A study was made of the role played by zeolite de-alumination in the altered electrical properties of a protonic HY zeolite. The ac impedance exhibited a high-frequency Cole-Cole dependence which was indicative of protonic conduction. The imaginary part revealed a band which was associated with ionic relaxation. Its maximum shifted to higher frequencies, above 413K, in a manner which was useful for estimating the relaxation time and activation energy (7.9 x 10−10s, 0.53eV). The low-frequency real part revealed a band dependence upon temperature, leading to a maximum at 413K. Both results suggested transfer of the protonic conduction from low-temperature water-assisted to high-temperature thermally-enhanced mechanisms. Their average activation energies were 0.14 and 0.46eV, respectively. The lower activation energy confirmed the role played by water in mobilizing the conduction protons as H3O+ ions. Distinct from the predominant protonic conduction characterizing H-form zeolites, a concomitant dielectric conduction was found. This was reflected by a high-frequency Cole-Cole dependence. The real part indicated a band that was associated with electronic relaxation above 413K. Its time constant and activation energy were 6.28 x 10−8s and 0.37eV. The contribution of such a dielectric conduction could be explained in terms of strong dipole-dipole interaction at the nest silanols, created as lattice defects which could survive up to 823K. Strong association of these sites raised the thermal activation to 413K, rather than the 373K for non-modified zeolites.

A Concurrent Protonic-Electronic Conduction in Dealuminated HY Zeolite. M.B.Sayed: Journal of Physics and Chemistry of Solids, 1992, 53[8], 1041–8