Epoxidation of styrene by anhydrous t-butyl hydroperoxide over gold supported on Al2O3, Ga2O3, In2O3 and Tl2O3

Group IIIa metal (viz. Al, Ga, In and Tl) oxide-supported gold nanoparticles, prepared by deposition-precipitation (DP) using NaOH and by homogeneous deposition-precipitation (HDP) using urea, were employed as highly active/selective and reusable catalysts for the epoxidation of styrene (at 82 degreesC) by anhydrous t-butyl hydroperoxide (TBHP). The loading and average particle size of gold, when it was deposited on the Gr. IIIa metal oxides by the HDP, was found to increase in the following order: Al2O3 (6.36 wt.%, 4.1 +/- 2.3 nm) < Ga2O3 (6.43 wt.%, 6.67 +/- 3.7 nm) < In2O3 (6.81 wt.%, 15.6 +/- 6.3 nm) < Tl2O3 (8.00 wt.%, 24.4 +/- 13.1 nm). Both the activity and the epoxide selectivity of the supported gold catalysts are in the following order: Au/Al2O3 < Au/Ga2O3 < Au/In2O3 < Au/Tl2O3. Using the DP method, the Au loading on Al2O3 and Tl2O3 was found to be 2.10 and 5.42 wt.%, respectively, such values are much lower than those achieved by the HDP method. The Al2O3, Ga2O3 and In2O3 supports alone showed little or no epoxidation activity/selectivity. However, the Tl2O3 support alone showed the activity and epoxide selectivity comparable to that of the Au/Tl2O3 Catalysts. The surface species on the Au/Al2O3 were found to be only metallic gold (Au-0) ones and Al in single oxidation state (Al3+). However, the surface species on the Au/In2O3 were both the metallic and ionic gold (Au-0 and Au3+) and the indium in two oxidation states (In3+ and In2+ or In1+). The gold loading and both the epoxidation activity and selectivity are increased with increasing the basicity and/or reduction potential of the support used in the supported Au catalysts. (C) 2004 Elsevier B.V. All rights reserved.