Catalytic Oxidation of CO and H₂ Mixture over Cobalt-Containing Oxides

Abstract

Oxidation of CO/H₂ mixed gas on Co₃O₄ catalysts calcined at different temperatures and spinel oxide catalysts such as ZnCo₂O₄, CoAl₂O₄ and Fe₂CoO₄ was conducted to clarify the relation between the activity of CO/H₂ oxidation and surface cobalt species of the catalyst. The rate of the oxidation on Co₃O₄ was evaluated based on first order reaction with respect to the partial pressure of CO and H₂. The rate constant of the H₂ oxidation per surface area was identical regardless of the calcination temperature of Co₃O₄. On the other hand, the Co₃O₄c atalysts which were calcined at lower temperatures showed higher activities and selectivities for CO oxidation. Among the substituted spinel oxides containing cobalt, ZnCo₂O₄ showed the highest activity and selectivity for CO oxidation. CoAl₂O₄ and Fe₂CoO₄ showed lower activity for CO/H₂ oxidation compared with Co₃O₄. The XPS results showed that the predominant species on Co₃O₄ surface were divalent cobalt ion in tetrahedral coordination and trivalent ion in octahedral coordination. The predominant ones on ZnCo₂O₄, CoAl₂O₄ and Fe₂CoO₄ are trivalent ion in octahedral coordination, divalent ion in tetrahedral coordination and divalent ion in octahedral coordination, respectively. It was concluded that the main factor determining the activity and selectivity for CO oxidation in the presence of H₂ was the trivalent cobalt ion in octahedral coordination on the surface of the catalyst.