Hydrocarbon chain growth and hydrogenation on V(100): a density functional theory study

The activation of CO, hydrogenation of CHx (x = 0-4) and C2Hy (y = 0-5) species and carbon chain propagation on V(100) were studied by means of periodic density functional theory (DFT) calculations. The results indicate that the activation of CO is very facile on V(100) via direct dissociation rather than H-assisted pathways. The hydrogenation of CHx/C2Hy (except for CC) and the C-C coupling elementary steps are thermodynamically and kinetically unfavorable. The energy barriers to the former reactions are lower than those to the latter ones. The high coverage of reactants and the entropic effect may be the dominant factors responsible for the hydrogenation and carbon chain propagation. The simple microkinetic model built on the basis of the above results shows that CH2 is the dominant CHx species on the surface in the temperature range of 300-800 K. Starting from a high coverage of CH2, the building block of the C-chain, CH2CH2 forms via a coupling reaction and then desorbs from the surface. CH2CH, appearing as the precursor, mainly forms from the coupling of CH2 + CH followed by CH2 insertion leading to CH2CHCH3. Although CH is more likely responsible for the chain propagation than CH2 in view of energy barriers, its contribution suffers from its low coverage at the considered conditions. These results are in good agreement with the experimental results.