Valence state of transition metal ions in Co1−Fe Cr2O4 (x= 0.1, 0.2, 0.5) ceramics from X-ray photoelectron and Mössbauer spectroscopy data

Synthesis and characterization of Co–Al–Fe nonstoichiometric spinel-type catalysts for catalytic CO oxidation

“…25 In the lattice of a normal spinel AB 2 O 4 A 2+ ions occupy the sites with tetrahedral oxygen environment while B 3+ ions have octahedral oxygen coordination. 26 Co 3 O 4 with a spinel structure containing Co 3+ in an octahedral coordination and Co 2+ in a tetrahedral coordination 12,27 is a very active oxide catalyst for the oxidation of CO. In such catalysts, octahedrally coordinated Co 3+ is considered to be the active site, while tetrahedrally coordinated Co 2+ is assumed to be basically inactive.…”