Paramagnetic complexes of the probe molecules with electron accepting sites on the surface of M2O3-ZrO2: (M = Al,Ga)

The electron accepting and Lewis acid properties of dehydroxylated surfaces of M2O3-ZrO2 (M = Al, Ga) were investigated. The investigation was carried out by EPR with 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) and anthraqui none probe molecules. With the help of TEMPO two types of Lewis acid sites on the Al2O3-ZrO2 (Ga2O3-ZrO2) surface were defined: coordinatively unsatur ated aluminium cation Al-cus(3+) or gallium cation Ga-cus(3+) and coordinat ively unsaturated zirconium cation Zr-cus(4+). It was found out that electr on accepting sites which are able to ionize anthraquinone are presented on the zirconia and Al2O3-ZrO2 (Ga2O3-ZrO2) surfaces as well. In the case of A l2O3-ZrO2 obtained results can be explained with the presence of amorphous Al2O3 that covered microcrystals of metastable tetragonal zirconia. In the case of Ga2O3-ZrO2 surface Lewis acid properties are in accordance with the assumption of solid solution formation. (C) 1999 Elsevier Science B.V. All rights reserved.