Manganese based materials for diesel exhaust SO2 traps

The storage of SO₂ in manganese based materials was investigated in flow reactor experiments. Manganese oxide precipitated with ammonia and hydrogen peroxide stored about 76 wt.% of SO₂ at a high diffusion rate into the bulk. Doping with potassium increases the SO₂ storage rate substantially at 200 °C, but has an only minor effect at 400 °C. Kinetic studies showed that the storage of SO₂ in pure and potassium doped manganese oxide is controlled by the kinetics of the sulfate formation reaction on the catalyst surface up to complete sulfation, whereas the storage on manganese cerium mixed oxide is limited by internal diffusion of the formed sulfate. The sulfate formation reaction was found to be first order with respect to both SO₂ and manganese oxide. For the potassium doped catalyst sulfur was found to be bound on manganese sites being transferred to potassium afterwards.