SURFACE INTERACTIONS OF NAY AND DECATIONATED Y ZEOLITES WITH NITRIC OXIDE AS DETERMINED BY ELECTRON PARAMAGNETIC RESONANCE SPECTROSCOPY

The epr spectrum of the adsorbed NO molecule was used to determine crystal-field interactions on the surface of NaY and decationated Y zeolites. The crystal-field splitting of the 2pπx* and 2pπy* levels of NO was found to be 0.21 and 0.60 eV, respectively, for these two zeolites. Comparison of these results with other investigations shows that the extent of interaction is given by the sequence: decationated Y > ZnO > BaY > ZnS ≃ MgO > NaY. Spectra of NO on decationated Y zeolites indicated considerable hyperfine coupling with 27Al nuclei at the adsorption sites. The concentration of NO species was found to be a function of the dehydration procedure as well as the extent of exchange for the decationated Y zeolites. A maximum concentration was found following dehydration in the temperature range from 600 to 700°. The importance of these results in establishing a valid model for the catalytic activity of zeolites is considered.