VIBRATIONAL SPECTROSCOPY OF HYDROCARBON INTERMEDIATES ON RU(001)
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High Resolution Electron Energy Loss Spectroscopy (HREELS) and Temperature Programmed Desorption (TPD) were used to examine the adsorption and reaction of ethylene on a Ru(001) surface under ultra-high vacuum conditions. Ethylene adsorbed with sticking probability of order one on the clean Ru(001) surface at 180 K. HREELS results showed that the molecule was perturbed relative to the gas phase: the adsorbed species is di--bonded to the surface, with rehybridization of the carbons from sp2 to sp3 and reduction of the C-C bond order. Upon heating to 280 K this species rearranges to ethylidyne, CH3-C , oriented perpendicular to the surface. The ethylidyne decomposes in a series of steps between 300 and 600 K to liberate hydrogen and deposit surface carbon atoms. HREELS provided direct evidence for the hydrogenation of surface carbon. Following exposure of surface carbon to hydrogen and heating to 370 K, strong CH stretch modes characteristic of surface CH species were observed; however, no CH4 was produced under UHV conditions. Preadsorption of surface oxygen or hydrogen atoms strongly altered the reaction of ethylene: oxygen inhibited ethylene rearrangement while surface hydrogen promoted hydrogenolysis and prevented ethylidyne formation. Previous observations on the selectivity of hydrocarbon synthesis on Ru catalysts are considered in the light of these results. 1984.
