Geometry of the Cu+ 540 nm luminescence centres in zeolites

Cu+ ions, with characteristic emission at 540 nm, have been considered to b e responsible for the high activity of Cu-ZSM-5 in NO decomposition. Howeve r, two types of Cu+ ions located in different structures, i.e. in ZSM-5 and Y, exhibit the 540 nm emission, but the Cu ions in Y zeolite do not exhibi t such a unique activity in NO decomposition. Therefore, Cu+ emission spect ra and luminescence decay of the Cu2+ ion exchanged and reduced in CuH-ZSM- 5, CuH-, CuRb-, CuCs- and CuBa-mordenites and Cu-Y zeolites were used to id entify cationic sites corresponding to the Cu+ luminescence centres in thes e zeolites emitting at 540 nm. The Cu+ ions with a single luminescence deca y correspond to those with C-3v symmetry in Y zeolite, while the Cu+ ions p ossessing a double-exponential decay represent Cu+ cationic sites in ZSM-5 and mordenite, different from that described for Cu-Y, but the local arrang ement of these Cu+ sites is similar in Cu-ZSM-5 and Cu-mordenite. The effec t of the presence of Rb, Cs and Ba co-cations and pyridine adsorption in Cu H-mordenites on the luminescence spectra was used to identify the cationic site represented by the 540 nm emission in mordenite. These Cu+ ions are lo cated in site E of the mordenite main channel. The elongated six-ring of th is site is composed of two five-rings sharing two oxygens, and the Cu+ ions are suggested to be coordinated close to the rectangle of the main channel wall. The 540 nm Cu+ emission of the Cu-ZSM-5 was attributed to the Cu+ io n in a site with a local arrangement similar to that of mordenite. The Cuions are located in the main (straight) channels of the ZSM-5 matrix and ar e coordinated to the oxygen oblong of the channel wall. The cationic site i s formed, as in mordenite, by an elongated six-ring composed of two five-ri ngs. Thus, the structure of the Cu active site in Cu-ZSM-5 was suggested.