Tungsten carbides with surface areas ranging from 4 to 39 m(2)/g were
prepared by the temperature-programmed carburization of tungsten oxide
and nitride powders with pure CH4 or a 48.9% CH4 in H-2 mixture. Oxyg
en uptakes on the carbides were low most likely because of the presenc
e of graphitic carbon at the surface. Nevertheless, the carbides were
active and selective for the dehydrogenation of butane at temperatures
between 623 and 723 K and atmospheric pressure with and without H-2 i
n the reactant feed. With H-2 in the feed, the higher surface area car
bides (greater than or equal to 36 m(2)/g) were as active as a Pt-Sn/g
amma-Al2O3 catalyst, but their selectivities were different. Without H
, in the feed, the selectivities of the carbides were similar to those
of the Pt-Sn/gamma-Al2O3 catalyst, but their reaction rates were 1-3
orders of magnitude lower. The high surface area materials were also a
ctive for the hydrogenolysis of butane. Because the catalytic properti
es of the carbides varied with the average particle size, we concluded
that butane dehydrogenation was structure-sensitive over these materi
als, and suspected that this behavior was due to variations in the sur
face stoichiometry as well as the particle faceting.