(474f) Effects Of Thermal Degradation On Key Nox Storage/reduction Catalyst Reactions

NOX storage/reduction (NSR) catalysts are being used to meet the EPA NOX reduction regulations on light-duty diesel vehicles. Furthermore, this technology is a potential solution for NOX control in lean-burn gasoline engines. A significant challenge that questions their long-term durability is poisoning by sulfur compounds inherently present in the exhaust. Therefore, during operation, NSR catalysts require an intermittent high-temperature exposure to a reducing environment to purge the sulfur compounds from the catalyst. This desulfation protocol ultimately results in thermal degradation of the catalyst.

To evaluate the effects of thermal degradation, the performance of a commercial NSR catalyst was characterized before and after several high-temperature treatments. The characterization included ?standard? storage and reduction cycling experiments conducted between 200 and 500°C, evaluating H2 versus CO as the reductant source, oxygen storage capacity measurements and water-gas-shift and NO oxidation abilities. For the fresh catalyst sample, the performance improved as the amount of reductant was increased from 0% to 3%, while no significant change was observed with higher amounts used. H2 proved a better reductant at low test temperatures. Standard cycling conversion data indicate that the performance of this catalyst decreased after heating, but, the performance and reactivity trends of the burned catalyst are analogous to the trends observed with the fresh catalyst.