Selective oxidation of hydrocarbons using supported gold, silver, copper and bimetallic catalysts

Supported gold catalysts can provide tuneable activity for liquid phase selective oxidation of alkenes, in particular cyclohexene and cis-cyclooctene, using molecular oxygen from air under mild conditions. Selective oxidation can be readily kick-started using a nano-crystalline gold catalyst supported on carbon along with a small amount of TBHP as initiator. Extremely high selectivity, ca. 98%, for partial oxidation products with significant conversion has been obtained using a bismuth-modified gold catalyst for selective oxidation of cyclohexene. In the case of cis-cyclooctene oxidation, high selectivity to partial oxidation products has also been achieved at a high rate of reaction, without the use of solvent, which is a major tenet of green chemistry. Gold catalysts are also active for the selective oxidation of cyclohexane to cyclohexanol and cyclohexanone. The gas-phase epoxidation of propene to propene epoxide (PO) has been studied using only molecular oxygen as oxidant over a series of supported Ag, Cu, Au and bimetallic (Au-Cu, Cu-Ag and Au-Ag) catalysts. It has been found that the support has an important effect on the catalyst performance. A Au-Cu catalyst exhibited very high selectivity to PO, ca. 96%, at a propene conversion, ca. 0.14%, at relatively low temperature, 200 C. The intrinsic instability of PO leads to the observation of high selectivity to PO only at low temperature.