HIGH-RESOLUTION ELECTRON ENERGY-LOSS STUDIES OF HYDROCARBON FORMATION FROM METHANE DECOMPOSITION ON RU(0001) AND RU(11(2)OVER-BAR-0) CATALYSTS

The reaction of methane with single-crystal ruthenium catalysts has been studied utilizing an elevated-pressure microreactor (contiguous to a surface analysis system), high-resolution electron energy-loss spectroscopy (HREELS), and temperature-programmed desorption (TPD). Methane is found to dissociate on Ru(0001) and Ru(1120) surfaces to form various hydrocarbon intermediates. On the Ru(1120) surface, three distinct forms of surface hydrocarbon species are identified: methylidyne (CH), vinylidene (CCH2) and ethylidyne (CCH3). On the Ru(0001) surface only the methylidyne and vinylidene species were observed. At reaction temperatures exceeding 700 K, no loss features associated with surface hydrocarbon species are found. HREELS measurements and CO titration experiments indicate the presence of a surface graphitic phase at temperatures >700 K. A comparison is also made between the surface carbon species found in the present study and the carbon types found on supported catalysts.