Catalytic combustion of methane over transition metal oxides.

Simple and mixed metal oxides containing Co, Mn, Cr and Fe have been investigated as catalysts for the combustion of methane in the temperature range 300-600 degrees C under diluted conditions. The effect of the catalyst composition on the catalytic performances and on the redox properties has been evaluated. Single metal oxides containing Cr, Co and Mn show comparable activities and were found more active than Fe2O3. Mixing of Co with Cr oxide and Fe oxide with Mg and Zn to give spinels, improves the catalytic activity with respect to pure compounds. Temperature programmed reduction (TPR) shows that redox properties are strongly dependent on the catalyst composition. Fe based mixed oxides are more hardly reducible than the other catalysts, this effect being related to the dilution of Fe with bivalent cations. The comparison of the kinetic parameters, evaluated on the base of a first order rate equation, gave evidence of a correlation between the activation energy values and the ease of the reduction showing that the oxides reducible at lower temperature give rise to a reaction mechanism with a lower activation energy.