A Novel Process for Preparation of Unsupported Mesoporous Intermetallic NiZn and PdZn Catalysts
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A Novel Process for Preparation of Unsupported Mesoporous Intermetallic NiZn and PdZn Catalysts Satoshi Kameoka Æ Tomofumi Kimura Æ An Pang Tsai
Received: 23 March 2009 / Accepted: 29 May 2009 / Published online: 13 June 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Unsupported mesoporous intermetallic (usmpIM) NiZn and PdZn catalysts are successfully prepared by means of a two-step procedure: (1) leaching of Al-based intermetallic compounds (Al3Ni, Al21Pd8) with 20 wt% NaOH aqueous solution and (2) immersion of ZnCl2 aqueous solution into unsupported porous Ni or Pd followed by alloying treatment under H2 flow at 500 °C, i.e., immersion alloying process. Thermal stability of the mesoporous structures is found to be improved by alloying with Zn. The catalytic properties for steam reforming of methanol (SRM) were completely different from the original unsupported porous Ni and Pd, where the decomposition of methanol and the SRM occurred preferentially on usmpIM NiZn and usmpIM PdZn, respectively. Keywords Mesoporous Intermetallic compound NiZn PdZn Immersion alloying Leaching Steam reforming of methanol
S. Kameoka (&) A. P. Tsai Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan e-mail: [email protected] T. Kimura Department of Materials Processing, Graduated School of Engineering, Tohoku University, 6-6 Aramaki Aza Aoba, Aoba-ku, Sendai 980-8579, Japan A. P. Tsai National Institute for Materials Science, 1-2-1 Sengen, Tsukuba 305-0047, Japan
1 Introduction Unsupported porous metals such as Raney-type catalysts are widely used as heterogeneous catalyst for liquid-phase and gas-phase reactions [1]. In general, these catalysts are produced by alkaline leaching of aluminum from Al-TM (TM = Ni, Cu, Co etc.) alloys, which consist of Al-based intermetallic compounds (IMCs: NiAl3, CuAl2 etc.) and pure Al [1]. The addition of a second component in metal catalysts is widely performed in order to improve activity, selectivity and stability of metal catalysts. To add small amounts of a second metal during the alloy preparation stage is known as the simplest process to modify catalytic properties for Raney-type catalysts. Although several metals have been used in laboratory studies, among them the most common metals used to promote Raney-type catalysts such as Raney Ni employed industrially are Co, Cr, Cu, Fe and Mo [1]. Binary alloy catalysts so-call bimetallic catalysts have been investigated from fundamental and/or practical viewpoints so far [2–4]. Bimetallic nanoparticles, composed of two metal elements, are of greater interest than monometallic ones. This is due to that alloying can either improve or create catalytic properties, which could not be achieved by monometallic catalysts. These effects owing to addition of metal component can often be explained in terms of an ensemble and/or a ligand effect in catalyses [2, 5]. For a good example, it has been shown recently that an intermetallic compound (IMC) ca
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