Journal of Catalysis 221 (2003) 378–385 www.elsevier.com/locate/jcat Characterizations and catalytic properties of fine particles of Ni–Sn intermetallic compounds supported on SiO 2 Ayumu Onda, ∗ Takayuki Komatsu, and Tatsuaki Yashima Department of Chemistry, Tokyo Institute ofTechnology, 2-12-1 Ookayama, Meguro-ku, Tokyo, Japan Received 11 June 2003; revised 19 August 2003; accepted 20 August 2003 Abstract Fine particles of Ni–Sn intermetallic compounds (IMCs) of Ni 3 Sn, Ni 3 Sn 2 , and Ni 3 Sn 4 with specific crystal structures were selectively prepared on SiO 2 by chemical vapor deposition (CVD) of Sn(CH 3 ) 4 onto Ni/SiO 2 . X-ray photoelectron spectroscopy (XPS) and temperature- programmed reduction (TPR) measurements indicated that the near surface of these fine particles with atomic Ni/Sn ratios of 3/1, 3/2, and 3/4 are similar to those of corresponding unsupported Ni–Sn IMCs. X-ray diffraction (XRD) patterns of the fine particles showed peaks too broad to determine these crystal structures. Each unsupported Ni–Sn IMC was clarified to exhibit a specific Ni K-edge and Sn K-edge X-ray absorption near-edge structure (XANES) spectrum. The crystal structures of fine particles were by the identified by the fingerprinting method by Ni K-edge and Sn K-edge XANES spectra. Both these XANES spectra of Ni–Sn IMC/SiO 2 catalysts with Ni/Sn atomic ratios of 3/1, 3/2, and 3/4 were similar to those of unsupported Ni 3 Sn, Ni 3 Sn 2 , and Ni 3 Sn 4 , respectively. The particles would have an average diameter of 3–4 nm obtained by TEM. Each Ni–Sn IMC particle showed intrinsic properties for the adsorption of carbon monoxide and hydrogen. The fine-particle catalysts exhibited high benzene selectivity (> 99% C) at high conversion for cyclohexane dehydrogenation. The selectivity was almost the same as that of the Ni–Sn IMC/SiO 2 catalysts with large particle sizes (about 15 nm), whose crystal structures were clearly determined by XRD, but was completely different from that of the Ni/SiO 2 catalyst. The activities of fine-particle catalysts were about 15 times higher than those of the large-particle catalysts.  2003 Elsevier Inc. All rights reserved. Keywords: Ni–Sn; Intermetallic compounds; Fine particles; Absorptions of CO and H 2 ; Cyclohexane dehydrogenation 1. Introduction Two kinds of metals in intermetallic compounds (IMCs) interact strongly with each other. This interaction includes a small contribution of a covalent bond. IMCs are expected to have unique catalytic properties because the surface atoms of IMCs have different electronic and geometric structures from those of pure metals. However, the catalytic proper- ties of IMC itself have not been clarified satisfactorily. Most of the investigations on catalysis by IMC have dealt with so-called hydrogen-storage alloys [1–4] because of their unique activity for hydrogen dissociation and the possibil- ity for the stored hydrogen to participate in the reactions. On the other hand, we have already reported unique cata- lytic selectivities of Co–Ge [5], Pt–Ge [6], and Ni–Sn [7] * Corresponding author: Research Laboratory of Hydrothermal Chem- istry, Faculty of Science, Kochi University, Akebono-cho 2-5-1, Kochi 780- 8520, Japan. E-mail address: onda@cc.kochi-u.ac.jp (A. Onda). IMCs, which are not hydrogen-storage alloys. The surface of these compounds is composed of metallic atoms after re- duction treatment. The IMC catalysts containing Co or Ni show much lower activity than pure Co or Ni for H 2 –D 2 equilibration but give high selectivity to ethylene in the hy- drogenation of acetylene. Pt–Ge IMCs show high selectivity to butene in the hydrogenation of 1,3-butadiene. Pd 3 Pb cata- lysts show high selectivity to methyl methacrylate for the oxidative esterification of methacrolein and methanol [8]. These IMC catalysts show lower activities than their com- ponent monometallic catalysts, such as pure Pt catalyst. In contrast, Pt 3 Ti catalysts show higher activity than those of pure Pt catalysts for H 2 –D 2 equilibration and ethylene hy- drogenation [9]. However, the activities of the above-noted IMC catalysts, except for Pd 3 Pb, suffer from low specific surface areas because they are prepared by melting the mix- ture of two component metals at higher temperatures than their melting points and crushing the ingots of IMC. The di- ameters of these unsupported IMC powder are about 30 μm. 0021-9517/$ – see front matter  2003 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2003.08.012