Electron donor sites and acid-base properties of oxide surfaces, as studied by electron spin resonance spectroscopy

Abstract

The electron donor properties of several oxide powders (CaO, MgO, ZnO, Al₂O₃, SiO₂–Al₂O₃), activated in vacuo at temperatures up to 1200 K, have been investigated using the e.s.r. of adsorbed nitrobenzene radicals as a probe.

The results show the existence of a correlation between the electron donor activity of oxides and their Lewis base strength, indicating a direct connection between basic centres and donor surface states.

The variations of the A^N_| parameter of adsorbed nitrobenzene radicals with the nature of the surface are attributed to the extent of interaction of radicals with surface protons, and are therefore related to the Brønsted acidity of the surface. The dual nature of the active site is discussed.