Lignin has been gasified with a Ni/Al2O3-SiO2 catalyst in sub/supercritical water (SCW) to produce gaseous fuels. XRD pattern at 60 angle shows characteristic peaks of crystalline NiO, NiSi, and AlNi3, suggesting that Al2O3-SiO2 not only offers high surface area (122 m(2) g) for Ni, but also changes the crystal morphology of the metal. 9 mmol/g of H-2 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 degrees 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 H-2 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. (C) 2014 Elsevier B.V. All rights reserved.