Ageing Mechanisms in Automotive Catalysts

Finally, using the results achieved from these laboratory ageing methods, recommendations were made as to how ageing models reviewed in the literature could be improved.<br><br>From experimental results alone, it was seen that no correlation existed between the light-off performance of cored catalyst samples and the full size bricks from which they were taken. However, the QUB global catalyst model was able to consider variations in precious metal dispersion between samples, differences between inlet temperature and gas concentrations, inconsistencies in light-off ramp rates and heat transfer characteristics of the two reactors.

The simulations performed were able to show good correlation between the test methods. However, the two test methods showed differently the activity rank of the samples, indicating the variation in precious metal loading and dispersion throughout each full size brick. In other results, static ageing for palladium loaded catalyst samples was found not to show ageing effects due to time for ageing temperatures below 1000 ᵒC, and does not correlate well to dynamic ageing.

Static ageing methods were also shown to cause deactivation at a slower rate than dynamic methods. It was shown that the Toyota ageing expression would better predict catalyst deactivation if it incorporated an oxygen factor, to describe ageing when no oxygen is present. However, further testing is required<br>if a more accurate ageing algorithm is to be developed.