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

Abstract

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.