The main concern about the technology for the production of hydrogen and transport fuels by biomass gasification is the presence of contaminants (H2S, tars, fly ash, alkali, and heavy metals, ammonia) that are poisonous for the catalysts used for upgrading the biomass-generated gas. The impact of the main contaminants on a Ni/MgAl(O) reforming catalyst as studied in a laboratory environment, by exposing the studied sample to H2S, NH3, K2SO4, KCl, ZnCl2, and a solution derived from biomass fly ash. Lastly, the catalyst was also streamed with a gas produced by a bench-scale downdraft gasifier. The extent of deactivation was examined in the methane steam reforming reaction, under different operational conditions. The main effect of the treatments was a decrease in the bulk surface area and in the metal dispersion. Streaming H2S quickly deactivated the catalyst; however, the activity was recovered by increasing the inlet temperature or by adding O-2 to the stream. In further laboratory tests, the performances of the catalyst seemed not to be greatly affected by either the above treatments or by the presence of ammonia in the fed water. The catalyst produced a syngas composition close to that predicted at equilibrium even after being streamed with the biomass-generated gas. (c) 2007 Elsevier Ltd. All rights reserved.