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Car Exhaust Catalyst Characterisation |
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Thursday, 01 March 2007 13:18 |
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Page 1 of 3 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 NOx 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.
Ce1-x Zrx 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.
| Element | As Introduced
(atomic %) | After Sputter
(atomic %) | | cerium | 10 | 18 | | zirconium | 10 | 11 | | oxygen | 49 | 53 | | carbon | 31 | 18 | Table 1: Quantification results of Ce1-x Zrx O2 surface
as introduced and after 450 seconds Ar+ sputtering.
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Last Updated on Thursday, 01 March 2007 13:50 |
Application Topics 