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Targeting the complete range of soot components through the catalytic oxidation of diesel particulates

Ramdas, Ragini 2014. Targeting the complete range of soot components through the catalytic oxidation of diesel particulates. PhD Thesis, Cardiff University.
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Abstract

While total exhaust emissions from individual road vehicles continue to be reduced, it is becoming increasingly important to identify and quantify the residual chemical compounds in tail-pipe emissions that are potential hazards to the environment and to human health. Diesel particulate matter (DPM) is known to consist mostly of carbonaceous soot together with minor components, such as volatile organic fractions (from unburned fuel), lubricating oil, and inorganic compounds that include ash and sulphur compounds. Polycyclic aromatic hydrocarbons (PAHs) are invoked as the key intermediates in diesel soot formation. These are mutagenic air pollutants formed as by-products of combustion. PAH-precursors identified in soot include single ring structures such as benzene and toluene. Soot nucleation and growth gradually leads to the formation of five to six membered ring structures, such as benzopyrene, dibenzopyrene and coronene. Several methods have been devised to reduce the emissions of DPM, which include the use of a diesel particulate filter, or a technology which combines selective catalytic reduction of NOx with a regenerating particulate trap in a single unit. These oxidise the combustible content of the particulate matter collected on the filter through a non-catalytic reaction with NO2. As an alternative, the more difficult catalysed oxidation of soot by direct reaction with O2 has been gaining a lot of attention. Several studies have shown that the oxidation of soot requires a redox catalyst, such as CeO2, CeO2-ZrO2 and CeO2-ZrO2-Al2O3, or other reducible metal oxides including perovskites and spinels. In the past, proposed mechanisms have assumed that exhaust soot is simply graphitic carbon, and so have not taken into account the other organic components. In this work, we have carried out a speciation of soot that has been sourced from a diesel particulate trap. The soluble components have been identified by GC-MS, following extraction by Soxhlet and ultrasonication techniques. The speciation has been repeated as a function of temperature during the non-catalysed and catalysed combustion of the soot, allowing the conversion of individual components to be tracked. The results provide important catalyst design information, which should allow the formulation of materials that will be catalytically active in the combustion both of graphitic carbon and the complete range of retained organic species.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Funders: Johnson Matthey
Date of First Compliant Deposit: 30 March 2016
Last Modified: 19 Mar 2016 23:39
URI: https://orca.cardiff.ac.uk/id/eprint/59466

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