Lead Species in Vehicle Exhaust A Thermodynamic Approach to Lead Tolerant Catalyst Design

As part of a programme to develop lead tolerant emission control catalysts for Europe, a fundamental thermodynamic approach has been used to achieve an understanding of the lead species in vehicle exhaust under widely varying conditions and to consider the possible interactions which may occur between the catalyst and lead species and which may give rise to poisoning. A model has been developed which calculates the gas stream equilibrium and identifies the most stable solid phases which precipitate from the gas phase, until a final equilibrium has been reached. Results covering a wide range of conditions are presented, and compared with rig and engine test data - providing a means for determining the proportion and composition of gaseous and solid lead compounds, and the effect of oxygen content and temperature of the exhaust on the lead species formed. The data assist in the design of total vehicle emission systems with improved lead tolerance.