The surface diffusion of n-alkanes on Ru(OOI) was measured using laser-induced thermal desorption (LITD) techniques. The surface diffusion coefficients for propane, n-butane, npentane, and n-hexane all displayed Arrhenius behavior. The surface diffusion activation energies increased linearly with carbon chain length from Edif = 3.0 ± 0.1 kcallmol for propane to Edif = 4.8 ± 0.2 kcallmol for n-hexane. In contrast, the surface diffusion preexponentials remained nearly constant at Do =0.15 cm 2 Is. Measurements performed at different coverages also revealed that the surface diffusion coefficients were coverageindependent for all the n-alkanes on Ru(OOI). The surface corrugation ratio 0 was defined as the ratio of the diffusion activation energy to the desorption activation energy, 0 = Edif IE des ' The surface corrugation ratio was observed to be remarkably constant at 0=0.3 for all the nalkanes. This constant corrugation ratio indicated a linear scaling between the diffusion activation energy and the desorption activation energy. This behavior also suggested that the nalkanes move with a rigid configuration parallel to the Ru(OOI) surface.5136

The surface diffusion coefficient for hydrogen on Ru(001) at low coverage was measured using laser-induced thermal desorption techniques. In the temperature range between 260 and 330 K, the diffusion coefficients displayed Arrhenius behavior with an activation barrier Ediff=4.0±0.5 kcal and a preexponential factor D0=6.3×10−4 cm2/s. Agreement between the experimental and theoretical parameters suggests that hydrogen diffuses on the surface by moving from a threefold site to a neighboring threefold site via a twofold site. Surface contaminants such as carbon and oxygen were observed to produce dramatic effects on the hydrogen surface diffusion rate.

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The decomposition reaction of methanol on Ru(001) was studied using laser induced thermal desorption (LITD). The LITD studies, combined with temperature programmed desorption and Auger electron spectroscopy measurements, allowed absolute product yields for the three competing surface pathways to be determined over the entire range of chemisorbed methanol coverages at a heating rate of β=2.6 K/s. At the lowest methanol coverages of θ≤0.07θs, where θs is the surface coverage of a saturated chemisorbed layer, all the methanol reacted between 220–280 K. This methanol decomposition reaction yielded desorption-limited H2 and CO as reaction products. At higher coverages, molecular desorption and the second methanol decomposition reaction involving C–O bond breakage became increasingly important. At θ=θs, 50% of the initial methanol coverage desorbed, 24% produced H2 and CO and 26% left C on the surface. Isothermal LITD kinetic measurements were carried out at low methanol coverages of θ≤0.07θs at various temperatures from 180 to 220 K. The initial decomposition rates obtained from the isothermal LITD studies displayed first order kinetics. The decomposition kinetics at later times could not be fit by first order kinetics and suggested a self-poisoned reaction. Subsequent LITD studies revealed that CO inhibited the decomposition reaction. The product CO inhibition was modeled by first order kinetics with a CO-coverage dependent activation barrier. The observed first order reaction kinetics at low methanol coverage could be expressed by the pre-exponential ν=106 s−1 and the coverage-dependent activation barrier E=7 kcal/mol+αθCO/θCO,s, where α=20 kcal/mol and θCO/θCO,s is the dimensionless CO coverage normalized to the CO saturation coverage θCO,s. Isotopic LITD studies revealed that the decomposition kinetics of CH3OH, CD3OH, and CH3OD were identical. This equivalence suggested that the hindered rotation of the surface methoxy species is the reaction coordinate for the rate-limiting step in the decomposition reaction.

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