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Preparation of Multi-Layer Washcoats for Automobile Catalyst via Chemical Methods

Recently the concept of a three-layered washcoat where various noble metals are dispersed within different supports has been proposed for automobile catalysts [1]. By exploiting enhanced metal-support interactions, this three-layered structure exhibits greater catalytic activity than commercially available alumina-supported platinum-rhodium catalysts, incorporating at the same time much less amount of noble metals. In this work the potential of preparing these multi-component systems by Sol-Gel methods is explored. Alumina, titania and zirconia-supported noble metal catalyst systems were prepared from both organic and inorganic liquid precursors and deposited upon cordierite honeycombs. The impregnation conditions (solids content, pH) for each system were optimized and uniform coatings with the desired amount of loading were achieved. The physicochemical properties of the individual washcoats were evaluated and compared to conventionally-prepared analogous systems. It was demonstrated that Sol-Gel methods can be easily fine-tuned to produce washcoats with similar pore size distribution to that of commercial catalysts but with greater surface area. An additional advantage is that the incorporation of the various dopants is greatly facilitated. Last but not least, Sol-gel prepared washcoats exhibit much better adhesion to the catalyst support both from conventionally-made ones as well as from commercially available catalyst systems.