Cobalt nanoparticles encapsulated in carbon shells have been synthesized by catalytic chemical vapor deposition (CCVD) in high yield by reducing with a H 2 /CH 4 gas mixture a Mg 0.9 Co 0.1 O solid solution impregnated MgO (SSI-MgO) catalyst. The carbon-encapsulated Co nanoparticles have a narrow distribution of diameters within the range 5-15 nm. They are made of (fcc)-Co as shown by XRD and are very stable to air oxidation; the magnetic properties have been investigated using a SQUID magnetometer and confirm that Co is present in the metallic state.

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