Effect of chloride on the sinterization of Au/CeO2 catalysts

Gold was loaded on commercial CeO2 and on ceria prepared by the solvothermal method (at pKa = 8.5 at T = 120, 150 and 220 °C, and pKa = 26.5 at T = 150 °C) by a traditional impregnation method (IMP) and by liquid-phase reductive deposition (LPRD). Activities for CO oxidation were compared and results discussed. Ceria samples prepared by IMP showed up to 1.1 wt.%. chloride present and much lower activity than those prepared by LPRD, which had no residual chloride. Full CO conversion was obtained at ∼200 °C for most LPRD samples, while at that same temperature, for the IMP samples, the conversion varied from 2% (commercial ceria) to 16% (solvothermal ceria prepared at pKa = 8.5 and T = 120 °C). Sintering of gold was quite evident in all IMP materials, possibly due to the presence of chloride. The commercial CeO2 was the most sensitive to chloride, only achieving full CO conversion at ∼700 °C, thus behaving similarly to the support. This was likely due to the large Au nanoparticle size (up to 400 nm), when compared with the solvothermal ceria (up to 200 nm). LPRD samples had lower particle sizes (ranging from 3 to 50 nm) and contain gold in the oxidic form, while IMP samples showed gold in the reduced form.