Insight into the C[sbnd]C chain growth in Fischer-Tropsch synthesis on HCP Co(10-10) surface: The effect of crystal facets on the preferred mechanism

Abstract

Spin-polarized DFT calculations are performed to probe into the preferred mechanism of CC chain growth in Fischer-Tropsch synthesis on HCP Co(10-10) with the higher surface area exposed. The effect of HCP Co crystal facets on the preferred mechanism of CC chain growth is identified among carbide mechanism and C(H)O mechanism in the processes of C1 to C4 hydrocarbons. CH2 is the most favored CHx monomer. The C2 hydrocarbon is dominantly formed via carbide mechanism, and CH3CH2 is the most favored C2 hydrocarbon. Subsequently, the most favored C3 hydrocarbon, CH3CH2CH2, is formed via carbide mechanism of CH3CH2 coupling with CH2. Further, the most favored C4 hydrocarbon, CH3CH2CH2CH2, is formed via carbide mechanism of CH3CH2CH2 coupling with CH2. Thus, the preferred mechanism of CC chain growth on Co(10-10) mainly focus on carbide mechanism instead of C(H)O insertion mechanism. The carbide mechanism is that RCH2 coupling with CH2 to R'CH2 (R'RCH2), followed by coupling with CH2 to R''CH2(R''R'CH2) can realized the CC chain growth cycle to form higher hydrocarbons. Finally, the crystal facet of HCP Co catalyst affects the preferred mechanism of CC chain growth, and Co(10-10) via carbide mechanism is more favorable than Co(0 0 0 1) via CHO insertion mechanism.