Effect of Support Particle
Size in Steam Reforming
of Ethanol over Co/CeO<sub>2</sub> Catalysts
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Abstract
Co catalysts supported on ceria supports with two different
particle
sizes, one in the micro- and the other in the nano-range, were investigated
for their ethanol and ethylene steam reforming performance. Pre- and
post-reaction characterization techniques, including high-resolution
transmission electron microscopy, temperature-programmed oxidation,
dispersion, pore size measurements, in situ X-ray diffraction (XRD)
and X-ray absorption fine structure spectroscopy (XAFS) studies were
performed to examine the reducibility of the catalysts. Steady-state-activity
testing has shown nanoparticles to have a higher reforming activity
for ethanol, but also high ethylene yields. In spite of the high ethylene
yields, catalysts supported on nanoparticles proved to be highly resistant
to coking while the catalysts supported on larger ceria particles
suffered from coke formation. Reforming experiments performed with
ethylene showed significant differences in activity and stability.
Bare supports were also tested for activity and the nanoparticle support
was seen to have high dehydration activity. <i>Operando</i> DRIFTS experiments performed during ESR showed differences in surface
species. Pulse experiments performed to use methanol oxidation as
a probe reaction suggested differences in the relative abundance of
redox sites and basic sites. The bare ceria supports also exhibited
significant activity for ethanol dehydration, but not for C–C
cleavage. The superior performance of the catalysts supported on nanoparticles
is thought to be due to a combination of factors, including increased
reducibility, improved metal dispersion, and a difference in relative
abundance of redox sites on the surface. All of these properties and,
in turn, the catalytic performance, appear to be affected by the particle
size of the support