Thermal and Poisoning Effects on the Performance of Motorcycle Emission Control Catalysts

The use of catalytic aftertreatment to reduce harmful gases in the exhaust streams of 2-wheel vehicles powered by small engines is becoming widespread as increasingly restrictive emissions standards are enacted. The primary exhaust gas pollutants are carbon monoxide (CO) and hydrocarbons (HC) for vehicles equipped with 2-stroke engines and CO for those using 4-stroke power plants. Because the exhaust streams of these small engines also contain significant concentrations of oxygen, catalytic aftertreatment is a very effective approach for oxidizing these contaminants to carbon dioxide and water. In order to assure the maximum long term benefits of catalytic aftertreatment, it is necessary to understand not only the factors responsible for high initial activity, but also the mechanisms by which a catalyst's performance is negatively impacted. The major contributors to deterioration in catalyst performance over time are extended operation at elevated temperatures and exposure to exhaust borne catalyst poisons. This paper investigates the impact of both thermal and poisoning related deactivation mechanisms on the performance of catalysts in 2-wheel vehicle applications.