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

Abstract

Abstract Perovskite-type mixed oxides LaBO 3 (with B = Co, Mn, Fe) with high specific surface area were prepared by reactive grinding. These catalysts were characterized by N 2 adsorption, X-ray diffraction, H 2 temperature-programmed reduction (TPR-H 2 ), O 2 -, CH 3 OH- and CO 2 -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 CO 2 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 CO 2 . 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 CO 2 . 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.