Deactivation of Ni spinel derived catalyst during the oxidative steam reforming of raw bio-oil

Deactivation of a bulk catalyst derived from NiAl₂O₄ spinel during the oxidative steam reforming (OSR) of raw bio-oil has been studied. The experiments were performed in a continuous system with two units in series: a thermal treatment unit at 500 °C for the controlled deposition of pyrolytic lignin, and a fluidized bed reactor (700 °C; S/C, 6; O/C, 0.34; space time, 0.15 g_catalysth·g_bio-oil⁻¹; time on stream, 1, 2, 4 and 6 h) for the OSR of the remaining oxygenates. The deactivation affects the reforming of bio-oil oxygenates according to their reactivity (from lower to higher), with the reforming of phenols being rapidly affected. The causes of deactivation are: i) coke deposition on the Ni⁰ sites and on the Al₂O₃ support (6 wt% of each coke type after 6 h on stream), and; ii) sintering of Ni⁰ crystals (with an increase in crystal size from 10.8 to 17.7 nm (measured by TEM)). The catalyst deactivation rate increases with time on stream, with the bio-oil oxygenates being the main coke precursors.