Alumina-supported bimetallics of palladium alloyed with germanium, tin, lead, or antimony from organometallic precursors: I. Preparation and characterization

Abstract

Bimetallic PdSn, PdSb, PdPb, and PdGe on alumina catalysts with a low metal content have been prepared using either chloride or Organometallic precursors. For the catalysts obtained from chloride precursors no interaction was observed between the two metals, and the catalysts behaved like pure Pd Al 2O 3 . In contrast, the reactions of (C 4H 9) 4Sn, (C 4H 9) 4Pb, (C 4H 9) 4Ge, or (C 4H 9) 3Sb in n-heptane solution with reduced Pd Al 2O 3 catalyst yielded a supported alloy. The interaction between metallic palladium and the organic modifier is highly selective and leads to the formation of a well-tailored bimetallic catalyst. When these final solids are reduced at 573 or 773 K, the second metal locates preferentially at the outer layer of the bimetallic aggregates. After reduction at 773 K large metallic aggregates are obtained (particle size ≅ 15 nm), and the formation of β-palladium hydride, which can be formed with pure palladium catalysts, is suppressed by the addition of a small amount of the second metal. The specific activity of the palladium surface atoms for isoprene hydrogenation is then lowered, and the selectivity increased.