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 investi gations, were utilized to detect precious metal/support interactions o n catalysts containing various precious metals. The Klemm-Bronger reac tion 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 surfa ces 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 gam ma-Al2O3 showed that, even at temperatures around 500-degrees-C, Rh/Al interactions can appear to a small extent in the topmost atomic layer s, whereas the Pt/gamma-Al2O3 specimens did not show any measurable ef fects. After on-road operation, enhanced SIMS cluster-ion signals as w ell as anomalous XPS signal contributions were measured on the surface s of used three-way automotive emission control catalysts. These signa ls did not appear for the fresh catalysts. By analogy with the related results reported on the methane/ammonia catalysts, the ion signals we re used as qualitative surface probes indicating the presence of preci ous metal/support interactions, especially between Rh and Al.