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Free keywords:
Methane dissociation;
Methane coupling;
Density functional theory;
Sum frequency generation
Abstract:
Understanding the relative stability of CHx species on surfaces is necessary for mechanistic description of much important catalytic chemistry. Here, we experimentally quantify the barrier of the reaction CH2→CH+HCH2→CH+H on Ru(0001) in UHV and find an activation energy, 65 ± 6 kJ/mol, that is >4× higher than previous computational results with 0, 1, or 2 coadsorbed H atoms per CH2, i.e. 16 kJ/mol. Employing density functional theory calculations, we show that this disagreement can be reconciled if 3 coadsorbed H atoms per CH2 are present in our experiment. 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 additional hydrogen surface coverage requires non-equilibrium conditions. Such conditions may be important at the high temperatures and pressures of real catalytic systems.
