EPR study of the mobility of paramagnetic species on the surface and in the bulk of solids

The temperature dependence of EPR spectra provides information on the mobility of paramagnetic species at the gas (liquid)/solid interface and in the bulk of solids. Changes in the environment of molecules on solid surfaces caused by their motion occurring upon thermal treatment at various temperatures are observed. Superoxide radical can migrate from Co(III) to Mg(II) surface sites of the CoO-MgO solid solutions. In aqueous solutions transition metal ions coordinate water molecules, forming aquacomplexes which are usually free to tumble within the liquid medium. Their mobility is, however, strongly modified in the vicinity of the solid surface or inside the narrow pores. In solids the migration of paramagnetic species from the surface into the bulk is controlled by the temperature of thermal treatment. In the case of V2O5-ZrO2 catalyst this process is strongly influenced by the phase transitions occurring in the solid matrix and by the presence of alkali metals. (C) 1998 Elsevier Science S.A. All rights reserved.