Abstract
Fuel processors are required to convert sulfur-laden logistic fuels into hydrogen-rich reformate and deliver to the fuel cell stack with little or no sulfur. Since sulfur poisons and deactivates the reforming catalyst, robust sulfur-tolerant catalysts ought to be developed. In this paper, the development, characterization and evaluation of a series of reforming catalysts containing two noble metals (with total metal loading not exceeding 1 weight percent) supported on nanoscale ceria for the steam-reforming of kerosene is reported. Due to inherent synergy, a bimetallic catalyst is superior to its monometallic analog, for the same level of loading. The choice of noble metal combination in the bimetallic formulations plays a vital and meaningful role in their performance. Presence of ruthenium and/or rhodium in formulations containing palladium showed improved sulfur tolerance and significant enhancement in their catalytic activity and stability. Rhodium was responsible for higher hydrogen yields in the logistic fuel reformate. Duration of steady hydrogen production was higher in the case of RhPd (75 h) than for RuPd (68 h); hydrogen generation was stable over the longest period (88 h) with RuRh containing no Pd. A mechanistic correlation between the characteristic role of precious metals in the presence of each other is discussed.
Highlights
In the light of the recent quest for cleaner and greener energy, fuel cells running on hydrogen feeds derived from abundant logistic fuels are attractive options, provided strategies for effective desulfurization and sustained reforming via robust sulfur-tolerant catalysts are in place
The contrasting light and dark particle contours in these images belong to the gadolinia-doped ceria (GDC) support and the noble metals, respectively
Steam reforming of kerosene at 800◦C and atmospheric pressure with steam-tocarbon (S/C) ratio equals to 3.0 on these formulations produces hydrogen-rich reformates over long durations before deactivation sets in, which is rather slow and monotonic than sudden and precipitous
Summary
In the light of the recent quest for cleaner and greener energy, fuel cells running on hydrogen feeds derived from abundant logistic fuels are attractive options, provided strategies for effective desulfurization and sustained reforming via robust sulfur-tolerant catalysts are in place. The catalysts were capable of in situ methanation; this was verified by theoretical calculations which corroborated the experimental data on carbon balance This communication highlights the performance of bimetal-supported ceria nanocatalysts in terms of hydrogen yield and sulfur tolerance as a function of time on stream. In a reducing environment, Ce2O3 has higher sulfidation equilibrium constant than CeO2, suggesting a possibility of formation of either cerium oxysulfide (partial sulfidation) or cerium sesquisulfide (complete sulfidation) This mechanism might help mitigate sulfurmediated poisoning and deactivation of ceria-based catalysts in the long run. This sacrificial role may allow precious metal(s) to remain active longer, resulting in better catalyst life. A plausible mechanistic correlation between the synergistic role of precious metals in presence of one another and the behavior of the catalysts in terms of the above-mentioned features is suggested
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