ELECTRON-ACCEPTOR PROPERTIES AND COORDINATION OF CU2-ZSM-5( CATIONS IN CUH)

ESR spectroscopy is used for monitoring of interaction between H-ZSM-5 and CuH-ZSM-5 zeolites precalcined at different temperatures and arom atic probe-molecules (benzene, anthracene, phenanthrene). The major pa rt of CU2+ cations in the ion-exchanged CuH-ZSM-5 and in the sample pr epared by H-ZSM-5 impregnation with a Cu(NO3)(2) solution followed by subsequent oxidative calcination are not capable of interacting with p henanthrene molecules, i.e., cationic sites are located inside zeolite channels. Interaction of benzene and anthracene at 20 degrees C with the most reactive square-planar CU2+ cations (CuH-ZSM-5 calcined at 50 0-550 degrees C) results in the reduction of cupric ions and formation of aromatic cation-radicals, High-temperature calcination of CuH-ZSM- 5 resulting in rearrangement of the local structure of sites leads to a drastic fall in the electron-acceptor strength of Cu2+ ions: the oxi dizing ability of the altered cationic sites, which are still isolated and accessible to probe-molecules, reduces drastically.