A NEW APPROACH FOR DETERMINING THE STRENGTH OF ELECTRON-ACCEPTOR SITES OF SOLID ACIDS

The interaction of radicals formed from ethylbenzene adsorption with electron-acceptor sites (EASs) on acid-dealuminated H-mordenite samples has been investigated by EPR methods. Partial electronic transfer from the radicals to the EAS was observed. The extent of the charge transfer is affected by small modifications of the environment of the EAS as reflected by the measurable variation of the hyperfine splitting constants (hfscs) of the radicals. In the studied H-mordenites, a linear decrease of hfsc was obtained with respect to aluminium content, showing that the EASs become more attractive to the unpaired electron when the zeolite undergoes dealumination. The strength of the EASs is discussed in the framework of the theory suggested by McConnell for calculating the hfsc of radicals with respect to the spin density.