SO(2) Poisoning of Cu-CHA deNO(x) Catalyst: The Most Vulnerable Cu Species Identified by X-ray Absorption Spectroscopy

[Image: see text] Cu-exchanged chabazite zeolites (Cu-CHA) are effective catalysts for the NH(3)-assisted selective catalytic reduction of NO (NH(3)-SCR) for the abatement of NO(x) emission from diesel vehicles. However, the presence of a small amount of SO(2) in diesel exhaust gases leads to a severe reduction in the low-temperature activity of these catalysts. To shed light on the nature of such deactivation, we characterized a Cu-CHA catalyst under well-defined exposures to SO(2) using in situ X-ray absorption spectroscopy. By varying the pretreatment procedure prior to the SO(2) exposure, we have selectively prepared Cu(I) and Cu(II) species with different ligations, which are relevant for the NH(3)-SCR reaction. The highest reactivity toward SO(2) was observed for Cu(II) species coordinated to both NH(3) and extraframework oxygen, in particular for [Cu(II)(2)(NH(3))(4)O(2)](2+) complexes. Cu species without either ammonia or extraframework oxygen ligands were much less reactive, and the associated SO(2) uptake was significantly lower. These results explain why SO(2) mostly affects the low-temperature activity of Cu-CHA catalysts, since the dimeric complex [Cu(II)(2)(NH(3))(4)O(2)](2+) is a crucial intermediate in the low-temperature NH(3)-SCR catalytic cycle.