INVESTIGATIONS ON PRECIOUS-METAL ALUMINA INTERACTIONS ON 3-WAY AUTOMOTIVE EMISSION CONTROL CATALYSTS, BMA CATALYSTS AND MODEL SAMPLES

Combined XPS and SIMS measurements, partly supplemented by XRD investigations, were utilized to detect precious metal/support interactions on catalysts containing various precious metals. The Klemm-Bronger reaction between Pt and alpha-Al2O3 on methane/ammonia catalysts was used as a standard reference. Evidence was found for different stages of Pt/Al interactions and changing electronic properties of Pt on the surfaces of these Pt/alpha-Al2O3 catalysts by means of XPS and SIMS, and in the bulk material by XRD. The SIMS investigations on Pt and Rh on gamma-Al2O3 showed that, even at temperatures around 500-degrees-C, Rh/Al interactions can appear to a small extent in the topmost atomic layers, whereas the Pt/gamma-Al2O3 specimens did not show any measurable effects. After on-road operation, enhanced SIMS cluster-ion signals as well as anomalous XPS signal contributions were measured on the surfaces of used three-way automotive emission control catalysts. These signals did not appear for the fresh catalysts. By analogy with the related results reported on the methane/ammonia catalysts, the ion signals were used as qualitative surface probes indicating the presence of precious metal/support interactions, especially between Rh and Al.