Regensburg 2016 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 31: Heterogeneous Catalysis: Theory
O 31.6: Vortrag
Dienstag, 8. März 2016, 11:45–12:00, S053
CH2 stabilization and dissociation at steps on Ru(0001) in UHV — •Harald Kirsch, Xunhua Zhao, Sergey Levchenko, and R. Kramer Campen — Fritz-Haber-Institut Berlin, Faradayweg 4-6, 14195 Berlin
In this study we investigated the dissociation of defect(step) bonded CH2, produced by methane dissociation on Ru(0001) under UHV conditions. Dissociated sticking of CH4 was performed by using a supersonic molecular beam source. By using vibrational sum frequency generation(SFG) spectroscopy, we found the characteristic CH-stretch vibration of step adsorbed CH2 at 2925cm−1. The observed species saturated at coverages of about 3-5% of a monolayer of carbon. An Arrhenius analysis of the temperature dependent stability gave an activation energy for the depletion of our signal of 45 kJ/mol. This value is 3 times higher than the calculated dissociation barrier of isolated CH2 at terrace sites. DFT calculations, performed on this system rationalize this observation by a two step process. First by the diffusion and subsequent dissociation of CH2 to CH + H, when moving from a step to a nearby terrace site(barrier ≈ 14 kJ/mol). This CH stabilizes remained CH2 at steps, produced by ongoing dosing of methane, by increasing the combined diffusion and dissociation barrier to ≈ 37 kJ/mol. These results may contribute to a better understanding of the active species in the Fischer-Tropsch Synthesis.