On the beneficial effect of MgO promoter on the performance of Co3O4/Al2O3 catalysts for combustion of dilute methane

The present work deals with the analysis of a series of cobalt catalysts (20 and 30%wt.Co) supported on alumina modified with MgO (7-18%wt.Mg with respect to the support) for the combustion of dilute methane. Both modified supports and the resulting cobalt catalysts were characterised by N-2 physisorption, wavelength dispersive X-ray fluorescence, X-ray diffraction, Raman spectroscopy and temperature-programmed reduction with hydrogen. A beneficial effect on catalytic activity was found with respect to the reference samples supported on blank alumina. As evidenced by the kinetic results in terms of specific reaction rate and apparent activation energy, this positive influence was related to a partial inhibition generation of less active CoAl2O4 due to MgO coverage of the support in favour of increasing the amount of easily reducible cobalt species, mainly in the form of Co3O4. The optimum magnesium loading was 12%wt. irrespective of the cobalt content, while the catalysts with 30%wt.Co were significantly more active than their counterparts with 20%wt.Co. Finally, a good catalytic stability with time on stream (150 h) was observed.