The Impact of Sulphur Storage on Emissions From Three-Way Catalysts

The relationship between H₂S emissions from three-way catalysts and the storage of sulphur on the catalyst surface has been investigated.

Thermodynamic data predict that sulphur storage primarily will occur on Al₂O₃ and CeO₂ under lean and stoichiometric conditions, at up to 500°C. Rich transients could then induce the decomposition of the Ce-S-O and Al-S-O compounds, releasing sulphur into the gas phase. Experimental studies have supported this model. A mechanism has been proposed for the subsequent formation of H₂S.

The mechanism by which catalyst poisons attenuate H₂S emissions from engine-aged catalysts also has been studied. The effect has been shown to be related to decreased storage of sulphur, caused by stable catalyst-poison species at the catalyst surface.