The Effect of Three-Way Catalyst Formulation on Sulphur Tolerance and Emissions from Gasoline Fuelled Vehicles

In a collaborative programme, the effects of gasoline sulphur content on regulated emissions from three-way catalyst equipped vehicles have been studied. The programme evaluated the sulphur tolerance of three different catalyst formulations on the same range of vehicles. The catalyst chemistries were chosen to be representative of typical current formulations in different markets, as follows:

1. 1.
   Platinum/Rhodium (Pt/Rh)
2. 2.
   Platinum/Rhodium/Nickel (Pt/Rh/Ni)
3. 3.
   Palladium/Rhodium (Pd/Rh)

Each vehicle/catalyst combination was tested with fuels containing sulphur at nominal levels of 50, 250 and 450 ppm weight. All fuels were produced using the low sulphur fuel as a base and doping to 250 and 450 ppm S with a mixture of nine sulphur compounds, typical of those actually occurring in European gasolines.

The results show clear differences between the magnitudes of the sulphur effect with different catalyst formulations. Furthermore, it was apparent that several vehicles, fitted with catalysts of identical chemistry and precious metal loading, did not all respond to sulphur in the same way. It is concluded that the influence of fuel sulphur content on regulated emissions from current three-way catalyst vehicles in a particular market place depends strongly on the catalyst and engine technology that predominates in that market.