Study of the preparation of bulk tungsten carbide catalysts with C2H6/H-2 and C2H4/H-2 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 H-2 to form WC. Temperature-programmed reaction spectra obtained with CH4, C2H6 and C2H4 have been measured. In presence of the CH4-H-2 mixture, H-2 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 m(2)/g with C2H6 and C2H4 and 10 m(2)/g with CH4. During the carburization, the deposit of excess carbon on the WC surface is larger with the C-2 hydrocarbons than with CH4, but it protects the carbide and can be removed by hydrogen treatment.