Stability of a NiAl₂O₄ Derived Catalyst in the Ethanol Steam Reforming in Reaction-Regeneration Cycles: Effect of Reduction Temperature

The catalyst regeneration is still a challenge to make the ethanol steam reforming (ESR) process feasible for sustainable H₂ production. NiAl₂O₄ spinel derived catalysts are highly active and selective for ESR, but they require avoiding irreversible deactivation to ensure their regeneration. Their stability depends on the catalyst structure, and herein we report different Ni/Al₂O₃-NiAl₂O₄ catalysts obtained upon reduction of a NiAl₂O₄ spinel at 700, 750, or 850 °C. The catalysts were tested in ESR reaction-regeneration cycles, with reaction at 600 °C and regeneration by coke combustion at 850 °C followed by reduction at the corresponding temperature. The fresh, spent, and regenerated catalysts were characterized using X-ray diffraction, N₂ physisorption, temperature programmed reduction and oxidation, and scanning electron microscopy. The irreversible deactivation is due to Ni volatilization and catalyst particle fragmentation. These phenomena are prompted by a high filamentous carbon deposition favored by the Al₂O₃ content in the catalyst. The reduction in the 700–750 °C range is optimum for controlling the Al₂O₃ content, increasing the NiAl₂O₄/Al₂O₃ ratio in the resulting catalyst. These catalysts show a period of partial reversible deactivation by coke with a change in the H₂ formation mechanism reaching a pseudo-stable state with a H₂ yield of 40% and a reproducible performance in successive reaction-regeneration cycles.