Nature of active sites in decane-SCR-NOx and NO decomposition over Cu-ZSM-5 zeolites

Decane-SCR-NOx in the presence of water vapor and NO decomposition were investigated over Cu ions exchanged in ZSM-5 zeolites with various Si/Al and Al distribution. The local environment of the Cu ions in cationic sites was characterized by the combination of 29Si MAS NMR, Vis–NIR spectroscopy of Cu(II) ions, Cu(I) Vis emission spectroscopy and UV–Vis spectroscopy of Co(II) ions as probes for the presence of Al pairs in the framework. The Cu(II) ions coordinated to four framework oxygens of the α- or β-type cationic sites containing Al-O-(Si-O)2-Al sequences represent the most active sites in decane-SCR-NOx. On contrary, the Cu(I) ions coordinated to two or three framework oxygens and located at the channel intersection adjacent to the single Al atoms in the α- or β-site control predominantly reaction of NO decomposition.