Biomass gasification in supercritical water: II. Effect of catalyst Jale Yanik*, Steve Ebale, Andrea Kruse**, Mehmet Saglam, Mithat Yu ¨ ksel Institue for Technical Chemistry, Division of Chemical-Physical Processing, Forschungszentrum Karlsruhe, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany article info Article history: Received 6 September 2007 Received in revised form 26 March 2008 Accepted 18 June 2008 Available online 16 August 2008 Keywords: Biomass gasification Supercritical water Trona Red mud abstract In this study, the effect of the type of catalyst on hydrothermal gasification of three specif- ically 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 K 2 CO 3 , Trona (NaH- CO 3 $Na 2 CO 3 $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  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 K 2 CO 3 . The results indicate that iron based catalysts can also be effective in gasification of biomass. In conclusion, the supercrit- ical 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. ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Recently, a considerable effort has been made to find clean, renewable resources for a sustainable development. Biomass is one of the most abundant renewable resources. Biomass can be converted into liquid and gaseous fuels by thermal processes [1,2]. One of the methods for producing gaseous fuels is the gasification of biomass in supercritical water [3–7]. Compared to other gasification technologies, supercritical water gasification (SCWG) directly deals with wet biomass without drying and it has high gasification efficiency due to low amount of char and tar production. The chemical mechanisms of SCWG are very complex, including hydrolysis, steam reforming, water–gas shift, methanation and other reactions. Moreover, more hydrogen can be produced at ther- modynamic equilibrium in SCWG than that in conventional gasification techniques due to the different operating condi- tions. In SCWG, about half of the hydrogen formed originates from the water rather than from the biomass [8]. Fundamental studies concerning SCWG have been per- formed with model compounds such as cellulose, lignin and glucose [9–16]. Many studies have also been reported on gasi- fication or H 2 production from biomass or biomass model compounds in SCWG with catalysts (such as KOH, Na 2 CO 3 , * Corresponding author. Permanent address: Department of Chemistry, Faculty of Science, Ege University, Bornova, 35100 Izmir, Turkey. Tel./fax: þ90 232 3888264. ** Corresponding author. E-mail address: jale.yanik@ege.edu.tr (J. Yanik). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.06.024 international journal of hydrogen energy 33 (2008) 4520–4526