The regenerability of Ni catalysts in reforming reactions is a key factor for process viability. Accordingly, this study addresses the regeneration of two spinel NiAl₂O₄ type catalysts by reaction-regeneration cycles in the oxidative steam reforming (OSR) of raw bio-oil. The spinel type catalysts were prepared by different methods including a supported Ni/La₂O₃-αAl₂O₃ catalyst and a bulk NiAl₂O₄ catalyst. The experimental set-up consists of two units connected in series for i) the thermal treatment of bio-oil at 500 °C, in order to control the deposition of pyrolytic lignin, followed by; ii) the oxidative steam reforming (OSR) of the remaining oxygenates in a fluidized bed catalytic reactor. The conditions in the OSR reaction step were: 700 °C; oxygen/steam/carbon ratio (O/S/C), 0.34/6/1; space time, 0.75 g_catalysth/g_bio-oil (for supported catalyst) and 0.15 g_catalysth/g_bio-oil (for bulk catalyst). Three different strategies have been studied in the regeneration step by coke combustion, including the in situ regeneration inside the reactor at 650 °C and 850 °C, and the ex situ regeneration in an external oven at 850 °C, for 4 h in all the cases. The behavior of the fresh and regenerated catalysts has been explained according to their metallic properties, determined by different characterization techniques (temperature programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electronic microscopy (TEM)). According to these results, the combustion ex situ of the catalyst at 850 °C is able to completely regenerate the bulk catalyst, since these regeneration conditions lead to the total recovery of the NiAl₂O₄ spinel phase together with negligible loss of Ni on the surface in the catalyst. These novel results are crucial for future industrial implementation of the process.

The oxidative steam reforming (OSR) of raw bio-oil (obtained by fast pyrolysis of pine sawdust) has been studied on a Rh/CeO₂-ZrO₂ catalyst under a wide range of operating conditions (600-750 °C; steam-to-carbon molar ratio, 3-9; oxygen-to-carbon molar ratio, 0.34; space time, 0.15-0.6 g_catalyst h/g_bio-oil) in order to delimit the suitable conditions for high and stable H₂ production. The runs were conducted in a two-step system provided with a thermal step (at 500 °C) for bio-oil vaporization and pyrolytic lignin retention, followed by an online catalytic reforming step in a fluidized bed reactor. The spent catalyst was characterized by temperature-programmed oxidation, temperature-programmed reduction, and transmission electron microscopy in order to ascertain the causes of deactivation and the effect of the reaction conditions on these causes. The evolution with time on stream of both bio-oil oxygenates conversion and yields of reaction products shows different periods and catalyst states, with two sharp changes associated with different catalyst deactivation causes: (i) change in the states of Rh species and aging of the support (with fast dynamics) and (ii) coke deposition (at low temperature) or Rh sintering (at high temperature, with slow dynamics).

A reaction scheme has been proposed for the oxidative steam reforming (OSR) of raw bio-oil on a Rh/CeO₂-ZrO₂ catalyst, based on the study of the effect reaction conditions (temperature, space time, oxygen/carbon ratio and steam/carbon ratio) have on product yields (H₂, CO, CO₂, CH₄, hydrocarbons). The runs were performed in a two-step system, with separation of pyrolytic lignin (first step) followed by catalytic reforming in a fluidized bed reactor (second step), under a wide range of reaction conditions (600–750 °C; space time, 0.15–0.6 g_catalysth/g_bio-oil; oxygen to carbon molar ratio (O/C), 0–0.67; steam to carbon molar ratio (S/C), 3–9). The catalyst is very active for bio-oil reforming, and produces high H₂ yield (between 0.57 and 0.92), with low CO yield (0.035–0.175) and CH₄ yield (below 0.045) and insignificant light hydrocarbons formation. The proposed reaction scheme considers the catalyzed reactions (reforming, water gas shift (WGS) and combustion) and the thermal routes (decomposition/cracking and combustion). The deactivation of the catalyst affects progressively the reactions in the following order: CH₄ reforming, hydrocarbons reforming, oxygenates reforming, combustion and WGS.