Palladium–gallium intermetallic compounds for the selective hydrogenation of acetylenePart I: Preparation and structural investigation under reaction conditions

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.