(280e) The Effect of Sulfur Dioxide on Hydrogen Promotion of the Hydrocarbon Selective Catalytic Reduction of Nitric Oxide under Lean Conditions over Ag/Al2O3

The reduction of NO_x in the exhaust from lean-burn engines has garnered considerable attention. Ag/Al₂O₃ has been widely studied as a catalyst for the selective catalytic reduction of NO_x under lean conditions with an array of hydrocarbons. Unfortunately, Ag/Al₂O₃ shows little activity at low temperatures. Recently, however, it has been shown that the addition of H₂ dramatically increases SCR performance at low temperatures. In contrast, the effect of the addition of SO₂ has been more ambiguous. Some researches report that low levels of SO₂ inhibit catalyst performance, while others have observed a modest increase in catalytic activity, particularly at higher loadings of silver. Work in our group has shown that the effect of SO₂ is dependent on the level of exposure. With limited exposure, SO₂ results in a small increase in catalytic activity in the presence of H₂. However, following long-term exposure to SO₂, the improvement typically seen with the addition of H₂ is inhibited. We will discuss the effect of different levels of SO₂ exposure on catalytic activity, with and without H₂ in the stream, and correlate these results to structural changes within the materials resulting from the interaction with SO₂. The effect of the choice of hydrocarbon on SO₂ tolerance will also be discussed.