Overview

All modern car exhausts are fitted with an exhaust catalyst to reduce harmful emissions of hydrocarbons, carbon monoxide and nitrogen oxides into the atmosphere. The role of these catalysts is to oxidise hydrocarbons and CO to CO₂ while reducing NO_x to N₂. Ceria is widely used as a promoter for alumina-noble metal exhaust catalyst and more recently zirconium has been introduced into the ceria matrix to enhance the thermal stability of the catalyst. X-ray photoelectron spectroscopy is ideally suited to the surface characterisation of such materials, where the surface of the material will determine the catalytic activity.

The Catalyst Samples

The Ce-Zr mixed metal oxide catalysts were prepared by co-precipitation of the metal salts. After washing and drying, the resulting finely divided powders were pressed into 10mm diameter discs and annealed at 900°C to form robust pellets. These pellets were introduced into vacuum and analysed by XPS without further surface preparation.
Ce_1-x Zr_x O₂ samples are known to be insulators and therefore subject to charging during surface analysis. The configuration of the AMICUS instrument means that sample charging due to the photoelectron emission process is minimised. Where sample charging was observed, peaks have been shifted so as to align adventitious hydrocarbon C 1s photoemission to 285eV binding energy.