Catalytic activity of atomized Ni 3 Al powder for hydrogen generation by methane steam reforming Yan Ma, a,b, * Ya Xu, a Masahiko Demura, a Dong Hyun Chun, a,c Guoqiang Xie, d and Toshiyuki Hirano a,b a National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan b Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047, Japan c Department of Materials Science and Engineering, KAIST, Daejeon, 305-701, Korea d Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-Ku, Sendai, 980-8577, Japan Received 18 July 2006; accepted 19 September 2006 The catalytic activity of Ni 3 Al for methane steam reforming was investigated for the first time using its atomized powder. It was found that the activity was significantly enhanced by the combined pretreatment of acid and alkali leaching, while it was quite low for the as-received powder. The high activity was attributed to the formation of fine Ni particles on the porous surface of the powder. KEY WORDS: Ni 3 Al; atomized powder; catalytic activity; methane steam reforming. 1. Introduction Hydrogen is mostly produced from natural gas by steam reforming of methane. Methane reacts with steam over a catalyst in the temperature range of 973–1373 K to yield hydrogen, together with carbon dioxide and/or carbon monoxide [1,2]. Much effort has already been made to develop efficient and inexpensive heterogeneous catalysts. Nickel-based catalysts are typical catalysts for this reaction [3]. However, their performance is not satisfactory and more efficient catalysts are required [4]. In Ni–Al system there are four stable compounds, namely NiAl 3 , Ni 2 Al 3 , NiAl and Ni 3 Al. Among them, a mixture of NiAl 3 and Ni 2 Al 3 is used as a precursor alloy for Raney nickel catalysts [5,6]. Raney nickel catalysts are produced from this precursor alloy by selectively leaching aluminum in a concentrated NaOH solution. As a result, a porous, high surface-area nickel residue is formed on the surface, which contributes to its high catalytic activity. In contrast, NiAl and Ni 3 Al are not used as precursors. It has been thought to be difficult to effectively leach aluminum from them due to their low aluminum concentration, and thus a high catalytic activity has not been expected [7]. Both compounds are well known as excellent high-temperature structural materials with a high-temperature strength and good corrosion/oxidation resistance [8,9]. Recently, our group found that Ni 3 Al, both in the form of a powder and foil, exhibits a high catalytic activity for methanol decomposition, leading to hydro- gen generation (CH 3 OH fi 2H 2 + CO) [10–12]. These results suggest the possibility of a catalytic activity for steam reforming of methane in Ni 3 Al. In the present study, we examined the catalytic activity of Ni 3 Al for methane steam reforming using its atomized powder. The effects of chemical pretreatments on the catalytic activity of the powder were investigated. 2. Experimental A stoichiometric Ni 3 Al (Ni–25 at.% Al) powder was obtained from Kojunndo Chemical Lab. Co. Ltd., Japan. It was prepared by a gas atomizing process and sieved for less than 150 in. size. The as-received powder was chemically pretreated in the following four ways before the catalytic experiments as listed in table 1. Processes (a) and (b) are single-step treatments. Process (a) is a dip treatment at 366 K for 300 min in a stirred 20 wt% aqueous NaOH solution (alkali leaching), and process (b) is the one at 298 K for 15 min in 2 vol.% aqueous HNO 3 (acid leaching). Processes (c) and (d) are two-step treatments in combination with processes (a) and (b). Process (c) is the treatment using process (b) followed by process (a), and process (d) is that of the reverse order. After each step of the pretreatments, the solution was subjected to an inductively coupled plasma (ICP) analysis in order to measure the amounts of alu- minum and nickel leached from the powder. After rinsing in deionized water and dring at 323 K for 8 h, the surface area of the powder was determined by the Brunauer–Emmett–Teller (BET) surface area analysis method using krypton adsorption (Micromeritics, ASAP 2020). The surface morphologies of the powder *To whom correspondence should be addressed. E-mail: MA.Yan@nims.go.jp Catalysis Letters Vol. 112, Nos. 1–2, November 2006 (Ó 2006) 31 DOI: 10.1007/s10562-006-0160-5 1011-372X/06/1100–0031/0 Ó 2006 Springer Science+Business Media, Inc.