THF solutions of the new organometallic precursor Co(η 3 -C 8 H 13 )(η 4 -C 8 H 12 ) react with 3 bar dihydrogen in the presence of polyvinylpyrrolidone (PVP) at three different temperatures, namely, 0, 20, and 60 °C to give colloidal solutions containing fcc cobalt particles of respectively e1 nm (Coll. 1) and ca. 1.5 nm (Coll. 2 and Coll. 3) mean sizes, as evidenced by HREM analysis. All colloids react with carbon monoxide to give new colloids (Coll. 1′-3′) displaying broad CO stretches near 2000 and 1890 cm -1 on their infrared spectra recorded in KBr disks. The magnetic behavior of the colloids was studied by SQUID techniques. Coll. 1-3 display a typical superparamagnetic behavior with blocking temperatures in the range 9-10 K. From magnetization studies above and below the blocking temperature, it was possible to determine that Coll. 3 shows a mean size of 1.6 nm and a very narrow size distribution. Because of a magnetic surface effect, the magnetic moment per atom (µ Co ) 1.94 ( 0.04 µ B ) appears significantly larger than the value admitted for bulk cobalt. In contrast, Coll. 2′ shows a weak magnetization and disappearance of the blocking temperature as a result of CO coordination.

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A Ni 0 (15 wt %)/Al 2 O 3 catalyst is prepared by impregnation using [Ni(en) 2 (H 2 O) 2 ](NO 3 ) 2 as precursor salt containing the chelating ligand ethylenediamine (en). Due to the low solubility of this salt and the high viscosity of its solution, large crystals of the salt deposit on the support, clogging the porosity of alumina. These crystals split during the thermal treatment in argon; hydrogen produced in situ from organic residues reduces quantitatively nickel (II) to monodisperse small Ni 0 particles, compared with only one half of nickel reduced by hydrogen when catalysts are prepared from [Ni(H 2 O) 6 ](NO 3 ) 2 . To cite this article:

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