Role of oxygen vacancies and Mn4+/Mn3+ ratio in oxidation and dry reforming over cobalt-manganese spinel oxides

Spinel type cobalt-manganese oxides MnxCo3-xO4 (x = 0; 0.05; 0.10; 0.15) were prepared by co-precipitation method, from cobalt and manganese salts in the presence of ammonium carbonate. X-ray diffraction (XRD), texture measurements (BET/BJH), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used for their characterization. Their catalytic behavior in ethanol combustion, dry reforming with CO2 and dehydrogenation was investigated. The results showed that the cubic structure of Co3O4, corresponding to spinel network, is not disturbed by adding manganese. Results obtained revealed that Mn0.15CO2.85O4 catalyst, with the highest content of Mn4+ cations in the octahedral sites and oxygen defects, display superior catalytic activity compared to the others. The apparent activation energies, calculated from Arrhenius plots, are as follows: E-a combustion < E-a non-oxidative dehydrogenation < E-a dry reforming, showing that cobalt-manganese spinel type oxides are good candidates for combustion.