Etching of the intermetallic compounds PdGa and Pd3Ga7: An effective way to increase catalytic activity?

The structurally ordered intermetallic compounds PdGa and Pd3Ga7 constitute highly selective catalysts for the selective semi-hydrogenation of acetylene. The milling of as-synthesized samples, followed by etching with ammonia solution increased the activity of the catalysts by factor of 60. Chemically etched samples possess high activity and simultaneously keep their high selectivity. Chemical analysis confirms that the etching procedure is mostly specific to gallium species, thus less affecting the palladium. Detailed investigations reveal the influence of the chemical etching on the morphology and surface of the particles. As a result of the etching, nano-caverns are formed (SEM and BET), and the surface is enriched in palladium (XPS and EDX), while the bulk crystal structure is not affected (XRD). The mechanism and applicability of the etching procedure is discussed in view of the active-site isolation concept.