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

Abstract

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. H2-TPR and O2-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.