Study of the isomerization of 13C labelled methylpentanes on oxygen modified bulk tungsten carbides
Abstract
The
reactions of labelled 2- and 3-methylpentanes were carried out on three different oxygen modified bulk tungsten carbides varying by their oxygen treatment temperature. In all cases, isomerization took place ia bond
shift mechanisms; no cyclic mechanism was involved in contrast to metals like Pt, Pd or Ir where such mechanism
occurs. Alkoxy and σ-alkyl intermediates were put forward as adsorbed species responsible for isomerization
for bulk tungsten carbides treated by O2 at moderate temperature (350°C) over a short period of time (5 min)
and at high temperature (700°C) for 4 h, respectively. These intermediate species are respectively correlated
to an acidic and a metallic behavior of the catalytic surfaces. The increase of the O2 treatment time at 350°C
results in the presence of both kinds of these mechanisms for isomerization, a bifunctional behavior takes place
where metallic and acidic characters are present. To explain the presence of terminal-13C on acidic