Mechanistic and kinetic studies of the surface chemistry of iridium and ruthenium
Quantitative investigations of the mechanisms and the kinetics of the surface-catalyzed activation of C-H, N-H, C-C, and C-N bonds on the close-packed surfaces of Ir(111) and Ru(001) have been performed. The interaction of CH_3NH_2 with Ru(001) was investigated in ultrahigh vacuum with the techn...
| Summary: | Quantitative investigations of the mechanisms and the kinetics of the
surface-catalyzed activation of C-H, N-H, C-C, and C-N bonds on the close-packed
surfaces of Ir(111) and Ru(001) have been performed. The interaction
of CH_3NH_2 with Ru(001) was investigated in ultrahigh vacuum with the
techniques of high-resolution electron energy loss spectroscopy and thermal
desorption mass spectrometry. Activation of the central C-N bond is
observed, but it is less favored than the competing channel of complete
dehydrogenation, by a ratio between 2:1 to 3:1. The decomposition
mechanism has been characterized with several surface intermediates and
gas-phase products identified. A pronounced preference for the activation of
C-H over N-H and C-N bonds has been established. Additionally, the kinetics
of the initial dissociation of short chain alkanes on Ir(111) has been
examined, and the rate parameters of the activation of C-C bonds and
primary, secondary, and tertiary C-H bonds have been determined. The
formation of primary alkyl products is favored, over most of the experimental
temperature range, despite the thermodynamic preference for the activation
of individual secondary and tertiary C-H bonds in comparison to individual
primary C-H bonds. At higher surface temperatures, the activation of C-C
bonds occurs at competitive rates to the C-H reaction channel. The measured
deuterium kinetic isotope effect implicates substantial deformation of the
terminal methyl group in the transition state of C-C bond cleavage. Finally,
the surface structure sensitivity of C-H bond cleavage has been quantified for
smooth (111) and corrugated (110) surfaces of iridium and platinum, as well
as for step edge defect sites on Ir(111).
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