Origin of Active Oxygen in a Ternary CuO_<i>x</i>/Co₃O₄–CeO₂ Catalyst for CO Oxidation

We have studied CO oxidation over a ternary CuO_<i>x</i>/Co₃O₄–CeO₂ catalyst and employed the techniques of N₂ adsorption/desporption, XRD, TPR, TEM, <i>in situ</i> DRIFTS, and QMS (quadrupole mass spectrometry) to explore the origin of active oxygen. DRIFTS-QMS results with labeled ¹⁸O₂ indicate that the origin of active oxygens in CuO_<i>x</i>/Co₃O₄–CeO₂ obeys a model, called a queue mechanism. Namely gas-phase molecular oxygens are dissociated to atomic oxygens and then incorporated in oxygen vacancies located at the interface of Co₃O₄–CeO₂ to form active crystalline oxygens, and these active oxygens diffuse to the CO–Cu⁺ sites thanks to the oxygen vacancy concentration magnitude and react with the activated CO to form CO₂. This process, obeying a queue rule, provides active oxygens to form CO₂ from gas-phase O₂ via oxygen vacancies and crystalline oxygen at the interface of Co₃O₄–CeO₂