Methanol oxidation on LaBO3 (B=Co, Mn, Fe) perovskite-type catalysts prepared by reactive grinding

Perovskite-type mixed oxides LaBO3 (with B = Co, Mn, Fe) with high specific surface area were prepared by reactive grinding. These catalysts were characterized by N2 adsorption, X-ray diffraction, H2 temperature-programmed reduction (TPR-H2), O2-, CH3OH- and CO2-temperature-programmed desorption (TPD). The catalytic performance of the samples for methanol oxidation was evaluated. The reaction rates were found to be strongly related to the amount of α-oxygen available and to the density of surface anion vacancies. A mechanism for total oxidation of methanol into CO2 was also proposed in which the amount of α-oxygen was an important parameter of the reaction rate. Indeed two kinds of reaction intermediates can be produced depending on the surface density of α-oxygen. Under an excess of α-oxygen the reaction intermediate was found to be a monodentate carbonate which decomposes into CO2. However, as soon as a lack of α-oxygen was observed in the structure, the dominant reaction intermediate was a bidentate carbonate which induces a consumption of anion vacancies in spite of the production of CO2. The differences observed between the three catalysts under study were discussed according to the observations of the characterization, the activity over methanol oxidation and the proposed mechanism.