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HASYLAB at DESY: Hasylab Jahresbericht 2004, 537-538 (2004).
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ABSTRACT: The intermetallic compounds PdGa and Pd3Ga7 are introduced as selective catalysts for the hydrogenation of acetylene. Single phase PdGa and Pd3Ga7 can readily be prepared by the appropriate thermal treatment of the stoichiometric mixtures of the corresponding elements. The initial low surface areas of the as-prepared materials can be increased by careful mechanical treatment without decomposition. Detailed investigations of PdGa and Pd3Ga7 by DSC/TG, in situ powder X-ray diffraction and in situ X-ray absorption spectroscopy during thermal treatment under various inert or reactive gas atmospheres showed a high thermal stability. The long-range and short-range order in the crystal structures remained intact up to temperatures of about 600 K. Neither phase transitions nor decomposition were detectable. In addition to high thermal stability—preserving the active-site isolation under reaction conditions—no incorporation of hydrogen or carbon in the intermetallic compounds under reducing conditions was observed. Besides being interesting model systems, palladium–gallium intermetallic compounds are promising candidates for the application as highly selective hydrogenation catalysts.
Journal of Catalysis.
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ABSTRACT: The structurally well-defined intermetallic compounds PdGa and Pd3Ga7 constitute suitable catalysts for the selective hydrogenation of acetylene. The surface properties of PdGa and Pd3Ga7 were characterized by X-ray photoelectron spectroscopy, ion scattering spectroscopy and CO chemisorption. Catalytic activity, selectivity and long-term stability of PdGa and Pd3Ga7 were investigated under different acetylene hydrogenation reaction conditions, in absence and in excess of ethylene, in temperature-programmed and isothermal long-term experiments. Chemical treatment with ammonia solution—performed to remove the gallium oxide layer introduced during the milling procedure from the surface of the intermetallic compounds—yielded a significant increase in activity. Compared to Pd/Al2O3 and Pd20Ag80 reference catalysts, PdGa and Pd3Ga7 exhibited a similar activity per surface area, but higher selectivity and stability. The superior catalytic properties are attributed to the isolation of active Pd sites in the crystallographic structure of PdGa and Pd3Ga7 according to the active-site isolation concept.
Journal of Catalysis.
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Hasylab Jahresbericht 2003, Annual Report, 443-444 (2003).
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