Article,
Isomerization and hydrogenation of cis-2-butene on Pd model catalyst
Journal of Physical Chemistry C, (2008)
DOI: 10.1021/jp800205j
Abstract
The adsorption and kinetics of conversion of cis-2-butene with deuterium
on model supported Pd catalyst
(Pd/Fe3O4/Pt(111)) were characterized by reflection-absorption infrared
spectroscopy (RAIRS), temperatureprogrammed
desorption (TPD), and isothermal molecular beam (MB) experiments.
It was found that selectivity
toward cis-trans isomerization and hydrogenation depends critically
on the nature of the carbonaceous deposits,
which are typically present during reaction on real catalysts. At
low temperatures (190-210 K) both reaction
pathways were found to proceed on the initially clean surface, but
the catalytic activity was observed to
quickly vanish, presumably because of the accumulation of hydrocarbon
species on the surface. At temperatures
above 250 K, on the other hand, a sustained catalytic activity toward
cis-trans isomerization was observed
over long periods of time. Interestingly, no catalytic activity could
be sustained for the competing hydrogenation
on the initially clean catalyst even at these temperatures. Only when
highly dehydrogenated carbonaceous
fragments were preadsorbed on the surface was it possible to induce
a persistent catalytic activity for the
hydrogenation (and also the isomerization) of the alkene on our supported
palladium particles. Possible reasons
of this unique vacuum catalytic behavior are discussed, including
different spatial requirements for the
competing reaction pathways and changes in the adsorption state of
deuterium on and beneath the surface
modified by the carbonaceous deposits.
