Sulphur Poisoning and Regeneration of NOx Trap Catalyst for Direct Injected Gasoline Engines

Sulphur poisoning and regeneration of NO_x trap catalysts have been studied in synthetic exhausts and in an engine bench. Sulphur gradually poisoned the NO_x storage sites in the axial direction of the NO_x trap. During sulphur regenerations, hydrogen was found to be more efficient than carbon monoxide in removing the sulphur from the trap. The sulphur regeneration became more efficient the richer the environment (λ<1) and the higher the temperature (at least 600°C). H₂S was found to be the main product during the sulphur regeneration. However, it was possible to reduce the H₂S formation and instead produce more SO₂ by running with lambda close to one or by pulsing lambda. Even if a relatively large amount of sulphur was removed from the NO_x trap, these methods gave a much less efficient regeneration per sulphur atom removed than when running relatively rich constantly. Finally, a model that could explain this observation was proposed.