Abstract
Platinum-rhodium based three-way-catalysts (TWC) are the primary catalytic system for control of hydrocarbon, CO, and NOx automotive emissions. Mixed Al2O3/CeO2 oxides are often dispersed on a cordierite honeycomb monolith as a washcoat and act as a high-surface-area carrier for the heavy metal catalyst clusters. There are both regulatory and marketplace demands for improved performance, lifetime, cost and reliability of these catalytic converters. The conversion efficiency and lifetime of a converter is determined by the microstructure of the washcoat/monolith and its evolution during high temperature exposure to the exhaust gas stream. Scanning electron microscopy (SEM), electron microprobe analysis, and analytical electron microscopy (AEM) were utilized to characterize these catalysts. Some AEM was performed on crushed washcoat specimens dispersed on holey carbon films. In addition, an innovative technique was developed for the preparation of transverse section specimens from the monolith, which preserves the spatial correlation of microstructure and elemental distribution with respect to position in the washcoat/cordierite.
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