Electron accepting properties of ZrO₂ based catalysts studied by EPR of paramagnetic complexes of probe molecules

Abstract

Zirconia is of great interest as a catalyst and support. The tetragonal and cubic modifications are most important for these purposes because of significant specific surface area. Surface properties of these modifications are defined by the presence of Lewis acid sites — coordinatively unsaturated zirconium (IV) ions. These modifications are metastable at ambient conditions, and the use of dopants (metal cations of II or III groups) is necessary. The most known dopants are yttrium and cerium oxides [1-3]. Other metals of III group (Al, Ga) are also studied as possible stabilizers of the tetragonal zirconia [4-6]. The change of the dopant content causes the changes in the nature and concentration of the Lewis acid sites on the surface [7]. In order to improve catalytic properties of zirconia-based catalysts the complex systems (containing more than two components) are studied. Nevertheless there are few data on the surface properties of these systems, especially on the Lewis acidity, which is very important for predicting the adsorption and catalytic properties.