Benjamin R. Wood, Dan Hancu, Frederic Vitse, Venkat S. Venkataramani, Benjamin H. Winkler, Alison L. Palmatier, Richard J. Kilmer, Stanlee T. Buddle, Linda J. Briel, and Stanley J. Stoklosa. Global Research, General Electric, One Research Circle, Niskayuna, NY 12309
The reduction of NOx 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 NOx 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.