Catalytic activity of rare earth oxides in flameless methane combustion

The following rare earth oxides, which were prepared by the precipitation of hydroxides, were studied as catalysts for the reaction of complete methane oxidation: CeO₂, a hydrated phase of La₂O₃, Pr₆O₁₁, Tb₄O₇, and Gd₂O₃. The catalytic activities of the oxides were compared in terms of first-order reaction rate constants per unit surface area of the catalyst. With consideration for data on the reduction of CeO₂, Pr₆O₁₁, and Tb₄O₇, the previously proposed redox reaction mechanism on transition metal oxides was supported. The high activity of hydrated La₂O₃ was found, and it was hypothesized that, in this case, the process occurred by the mechanism of oxidative methane condensation followed by the rapid oxidation of the resulting intermediate products.