Coadsorption of benzene and oxygen on Ru(001)

Abstract

The coadsorption system benzene + O on Ru(001) has been studied using HREELS, TDS, LEED and Δø-measurements. For increasing amounts of oxygen ( θ O < 0.22) the starting points of benzene dissociation as well as of molecular desorption are strongly shifted to higher temperatures. A direct correlation between these processes can be stated. For θ O = 0.16–0.22 a well-ordered (3 × 3) LEED superstructure is found. HREEL spectra show that the mutual distortion of the vibrational modes of both coadsorbates is substantial. From comparison with the results for the pure layers it is deduced that a net charge transfer from benzene to the oxygen atoms is the most likely origin for these observed mutual influences. An increase of temperature leads to an autocatalytic destruction of this ordered layer which may be triggered by molecular desorption of benzene followed by instantaneous dehydrogenation of neighbouring molecules. The reaction path at higher temperatures ( T⩾500 K) is strongly influenced by the oxidation of surface carbon to form CO. A parallel dehydrogenation of the benzene fragments is observed, and the two processes seem to also affect each other.