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J. Phys. Chem. C 2007, 111, 3908-3913
Genesis of RuxSey Nanoparticles by Pyrolysis of Ru4Se2(CO)11: A Combined X-ray in Situ and DFT Study W. Vogel,† P. Kaghazchi,† T. Jacob,† and N. Alonso-Vante* Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin, Germany, and Lab. Electrocatalysis, UMR CNRS 6503, UniVersity of Poitiers, 40 AV. Recteur Pineau, F-86022 Poitiers Cedex, France ReceiVed: September 18, 2006; In Final Form: January 6, 2007
The cluster-like RuxSey (x ≈ 2, y ≈ 1) compound can be prepared by simple pyrolysis of the carbonyl complex Ru4Se2(CO)11 in inert gas. We have observed this process in situ using X-ray diffraction. The clusters exhibit a disordered hcp-type structure with an average size of 1.7 nm. Selenium is probably coordinated at the surface of ruthenium nanoparticles. Up to 430 °C, these nanoparticles are stable in an inert ambient, except for a certain growth in size. Above this temperature, the system splits into two phases: hcp-type ruthenium particles, which are probably free of Se, and a ruthenium-diselenide phase: RuSe2. Using density functional theory (DFT), we studied the surface structure of RuSe2 and found a preference for Se-rich surfaces. Transferring to the nanoparticles, this might correspond to the picture of a Ru core and either a RuxSey- or a pure Se shell (adsorbate layer).
Introduction The electrocatalytic activity toward the oxygen reduction reaction (ORR) in acid medium, as well as the selectivity in the presence of methanol, has been studied on ruthenium chalcogenide-like clusters.1-3 We have shown that the clusterlike compound RuxSey prepared from the precursor Ru3(CO)12 and addition of selenium in xylene or 1,2-dichlorobenzene has superior properties against pure Rux clusters with respect to its structural stability and its resistance to oxidation in the presence of oxygen in the gas phase.4 Albeit ruthenium and selenium are immiscible in the bulk phase but only form the single compound RuSe2; no separate Se-containing phase has been observed during the cluster formation, and the electronic state of Se in our RuxSey cluster compound is still an open question. Using the same chemical synthesis route, other authors prepared similar compounds with a consecutive sintering in selenium atmosphere.5 However, the descriptive stoichiometry is most probably the result of an incomplete reaction time of pyrolysis of the chemicals and makes the comprehension of the electrocatalysis versus materials science research difficult. A review summarizing the use of transition-metal carbonyl complexes as chemical precursors for tailoring catalyst materials for anodes and cathodes has been reported recently.6 In this work, to clarify the fate of the selenium during cluster formation, we have performed an in situ X-ray diffraction study, starting with the heteronuclear carbonyl complex Ru4Se2(CO)11 that forms during the RuxSey cluster preparation,7-9 by pyrolytical decomposition of this compound in an inert gas ambient. The intention of this study is to get more insight into the structure of the intermediates and mechanisms of their formation. Experimental Section Synthesis of Ru4Se2(CO)11 in 1,2-Dicholorobenzene. The synthesis of Ru4Se2(CO)11 occurs during the first 60 min of the * Corresponding author. E-mail:
[email protected]. University of Poitiers. Tel.: +3354945-3625; fax: +3354945-3580. † Fritz-Haber-Institut.
reaction of 0.15 mmol of Ru3(CO)12 (99% assay, Alfa Aesar) with 2.3 mmol of selenium (Alpha no. 36208,
