Gold nanoparticles: Support effects for the WGS reaction

Abstract

Gold nanoparticles supported on reducible (TiO 2 and CeO 2) and non-reducible oxides (Al 2O 3 and SiO 2) 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 TiO 2, CeO 2 and Al 2O 3. Cationic adsorption was used as preparation method in the case of SiO 2. Metal loading was fixed to 4 and 8 wt.%. The WGS reaction was studied in the temperature range from 50 to 400 °C in a flow reactor at atmospheric pressure. Before reaction the samples were calcined at 200, 300 or 400 °C to study the effect of calcination temperature in the catalyst activity. The Au/CeO 2 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/TiO 2 catalyst. When supported on TiO 2 and CeO 2, the activity of gold nanoparticles was much higher than the one observed when supported on Al 2O 3 and SiO 2 being the Au/SiO 2 catalyst practically inactive. For samples calcined at 300 °C and reaction temperatures below 225 °C the activity varied as follows: TiO 2 > CeO 2 ≫ Al 2O 3. CO adsorption in the presence of H 2O was followed by DRIFT. Bands coming from C–H stretching associated to formate species were clearly observed on CeO 2. Intensity of these bands decreased when Au is present on the supports. Au 0-CO adsorption band was evidenced when Au is supported on TiO 2, CeO 2 and Al 2O 3. Fast conversion of formate species in Au/TiO 2 and Au/CeO 2 takes place and this explains the higher activity displayed by these catalysts.