In this study, the effect of the type of catalyst on hydrothermal gasification of three specifically chosen samples of natural biomass was investigated. Biomass feedstocks, including lignocellulosic materials (cotton stalk and corncob) and the tannery waste, were gasified in supercritical water by the addition of catalyst. The catalysts used were K2CO3, Trona (NaH-CO3 center dot Na2CO3 center dot 2H(2)O), red mud (Fe-oxide containing residue from Al-production) and Raney-Ni. The gasification experiments were performed in a batch autoclave at 500 degrees C. The amounts and compositions of the gases and the amounts of water soluble compounds from gasification were determined. The effect of catalysts on gasification varied with the type of biomass. The catalysts significantly increased the hydrogen yield by supporting the water-gas shift reaction and the methane reformation. The gasification activity of Trona was similar to that of K2CO3. The results indicate that iron based catalysts can also be effective in gasification of biomass. In conclusion, the supercritical water gasification of biomass by addition of red mud and Trona is said to be promising method to produce H-2 from biomass efficiently similar to gasification with commercial alkali catalysts. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.