Mechanochemical activation of MoS₂—Surface properties and catalytic activities in hydrogenation and isomerization of alkenes and in H₂/D₂ exchange

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• 作者：Mykola Polyakov ; Sylvio Indris ; Stefanie Schwamborn ; Aliaksei Mazheika ; Martha Poisot ; Lorenz Kienle ; Wolfgang Bensch ; Martin Muhler ; Wolfgang Grü ; nert
• 关键词：Molybdenum sulfide ; Active sites ; Ball milling ; TEM ; Hydrogenation ; H₂/D₂ scrambling ; Double-bond isomerization
• 刊名：Journal of Catalysis
• 出版年：2008
• 出版时间：10 December 2008
• 年：2008
• 卷：260
• 期：2
• 页码：236-244
• 全文大小：1170 K

文摘

High-energy ball milling has been employed to convert a microcrystalline, stoichiometric (S/Mo = 2), catalytically completely inactive MoS₂ (prepared by high-temperature decomposition of ammonium tetrathiomolybdate, ATM) into an active catalyst, the activity profile of which was studied with test reactions (ethylene hydrogenation, H₂/D₂ scrambling, cis–trans isomerization of cis-but-2-ene, double-bond isomerization of 2-methyl-1-butene). Structural and surface properties of the materials were studied by XRD, SEM, TEM, XPS, nitrogen physisorption, oxygen chemisorption, and isotope exchange with D₂ (quantity of exchangeable surface hydrogen). The reaction rates obtained after mechanochemical activation were compared with data from a reference MoS₂ made by low-temperature decomposition of ATM. Ball-milled MoS₂ became active for most of the test reactions (except double-bond isomerization) only after reductive treatments that were effective also with the reference MoS₂. After identical treatments, the ball-milled MoS₂ was much more active in hydrogenation than the reference MoS₂, whereas H₂/D₂ scrambling proceeded more slowly, and cis–trans isomerization not at all. On the basis of earlier conclusions about the site selectivity of these reactions, the activity pattern indicates that mechanochemical activation led to a site structure dominated by sites with multiple vacancies whereas single-vacancy sites were not present at all, which is in agreement with TEM results showing highly defective bent nanoslab structures after ball milling. The results confirm that ethylene hydrogenation, H₂/D₂ scrambling and cis–trans isomerization of cis-but-2-ene may be employed as test reactions for sites on MoS₂ surfaces whereas data for the double-bond shift in 2-methyl-1-butene suggest that the Brønsted sites catalyzing this reaction are related to structural defects rather than to the regular MoS₂ structure.