Oxidative steam reforming of raw bio-oil over supported and bulk Ni catalysts for hydrogen production

Several Ni catalysts of supported (on La ₂O ₃-αAl ₂O ₃, CeO ₂, and CeO ₂-ZrO ₂) or bulk types (Ni-La perovskites and NiAl ₂O ₄ spinel) have been tested in the oxidative steam reforming (OSR) of raw bio-oil, and special attention has been paid to the catalysts’ regenerability by means of studies on reaction-regeneration cycles. The experimental set-up consists of two units in series, for the separation of pyrolytic lignin in the first step (at 500°C) and the on line OSR of the remaining oxygenates in a fluidized bed reactor at 700°C. The spent catalysts have been characterized by N ₂ adsorption-desorption, X-ray diffraction and temperature programmed reduction, and temperature programmed oxidation (TPO). The results reveal that among the supported catalysts, the best balance between activity-H ₂ selectivity-stability corresponds to Ni/La ₂O ₃-αAl ₂O ₃, due to its smaller Ni ⁰ particle size. Additionally, it is more selective to H ₂ than perovskite catalysts and more stable than both perovskites and the spinel catalyst. However, the activity of the bulk NiAl ₂O ₄ spinel catalyst can be completely recovered after regeneration by coke combustion at 850°C because the spinel structure is completely recovered, which facilitates the dispersion of Ni in the reduction step prior to reaction. Consequently, this catalyst is suitable for the OSR at a higher scale in reaction-regeneration cycles.