In situ spectroscopic studies of the effect of water on the redox cycle of Cu ions in Cu-SSZ-13 during selective catalytic reduction of NO_x

The effect of water on the NH₃-assisted selective catalytic reduction of NO_x (NH₃-SCR) has been largely neglected, despite the inevitable presence of water vapor in real emissions produced by fuel combustion. In this work, we investigated the role of water in the behavior of active Cu²⁺ ions in Cu-SSZ-13 in the NH₃-SCR reaction. The addition of water to the reactant feed leads to significantly increased NO_x reduction over the catalyst. By combining in situ DRIFTS and XANES analyses during the NH₃-SCR reaction, we found that the redox cycle of Cu ions is promoted by the presence of water.