Combined effect of bio-oil composition and temperature on the stability of Ni spinel derived catalyst for hydrogen production by steam reforming

Abstract

• Raw bio-oil composition modified by pre-reforming with dolomite or phenols extraction. • Stability of a Ni catalyst in the SR of the bio-oils at 600 and 700 °C. • Coke nature and location depends on bio-oil composition and reforming temperature. • Catalyst deactivation is slower at 600 °C for bio-oils rich in phenols. • Phenols extraction and reforming at 700 °C minimize Ni catalyst deactivation. A challenge for scaling up hydrogen production by raw bio-oil steam reforming (SR) is the rapid catalyst deactivation that is strongly sensitive to the temperature and bio-oil composition. This work studies the combined effect of both variables on the stability of a Ni/Al 2 O 3 catalyst with high Ni dispersion in the internal and external surfaces of the particles, obtained by reduction of a NiAl 2 O 4 . The raw bio-oil composition is modified by (i) removal of phenolic compounds by liquid–liquid extraction or (ii) use of an online pre-reforming step with dolomite. Then, SR tests of the bio-oils at 600 and 700 °C are carried out in a system with two online units, the first one for controlled deposition of pyrolytic lignin (and also pre-reforming with dolomite) and the second one (fluidized bed reactor) for the SR of the volatile oxygenates. The time on stream evolution of the conversion and products yields is related to the amount, nature and location of coke in the catalyst particles, determined with several techniques. For bio-oils with high or moderate phenolic content (raw or pre-reformed bio-oil, respectively), the SR at 600 °C leads to a moderate deactivation. However, at 700 °C, a refractory coke is formed, mainly composed of carbon filaments and turbostratic carbon among them that causes a rapid catalyst deactivation by blocking the external surface of the catalyst particle. Conversely, the removal of phenolic compounds from raw bio-oil leads to a more stable SR operation at 700 °C, because the formation of turbostratic carbon is slowed down.