Synthesis, characterization and cyclohexene hydrogenation activity of high surface area molybdenum disulfide catalysts
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Catalysis Letters, Vol. 113, Nos. 3–4, February 2007 ( 2007) DOI: 10.1007/s10562-007-9030-z
Synthesis, characterization and cyclohexene hydrogenation activity of high surface area molybdenum disulfide catalysts M. Soto-Puente,a M. Del Valle,a Eric Flores-Aquino,b M. Avalos-Borja,b S. Fuentes,b and J. Cruz-Reyesa,* a Facultad de Ciencias Quı´micas e Ingenierı´a, Universidad Auto´noma de Baja California, Tijuana, BC, Mexico Centro de Ciencias de la Materia Condensada, Universidad Nacional Auto´noma de Me´xico, Ensenada, BC, Mexico
b
Received 5 November 2006; accepted 21 December 2006
An ammonium tetrathiomolybdate (ATTM) catalyst precursor is synthesized and then thermally decomposed at different temperatures in N2 or H2 atmosphere. Characterization of the resulting compounds by powder X-ray diffraction (XRD) and surface area analysis indicates the formation of MoS2–2H with a surface area of 5–9 m2/g. When ATTM is treated with cetyltrimethylammonium chloride and then decomposed in N2 at 723 K, the resulting material has a surface area nearing 200 m2/g. If treatment also includes hydrazine, the surface area of the resulting MoS2–2H reaches 215 m2/g. Analysis by XRD and electron microscopy shows a noticeable dispersion in the layers of the resulting MoS2. The catalytic activity of the materials is tested in a batch reactor for cyclohexene hydrogenation, where the highest activity sulfides are those obtained by thermal decomposition of the chemically treated precursors in N2. KEY WORDS: high surface area MoS2; hydrogenation; cyclohexene.
1. Introduction The field of solid state chemistry has produced numerous studies on the optical, electrical, electrochemical and catalytic properties of transition metal sulfides (TMS). In general, TMS with layered structures exhibit similar catalytic behavior in hydrotreating reactions [1]. While some preparation methods yield highly crystalline, low surface area compounds [2,3], others lead to materials with poor crystallinity and greater surface area, along with appreciable catalytic activity. Such methods include co-maceration [4], precipitation [5, 6], and thiosalt decomposition [7]. In the search for new catalysts, some in situ methods have been developed which yield high surface area sulfides. The introduction of alkyl ammonium thiometallate precursors, for example, has produced compounds with greater surface areas than earlier generations of sulfide catalysts [8,9]. The synthesis of MoS2 by a hydrothermal route also leads to the formation of a highly dispersed compound. Thus, the decomposition of ATTM in water under 20 bar N2 or H2S atmosphere has been studied at 15 min intervals for up to 4 h and at different temperatures in the region of 473–573 K, yielding catalysts with areas between 50 and 95 m2/g [10]. Increasing attention has been paid to the role of carbon in the stability of MoS2 and RuS2 catalysts, with some studies suggesting that the active phase of
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these compounds involves a high surface area MoS2
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