Synthesis and study of palladium colloids and related catalysts

Colloidal palladium particles were prepared by reduction with hydrogen of H 2PdCl4 in a mixture of H2O, trioctylamine (TOA), and cyclohexane. According to N-14 NMR, Cl-35 NMR and EXAFS data, the reduction of Pd was found to pr oceed under an auto-catalyzed regime via (HTOA)(2) [PdCl4] complex formatio n. After complete reduction of Pd(II) (1 mol H-2 consumed per 1 Pd atom), H -2 consumption abruptly changed to 0.7 H-2 mol per 1 Pd atom. Unusually lar ge amounts of H-2 adsorbed per Pd-atom could be due to the formation of pal ladium hydride by highly dispersed and defected Pd particles. TEM shows tha t Pd particles in catalysts obtained by metal particles deposition on carbo n material Sibunit look like "hedgehogs" with needles 100 Angstrom long and 20-40 Angstrom in diameter. (C) 2000 Elsevier Science B.V. All rights rese rved.