Critical influence of adsorption geometry in the heterogeneous epoxidation of allylic alkenes

F. J. WILLIAMS; R. L. CROPLEY; O. P. H. VAUGHAN; A. J. URQUHART; M. S. TIKHOV; C. KOLCZEWSKI; K. HERMANN; R. M. LAMBERT

San Carlos de Bariloche, Argentina

Conferencia; 13th International Conference on Solid Films and Surfaces (ICSFS-13); 2006

International Conference on Solid Films and Surfaces

Propene epoxide is a valuable and versatile chemical intermediate used in a wide range of process technologies. Although direct heterogeneous epoxidation of propene by oxygen is desirable, approaches based on existing heterogeneous methodology fail. It has been hypothesized that this is due to the presence of labile "allylic" hydrogen atoms in propene and related higher alkenes. Here, we show that three phenylpropene isomers adsorb on Cu(111) with distinctly different geometries that result in three very different types of behavior towards the oxygenated surface?extensive combustion, extensive epoxidation and almost no reaction at all. A clear correlation between the chemistry and the proximity to the surface of the allylic and olefinic functionalities emerges demonstrating the critical role played by molecular conformation in determining reactive behavior.