Catalytic performance of manganese cobalt oxides on methane combustion at low temperature

Manganese cobalt oxides with different Co/Mn ratios have been prepared by co-precipitation methods. and their catalytic performance on methane combustion were evaluated from 250 degrees C to 400 degrees C at a space velocity of 36,000 h(-1). A significant improvement of activity was observed over Co5Mn1 catalysts with a Co/Mn molar ratio of 5:1, and the catalytic activity reached 90% of methane conversion at 320 degrees C. Oxygen mobility - reflected by the appearance of O-2(-) - was probably a key factor that influenced the oxidation rate of methane below 320 degrees C. The doping of manganese into the spinel structure of cobalt oxide increased crystal defections, which probably caused the increase of the amount of octahedrally coordinated divalent cobalt cations that are responsible for catalytic activity. The hydroxyl groups observed on the manganese-doped catalysts would also explain the promotional effects. (C) 2009 Elsevier B.V. All rights reserved.