Abstract: Tungsten carbides with different crystal phases were prepared by temperature-programmed reaction of WO3 in a CH4/H2 atmosphere, and the phase transition occurring during this process was described. The catalytic activity of the tungsten carbides for hydrazine decomposition was investigated, and the active sites were determined by CO adsorption microcalorimetry. The results showed that the CO adsorption became strong with the formation of a W2C crystal phase, and the W2C exhibited the best catalytic performance for N2H4 decomposition. However, when the preparation temperature was higher than 750 ℃, there was a significant amount of carbonaceous species deposited on the catalyst surface, which resulted in severe deactivation. The surface-clean WC possessed a higher intrinsic activity for N2H4 than the W2C owing to its stronger noble metallic properties.

Key words: tungsten carbide, temperature-programmed reaction, hydrazine decomposition, microcalorimetry, carbon deposition