The structure of carbon encapsulated NiFe nanoparticles

Carbon encapsulated NiFe nanoparticles (NiFe@C) have been prepared by high- temperature methane encapsulation of the bare bimetallic particles on alumi na. High-resolution transmission electron microscopy pictures show that abo ut 6-nm thick carbon layers encapsulate 10-20-nm diameter NiFe nanoparticle s. The NiFe nanoparticles are shown to be single-crystalline and no carbide is found at the NiFe-C interface. This is confirmed by the electron energy -loss spectroscopy (EELS) measurements that in addition show that both Ni a nd Fe have a zero (metal) valence and that only graphite is present. EELS a lso shows that the nickel-to-iron ratio is exactly unity for all particles studied. Metallic Pd nanoparticles with a diameter of 1-2 nm can be anchore d on the carbon layers, which creates a Pd/NiFeC&C type of catalyst that co uld be used for liquid phase reactions. The EELS analysis reveals that part of the nanoparticles present are not Pd but other oxidic carbon encapsulat ed nanoparticles. (C) 2001 Academic Press.