Abstract :
The electronic structures of vanadium carbides have been examined using X-ray photoelectron spectroscopy XPS.
before and after Ar sputtering. After Ar ion sputtering for 1 h, there was no significant variation observed in both the surface
electronic structure and the amounts of core levels of V 2p, C 1s, and O 1s for vanadium carbides used in the present study.
A species with a binding energy of 513.2"0.2 eV from vanadium carbides was newly observed, and was estimated to be
V1.3q using the plot of the V 2p3r2 binding energies against the oxidation number. This value indicates that the absolute
magnitude of charge transfer from V 3d states to C 2p states is 1.3 electrons per vanadium in vanadium carbides. Among the
deconvoluted three carbon peaks, the carbidic carbon peak appeared at 282.4"0.2 eV and was considered to be due to the
photoelectrons ejected from the carbon in vanadium carbide lattice. For all of 1-h sputtered vanadium carbides except for
V8C7-4, the average ratio of CcrVdq was nearly unity. Using NH3 decomposition reaction, the catalytic activity
measurements exhibited that the vanadium carbide with the smallest CcrVdq ratio had the highest activity. These results
indicate that the most active catalyst was carbon-deficient at surface of the vanadium carbide used in this study. q1999
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