The chemical nature of SO2 poisoning of Cu-CHA-based SCR catalysts for NOx removal in diesel exhausts

This study addresses the impact of SO2 exposure on the catalytic performance of a Cu-chabazite-based SCR catalyst, as used in diesel exhausts, to reduce the emission of NOx through the NH3-SCR reaction. The SCR activity is determined by a reaction of NO with the [Cu2II(NH3)4O2]2+ intermediate. The same intermediate is also the most reactive Cu-species towards SO2. We demonstrate here that the reaction with NO at 200 °C is limited after exposure of the [Cu2II(NH3)4O2]2+ complex to SO2 or SO2/O2. Heating the catalyst to 300 °C in NO restores the reaction, albeit at a significantly lower rate. The lower reactivity towards NO indicates that exposure of [Cu2II(NH3)4O2]2+ to SO2 induces changes in the chemistry of Cu in the catalyst. This implies that poisoning of Cu-chabazite catalysts by SO2 is, at least in part, of the chemical nature, and may be not limited to the physical pore blocking.