Site-specific characterisation of an auto catalyst using EPMA, FIB and TEM/STEM

Abstract

Auto-catalysts are used to cut down harmful emissions from car exhausts. The catalysts are usually made up of platinum, rhodium and palladium nanoparticles supported on alumina and/or ceria zirconia. Particle size investigations of aggregation of the noble metal particles form an important part of the analysis of these systems. The aggregation, localised to only a few areas, can be detected using electron probe micro analyser or scanning electron microscopy, using an elemental mapping using an X-ray wavelength or energy dispersive spectrometer. Although these techniques spot the enriched areas it then becomes very difficult to characterise particle sizes from this specific area. This problem is addressed by extracting focussed ion beam samples from these areas. The samples are then characterised using a combination of bright field and high angle annular dark field imaging in the transmission electron microscope. © 2006 IOP Publishing Ltd.