THE EFFECT OF SURFACE-COMPOSITION ON THE ACTIVITY AND SELECTIVITY IN SKELETAL REARRANGEMENT OF HYDROCARBONS ON BULK AND MODEL TUNGSTEN CARBIDES

Methylcyclopentane and 2-methylpentane reactions have been studied on several tungsten carbide surfaces: model surfaces prepared from tungst en ribbon for one part, and bulk carbide powders in another part. The presence of oxygen under oxidic form WO(X), has a decisive influence o n the reaction mechanisms. On the carbide surfaces without oxidic spec ies, the catalytic reactions give mainly acyclic cracking and isomeris ation. When oxidic species are present on the surface, the main reacti on is the methylcyclopentane ring enlargement, giving cyclohexane and benzene. The results could be interpreted by a bifunctional mechanism, taking into account the metallic and carbidic sites on one hand, and the oxidic acid sites on the other hand.