The Chemistry and Control of H<sub>2</sub>S Emissions in Three-Way Catalysts

Abstract

<div class="htmlview paragraph">Recent reports of significant H<sub>2</sub>S emissions from single-bed three-way catalyst equipped vehicles have prompted vehicle and laboratory studies of the mechanism of H<sub>2</sub>S formation over three-way catalysts. Vehicle studies have shown the occurrence of short duration H<sub>2</sub>S emissions significantly higher than fuel sulfur inlet levels under certain transient conditions. These emissions cannot be explained by the previously reported steady-state conversion of SO<sub>2</sub> to H<sub>2</sub>S. Laboratory flow reactor studies have identified a second mechanism for H<sub>2</sub>S formation involving the rapid reductive release of sulfur stored on the catalyst surface. This mechanism can account for H<sub>2</sub>S emission levels which can significantly exceed inlet fuel sulfur levels for short durations. Results are presented to define factors which affect H<sub>2</sub>S formation under these two mechanisms and to determine methods for controlling these emissions under vehicle operation.</div>