Pd/Ce/Al/蜂窝陶瓷催化剂制备方法的研究

Preparation Method Study on Pd/Ce/Al/Monolith Honeycomb Catalyst

本文应用溶胶-凝胶技术对蜂窝陶瓷表面进行涂层,然后负载活性组分,以CO氧化作模型反应,考察了催化剂干燥方法、浸涂原液类型以及助剂CeO2对汽车尾气净化催化剂活性的影响,并应用TPR、XPS等手段对其进行表征。由催化剂活性测试结果表明:干燥方法对催化剂活性影响不大,加入分散剂的氧化铝溶胶作浸渍原液的催化剂活性最高,同时活性评价实验结果还表明,加入CeO2作助剂的催化剂的活性明显提高,这可能是由于PdO与CeO2之间发生的协同效应所致,XPS谱图结果显示:CeO2与PdO之间存在协同作用,且Pd处于较高的氧化状态,这可能起因于从Pd到Ce的电子转移作用,Ce处于较低的还原状态,导致Ce-O键结合强度的降低。H2-TPR表征结果同样证实了PdO与CeO2之间存在协同效应,CeO2的引入,促进了PdO的还原,而PdO的存在降低了CeO2表面氧的还原温度,同时此现象也支持了XPS结论。

In this paper, monolith honeycombs were coated by sol-gel technology. Then active ingredient was added. Taking CO oxidation as a probe reaction, effects of drying methods, various kinds of dipping solutions and the addition of promoter CeO2 on the catalytic activity of automobile exhaust control catalyst were investigated. These catalysts were characterized by means of H-2-TPR and XPS techniques. The experimental results showed that the drying method had no noticeable influence on catalytic activity. Among three dipping solutions, the catalysts dipping by the alumina sol with the dispersant possessed the best activity. The experimental results also showed that CeO2 addition improves the catalytic activity obviously, which may derive from the synergic effect between CeO2 and PdO. XPS results about Pd3d(5/2) chemical shifts showed that there was a Pd-Ce interaction and Pd was more oxidized due to the interaction. A slight increase in noble metal oxidation state reflected charge transfer from metal to ceria. This indicated that ceria was slightly reduced and that the Ce-O bond strength was weakened. H-2-TPR profiles of catalysts also revealed the presence of synergism between CeO2 and PdO and indicated that the CeO2 addition shifted the reduction temperature of PdO to lower values, while palladium facilitated the reduction of the ceria surface oxygen. H-2-TPR results supported the inference from the XPS results.