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Surface Chemistry of CH3Br and Methyl Modified by Copper Deposition on Ru(001) T. Livneh and M. Asscher*
 

Summary: Surface Chemistry of CH3Br and Methyl Modified by Copper Deposition on Ru(001)
T. Livneh and M. Asscher*
Department of Physical Chemistry and the Farkas Center for Light Induced Processes, The Hebrew UniVersity,
Jerusalem 91904, Israel
ReceiVed: December 3, 1998; In Final Form: March 18, 1999
The chemistry of methyl bromide on Cu/Ru(001) has been studied utilizing work function change ( ) and
temperature-programmed desorption (TPD) measurements. The remarkable modification in the methyl
fragments dehydrogenation at the completion of a single copper layer and the significant difference in reactivity
of the Cu(2 ML)/Ru(001) or Cu(111) surfaces are the focus of this study. A decrease in work function at the
completion of 1 ML CH3Br of 2.15 ( 0.02 eV and 1.33 ( 0.05 eV was measured, respectively, for Ru(001)
and Cu(2 ML)/Ru(001) held at 82 K. Methyl bromide does not dissociate upon adsorption on clean or the
copper-covered surfaces, and it is bound with the bromine down. Copper modifies the reactivity of the Ru
substrate, gradually decreasing the dissociated fraction of CH3Br from 0.55 of the initial one monolayer on
clean Ru(001) to 0.06 on Cu(2 ML)/Ru(001), probably because of defects in the copper layer. The methyl
fragment dehydrogenation rate slows as the copper coverage increases. At a narrow copper coverage range
between 0.8 and 0.95 ML, adsorbed hydrogen and methyl fragments coexist on the surface in the temperature
range 230-280 K. Sequential decomposition channels of the parent molecules and the methyl fragment lead
to a unique enhancement of methane production rate, this on the account of further hydrocarbon
dehydrogenation, as reflected in both p and TPD measurements. Methane is formed on top of copper
terraces as a result of "spill-over" of both methyl and hydrogen atoms, similar to the chemistry over Cu(111)

  

Source: Asscher, Micha - Institute of Chemistry, Hebrew University of Jerusalem

 

Collections: Chemistry