Catalytic activity of neodymium substituted zinc ferrites for oxidative conversion of methane

The catalytic behavior for oxidative conversion of methane in large oxygen excess (methane combustion) and in reducing conditions (oxidative Coupling of methane) was comparatively investigated for the first time over pure and neodymium substituted zinc ferrites prepared by combustion method. The catalytic activity proved to be strongly related to the oxide structure, to the specific defects created by substitution as well as to the composition of the reaction Mixture. The neodymium substituted ferrites (ZnFe1.75Nd0.25O4, ZnFe1.5Nd0.5O4 and ZnFeNdO4) exhibited high activity for methane combustion but low activity for coupling reaction. On the other hand, the pure zinc ferrite (ZnFe2O4) and ZnNd2O4 were active to catalyze methane coupling whereas the activity for methane combustion was low. The catalytic activity of the oxides and the reaction mechanism on simple and mixed oxides is discussed in light of the experimental results. (C) 2008 Elsevier B.V. All rights reserved.