Niobia-supported palladium-manganese materials: Synthesis and structural investigation

Pd/niobia, Mn/mobia, and bimetallic Pd-Mn/niobia materials, which are catalysts for the total oxidation of ethanal, were prepared by anchoring molecular precursors, Pd(acaC)(2) and/or Mn(acaC)(2), on mobia before calcination at 400 degrees C and reduction by either soft chemical routes in liquid medium (Pd-based samples) or at 600 degrees C in H-2 (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 Xray 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 mobate MnNb2O6O6. 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 mobia. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).