(590e) Towards Understanding Chlorine Promotion Of Partial Oxidation On Au: Interactions Of Oxygen And Chlorine On Au(111)

Gold has recently been found as an active catalyst for olefin partial oxidation reactions. For the further development of gold catalysts for practical applications, improvement in selectivity becomes a challenging issue. In this regard, we find that chlorine dramatically increases the selectivity for olefin partial oxidation on Au(111) by completely inhibiting secondary oxidation products, including acids, CO2, H2O, and residual carbon. In order to further understand the promotion mechanism, we study interaction of oxygen and chlorine on Au(111) by using scanning tunneling microscopy (STM) combined with temperature programmed desorption (TPD), low energy electron diffraction (LEED), X-ray photo electron spectroscopy as well as density functional theory calculations.

On clean Au(111), chlorine exhibits complex desorption behavior at different coverages according to TPD experiments. LEED and STM further reveal that chlorine interacting with gold involves incorporation of gold atoms to form surface compound with different structural ordering. When co-adsorbed on Au(111), chlorine decreases oxygen desorption temperature (from 545 K to 510 K) and modifies oxygen desorption mechanisms. By using STM, it is visualized that chlorine effectively disperses and redistributes Au islands stabilized by oxygen on the surface. The dispersal of Au islands also prevents the ordering of oxygen on the surface at room temperature. The change of oxygen spatial organization upon interaction with chlorine is used to explain one of the major mechanisms for chlorine promotion of olefin oxidation by Au.