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The nature of the oxygen species adsorbed on slightly reduced CeO2/SiO2 supported catalysts has been investigated using oxygen enriched with 17O2. The observed hyperfine splitting was found to be associated with the central component of the g tensor; it indicated that the corresponding orbital contained the unpaired electron and therefore the central component was defined as gxx. With this assumption, the e.s.r. spectra are consistent with the adsorption of oxygen as O–2 at 77 K with gyy= 2.0109, gxx= 2.0158 and gzz= 2.028 with a hyperfine splitting (Axx) of 75 G about gxx. The O–2 is adsorbed with the internuclear axis along the surface of the catalyst at a site corresponding to a cerium ion. There is some indication that interaction with the metal ion orbitals is perturbing the energy levels of the adsorbed O–2 ion.
Che et al. (1973) studied this question.