Jean Marie Bastin

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.

Pore structure of bulk tungsten carbide powder catalysts

Bulk tungsten carbide catalysts are prepared by direct carburization/reduction of tungsten trioxide in methane-hydrogen mixtures. The catalytic properties of such catalysts have been studied by several authors. The porous structure of these catalysts is studied by adsorption of N2, Kr, CF4 and neohexane. Adsorption isotherms and hysteresis loops for the catalysts suggest the presence of a microporous structure made of parallel plates distant approximately by 20 Å. These results are compared to those obtained using such catalysts for hydrogen oxidation and where condensation in the porous structure was observed.