Berlin 2015 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 24: Catalysis: Structural Effects
O 24.9: Vortrag
Dienstag, 17. März 2015, 12:30–12:45, MA 144
Controlling CH2 dissociation on Ru(0001) through surface site blocking by adsorbed hydrogen — •Harald Kirsch1, Xunhua Zhao1, Sergey V. Levchenko1, Martin Wolf1, Zefeng Ren2, and R. Kramer Campen1 — 1Fritz-Haber-Institut, Faradayweg 4-6, 14195 Berlin, Germany — 2International Center for Quantum Materials and School of Physics, 100871 Beijing, China
Understanding the relative stability of CHx species on surfaces is necessary for mechanistic description of such important catalytic chemistry as the Fischer-Tropsch synthesis or the steam reforming process of methane. Here we investigate the thermal stability of surface bound CH2 radical on Ru(0001). We produce a CH2 covered surface in UHV at low temperatures (< 250 K) by employing a supersonic molecular beam source for CH4 dissociation and characterize CH2 population using vibrational sum frequency spectroscopy (> 5 cm−1 resolution). By this approach we experimentally quantify the barrier of the reaction CH2→CH+H via an Arrhenius analysis and find an activation energy of 65 ± 6 kJ/mol, which is > 4× higher than previous computational results [1]. Our density functional theory calculations show, that this disagreement can be reconciled if 3 coadsorbed H atoms per CH2 are present in our experiment [2] and that such hydrogen coverages require non-equilibrium with respect to the overlying gas phase.
[1] I.M. Ciobica et al, J. Phys. Chem. B 104, 3364 (2000); [2] H. Kirsch, X. Zhao, Z. Ren, S. V. Levchenko, M. Wolf, and R. K. Campen, J. Catal. 320, 89 (2014)