The structure of carbon encapsulated NiFe nanoparticles

Abstract

Carbon encapsulated NiFe nanoparticles (NiFe@C) have been prepared by high-temperature methane encapsulation of the bare bimetallic particles on alumina. High-resolution transmission electron microscopy pictures show that about 6-nm thick carbon layers encapsulate 10-20-nm diameter NiFe nanoparticles. 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 and Fe have a zero (metal) valence and that only graphite is present. EELS also 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 anchored on the carbon layers, which creates a Pd/NiFeC&C type of catalyst that could be used for liquid phase reactions. The EELS analysis reveals that part of the nanoparticles present are not Pd but other oxidic carbon encapsulated nanoparticles. (C) 2001 Academic Press.