| Abstract
| - Unsupported and MCM-41-supported Rh-doped FePO4 catalysts, which are effective for the oxidativecarbonylation of methane directly to methyl acetate in the presence of CO and N2O, have been characterizedby CO TPR in combination with XPS and FTIR spectroscopy of CO chemisorption. The CO TPR studiesprovide further evidence that the location of the Rh species is different in catalysts prepared by differentmethods. The CO TPR results and the correlation between the dispersion of the Rh species and the catalyticperformance support the speculation that the dual sites containing RhIII and FeIII connected by phosphategroups are responsible for the conversion of methane to methyl acetate. The CO TPR studies also provideinsight into the probable oxidation states of Rh and Fe during the catalytic reaction. We found that the RhIIIand FeIII sites undergo simultaneous reductions during the reaction on the Rh−FePO4 sample prepared froma mixed aqueous solution and the MCM-41-supported Rh−FePO4 sample prepared by a co-impregnationmethod, which can catalyze the conversion of methane to methyl acetate efficiently. On the other hand, thesample over which only RhIII species alone is reduced to Rh0 can catalyze only the undesirable consumptionof N2O via the reduction by CO. FTIR studies of CO chemisorbed on the MCM-41-supported Rh−FePO4sample prepared by the co-impregnation method showed the formation of a RhI geminal dicarbonyl species,i.e., RhI(CO)2, at proper temperatures similar to those for the catalytic formation of methyl acetate. A reactionmechanism via the RhI(CO)2 intermediate with the FeII functioning for the activation of N2O to generate anactive oxygen species for methane conversion is proposed.
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