H2S Suppression During the Desulfation of a Lean NOx Trap with a Nickel-Containing Catalyst

Lean NO_x Traps are used to treat the NO_x emissions from lean-burn engines by storing the NO_x under lean conditions and reducing the NO_x during periodic rich excursions. However, sulfur poisons the adsorption sites of the traps. The sulfur can be removed from the NO_x trap by operating rich at high temperatures for several minutes. This results in the release of some SO₂ but also large quantities of H₂S, which is a source of customer dissatisfaction that must be reduced or eliminated. This paper describes the use of a nickel-containing catalyst and air/fuel control to maximize the release of SO₂ and minimize the emissions of H₂S during the desulfation of a lean NO_x trap. We present laboratory and vehicle data with a nickel-containing catalyst located downstream of a lean NO_x trap during desulfations of the trap. The nickel effectively reduced the emissions of H₂S during the desulfation while improving the robustness to fluctuations in the air/fuel control.