Preparation of Carbide Catalysts

In heterogeneous catalysis, the catalytic properties of an element or a compound are always closely linked to an active and large specific surface. The production of high specific surface tungsten carbides requires special methods. Typical examples are listed below. 

During reactions with carbon-containing compounds, free (unreacted) carbon may form by cracking, which is undesirable because it changes the catalytic properties and shows an increased specific surface not due to the carbide phase. C2 hydrocarbons produce more excessive carbon than CH4. It can be removed in all cases by hydrogen treatment at 973 K. The carbide phase itself is not in any case pure and may consist of W2C/WC mixtures. 

WC behaves similarly to platinum in many catalytic reactions (e.g., gas-phase oxidation reactions). Unlike many metal and oxide catalysts, it is capable of operating under a wider range of conditions in oxidative as well as in reductive regimes. 

Kinetically, under oxidative conditions, due to an oxidic surface layer, WC acts similar to an oxide in heterogeneous oxidation reactions (the redox mechanism consisting of successive oxidation and reduction steps at the catalyst surface). Under reducing 

The heat of oxygen adsorption corresponds to 362 kJ-mol at 523K and 356 kJ mol at 723 K. Compared to metallic W (812 kJ mol ) it is lower, because the carbon atoms in the metal lattice reduce the adsorption affinity toward oxygen. 

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