To study its catalytic effect, nickel were inserted intentionally by impregnation into the biomass. In this context, the influence of the Ni amount in the solution during wood impregnation has been analyzed in terms not only of catalytic activity and samples compositions but also on the wood structure. Willow was impregnated with different concentrations of nickel nitrate solutions and then characterized with thermogravimetric and elementary analyses.
Using thermodynamic calculation, the speciation of Ni and the pH variation in the impregnation solution was predicted. It was found that the stable aqueous form of Ni were Ni2+ and NiNO3 +. It was also found that wood impregnation in high-concentrated solutions (more than 0.5 wt%), modified the wood structure and complicated the understanding of its behavior during thermal treatment. The amount of Ni which shows a maximum efficiency during char gasification is 1.6 wt% in the wood sample.
This amount corresponds to a sample prepared with a 0.5 wt% of Ni in the impregnation solution. However, to keep the wood structure during the impregnation step, it is recommended to impregnate the wood with lower amount of Ni, around 0.1 wt%. During gasification tests, Ni has shown a catalytic performance between 450 and 600 °C where the rate of char gasification was increasing. This result was confirmed with an increase in the syngas production. The presence of nickel has also generated a decrease in the char gasification temperature by 100 °C. ©
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