ELECTRON-MICROPROBE CHARACTERIZATION OF PHOSPHORUS CONTAINING DEPOSITS ON USED AUTOMOTIVE CATALYST SURFACES

Four catalyst samples from in-use vehicles with severely deteriorated performance were characterized using an electron probe microanalyzer to help explain the possible deactivation mechanism. Cross-sections of the samples were examined to reveal the morphology of glazes in washcoat surfaces. A major effort was made to ensure that the data collected had adequate accuracy and were truly representative of the samples in study. Over 600 data points were collected from dense glazes and contaminated gamma-alumina particles in four samples. These data were plotted against the atomic percentage of Al + Ce, which can be used as a measure of the penetration of the contaminants into gamma-alumina particles. These plots allow positive identification of the main contaminants present in various locations in a washcoat. Coupled with the morphological information, it is then possible to point out the likely deactivation mechanism in these catalysts. The deactivation was probably due to either the formation of an impervious glaze on the washcoat surface, the sintering of gamma-alumina particles by a glassy phase in the washcoat, or simply the poisoning from lead.