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Lowering the fuel requirement during active regeneration of soot

Cooper, Anna 2021. Lowering the fuel requirement during active regeneration of soot. PhD Thesis, Cardiff University.
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This thesis focuses on finding a single catalyst for the simultaneous removal of NOx and soot from a diesel car exhaust. Finding a single catalyst which can operate at low temperatures would remove the need to inject fuel to regenerate the soot filter. It has been shown that a Ag/CeO2-ZrO2-Al2O3 (CZA) catalyst was found to have the ability to simultaneously reduce NOx and oxidise soot and utilise in situ formed N2O to oxidise soot at low temperatures. This project develops the work by investigating ways to improve the NOx reduction and soot oxidation ability of the catalyst. Initially, the effect of preparation method on 2%Ag-20%K/CZA was carried out. Potassium was added to the catalyst, as it is a well-known enhancer of soot oxidation. Several preparation methods were carried out including wet impregnation, incipient wetness and chemical vapour impregnation (CVI) at four different temperatures. It was found that the wet impregnation technique was the superior preparation technique, however, the presence of potassium appeared to enhance soot oxidation but hinder the reduction of NOx. The wet impregnation catalyst showed the ability to utilise the in situ formed N2O to oxidise soot at low temperatures, but to a lesser extent than that observed over Ag/CZA. The effect of potassium weight loading was investigated, with the aim of determining whether a lower weight loading of potassium was sufficient to enhance soot oxidation, but not hinder the reduction of NOx. This was found not to be the case with an increase in potassium weight loading resulting in greater high temperature soot oxidation, but altering the potassium weight loading had little effect on the reduction of NOx. In situ XRD studies were carried out to investigate the nature of potassium under reaction conditions which suggested that the potassium becomes mobile under reaction conditions. A variety of Cu/CZA catalysts were studied for their ability to simultaneously remove NOx and soot. Copper zeolites are frequently used to reduce NOx from diesel exhausts. Under the preparation conditions used, the copper was present in the form of Cu2+ rather than the active Cu0 form, resulting in poor activity. The introduction of a range of secondary metals into Ag/CZA and Ag-K/CZA catalysts were investigated. The secondary metals were chosen based on their ability to either reduce NOx or oxidise soot under diesel exhaust conditions. As with the addition of potassium to the catalyst, the introduction of a secondary metal hindered the reduction of NOx. However, several metals such as Rh and Pt, were shown to enhance high temperature soot oxidation under reaction conditions.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Cardiff Catalysis Institute (CCI)
Funders: EPSRC, Jaguar Landrover
Date of First Compliant Deposit: 22 February 2022
Last Modified: 24 Feb 2022 10:56

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