Influence of the surface area of the support on the activity of gold catalysts for CO oxidation

In the preparation of 1% Au/TiO2 catalysts supported on either Degussa P-25 or anatase (90 m2 g−1) by deposition–precipitation, the gold content passes through a maximum at about the isoelectric point (pH ∼6), but maximum specific rates occur at pH 8–9 because the Au particle size becomes smaller as the pH is further increased. The gold uptake increases with the surface area of the support (anatase, rutile, P-25) and is complete above 200 m2 g−1; adsorption of the gold precursor at pH 9 is shown to be equilibrium-limited. Highest activities are found with supports of ∼50 m2 g−1. Catalysts made with high-area anatase (240 or 305 m2 g−1) are least active but show least deactivation.With Au/SnO2 catalysts, gold uptake does not depend on the area of the support, and is highest at pH 7–8; very active catalysts (T50 = 230–238 K) are obtained using SnO2 of 47 m2 g−1. Storing a catalyst at 258 K for 1 week dramatically improves its stability. Results for Au/CeO2 and Au/ZrO2 catalysts confirm that moderate support areas give the most active catalysts, and suggest that surface area is often more important than chemical composition.