Catalytic Performance of Pt Metal Particles at the Tips of Carbon Nanotubes
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Catalytic Performance of Pt Metal Particles at the Tips of Carbon Nanotubes S. Takenaka • T. Iguchi • E. Tanabe H. Matsune • M. Kishida
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Received: 9 February 2011 / Accepted: 24 March 2011 / Published online: 6 April 2011 Ó Springer Science+Business Media, LLC 2011
Abstract The catalytic performance of Pt metal at the tips of carbon nanotubes (CNT@Pt), which was prepared by ethylene decomposition over Pt/MgO, was compared with that of Pt metal on the outer surface of CNT (Pt/CNT). CNT@Pt showed excellent catalytic performance toward the hydrogenation of a, b-unsaturated aldehydes to unsaturated alcohols, which was similar to that of Pt/CNT and resulted from a strong interaction between Pt metal and the CNT. Keywords Pt metal particles Carbon nanotubes Ethylene decomposition Cinnamaldehyde hydrogenation
1 Introduction Multi-walled carbon nanotubes (CNTs) have unique physical and chemical properties that result from their specific structures. CNTs are expected to be applied to functional materials such as sensors, electronic devices and catalysts. In general, CNTs are used as supports in catalytic chemistry [1, 2]. Metal particles that are supported on CNTs show catalytic performances different from those supported on conventional supports such as silica and alumina. For example, Ru, Pd or Pt metal particles supported on a CNT surface was shown to S. Takenaka (&) T. Iguchi H. Matsune M. Kishida Department of Chemical Engineering, Graduate School of Engineering, Kyushu University, Moto-oka 744, Nishi-ku, Fukuoka 819-0395, Japan e-mail: [email protected] E. Tanabe Hiroshima Prefectural Technology Research Institute, 3-13-26 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-0046, Japan
catalyze the hydrogenation of a, b-unsaturated aldehydes to unsaturated alcohols with high selectivity while the selectivity toward unsaturated alcohols was low in the reactions that used conventional supports, such as, activated carbon and Al2O3 [3, 4]. Pt metal supported on CNTs as cathode catalysts in polymer electrolyte fuel cells was found to have higher activity for the oxygen reduction reaction than Pt metal supported on carbon black [5, 6]. However, to deposit metal nanoparticles onto CNT surfaces is challenging because the CNT surface is chemically inert. Therefore, CNT surfaces are frequently oxidized to form functional groups such as hydroxyl and carboxyl groups before the deposition of metal nanoparticles [1, 7, 8]. The functional groups on the CNTs can work as anchor sites for metal nanoparticles but the unique chemical properties of the CNTs may be lost by the introduction of functional groups to their surfaces. Therefore, a novel method to prepare composites of metal nanoparticles and CNTs is required. We have previously studied the formation of CNTs by hydrocarbon decomposition over supported metal catalysts such as Fe, Co, Ni and Pt [9–12]. The Pt metal nanoparticles that were supported on MgO (Pt/MgO) decomposed ethylene at 973 K to form CNTs with a uniform diameter. The CNTs that formed from Pt
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