Publication Catalysis 2008
J. Cheng, P. Hu, P. Ellis, S. French, G. Kelly, C. M. Lok, J. Phys. Chem. C 2008, 112, 9464.
Extensive d. function theory calcns. are performed to study the mechanism of the formation of aldehyde and alc. on Co surfaces in Fischer-Tropsch synthesis, a challenging issue in heterogeneous catalysis. Three possible pathways for the prodn. of formaldehyde and methanol on flat and stepped Co(0001) surfaces are investigated: (i) CO + 4H â†’ CHO + 3H â†’ CH2O + 2H â†’ CH3O + H â†’ CH3OH; (ii) CO + 4H â†’ COH + 3H â†’ CHOH + 2H â†’ CH2OH + H â†’ CH3OH; and (iii) the coupling reactions of CH2 + O â†’ CH2O and CH3 + OH â†’ CH3OH. It is found that these pathways are generally favored at step sites, and the preferred mechanism is pathway (i) via CHO.
Furthermore, the three traditional chain growth mechanisms in Fischer-Tropsch synthesis are semiquant. compared and discussed. Our results suggest that the two mechanisms involving oxygenate intermediates (the CO-insertion and hydroxycarbene mechanisms) are less important than the carbene mechanism in the prodn. of long chain hydrocarbons. However, the CO-insertion mechanism may be responsible for the prodn. of long-chain oxygenates.