2 research outputs found
Effect of Support Particle Size in Steam Reforming of Ethanol over Co/CeO<sub>2</sub> Catalysts
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
Molybdenum Carbides, Active and <i>In Situ</i> Regenerable Catalysts in Hydroprocessing of Fast Pyrolysis Bio-Oil
This paper describes
properties of molybdenum carbides as a potential
catalyst for fast pyrolysis bio-oil hydroprocessing. Currently, high
catalyst cost, short catalyst lifetime, and lack of effective regeneration
methods are hampering the development of this otherwise attractive
renewable hydrocarbon technology. A series of metal-doped bulk Mo
carbides were synthesized, characterized, and evaluated in sequential
low-temperature stabilization and high-temperature deoxygenation of
a pine-derived bio-oil. During a typical 60 h run, Mo carbides were
capable of upgrading raw bio-oil to a level suitable for direct insertion
into the current hydrocarbon infrastructure with residual oxygen content
and total acid number of upgraded oils below 2 wt % and 0.01 mg KOH
g<sup>–1</sup>, respectively. The performance was shown to
be sensitive to the type of metal dopant, Ni-doped Mo carbides outperforming
Co-, Cu-, or Ca-doped counterparts; a higher Ni loading led to a superior
catalytic performance. No bulk oxidation or other significant structural
changes were observed. Besides the structural robustness, another
attractive property of Mo carbides was <i>in situ</i> regenerability.
The effectiveness of regeneration was demonstrated by successfully
carrying out four consecutive 60 h runs with a reductive decoking
between two adjacent runs. These results strongly suggest that Mo
carbides are a good catalyst candidate which could lead to a significant
cost reduction in hydroprocessing bio-oils. We highlight areas for
future research which will be needed to further understand carbide
structure–function relationships and help design practical
bio-oil upgrading catalysts based on Mo carbides