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Origin and Nature of Coke in Ethanol Steam Reforming and Its Role in Deactivation of Ni/La₂O₃–αAl₂O₃ Catalyst

Montero, Carolina, Remiro, Aingeru, Valle, Beatriz, Oar-Arteta, Lide, Bilbao, Javier, Gayubo, Ana G.
Industrial & engineering chemistry process design and development 2019 v.58 no.32 pp. 14736-14751
Raman spectroscopy, X-ray diffraction, acetaldehyde, carbon monoxide, catalysts, encapsulation, ethanol, ethylene, fluidized beds, gasification, hydrogen, hydrogen production, methane, nickel, oxidation, process design, scanning electron microscopy, space and time, steam, temperature
Deactivation of Ni/La₂O₃–αAl₂O₃ catalyst in ethanol steam reforming (ESR) was studied in order to establish the optimal conditions for maximizing H₂ production and achieving steady behavior. The ESR reactions were conducted in a fluidized bed reactor under the following operating conditions: 500–650 °C; space-time up to 0.35 gcₐₜₐₗyₛₜ h/gEₜOH; and steam/ethanol (S/E) molar ratio in the feed, 3–9. The features of the deactivated catalysts and the nature and morphology of the coke deposited were analyzed by temperature-programmed oxidation, X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Catalyst deactivation was solely caused by coke deposition, especially by encapsulating coke, with acetaldehyde, ethylene, and ethanol being the main precursors, whose concentration was high for lower values of space-time. Conversely, the filamentous coke formed from CH₄ and CO (with their highest concentration for intermediate values of space-time) had a much lower impact on deactivation. Owing to the effect of space-time on the extent of reactions leading to the formation of coke precursors, the Ni/La₂O₃–αAl₂O₃ catalyst stability was enhanced by increasing space-time. The increase in temperature and S/E ratio was also beneficial since both variables promoted coke gasification. Consequently, a steady H₂ yield throughout 200 h reaction was attained at 600 °C, a space-time of 0.35 gcₐₜₐₗyₛₜ h/gEₜOH, and S/E > 3.