Kinetic and spectroscopic study of methane combustion over α-Mn2O3 nanocrystal catalysts

Abstract The kinetics of methane combustion was investigated on bulk and α -Mn 2 O 3 nanocrystal catalysts using a fixed bed microreactor. The kinetic behavior is profoundly affected by changes in the particle size of α -Mn 2 O 3 from 0.5 μm to ca. 50 nm. Real-time in situ Raman spectroscopy was used to probe the structure of both catalysts during the reaction. A reversible phase-transformation from α -Mn 2 O 3 to a Mn 3 O 4 -like species, as evidenced by the presence of a band at 648 cm −1 in He flow and at 660 cm −1 in methane combustion, was observed for α -Mn 2 O 3 nanocrystals only at or above 450 °C. This modification is probably due to the loss of lattice oxygen at high temperatures, leading to structural reconstruction. We infer from the study that the phase change of the α -Mn 2 O 3 nanocrystal catalyst might be responsible for the decrease of E a and the near zero-order dependence on oxygen partial pressure, and might be associated with the activation of the C H bonds in methane.