Uniform Co-B nanoparticles were synthesized for the first time by chemical reduction of cobalt ion with borohydride in all oil-in-water microemulsion system comprising cyclohexane, polyethylene glycol, and water. The particle size was controlled by modulating the cyclohexane content. With the characterization of X-ray diffraction, selective area electronic diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, the resulting Co-B nanoparticles were identified to be amorphous alloys ranging in size from 6 to 20 rim. During liquid-phase cinnamaldehyde hydrogenation, (lie as-synthesized Co-B catalyst was extremely active and more selective than the regular Co-B prepared ill aqueous Solution. Furthermore, this catalyst also was found to be more durable during the hydrogenation process. (c) 2008 Elsevier Inc. All rights reserved.