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The Adsorption and Decomposition of C2H4 on Ru(001): A Combined TPR and Work Function Change Study

Summary: The Adsorption and Decomposition of C2H4 on Ru(001): A Combined TPR and Work
Function Change Study
T. Livneh*, and M. Asscher
Department of Physical Chemistry and The Farkas Center for Light Induced Processes,
The Hebrew UniVersity, Jerusalem 91904, Israel
ReceiVed: January 21, 2000; In Final Form: February 1, 2000
Work function change () measurements during adsorption and surface heating in a -temperature
programmed reaction (TPR) mode combined with TPD are demonstrated to provide new information on the
interaction and chemistry of ethylene on Ru(001). Rearrangement of second layer ethylene molecules has
been observed between 82 and 120 K. This is a competing process with molecular desorption, interpreted as
a result of migration of second layer molecules toward the surface. Our results are consistent with and support
previous studies that suggested the formation of a surface intermediate (2(C,C)CHCH2) during ethylene
dehydrogenation to ethylidine. Employing a derivative mode with respect to temperature -d()/dT, we
find an early onset for ethylidine decomposition near 265 K. -TPR measurements in the range 560-720
K reveal three distinct CH decomposition peaks, reflecting different activation energies for the decomposition
reaction sites. The dipole moment of an adsorbed CH has been determined to be ) 0.43 D, suggesting a
rather polarized Ru-CH complex; its structure is independent of the adsorption site. Finally, carbide
polymerization to form graphite has been detected above Ts ) 560 K for the first time using work function
change measurements. Good agreement was found between the contribution to by the graphite layer
formed on the Ru(001) surface and ab initio calculations performed previously on this system.


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


Collections: Chemistry