AN EPR STUDY ON THE FORMATION OF THE SUPEROXIDE RADICAL ION ON MONOCLINIC ZIRCONIA

Zirconium oxide is capable of forming and stabilizing the superoxide radical ion O2- at its surface according to various routes. These include both an electron transfer from the solid to molecular oxygen and the capture of superoxide ions formed along a different surface process like the catalytic disproportionation of hydrogen peroxide. The EPR spectrum is characterized by an anisotropic g tensor with g(zz) = 2.0336, g(yy) = 2.0096 and g(xx) = 2.0034. A less abundant species is sometimes observed with g(zz) = 2.0255. The superoxide formation from molecular oxygen is favored by partial rehydration of the surface.