NOx Storage and Reduction on Differentiated Chemistry Catalysts for Lean Gasoline Vehicles

NO_x storage and reduction (NSR) catalysts are a widely investigated solution for lean gasoline applications. Open coating on metallic substrates gives a new opportunity to combine low and high temperature NSR catalysts into a converter by using differentiated chemistry on separate foils. A wide operation window for NO_x conversion between 200-600°C was reached with alumina based NSR catalyst in appropriate conditions. Differentiation on separate foils can be made by NO_x adsorption compounds, active metals (Pt, Rh), exhaust gas conditions or desulfation strategy. The desulfation, particularly from potassium-containing high temperature NSR catalysts, was decreased by 100°C by the addition of a small amount of TiO₂. The combination of 3-way and NSR catalyst was designed by the size and lean-rich timings in laboratory and engine conditions. Low OSC PdRh (7:1) catalysts with higher loadings were used as 3-way catalysts.