CATALYTIC-OXIDATION OF CO AND H-2 MIXTURE OVER COBALT-CONTAINING OXIDES

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 Co3 O4. On the other hand, the Co3O4 catalysts which were calcined at lower temperatures showed higher activities and selectivities for CO oxidation. Among the substituted spinel oxides containing cobalt, ZnCo2 O4 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.