FULL PAPER DOI: 10.1002/ejic.200701018 Niobia-Supported Palladium–Manganese Materials: Synthesis and Structural Investigation Roberta Brayner, [a] Françoise Villain, [b] Leon Gengembre, [c] Souad Ammar, [a] and François Bozon-Verduraz* [a] Keywords: Palladium / Manganese / Niobia / XAS / CO adsorption Pd/niobia, Mn/niobia, and bimetallic Pd–Mn/niobia materi- als, which are catalysts for the total oxidation of ethanal, were prepared by anchoring molecular precursors, Pd(acac) 2 and/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 H 2 (Mn/niobia sample). The structure of the obtained materials was investigated by FTIR spectroscopy of adsorbed CO, transmission electron mi- croscopy, X-ray photoelectron spectroscopy, and extended X- ray absorption fine structure–X-ray absorption near edge spectroscopy. On Mn/niobia, Mn 2+ is largely predominant, in Introduction Manganese-containing materials have wide applications in metallurgy, dry-cell batteries, and magnetic devices. Ap- plications in the field of catalysis are not numerous, but they are now growing. Restricting to monometallic-sup- ported MnO x , surface characterization [1,2] as well as the in- teraction of NH 3 and NO x [3] have been studied on alumina- supported MnO x , whereas selective catalytic reduction of NO x has been investigated on carbon-supported MnO x [4] and dehydrogenation of 1-butene into 1,3-butadiene ex- plored on MnO 2 /zirconia. [5] The nature of the manganese species in these materials is strongly influenced by the prep- aration methods and the thermal treatments; hence several oxidation states may coexist. In palladium–manganese catalysts, the “bimetallic” des- ignation may be confusing, as manganese is often present in the +2 or +3 oxidation state and palladium either as Pd 0 or Pd 2+ . The synergistic effect of Pd and Mn 2 O 3 has been reported with regard to the oxidation of CO and CH 4 , [6] whereas the activity of alumina-supported PdO x MnO y cat- alysts in formaldehyde/methanol combustion has been re- ported. [7] Renouprez et al. have performed a detailed study [a] ITODYS, UMR-CNRS 7086, Université Paris Diderot, 75251 Paris, France [b] LCI2M, UMR-CNRS 7071, Université Pierre et Marie Curie, 75252 Paris, France [c] UCCS, UMR-CNRS 8181, Université des Sciences et Technol- ogies de Lille, 59655 Lille, France Supporting information for this article is available on the WWW under http://www.eurjic.org or from the author. Eur. J. Inorg. Chem. 2008, 1623–1631 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 1623 spite of the high reduction temperature used for this sample, and it is mainly engaged in manganese niobate MnNb 2 O 6 . On Pd/niobia, nanoparticles of palladium metal (mean par- ticle size 2.7 nm) are predominant, with a contribution of Pd 2+ . The surface structure of Pd–Mn/niobia is rather com- plex. Palladium is distributed between Pd 3 Mn nanoparticles and palladium clusters, and both are partially covered by oxygen atoms, whereas Mn 2+ ions are engaged in MnO clus- ters linked to niobia. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) of Pd–Mn silica-supported catalysts prepared from Pd and Mn acetylacetonate impregnation by using thermal meth- ods, extended X-ray absorption fine structure (EXAFS), X- ray diffraction, transmission electron microscopy (TEM), infrared (IR) spectroscopy of adsorbed CO and NO, with density functional theory calculations. [8,9] They showed that manganese is mostly present as a thin oxide layer spread on the silica surface, whereas the remaining part is incorpo- rated in Pd–Mn alloy particles surface-enriched in Mn. Niobium oxide, a wide gap n-type semiconductor, [10] has received growing attention in the field of catalysis as both an active phase and a support. [11,12] It is considered by Uch- ijima as a typical SMSI (strong metal–support interaction) oxide, [13] and SMSI effects have been reported on palla- dium/niobia after reduction at 773 K [14] and on Co/niobia model catalysts. [15] Palladium/niobia and palladium/niobia– alumina catalysts have been studied in methane, [16] pro- pane, [17] and toluene [18] combustion, ethylene hydrofor- mylation, [14] and hexa-1,5-diene hydrogenation. [19] Among bimetallic palladium systems supported on niobia, Pd–Co [20] and Pd–Cu [21] catalysts have been characterized. Abatement of ethanal, an undesired compound emitted, among others, by automobile exhaust of vehicles using ethanol as a fuel has been recently investigated on niobia-supported Pd, Pd- Cu, and Pd-Au. [22] Monometallic Pd catalysts presented a severe deactivation (conversion drop of 80% within 50 min), whereas addition of Au or Cu limited the deactiva- tion to 50%. The present study is devoted to niobia-sup- ported Pd–Mn catalysts that, to the best of our knowledge, have not yet been studied. Our investigations focus on