Catalyst deactivation during steam reforming of transportation fuels, primarily due to sulfur poisoning
and carbon deposition, is a major hurdle in the commercialization of fuel cell technologies. In an attempt
to better understand the phenomena, a previously formulated multi-component (Ni, Pd, Rh) catalyst
supported on -Al2O3 was studied under steam reforming of Jet A spiked with thiophene to achieve
a total sulfur content of 1000 ppm by weight. Analysis of fresh catalysts showed the presence of two
groups of active metal particles, primarily distinguished by their size and composition; small particles
(1–5 nm) largely comprised of Rh and large particles (10–20 nm) that were predominantly Ni, with or
without the presence of Pd. Analysis of used catalysts showed sintering of crystallites containing Ni but
no identifiable growth in Rh crystallites. When complete conversion of sulfur compounds to hydrogen
sulfide was observed, catalyst deactivation was minimized. However, when the conversion of sulfur
compounds was low, significant catalyst deactivation was noted. In the presence of sulfur, increased
amounts of cracking products were observed, suggesting that sulfur primarily affected the active sites
responsible for steam reforming. Sulfur was preferentially adsorbed on the surface of Ni crystallites. It
has been postulated that sulfur adsorption on Ni sites causes the initial deactivation of the catalyst which
suppresses carbon gasification on the active sites, leading to the accumulation of carbon deposits over
time.
Catalyst deactivation during steam reforming of transportation fuels, primarily due to sulfur poisoningand carbon deposition, is a major hurdle in the commercialization of fuel cell technologies. In an attemptto better understand the phenomena, a previously formulated multi-component (Ni, Pd, Rh) catalystsupported on -Al2O3 was studied under steam reforming of Jet A spiked with thiophene to achievea total sulfur content of 1000 ppm by weight. Analysis of fresh catalysts showed the presence of twogroups of active metal particles, primarily distinguished by their size and composition; small particles(1–5 nm) largely comprised of Rh and large particles (10–20 nm) that were predominantly Ni, with orwithout the presence of Pd. Analysis of used catalysts showed sintering of crystallites containing Ni butno identifiable growth in Rh crystallites. When complete conversion of sulfur compounds to hydrogensulfide was observed, catalyst deactivation was minimized. However, when the conversion of sulfurcompounds was low, significant catalyst deactivation was noted. In the presence of sulfur, increasedamounts of cracking products were observed, suggesting that sulfur primarily affected the active sitesresponsible for steam reforming. Sulfur was preferentially adsorbed on the surface of Ni crystallites. Ithas been postulated that sulfur adsorption on Ni sites causes the initial deactivation of the catalyst whichsuppresses carbon gasification on the active sites, leading to the accumulation of carbon deposits overtime.
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