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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Pd/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 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-凝胶法制得的Al2 O3载体上所获得的催化剂比表面积较大,活性较好. 添加CeO2的样品活性总体上比Pd/Al 2O3样品高. 其中采用溶胶-凝胶法制备的样品比表面积不大,并且XRD数据表明Al2O 3和CeO2是高度分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 形式存在,因而CeO2的助剂作用没有充分体现出来,催化剂的活性比浸渍法制备的样品差一 些.

Alumina-supported Pd catalysts were prepared by three different methods: impreg nation (im), sol-gel-impregnation (gel-im) and sol-gel (gel). The surface ar ea measurement implies that, for the sample Pd/Al2O3, using gel-im and gel methods can achieve high surface area compared with using im method, but the sam ples sinter heavily at high temperature. Pd/Al2O3 sample prepared by one-st ep gel method shows lower activity in the selective catalytic reduction of NO, b ecause Pd may exist in bulk phase; while the samples prepared by impregnating Pd onto the sol-gel-made Al2O3 support have high surface area and high acti vity. The addition of CeO2 increases the activity of all samples. The gel-im and gel methods have no advantage over im method on aspect of surface area; furt hermore, the XRD data show that CeO2 is well mixed with Al2O3 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 CeO2 and decreases the catalyst ac tivity.