DONOR-ACCEPTOR PROPERTIES OF ALUMINUM-OXIDE SURFACE-MODIFIED BY SODIUM AND CALCIUM CATIONS

Electron-acceptor properties of gamma-Al2O3 modified by sodium and cal cium cations are studied by the ESR method using 2,2,6,6-tetramethylpi peridine-1-oxyl (TEMPO) and anthraquinone as molecular probes and by I R spectroscopy using adsorbed carbon monoxide. It is shown that this t reatment of gamma-Al2O3 results in a decrease in the total and local c oncentrations of Lewis acid sites (LASs), which are three-coordinated aluminum ions, and the strongest LAS disappear first. It is found that , when the concentration of Ca2+ ions increases, new LASs appear, whic h are suggested to be coordinatively unsaturated calcium ions. Enhance ment of the electron-acceptor ability of the gamma-Al2O3 surface due t o the modification by sodium and calcium ions is established by measur ing the concentration of anthraquinone radical anions formed by the re action of anthraquinone with electron-donor surface sites.