Hydrocarbon and NOx Trapping for Low Temperature Emissions Control

William  Epling, University of Virginia

Increasingly stringent emissions regulations are driving the development of new catalytic technologies for exhaust systems. One emissions aspect that has been consistently challenging is controlling/mitigating cold start emissions. More fuel-efficient engine designs, which typically result in lower exhaust gas temperatures, exacerbate the problem. Current after-treatment systems may not be able to meet the stricter regulations, especially with more prolonged cold start periods or excursions into low temperature ranges, specifically those below those where hydrocarbon and CO oxidation rates are appreciable over catalysts designed for those reactions. To mitigate NOx and hydrocarbon emissions during these low temperature periods, trapping materials have been proposed and investigated. These materials, ideally, would adsorb/trap NOx and hydrocarbons when exhaust temperatures are low, and release the NOx and hydrocarbons when the exhaust gas temperature exceeds that required by the downstream or integrated oxidation and reduction catalysts. This release “regenerates” the trap for the next low temperature excursion. Therefore, capacity and release temperature and rate are critical parameters.

In this talk, results from hydrocarbon and NOx trapping research will be presented. Emphasis will be put on integration of the trapping materials with oxidation catalysts, and where possible, mechanistic insight will be provided. Topics will include layering a hydrocarbon trapping material onto an oxidation catalyst, the impacts of different hydrocarbons on the trapping of others, and possible passive NOx adsorption deactivation and/or inhibition mechanisms.