Biomass char, by-product of Dunaliella salina pyrolysis at a final pyrolysis temperature of 500 degrees C, was used as feedstock material in this study. The reactions of biomass char with CO2 were performed in a fixed-bed reactor to evaluate the effect of temperature and steam on the CO2 conversion, CO yield and gas composition. The CO2 conversion and CO yield without steam and catalyst reached about 61.84% and 0.99 mol/(mol CO2) at 800 degrees C, respectively. Steam and high temperature led to high CO2 conversion. A new approach for improving H-2 was carried out by using biomass char and Au/Al2O3 catalyst, which combined steam gasification of biomass char and water gas shift reaction, and the H-2 concentration was 1.8 times higher than without catalyst. The process not only mitigated CO2 emission and made use of residual biomass char, but also created renewable source. (C) 2012 Elsevier Ltd. All rights reserved.