A comparative surface science study of carbide and oxycarbide: the effect of oxygen modification on the surface reactivity of C/W(1 1 1)

The dehydrogenation of cylohexene to benzene has been used as a probe reaction to study the properties of oxygen-modified C/W(1 1 1) surfaces by temperature programmed desorption, Auger electron spectroscopy and high-resolution electron energy loss spectroscopy. The reactivity of oxygen-modified C/W(1 1 1) depends strongly on the temperature at which the C/W(1 1 1) surface is exposed to oxygen. The oxygen-modified C/W(1 1 1) surface, after exposing to oxygen at 900 K, promotes the selective dehydrogenation of cyclohexene to benzene. The selectivity to benzene on this surface is ∼83%, which is slightly higher than that observed on unmodified C/W(1 1 1) and on Pt(1 1 1). In contrast, oxygen-modified C/W(1 1 1) surfaces with low temperature (<600 K) oxygen exposure are relatively inert towards the dehydrogenation or decomposition of cyclohexene. We propose that the different reactivities of these surfaces are related to the different types of oxygen binding sites on C/W(1 1 1).