Characterization of Ag and Ba-modified manganese oxide catalysts: unraveling the factors leading to their enhanced CH4 oxidation activity

Catalysts based on manganese oxide and modified with Ag (AgMn0.10) or Ba (B aMn0.10) were prepared and applied to CH4 deep oxidation. The catalysts wer e characterized by means of N-2-BET, XRD, XPS, CH4-TPR and O-2-TPD techniqu es. Catalytic evaluation results show that both AgMn0.10 and BaMn0.10 exhib it higher CH4 oxidation activity than the unmodified MnOx. However, compara tive studies on CO oxidation reveal that only AgMn0.10 displays markedly im proved activity for this reaction; the activity of BaMn0.10 remains unchang ed compared to unmodified MnOx. In AgMn0.10, a large amount of more mobile and reactive oxygen species is formed, which is thought to be the main reas on for its enhanced CH4 and CO oxidation activity. Whereas, in BaMn0.10, it is found that the mobility of the lattice oxygen is not increased, but som ewhat decreased, thus resulting in no enhanced CO oxidation activity on thi s catalyst. However, the basicity of the lattice O2- is thought to be incre ased via Ba addition, which is favorable for the activation and rupture of the first C-H bond in CH4, the rate-determining step for this reaction. Ind eed, this modification effect of Ba is believed to be the predominant facto r responsible for the enhanced CH4 oxidation activity of BaMn0.10.