COORDINATION OF CU IONS IN HIGH-SILICA ZEOLITE MATRICES - CU+ PHOTOLUMINESCENCE, IR OF NO ADSORBED ON CU2+, AND CU2+ ESR STUDY

The Cu ion siting-coordination in MFI, mordenite, erionite, and Y zeol ite matrices was investigated employing Cu+ luminescence, IR spectra o f NO adsorbed on Cu2+, and ESR spectra of Cu2+ ions. Four discrete Cu emission bands (with decays) at 450 nm (35 mu s), 480 nm (55 mu s), 5 10 nm, and 540 nn (120 mu s) were identified and ascribed to four indi vidual types of Cu ion sites. The Cu site distribution varied with the Cu loading and Si/Al framework ratio. It has been shown that the Cu s iting in high-silica zeolites is controlled by the local Si-Al sequenc es, which affects the redox properties of the individual sites. The Cu + emission bands were in sound agreement with characteristic shifts of the main LR bands of NO adsorbed on Cu2+ ions, found at about 1921, 1 912, 1906, and 1895 cm(-1). This indicated different charges on the fo ur Cu ion sites. The ESR spectra provide qualitative information on th e existence of two square pyramidal and one square planar Cu2+ complex es. It is suggested that the Cu sites balanced by pairs of framework A l atoms (Cu+ emissions at 450 and 480 nm) exhibit square pyramidal coo rdination, while those adjacent to a single framework Al atom are coor dinated close to square planar environment. The latter sites possess s ubstantially higher reducibility compared to the other sites and are r esponsible for the Cu-ZSM-5 unique activity in NO decomposition.