Ni/Al coprecipitated catalysts modified with magnesium and copper have been prepared by a constant pH technique and tested in the catalytic steam reforming of model compounds (acetic acid, acetol and butanol) from biomass pyrolysis liquids at 650 degrees C and atmospheric pressure. Catalysts with different copper contents, reduced at 650 degrees C for 1 h, were tested in the steam reforming of acetic acid with a steam/carbon (S/C) molar ratio of 5.6. The best performance and the highest hydrogen yield in these conditions were achieved with the 5% Cu catalyst. This catalyst reduced at 650 degrees C during 10 h showed a high activity, close to the thermodynamic equilibrium, and a stable performance during 12 h in the steam reforming of acetic acid with a S/C = 5.6, using a short space time of 1.00 g catalyst min/g acetic acid. Copper as a promoter produces counterbalanced effects: a decrease in the initial reforming activity and an enhancement of the catalyst stability. The initial steam reforming activity decreased and the CH4 yield increased concurrently with increasing the copper content, because of the Ni dilution effect. Copper has a positive effect inhibiting the formation of encapsulating coke, identified as the cause for deactivation in acetic acid steam reforming with a steam-to-carbon molar ratio (S/C) of 5.6. However, such a positive effect of copper has not been observed in acetic acid steam reforming with S/C = 14.7 or in the steam reforming of acetol and butanol. (C) 2012 Elsevier B.V. All rights reserved.