Niobia-Supported Palladium-Manganese Materials: Synthesis and Structural Investigation
Résumé
Pd/niobia, Mn/niobia, and bimetallic Pd-Mn/niobia materials, which are catalysts for the total oxidation of ethanal,were prepared by anchoring molecular precursors, Pd(acac)2and/or Mn(acac)2, on niobia before calcination at 400 °C and reduction by either soft chemical routes in liquid medium (Pd-based samples) or at 600 °C in H2 (Mn/niobia sample). The structure of the obtained materials was investigated by FTIR spectroscopy of adsorbed CO, transmission electron microscopy, X-ray photoelectron spectroscopy, and extended X-ray absorption fine structure-X-ray absorption near edge spectroscopy. On Mn/niobia, Mn2+ is largely predominant, in spite of the high reduction temperature used for this sample, and it is mainly engaged in manganese niobate MnNb2O6. On Pd/niobia, nanoparticles of palladium metal (mean particle size 2.7 nm) are predominant, with a contribution of Pd2+. The surface structure of Pd-Mn/niobia is rather complex. Palladium is distributed between Pd3Mn nanoparticles and palladium clusters, and both are partially covered by oxygen atoms, whereas Mn2+ ions are engaged in MnO clusters linked to niobia.