Graphite Oxide as a Novel Host Material of Catalytically Active Pd Nanoparticles
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Graphite Oxide as a Novel Host Material of Catalytically Active Pd Nanoparticles ´ gnes Mastalir Æ Zolta´n Kira´ly Æ Ma´ria Benk} A oÆ Imre De´ka´ny
Received: 17 March 2008 / Accepted: 23 April 2008 / Published online: 17 May 2008 Ó Springer Science+Business Media, LLC 2008
Abstract Graphite oxide (GO) was utilized as a novel host material for Pd nanoparticles of controlled crystallite size. Immobilization of the Pd nanoparticles from a stable Pd sol in GO resulted in the formation of organophilic Pd– GO, a layer-structured material, which was characterized by ICP-AES, XRD and TEM. Pd–GO proved to be a highly active and stereoselective catalyst in liquid-phase alkyne hydrogenations under mild conditions. Keywords Graphite oxide Palladium Nanoparticle X-ray diffraction Transmission electron microscopy Alkyne hydrogenation Turnover frequency Selectivity
1 Introduction Graphite oxide (GO) is an oxygen-rich carbonaceous material, synthesized by the controlled oxidation of graphite [1–6]. It is a non-stoichiometric compound, in which the lamellar structure of graphite is preserved, but its polyaromatic character is lost, as related to the presence of oxygen-containing functional groups [1–8]. The carbon atoms in GO are arranged in a regular, periodic manner. There are strong covalent bonds within the hexagonal layers and weaker interlayer contacts, hydrogen bonds, between intercalated water molecules [9]. Several models have been suggested for the structure of GO, in which ´ . Mastalir (&) A Department of Organic Chemistry, University of Szeged, Do´m te´r 8, 6720 Szeged, Hungary e-mail: [email protected] Z. Kira´ly M. Benk}o I. De´ka´ny Department of Colloid Chemistry, University of Szeged, Aradi vt. 1, 6720 Szeged, Hungary
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oxygen atoms are bonded to the hexagonal layers of carbon atoms as epoxy linkages [2, 5, 8, 10, 11]. According to recent studies, GO consists of intact graphitic regions interspersed with sp3 hybridized carbons containing hydroxyl and epoxy groups and sp2 hybridized carbons with carboxyl and carbonyl goups at the sheet edges [12–14]. GO is a hydrophilic material, which may be dispersed in water to form stable colloidal suspensions via exfoliation [2, 10–12, 15]. Similarly to clay minerals, GO readily undergoes intracrystalline swelling and disaggregation and is therefore suitable for the preparation of thin films and polymer nanocomposites [7, 10, 16]. As related to its pronounced cation exchange capacity and intercalation ability, GO has been employed as a host material for the accomodation of long chain aliphatic hydrocarbons and polymers [13, 17, 18]. As related to its favourable properties, GO may also be regarded as a catalyst support material and a promising host for the intercalation of catalytically active transition and noble metal nanoparticles. The present study is concerned with the immobilization of monodispersed Pd nanoparticles in GO, to be tested as a catalyst in liquid-phase hydrogenation. The synthesis procedure is based on the generation of Pd parti
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