1993-03-01

Deterioration of Three-Way Automotive Catalysts, Part I - Steady State and Transient Emission of Aged Catalyst 930937

Five field-aged catalysts with different mileages were analysed with respect to emission performance and structural changes. The FTP-75 emission results were compared to synthetic exhaust gas tests including: i) light-off, ii) lambda screening at stationary and oscillating stoichiometry, iii) space velocity variation. Several samples from different positions of one catalyst were used to achieve the spatially resolved activity profile for that catalyst. Surface characterisation was used to characterise accumulated catalyst poison.
Laboratory space velocity test was concluded to be a sensitive probe for catalyst performance: good correlation to vehicle emission data was found. An analysis of the influence of temperature and λ oscillation on the catalyst conversion performance was made, with particular emphasis on the ageing effects. The oxidation of hydrocarbons and CO, and the reduction of NO was significantly higher during oscillations at 753 K than at steady state, while this effect was not found at 653 K. The spatially resolved activity profile revealed large differences between the oxidation and NO reduction activities, the latter being the most significantly deteriorated catalyst function.

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