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 → CHO + 3H → CH2O + 2H → CH3O + H → CH3OH; (ii) CO + 4H → COH + 3H → CHOH + 2H → CH2OH + H → CH3OH; and (iii) the coupling reactions of CH2 + O → CH2O and CH3 + OH → 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.


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