The effect of powder characteristics on washcoat quality. Part II: Zirconia, titania washcoats — multilayered structures

Novel automotive catalyst designs based on the use of washcoat systems such as yttria-stabilized zirconia (YSZ) and titania, in combination with the traditionally used γ-alumina have been recently proposed. For the development of an integrated, robust multi-layered system, good adhesion of the inner layer on the support as well as among the various layers has to be ensured. In the present work, the adhesion of zirconia and titania washcoats on cordierite honeycombs was investigated. Irrespective of the nature of the powder used, reduction of the agglomerates’ size down to the order of few (2–5) microns is necessary in order to ensure firm adhesion of the washcoat to the support, comparable to that of commercial catalysts. In the deposition of multi-layered structures, particle size compatibility of the powders of the various washcoat layers can enhance the adhesion among them and induce better coherence of the overall washcoat.