Controlling CH2 dissociation on Ru(0001) through surface site blocking by adsorbed hydrogen

• We investigate the intermediates in methane dissociation on Ru(0001).
• We find experimentally the barrier for CH2 → CH conversion is 65 kJ/mol.
• We find computationally that this barrier requires 3 coadsorbed H atoms per CH2.
• Computation shows this barrier requires nonequilibrium between surface and gas phases.

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.

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