Characterisation of bimetallic diesel oxidation catalysts

• Main Author: Campbell, Steven Bruce
• Published: University of Aberdeen 2014
• Subjects: 540; Automobiles
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.606491

With mobile emission limits worldwide becoming more stringent, catalysts have increased in complexity to achieve improved activities and selectivities. This has required catalysts to be characterised under more severe conditions e.g. after extended thermal treatments to simulate catalyst lifetime. Detailed characterisation may allow a deeper understanding of the interactions within these catalysts and lead to improvements in catalyst design. The characterisation of these and other sophisticated catalysts may be improved by the development of an advanced characterisation technique using quantitative infrared spectroscopy. Bimetallic PtPd diesel oxidation catalysts which had been subjected to contrasting ageing processes were characterised using a variety of methods to study the surface composition and structure. Through FTIR studies, differences have been shown in the surface structure between the catalysts and using a semi-quantitative methodology, surface compositions have been determined. In addition to FTIR studies, characterisation has been performed using temperature programmed methods and simple oxidation reactions with in-situ diffuse reflectance spectroscopy. The results show clear evidence for the interaction of the two metals and also improved activity compared with the monometallic analogues. Simple oxidation reactions showed no significant structure sensitivity in either the CO or C3H6 oxidation reactions, however the NO oxidation reaction was shown to be sensitive to the catalyst structure following reduction. While FTIR was used to characterise the catalysts, experiments were performed with the aim to develop a quantitative methodology for FTIR applied to supported Pd catalysts. Investigations have shown the key considerations and factors required to develop an accurate quantitative method for CO adsorption on supported metal catalysts. The results of the investigations show a new method that can be applied for quantitative IR spectroscopy and the degree of complexity of the system when determining the molar absorption coefficients from complex spectra.