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 car bide (WC) has been studied for the reaction of pentanes, hexanes, hept anes, and two olefins (2-methyl-2-pentene and 4-methyl-1-pentene). Dep ending on the air treatment, at low (-78 degrees C), moderate (350 deg rees C), or high (700 degrees C) temperature, these alkanes lead to di fferent reaction products as a result of different reaction mechanisms . Whatever the oxygen treatment, heptanes react faster than hexanes, w hich are more reactive than pentanes. Furthermore, cyclanes (methylcyc lopentane 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 isomerizatio n proceeds only through two kinds of bond-shift mechanisms. In order t o obtain more information about the possible mechanisms, i.e., a bifun ctional mechanism with dehydrogenation/hydrogenation on metallic sites and carbenium ion rearrangement on acidic sites, two unsaturated reac tants (2-methyl-2-pentene and 4-methyl-1-pentene) have been tested. Th e reaction mechanisms and a kinetic model are discussed in detail in a forthcoming paper. (C) 1997 Academic Press.