Stability and complete regeneration of a Ni/MgAl2O4 catalyst in combined steam/dry reforming of raw bio-oil

The combined steam and dry reforming (CSDR) of bio-oil (the liquid product from biomass pyrolysis) represents an attractive pathway for CO₂ valorization along with sustainable syngas production. This study compares the performance in the CSDR process of a Ni catalyst supported on MgAl₂O₄ spinel with 15 wt% Ni (15Ni/MgAl₂O₄), with that of Ni catalysts supported on Al₂O₃ prepared by different methods. The reactions were carried out in an automatized equipment with two units, for controlled pyrolytic lignin deposition in the first unit while the feed is volatilized (thermal treatment), and for reforming of the remaining oxygenates in the second unit in-line (fluidized bed reactor). The catalysts have been used under reaction-regeneration cycles. The reaction conditions were: 700 °C, CO₂/C molar ratio, 0.6; steam/C ratio, 0.5; space time, 0.042 g_Ni·h/g_oxygenates, and; time on stream, 6 h. The regeneration is performed in-situ, by coke combustion with air at 850 ºC for 2 h. The catalytic performance (activity, selectivity, stability and regenerability) is explained on the basis of the characterization results of the used and regenerated catalysts and the deposited coke. Although the initial CO₂ conversion (in the 14–18 % range) and syngas yield (in the 88–98 % range) show no significant differences among the catalysts, variations in catalyst stability and regeneration capacity are remarkable. Specifically, the 15Ni/MgAl₂O₄ catalyst is the most suitable candidate for scaling up CSDR of bio-oil, due to its high stability (similar to that of the 36Ni/Al₂O₃-cp catalyst, obtained by reduction of a stoichiometric NiAl₂O₄ spinel) and reproducible behavior in reaction-regeneration cycles.