Deactivation of a Cu-CHA NH3-SCR catalyst by SO2 and SO3
Peter Sams Hammershøi, Haldor Topsøe A/S and DTU
The deactivation of a Cu-CHA NH3-SCR catalyst by SO2 and SO3 was studied by measuring the SCR activity before and after SOx exposure, and after regeneration at 550 °C. Since the SCR activity could only be partially regenerated, at least two different forms of deactivation by SOx exist. Measurements of the SO2 desorption during regeneration and heating to 900 °C after the final SCR measurement, allowed for estimations of the amounts of S-species related to the deactivation before and after regeneration. After SOx exposure, the activation energy is lower than that of the fresh catalyst, and the deactivation was up to 5 times higher than expected from a 1:1 correlation on the SO2/Cu ratio. Upon regeneration at 550 °C, the activation energy is the same as that of the fresh catalyst, and the remaining deactivation follows a 1:1 correlation with the SO2/Cu ratio. This is consistent with single SOx species deactivating single Cu-sites. This demonstrates two mechanistically very different deactivation forms inferred by sulfur oxides. Furthermore, the impacts of SO3, H2O and temperature on the deactivation were evaluated by systematically varying the SOx exposure conditions with respect to the three said parameters. We find that the presence of water always leads to a somewhat higher deactivation, and exposure of SO3 at 200 °C leads to a very strong deactivation of the Cu-CHA catalyst.