Deterioration of Automotive Catalytic Converters (Part 2): Catalytic Performance Characterisation

This is the second part of a two-part study that compared the degree of deterioration of catalytic converters taken from vehicles with low and high odometer readings. Part two details the catalytic performance characteristics of the catalysts that were physically characterised, according to chemical contamination and thermal degradation, previously in part one. The catalytic activity was determined using engine dynamometer and laboratory tests. The low odometer catalysts showed largely uniform light-off temperatures for CO, HC and NO that were increased in the order of 20 % relative to a new catalyst. The steady state activity was largely unaffected. The dominant deactivation mechanism of these catalysts was found to be the baseline thermal deterioration of the alumina washcoat under normal vehicle operating conditions. The deactivation shown in the high odometer catalysts was highly varied with the greatest loss of activity resulting from exposure to severe thermal conditions. The best performing catalyst in the group showed similar activity to the low odometer group whilst the worst catalyst was totally ineffective due to extreme thermal exposure.

An induced thermal deactivation of a catalyst in the low odometer group was conducted to simulate a prolonged high temperature excursion possible in a vehicle. The result was a large loss of HC conversion activity and a narrowing of the lambda window.