Berlin 2015 – scientific programme
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O: Fachverband Oberflächenphysik
O 24: Catalysis: Structural Effects
O 24.8: Talk
Tuesday, March 17, 2015, 12:15–12:30, MA 144
Stabilization of CH2 on Ru(0001) by hydrogen co-adsorption — •Xunhua Zhao1, Harald Kirsch1, Zefeng Ren1,2, R. Kramer Campen1, Sergey V. Levchenko1, Martin Wolf1, and Matthias Scheffler1 — 1Fritz-Haber-Institut der MPG, Berlin, DE — 2Present address: Peking University, Beijing, CN
Based on indirect experimental evidence, CH2 was proposed as a buidling block for hydrocarbon chain growth on the Ru(0001) surface during the Fischer-Tropsch process. However, previous calculations agreed that CH2 is not stable on Ru(0001) at the reaction conditions, and should quickly convert into CH. Employing density-functional theory, we show that this disagreement can be reconciled if coadsorbed hydrogen is present on the surface. All possible CHx+Hy configurations with adsorbates at hollow sites are calculated. CHx dissociation barriers are obtained using the string method. We further demonstrate, by calculating the surface phase diagram for one-carbon species on Ru(0001) as a function of H2 chemical potential, that the stablization of CH2 by co-adsorbed hydrogen requires non-equilibrium conditions. The calculated barrier for the CH2 dissociation in the presence of hydrogen is significantly increased, and is close to the one recently measured by vibrational sum-frequency generation spectroscopy [1]. Our results also explain why CH2 was not observed when C or CH are hydrogenated on Ru(0001) [2], although it is observed after methane decomposition.—[1] H. Kirsch, X. Zhao, Z. Ren, S. V. Levchenko, M. Wolf, and R. K. Campen, J. Catal. 320, 89 (2014); [2] T. K. Shimizu et al., J. Chem. Phys. 129, 244103 (2008).