Fe/MgO Formulations for the Catalytic Combustion of Methane

Fe/MgO catalysts containing between 1.5 and 9 wt% iron were prepared by impregnation and calcined at 1073 K for 10 h. The solids were characterized by XRD and Raman and Mössbauer spectroscopies. They all showed that the solids are made up of MgFe2O4 spinel clusters and Fe3+ dispersed in the MgO matrix. The concentrations of MgFe2O4 and Fe3+ were calculated from the Mössbauer data. The former increases by a factor of 23 while the latter remains almost constant when the iron loading varies between 1.5 and 9 wt%. The catalytic activity correlates with the spinel weight fraction in the Fe/MgO system. Both the SEM micrographs and the EPMA analyses of the catalysts indicate that the solid surface is made up of exposed patches of MgFe2O4 and MgO. This surface feature explains the plateau observed when the reaction rate constant is plotted versus the iron loading.