Enhancement of Regeneration Performance by a New Catalyzed DPF

Abstract

The diesel particulate filters (DPF) used to remove particulate matter (PM) in exhaust gas from diesel engines need to have periodical active regeneration for burning PM accumulated in DPF. Since active regeneration is carried out at high exhaust temperatures of 600 °C or more, it involves issues of fuel economy and emissions. This report describes the effort to resolve these issues by taking steps to promote the oxidation of PM and reduce DPF regeneration time by catalyst coated DPF. Attention was focused on Silver (Ag) catalyst, which possesses a PM oxidation function, as a new catalyst. An analysis of the mechanism on the PM oxidation activity, an evaluation of its properties by various model gas testing, and results from evaluation of performance conducted using an engine bench are reported on. As the result of a search for catalyst material that promotes a PM oxidation reaction, it was found that Ag2O was a highly active catalyst material. Furthermore, as the result of efforts to achieve greater stability in performance, Ag/Ce material was found to be a catalyst possessing both high performance and stability. The mechanism of Ag/Ce catalyst was analyzed by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). As a result, it was found that the supply of oxygen from complex oxides of Ce contributed to the formation of active species Ag2O, which played a role in stabilizing performance. In order to presume the performance of Ag/Ce catalyst in practical use, regeneration tests under various different conditions by using a model gas test equipment was conducted. As a result of that, the Ag/Ce catalyst exhibited high PM oxidation performance compared to the conventional Pt catalyst under all the conditions that were conducted. It was also found in regeneration testing by using engine bench that Ag/Ce catalyst showed greater PM oxidation performance, as in model gas testing, by comparison with conventional technology. As the result of DPF regeneration simulation under NEDC mode conditions, a 43 % shortening effect on regeneration time relative to regeneration conditions when using conventional technology was confirmed. Furthermore, the oil–ash, heat and sulfur durability test were conducted by accelerated aging test. It was found that although Ag/Ce catalyst exhibited some reduction of performance due to ash accumulation, no reduction due to heat or sulfur was observed, showing that this catalyst possesses high durability.