Catalytic gasification of lignin with Ni/Al2O3–SiO2 in sub/supercritical water

Abstract Lignin has been gasified with a Ni/Al2O3–SiO2 catalyst in sub/supercritical water (SCW) to produce gaseous fuels. XRD pattern at 6θ angle shows characteristic peaks of crystalline NiO, NiSi, and AlNi3, suggesting that Al2O3–SiO2 not only offers high surface area (122 m2 g) for Ni, but also changes the crystal morphology of the metal. 9 mmol/g of H2 and 3.5 mmol/g of CH4 were produced at the conditions that 5.0 wt% alkaline lignin plus 1 g/g Ni/Al2O3–SiO2 operating for 30 min at 550 °C. A kinetic model was also developed, and the activation energies of gas and char formation were calculated to be 36.68 ± 0.22 and 9.0 ± 2.4 kJ/mol, respectively. Although the loss of activity surface area during reuse caused slight activity reduction in Ni/Al2O3–SiO2, the catalyst system still possessed high catalytic activity in generating H2 and CH4. It is noted that sulfur linkage could be hydrolyzed to hydrogen sulfide in the gasification process of alkaline lignin. The stable chemical states of Ni/Al2O3–SiO2 grants its insensitivity to sulfur, suggesting that Ni/Al2O3–SiO2 should be economically promising for sub/supercritical water gasification of biomass in the presence of sulfur.