493
comprehensive kinetic models have been done either on an cobalt-based or ironbased catalyst. The major similarity among the model was the selection of α-olefin
re-adsorption as a secondary reaction. As discussed above and shown in Table 2,
although the models are complicated and the model development and validation is
a cumbersome task, the results are significantly good.
In a slightly different approach of comprehensive kinetic modeling, Botes et al.
[106] introduced the exponential relationship of the rate of formation of olefins with
the carbon number. They implemented the theory of physisorption of long-chained
olefin on the catalyst surface after the detachment of the catalyst site. And the affinity of olefin with surface increases with the carbon number in the chain, which in
turn decreases the probability of its desorption from the surface to the gas phase.
The intact olefin re-inserts into another growing chain. The effect of physisorption
and the chain length was incorporated through the addition of exponential terms in
the models. Based on this assumption, Todic et al. [91] developed the comprehensive kinetic model, combining CO insertion mechanism and chain length–dependent α-olefin desorption over an alumina-based cobalt catalyst. The model
successfully addresses the various shortcomings of earlier selectivity models, such
as a significant decrease in olefin to paraffin ratio with chain length and changing
the value of α. While deriving the model, they did not consider the reversibility of
secondary reaction as taken up by others [99, 100, 119]. In a road of extension of
this work, Bhatelia and co-worker [103] also applied CO insertion mechanism as
CO activation and α-olefin re-adsorption and chain length–dependent desorption
mechanism for model derivation over Co–Ru–La/Al 2 O 3 . They added an exponential
term in the olefin desorption reaction, and the term βn was added to incorporate the
re-adsorption of α-olefin. The model described its product distribution well.
However, the result does not differ much from the results by the model of Todic
et al. [91]. At the same time, simultaneous consideration of both chain length dependency and α-olefin readsorption increase the intricacy of the model, which increased
the time for the computation and affected the accuracy of results. In a similar line,
Pant et al. [90] performed detailed kinetic study over Fe-Co bimetallic catalyst to
determine the product formation rate. The models were developed considering both
chain length–dependent α-olefin desorption and α-olefin re-adsorption as a secondary reaction which was coupled with alky or alkenyl mechanism for chain propagation. Both the proposals of secondary reaction were tested and compared with the
experimental data over Fe-Co bimetallic catalyst to choose a more suitable model.
4 Conclusion
The complex chain reaction and related mechanism resulted in complexity in the
kinetics of the reaction. It always remains debated since several kinetic and mechanistic factors are involved, and the physio-chemical phenomena governing the
mechanism is still a topic of debate. The FT synthesis kinetic has been approached
by different pathways. In the first one, the simplification was made by using
Recent Advancements and Detailed Understanding of Kinetics for Synthesis Gas…
comprehensive kinetic models have been done either on an cobalt-based or ironbased catalyst. The major similarity among the model was the selection of α-olefin
re-adsorption as a secondary reaction. As discussed above and shown in Table 2,
although the models are complicated and the model development and validation is
a cumbersome task, the results are significantly good.
In a slightly different approach of comprehensive kinetic modeling, Botes et al.
[106] introduced the exponential relationship of the rate of formation of olefins with
the carbon number. They implemented the theory of physisorption of long-chained
olefin on the catalyst surface after the detachment of the catalyst site. And the affinity of olefin with surface increases with the carbon number in the chain, which in
turn decreases the probability of its desorption from the surface to the gas phase.
The intact olefin re-inserts into another growing chain. The effect of physisorption
and the chain length was incorporated through the addition of exponential terms in
the models. Based on this assumption, Todic et al. [91] developed the comprehensive kinetic model, combining CO insertion mechanism and chain length–dependent α-olefin desorption over an alumina-based cobalt catalyst. The model
successfully addresses the various shortcomings of earlier selectivity models, such
as a significant decrease in olefin to paraffin ratio with chain length and changing
the value of α. While deriving the model, they did not consider the reversibility of
secondary reaction as taken up by others [99, 100, 119]. In a road of extension of
this work, Bhatelia and co-worker [103] also applied CO insertion mechanism as
CO activation and α-olefin re-adsorption and chain length–dependent desorption
mechanism for model derivation over Co–Ru–La/Al 2 O 3 . They added an exponential
term in the olefin desorption reaction, and the term βn was added to incorporate the
re-adsorption of α-olefin. The model described its product distribution well.
However, the result does not differ much from the results by the model of Todic
et al. [91]. At the same time, simultaneous consideration of both chain length dependency and α-olefin readsorption increase the intricacy of the model, which increased
the time for the computation and affected the accuracy of results. In a similar line,
Pant et al. [90] performed detailed kinetic study over Fe-Co bimetallic catalyst to
determine the product formation rate. The models were developed considering both
chain length–dependent α-olefin desorption and α-olefin re-adsorption as a secondary reaction which was coupled with alky or alkenyl mechanism for chain propagation. Both the proposals of secondary reaction were tested and compared with the
experimental data over Fe-Co bimetallic catalyst to choose a more suitable model.
4 Conclusion
The complex chain reaction and related mechanism resulted in complexity in the
kinetics of the reaction. It always remains debated since several kinetic and mechanistic factors are involved, and the physio-chemical phenomena governing the
mechanism is still a topic of debate. The FT synthesis kinetic has been approached
by different pathways. In the first one, the simplification was made by using
Recent Advancements and Detailed Understanding of Kinetics for Synthesis Gas…