Steam reforming of raw bio-oil over Ni/La2O3-αAl2O3: Influence of temperature on product yields and catalyst deactivation

The hydrogen production by steam reforming (SR) of raw bio-oil (obtained by fast pyrolysis of pine sawdust) has been studied in a continuous two-step process, which consists of a thermal treatment at 500 °C, followed by SR in a fluidized bed reactor with Ni/La2O3-αAl2O3 catalyst. The effect of SR temperature on bio-oil conversion, product yields and catalyst deactivation was evaluated in the 550-700 °C range. The bio-oil conversion and H2 yield were significantly enhanced by increasing temperature. A H2 yield of around 88% and low catalyst deactivation were achieved at temperatures above 650 °C, for a S/C (steam/carbon) ratio of 6 and space-time of 0.10 gcatalysth/gbio-oil. The influence temperature has on product yields and catalyst deactivation was explained by the different nature of the coke deposited. The temperature-programmed oxidation (TPO) curves of coke combustion allow identifying two fractions: i) Coke I, which is the main responsible for deactivation (by encapsulating the Ni sites), whose formation depends on the concentration of bio-oil oxygenates; ii) Coke II, which has filamentous nature and CO and CH4 as main precursors. The effect of temperature on the formation of both types of coke depends on the space-time. Thus, for low values (0.04 gcatalysth/gbio-oil) there is significant formation of both types of coke, with their content increasing with temperature. For higher values (0.38 gcatalysth/gbio-oil), the increase in reaction temperature promotes the removal of coke I, and therefore this is the prevailing fraction at 550 °C and is negligible at 700 °C. This fact is of special relevance for attenuating the Ni/La2O3-αAl2O3 catalyst deactivation.