Effect of the CO coverage on the Fischer–Tropsch synthesis mechanism on cobalt catalysts

Recent Progresses in Understanding of Co-Based Fischer–Tropsch Catalysis by Means of Transient Kinetic Studies and Theoretical Analysis

“…PBE functional [124] or PW functional [123]), and other parameters were employed in these calculations. Despite this fact, similar trends can be observed Understanding of Co-Based F-T Catalysis 147 PBE functional, PAW pseudopotential in VASP package were employed [114,117], and the data in parentheses are calculated on Co (0001) with 1/3 ML CO coverage [117]. Perdew-Burke-Ernzerhor form (PBE) of generalized gradient corrections and Troullier-Martins norm-conserving scalar relativistic pesudopotential in SIESTA package were employed [116,120,121].…”

“…However, the small difference on CO and H adsorption energies between HCP and FCC Co, 0.08 and 0.07 eV, respectively [113], reveals the weak structure sensitivity for the adsorption of the reactant. The effect of CO coverage on the chemisorption of some surface species, H, CO, CH, CH 2 , CH 3 , HCO, HCOH, CH 2 O and so on, has been investigated on Co (0001) with different CO coverages, 1/4, 1/3 and 1/2 ML, as listed in Table 1 [32,40,117]. In general, the pre-covered CO molecule decreases the stability of other molecules, especially for larger molecules such as HCOH, due to the repulsive interaction between the adsorbed species.…”

“…Furthermore, Liu et al [115] elucidated that the barriers of hydrogen-assisted CO activation are 0.73, 1.04 and 0.72 eV on Co (0001), Co (10-12) and Co (11)(12)(13)(14)(15)(16)(17)(18)(19)(20) surfaces, respectively indicating that the hydrogen-assisted CO dissociation is also a structure sensitive reaction which depends on the local structure of the active sites. [40], where the data in the parentheses were calculated on the surface with 0.5 ML pre-covered CO b Ref [28] c Ref [114] d Ref [130 e Ref [131] f Ref [120] g Ref [119], where the data in the parentheses were calculated on O pre-covered surface h Ref [118] i Ref [29] j Ref [117], where the data in the parentheses were calculated on Co (0001) with 1/3 ML CO coverage k Ref [115] l Ref [113] m Ref [32], where the surface with 1/4 ML pre-covered CO Understanding of Co-Based F-T Catalysis 151…”

“…CH 2 are still the most possible chain growth pathways for C 2 ? C 1 coupling based on Table 4 The activation energies of elementary steps involved in chain propagation and termination for the carbide mechanism a Ref [116] b Ref [36] c Ref [119] d Ref [144] e Ref [117], where the data in the parentheses were calculated on Co (0001) 13 CO and H 2 , the isotopic content was monitored for propane formation. The carbide mechanism should produce all kinds of combination with 12 C and 13 C in propane; the CO insertion mechanism should produce 12 C-13 C-13 C and 13 C-13 C-13 C and the hydroxyl mechanism should produce 13 C-13 C-13 C. Based on the composition of the produced propane, it was concluded that only the carbide mechanism could produce the product compositions and the other mechanisms were therefore excluded.…”

“…However, the calculated TOF is still lower than the experimental TOF, owing to the effect of CO coverage on the energetic data that is not taken into account. Furthermore, the effect of CO coverage on the CO insertion mechanism was studied [117]. The higher CO coverage decreased the activation barrier for the CH 2 ?…”