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Structural Characterization of Nanocrystalline Mo and W Carbide and Nitride Catalysts Produced by Co2 Laser Pyrolysis

  • Xiang-Xin Bi (a1), K. Das Chowdhury (a2), R. Ochoa (a3), W. T. Lee (a3), S. Bandow (a4), M. S. Dresselhaus (a1) (a5) and P. C. Eklund (a3)...

Abstract

Using both XRD and HRTEM lattice imaging, we have shown that CO2 laser pyrolysis (LP) produces nanoscale transition metal carbide and nitride catalysts, including cubic Mo2C, Mo2N, and W2N, which possess highly crystalline structures in their as-synthesized form In contrast, LP-produced W2C in its hexagonal phase is disordered. Clear lattice expansion, induced by the small crystallite size of the nanoparticles has been observed for LP-produced Mo2C particles, which have a typical crystallite size of 2 nm. No carbon coating was observed in HRTEM for LP-produced Mo2C particles. Furthermore, Mo=N and Mo=C bonding in Mo2N and Mo2C, respectively, were identified by an XPS measurement, which also reveals the presence of a thin oxide layer formed on the particle surface during the passivation process. Finally, the average crystallite sizes determined from HRTEM and XRD are in good agreement, indicating that the line broadening observed in XRD is due to the small crystallite size of the nanoparticles.

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