Gold nanoparticles supported on reducible (TiO2 and CeO2) and non-reducible oxides (Al2O3 and SiO2) with comparable gold particle size (2.5-3.5 nm) were studied as catalysts in the WGS reaction. Deposition-precipitation with urea (DP Urea) was used to prepare gold nanoparticles supported on TiO2. CeO2, and Al2O3. Cationic adsorption was used as preparation method in the case of SiO2. Metal loading was fixed to 4 and 8 wt. %. The WGS reaction was studied in the temperature range from 50 to 400 degrees C in a flow reactor at atmospheric pressure. Before reaction the samples were calcined at 200, 300 or 400 degrees C to study the effect of calcination temperature in the catalyst activity. The Au/CeO2 catalyst showed an enhanced reduction at low-temperatures as evidenced by the H/Au ratio. The lowest reduction temperature was observed for gold in the Au/TiO2, catalyst. When supported on TiO2, and CeO2, the activity of gold nanoparticles was much higher than the one observed when supported on Al2O3 and SiO2, being the Au/SiO2, catalyst practically inactive. For samples calcined at 300 degrees C and reaction temperatures below 225 degrees C the activity varied as follows: TiO2 > CeO2 >> Al2O3. CO adsorption in the presence of H2O was followed by DRIFT. Bands coming from C-H stretching associated to formate species were clearly observed on CeO,. Intensity of these bands decreased when Au is present on the supports. Au-0-CO adsorption band was evidenced when Au is supported on TiO2, CeO2 and Al2O3. Fast conversion of formate species in Au/TiO2 and Au/CeO2 takes place and this explains the higher activity displayed by these catalysts. (c) 2007 Elsevier B.V. All rights reserved.