Decomposition of Ethanol Over Ru(0001): A DFT Study
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We studied decomposition pathways of ethanol on Ru(0001) with periodic slab-model calculations using a DFT-GGA approach. We calculated the adsorption modes of ethanol and several of its dehydrogenation products and we evaluated reaction energies as well as activation barriers of pertinent dehydrogenation, C–C, and C–O cleavage steps. The calculated barrier heights of C–C and C–O scission steps can be related to the number of hydrogen atoms bound to the C1–C2 and C1–O moieties of the intermediates, respectively. Two counteracting effects are at work, increasing with each dehydrogenation: (i) higher order of the pertinent bond of the adsorbate, and (ii) stronger substrate-surface interaction and thus better stabilization of the transition state. For most intermediates we determined C–O cleavage to be both kinetically and thermodynamically favored over C–C scission, except for the highly dehydrogenated species CHkCO (k = 1, 2). Based on the calculated energetics, the most likely decomposition pathway, with a rate-determining barrier at 77 kJ·mol−1, leads to the formation of ketene CH2CO and subsequent C–C cleavage yielding methylene and CO.