Decomposition of ethanol over Ru(0001): A DFT study

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 CH _k CO (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.