制备方法对Pd催化剂上丙烯选择性还原NO反应性能的影响

 采用三种不同方法制备了氧化铝负载的Pd催化剂．比表面积测定\r\n结果表明，与浸渍法相比，溶胶－凝胶加浸渍法和溶胶－凝胶法制备的\r\nPd／Al2O3样品具有较大的比表面积，但抗烧结性能不佳．其中采用溶\r\n胶－凝胶法制备的样品中，由于Pd分散于体相中，表面的活性位相对较\r\n少，造成催化剂在NO选择性还原反应中的活性较差；而将Pd浸渍于溶胶\r\n－凝胶法制得的Al2O3载体上所获得的催化剂比表面积较大，活性较好\r\n．添加CeO2的样品活性总体上比Pd／Al2O3样品高．其中采用溶胶－凝\r\n胶法制备的样品比表面积不大，并且XRD数据表明Al2O3和CeO2是高度分\r\n散并均匀地搀杂在一起的，不象在浸渍法制备的样品中那样以大晶粒的\r\n形式存在，因而CeO2的助剂作用没有充分体现出来，催化剂的活性比浸\r\n渍法制备的样品差一些．

Effects of Preparation Methods on Pd Catalysts for Selective Catalytic Reduction of NO by Propene

Alumina supported Pd catalysts were prepared by three different methods: impregnation (im), sol gel impregnation (gel im) and sol gel (gel). The surface area measurement implies that, for the sample Pd/Al 2O 3, using gel im and gel methods can achieve high surface area compared with using im method, but the samples sinter heavily at high temperature. Pd/Al 2O 3 sample prepared by one step gel method shows lower activity in the selective catalytic reduction of NO, because Pd may exist in bulk phase; while the samples prepared by impregnating Pd onto the sol gel made Al 2O 3 support have high surface area and high activity. The addition of CeO 2 increases the activity of all samples. The gel im and gel methods have no advantage over im method on aspect of surface area; furthermore, the XRD data show that CeO 2 is well mixed with Al 2O 3 in the form of high dispersion, instead of existing as big crystalline as in the case of im method. This hinders the promoter effect of CeO 2 and decreases the catalyst activity.