| Auger electron spectroscopy (AES), electron energy loss spectroscopy (ELS) and photoelectron spectroscopy (PES) employing both ultraviolet (UPS) and X-ray (XPS) excitation were used to study for the first time the electronic structure of a nitrided FeTi sample. The nitrided compound had been shown to have a lower activation energy for the synthesis of ammonia. We have provided further evidence for the dissociation of the FeTi lattice upon nitridation to form iron and titanium nitride (Fe/TiN). Additionally, no noticeable amount of charge transfer between the iron and the titanium nitride was observed, indicating that the enhanced activity of Fe/TiN is not due to an electronic effect. Future work should center on the geometric aspects of this catalyst. The above conclusions are based on the correlation of the data on Fe/TiN with the presented AES, PES and ELS work involving the interactions of iron and titanium foils with H(,2), O(,2), N(,2) and NH(,3) gases. Initial adsorption of O(,2) on iron causes oxidation to the 2+ valent state with further exposure causing the formation of Fe('3+). Bombardment of Fe by N(,2)('+) forms a surface iron nitride phase very similar to that produced by the adsorption of N(,2) or NH(,3). The He I UPS spectra of H(,2), O(,2) and N(,2) adsorbed on Ti with bonding levels formed approximately 5 eV below the Fermi level confirm previously published results. The N 2p-Ti 3d bonding level for N(,2)('+) bombarded Ti was shown to be virtually identical in position and shape to those for TiN. The ELS spectra of N(,2)('+)/Ti and higher exposures of O(,2) to a Ti surface were found to be qualitatively similar and are explained in terms of the molecular orbital and band structure calculations for TiN and TiO. The interpretation of the ELS spectra for clean Ti was aided by a comparison with that for H(,2) adsorbed on the surface. The He I UPS spectrum for ammonia adsorbed on Ti is reported for the first time and suggests that almost complete dissociation of NH(,3) on Ti at room temperature. The dissociation of NH(,3) in this case is also supported by ELS measurements. |
