XPS study of ceramic three-way catalysts

Three-way catalysts used in automotive exhaust converters were investigated by means of selected-area XPS. The main purpose of this study was to improve the understanding of deactivation processes occurring when the catalyst is operating in gas exhaust. The washcoat of the converter (gamma-alumina with ceria and other stabilising additives) was supported on a honeycomb monolith of cordierite. Catalysts (Pd and Rh) were doped in the washcoat surface. The samples of the new converter and the same converter after various treatments were analysed. From the characteristic shape and chemical shift of the XPS peaks, the chemical state of the active elements (Ce, La, Ba, Pd, Rh) and the contaminants (P, Pb, Zn, Ca, etc.) was determined before and after the sample treatments. These results together with the data of quantitative XPS testified that, after the medium operation time of 500 h, the gas converter was deteriorated. The main reasons and the consequences of this degradation are revealed.