Abstract

Molybdenum carbides have been prepared by the temperature programmed reaction method using mixtures of hydrogen and methane, hydrogen and ethane, and hydrogen and butane, and characterised with X-ray diffraction, transmission electron microscopy, ¹³C solid state NMR and EXAFS spectroscopy. The results show that the choice of hydrocarbon used to synthesise molybdenum carbide significantly affects the structure and texture of the resultant materials. Increasing the chain length of the carburising agent reduces the particle size and the temperature for complete phase transformation from molybdenum oxide to carbide is lowered. Carburising with a mixture of hydrogen and methane gives rise to hexagonal closed packed (hcp) carbide, while when using butane as the carbon source, molybdenum oxide is mainly reduced to face centred cubic (fcc) carbide. However, using ethane as the carbon source, the resultant carbide has a mixed phase composition with the hcp phase predominant. The molybdenum carbide prepared with ethane as the carbon source has the roughest surface and highest hydrogen adsorption capacity, while that prepared with butane has a very condensed surface. There is a substantial difference in the molybdenum co-ordination environments present among the carbides prepared with different carburising agents.