| Gold-based catalysts have been widely studied due to their promise for low-temperature oxidation processes including partial oxidation of olefins. Properties of gold-based catalysts, such as low operation temperature and high efficiency, have potential to make a big impact both environmentally and economically. However, there are still challenges to implementing Au-based processes. For instance, neither the origin of the catalytic activity of gold nor the underlying reaction mechanisms of many of the reactions carried out on gold catalysts are well understood. From a practical stand point, enhancing the selectivity toward partial oxidation products is also challenging.; The work described here uses an oxygen-covered Au(111) single crystal under ultra high vacuum conditions as a model system to gain insight into important reactions in Au-based catalysis. The use of an oxygen-covered Au(111) surface allows for the elimination of electronically isolated Au particles that may lead to quantum size effects and reduces the complexity of the system since no oxide support is used. Furthermore, it enables the use of surface science techniques such as scanning tunneling microscopy, temperature programmed reaction spectroscopy, x-ray photoelectron spectroscopy, high-resolution electron energy loss spectroscopy and low-energy electron diffraction to gain a fundamental understanding of reactions and to characterize surfaces and surface structures involved in these reactions.; We demonstrate that CO oxidation and olefin epoxidation are promoted by an oxygen-covered extended Au surface. We show, for the first time, that chlorine enhances the selectivity in olefin partial oxidation on Au(111) by inhibiting secondary oxidation including combustion and the deposition of residual carbon. The nature of the promoting effect is probed by characterizing the changes in surface morphology induced by the adsorption of oxygen and chlorine on the Au surface. |
