The reduction of [PdCl4]2- by hydrazine in the postmicellar region of even-numbered alkyltrimethylammonium bromides C n TABr (with n = 8 to 16) yielded fairly monodisperse Pd particles with mean diameters in the range 1.6−6.8 nm. Transmission electron microscopy (TEM) measurements indicated that the particle size decreases with increasing length of the alkyl chain, decreasing precursor concentration, and decreasing surfactant concentration. Kinetic measurements demonstrated that the nucleation is a fast process and well separated from the growth. TEM and high-resolution TEM micrographs of the particles suggested that the dominant morphology is cubooctahedral. Composition analysis (1H NMR, total organic carbon, and inductively coupled plasma atomic emission spectroscopy), titration microcalorimetry, and spectroscopic methods (IR, Raman, and UV−vis) revealed that [PdCl4]2- is not the real precursor species in the reduction process. In the presence of a large excess of Br-, [PdCl4]2- transforms to [PdBr4]2-. The ligand-exchange reaction is accompanied by the formation of stoichiometric complex−surfactant aggregates [C n TA]2[PdBr4], and followed by a slow, higher-order aggregation to microcrystals. The organic salt precipitates below the critical micelle concentration but undergoes solubilization above it, leading to the formation of palladate−surfactant metallomicelles. In the postmicellar region, the close proximity of the surfactant molecules to the reduction centers ensures rapid adsorption of the amphiphiles on the surface of the nascent particles, and a protective bilayer is formed, ultimately leading to long-term stability of the Pd hydrosols.

A viable colloid chemical preparation technique provided a series of low-loaded palladium-montmorillonite catalysts with cubooctahedral Pd particles ranging in size from 1.5 to 6.2 nm in mean diameter. These catalysts were used to test the structure sensitivity of the liquid-phase hydrogenation of styrene to ethylbenzene under mild conditions. An experimental correlation was sought between the specific rate of hydrogenation and the dispersion of the metal. The fractions of high-coordination terrace sites (face atoms) and low-coordination defect sites (edge and corner atoms) were calculated as a function of the crystallite size. The good correlation between the turnover frequencies and the defect site densities suggested that hydrogenation occurs on these defect sites and that terrace sites have only minimal catalytic activity or are inactive.

Finely divided Pd particles (2-3 nm in diameter) were synthesized by the reduction of Pd 2+ precursor ions in the presence of cationic (myristyltrimethylammonium bromide, MTA + Br -) or anionic (sodium dodecyl sulfate, Na + DS -) surfactants. The protective adsorption layer of the ionic surfactants around the particles ensured the long-term stability of the aqueous dispersions. When the palladium hydrosol stabilized with MTA + Brwas mixed with an aqueous suspension of sodium montmorillonite, Na + MM -(a cationic clay), the cation-exchange reaction between Na + and MTA + rendered the montmorillonite surface hydrophobic, in parallel with the incorporation of the released Pd particles into the MTA + MMorganoclay host. In a similar way, after addition of the palladium hydrosol stabilized with Na + DSto an aqueous suspension of hydrotalcite nitrate, HT + NO3 -(an anionic clay), the ion exchange between NO3and DSresulted in the formation of a hydrophobic clay, HT + DS -, with simultaneous deposition of the released Pd particles onto the clay lamellae. The low-loaded, highly dispersed Pd-organoclay materials displayed extremely high catalytic activities under mild conditions in the liquid-phase hydrogenations of styrene, hex-1-ene, and cyclohexene. Furthermore, the catalysts exhibited high selectivities for the partial hydrogenation of 1-phenyl-1-pentyne to 1-phenyl-cis-1-pentene. These high activities and selectivities were explained in terms of the high degree of dispersion of the Pd particles and the hydrophobic nature of the catalysts.

Palladium, platinum and PdPt bimetallic colloidal particles were prepared in atomic ratios of 4:1, 1:1 and 1:4 by the reduction of K 2 PdCl 4 and/or K 2 PtCl 4 in the presence of cationic surfactant, tetradecyltrimethylammonium bromide (C 14 TABr). The nanoparticles in the "as prepared" state were characterized by TEM, EDS and XPS, UPS, permitting to determine their mean particle size, bulk and surface composition. The bulk composition of the bimetallic samples determined by EDS was close to their nominal value, while XPS indicated Pt enrichment near to the surface. All samples in the "as received" state contained surface oxide impurity and contained carbon impurities. The monometallic samples contained considerably more C as the bimetallic ones. A quasi-in situ H 2 treatment at 473 K in the electron spectrometer resulted in cleaner metals, containing less carbon and oxygen, as shown by XPS and UPS.