Brian Harrison

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 to total vehicle emission systems with improved lead tolerance.

Car exhaust emission control in Europe

Abstract Although Europe is following the example of the USA in progressively lowering permitted emission levels of pollutants from motor vehicles, it seems unlikely that lead-free petrol will be introduced in the near future. Proposed regulations seek a level of emission control which will in all probability, necessitate the use of oxidation catalysts. In the presence of leaded fuel conventional autocatalysts used in the USA are susceptible to poisoning after relatively low mileages. Recent research has led to an improved understanding of the nature and type of the lead species involved and the feasibility of achieving 50 000 km road usage using lead-tolerant catalysts has been demonstrated.