro pore on the alumina would decrease the selectivity.The ultra fine titania particles prepared by the CVD method was useful as a catalyst support for the reaction with large heat of reaction Less