Unsupported and MCM-41-supported Rh-doped FePO4 catalysts, which are effective for the oxidative carbonylation of methane directly to methyl acetate in the presence of CO and N2O, have been characterized by CO TPR in combination with XPS and FTIR spectroscopy of CO chemisorption. The CO TPR studies provide further evidence that the location of the Rh species is different in catalysts prepared by different methods. The CO TPR results and the correlation between the dispersion of the Rh species and the catalytic performance support the speculation that the dual sites containing RhIII and FeIII connected by phosphate groups are responsible for the conversion of methane to methyl acetate. The CO TPR studies also provide insight into the probable oxidation states of Rh and Fe during the catalytic reaction. We found that the RhIII and FeIII sites undergo simultaneous reductions during the reaction on the Rh−FePO4 sample prepared from a mixed aqueous solution and the MCM-41-supported Rh−FePO4 sample prepared by ...