Catalytic performance of MnOx-NiO composite oxide in lean methane combustion at low temperature

A series of MnOx-NiO composite oxide catalysts were prepared by co-precipitation method and used in the catalytic combustion of lean methane at low temperature. Compared with the corresponding single NiO and MnOx oxides, the MnOx-NiO composite oxide with proper composition exhibits much higher catalytic performance in the lean methane oxidation. XRD and HRTEM results demonstrate that MnOx-NiO is in the form of a Ni-Mn-O solid solution. XAFS and XPS results indicate that the content of manganese in MnOx-NiO has a significant influence on the oxidation state of manganese and the crystal defect of nickel oxide. MnOx-NiO catalyst with an atomic Mn/(Mn + Ni) ratio of 0.13 is provided with abundant highly dispersed manganese species of higher valence (Mn4+) and higher coordination number as well as certain nickel vacancies, due to the strong interaction between Ni and Mn species. H-2-TPR and O-2-TPD results show that the MnOx-NiO composite oxide exhibits better reducibility and oxygen mobility than NiO. All these characterizations suggest a prominent synergism between NiO and MnOx in the MnOx-NiO composite oxide, which contributes to its high performance in the lean methane combustion. (C) 2012 Elsevier B.V. All rights reserved.