Study of the preparation of bulk tungsten carbide catalysts with C2H6/H2 and C2H4/H2 carburizing mixtures

The influence of the preparation procedure of tungsten carbide on the mechanism of carburization is discussed. This work is focused on the reduction and the carburization of tungsten trioxide by a mixture of hydrocarbon and H₂ to form WC. Temperature-programmed reaction spectra obtained with CH₄, C₂H₆ and C₂H₄ have been measured. In presence of the CH₄-H₂ mixture, H₂ is the reducing agent and the hydrocarbon is consumed for the carburization whereas C₂H₆ or C₂H₄ participates in the reduction of the tungsten oxide. The temperatures of reduction and carburization are lower by about 150 K using C₂H₆ or C₂H₄ instead of CH₄. Such a decrease of the temperature of reduction of tungsten oxide is needed to avoid the formation of poorly reducible compounds that can occur during the preparation of supported tungsten carbide. Furthermore, the surface area of the resulting carbide is 25 m²/g with C₂H₆ and C₂H₄ and 10 m²/g with CH₄. During the carburization, the deposit of excess carbon on the WC surface is larger with the C₂ hydrocarbons than with CH₄, but it protects the carbide and can be removed by hydrogen treatment. This revised version was published online in July 2006 with corrections to the Cover Date.