Hydrogen production from cellulose, lignin, bark and model carbohydrates in supercritical water using nickel and ruthenium catalysts

In this study, the catalytic activity and hydrogen selectivity of Ni/α-Al2O3, Ni/hydrotalcite, Raney nickel, Ru/C and Ru/γ-Al2O3 catalysts for hydrothermal hydrogen production from lignocellulosic biomass have been evaluated. The feedstocks included glucose, cellulose, fructose, xylan, pulp, lignin and bark. The experiments were carried out at 380 °C in a batch reactor with 2 wt% feed concentration. It was found that the gasification of glucose, fructose, cellulose, xylan and pulp resulted in comparable gas yields (±10% at 60 min), whereas lignin was substantially harder to gasify. Interestingly, gasification yield of bark which has a high lignin content was comparable to those of carbohydrates after 60 min reaction time. For a given feedstock, catalyst type affected both the gasification yield and the product distribution. Ni/α-Al2O3 and Ni/hydrotalcite catalysts were not only highly active for the gasification of carbohydrates, but also had better hydrogen selectivity when compared to Raney nickel, Ru/C and Ru/γ-Al2O3. In particular, gasification of bark in the presence of these catalysts resulted in negligible amounts of alkanes.

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► Supported nickel catalysts had a high hydrogen selectivity.
► Ru/C was found to be more active than Ru/γ-Al2O3.
► Metal dispersion significantly affected the methane formation rate.