Development of Novel Catalysts For Use in Diesel Particulate Filters

Diesel particulate matter (PM) is part of a complex mixture that makes up diesel exhaust, which has raised many health and environmental problems. Currently, the most efficient technique to reduce PM emissions is Diesel Particulate Filter (DPF). However, the collected particulates build up overtime and block the micropores of DPF, and subsequently reduce the engine performance. This problem makes the regeneration of DPF necessary. Among many possible regeneration techniques, catalytic regeneration is the most applicable. The commercial catalysts used in most catalytic DPF are the costly platinum based systems. The main aim of this dissertation is to develop novel, economical catalysts for DPF applications.

Within this central theme, my work encompasses two major parts: (1) combinatorial development of multiple-metallic oxides catalyst. Hundreds of single, mixed and complex metal oxides were synthesized and studied based on a combinatorial synthesis and characterization route. It was found alkali-doped metal oxides, especially the ones containing potassium, showed higher activity than the other tested compositions. Further investigation revealed that 'active' potassium is the active species in these catalysts and sublimation of potassium during the soot combustion process resulted in the fast degradation of the catalysts. These studies indicated the compounds that could timely release 'active' potassium might be promising economical and efficient catalysts for soot combustion.

(2) Study of glass-based catalysts. To realize this timely release process, several potassium-containing materials were examined. The potassium-glass was found to be particularly promising. Potassium-glass catalysts showed better catalytic stability than conventional potassium-catalysts and also possess resistance to common S, P and Zn poisoning. Activity and stability tests performed in TGA and fixed bed flow reactor indicated that the activity and degradation of glass catalysts are related to their composition, particle size, glass/soot mixing method (contact), and ambient gas. Moreover, some studies of microwave heating effects on diesel soot combustion were performed. A novel microwave heated Thermogravimetric Analyzer was designed. Measurements in microwave-TGA suggested that the apparent reduction in soot combustion temperature with microwave heating might be not due to the enhancement of microwave, but the result of the inability to measure the interior temperature of the soot/catalyst mass.