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Passive catalytic soot oxidation

Meredith, Owain 2017. Passive catalytic soot oxidation. PhD Thesis, Cardiff University.
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Increasingly stringent legislation limiting the emissions of particulate matter (commonly referred to as soot particulates) has led to the adoption of particulate filters in the exhausts of both diesel and gasoline passenger vehicles. While filters are highly effective at reducing these emissions, it is necessary to periodically remove trapped particulates in order to avoid their accumulation and the resulting loss of vehicle performance associated with backpressure build-up. An effective method of removing soot particulates is through combustion (oxidation) with the oxygen-containing species present in the atmosphere of the exhaust, however this is unattainable at the temperatures experienced under normal driving conditions. A catalyst able to lower the temperature of soot oxidation is therefore desirable in order to achieve passive regeneration of the filter. Previous studies have identified ceria, CeO2 as a promising soot oxidation catalyst due to its outstanding redox properties, and have shown that it can be enhanced by doping with various other metals. In this work, ceria-based catalysts have been prepared by the co-precipitation method. Ceria was doped with zirconium, lanthanum, praseodymium and neodymium in various ratios in order to enhance its catalytic properties. Each of these materials also contained alumina in order to improve their thermal stability. Of these materials, the most active for soot oxidation was found to be a CeO2-Nd2O3-Al2O3 catalyst prepared in a 7:3:10 molar ratio of Ce:Nd:Al and calcined at 750ºC under flowing air. This catalyst lowered the temperature at which soot oxidation reached its peak rate by over 100ºC. It was also demonstrated that the catalytic activity of these materials benefited considerably from the presence of alkali metals within their structure. The use of the ceria-based materials as supports by impregnating them with other species previously identified as active soot oxidation catalysts was also investigated, which resulted in a further lowering of the soot oxidation temperature. Structural characterisation of the materials was carried out by X-ray powder diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and surface area analysis (BET), while their redox properties were analysed by temperature-programmed reduction (TPR). The catalytic activity of the materials towards soot oxidation was investigated using thermogravimetric analysis (TGA).

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 3 April 2018
Last Modified: 16 Apr 2021 15:17

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