Catalytic activity of bulk tungsten carbides for alkane reforming .2. Catalytic activity of tungsten carbides modified by oxygen

The influence of oxygen on the reforming activity of bulk tungsten carbide (WC) has been studied for the reaction of pentanes, hexanes, heptanes, and two olefins (2-methyl-2-pentene and 4-methyl-1-pentene). Depending on the air treatment, at low (-78 degrees C), moderate (350 degrees C), or high (700 degrees C) temperature, these alkanes lead to different reaction products as a result of different reaction mechanisms. Whatever the oxygen treatment, heptanes react faster than hexanes, which are more reactive than pentanes. Furthermore, cyclanes (methylcyclopentane or ethylcyclopentane) are less reactive than linear alkanes (n-pentane, n-hexane, or n-heptane), which react more slowly than the branched ones (isopentane, 2-methylpentane, 3-methylhexane), Whatever the oxygen treatment, no cyclic mechanism is involved and isomerization proceeds only through two kinds of bond-shift mechanisms. In order to obtain more information about the possible mechanisms, i.e., a bifunctional mechanism with dehydrogenation/hydrogenation on metallic sites and carbenium ion rearrangement on acidic sites, two unsaturated reactants (2-methyl-2-pentene and 4-methyl-1-pentene) have been tested. The reaction mechanisms and a kinetic model are discussed in detail in a forthcoming paper. (C) 1997 Academic Press.