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Fischer Tropsch synthesis of syngas to liquid hydrocarbons 233

formation of CO 2 is inhibited [35,107,119]. The kinetic modeling of FT
synthesis over an industrial Fe Cu K catalyst was based on the carbide
polymerization mechanism [120]. The performance of the catalytic FT
catalyst over Ru/Co/Zr/SiO 2 described the kinetic model with the esti-
mation of kinetic parameters to predict the effect of the operating condi-
tions on hydrocarbon distribution and CO consumption [79]. The kinetic
study of Co-based catalysts is inclusive as comparison to Fe catalysts due
to the absence of the WGS reaction and less different catalytic sites. Also,
LHHW kinetic equations on Co-based catalysts are a reliable mechanistic
reaction for the CO conversion, and this is an appropriate approach for
modeling of multipart reaction steps, such as FT process [35,104,110,121].

7.4.2 Kinetics of water gas shift reaction

The WGS reactions have major effect on the partial pressure of FT syn-
thesis reactants to understanding its kinetics reaction. Several studies on
WGS kinetics were reported, and the proposed rate expressions are sum-
marized in Table 7.6. Co catalysts were not active in contrast to Fe-based
catalysts [35,68,123 127]. The WGS reaction could change the FT syn-
thesis rate due to adsorption and desorption reactions, which allows the
separation of H 2 O, H 2 , and CO 2 . The individual WGS kinetics was
widely reported and suggested the appearance of formiate species [35].
The formation of formiate could be due to reaction between hydroxyl
groups or H 2 O and CO in any phase. The WGS reaction was studied on
several supported and unsupported iron oxide and zinc oxide catalyst.
Some authors recommended the WGS reaction over unproven magnetite
process through straight oxidation reaction, while Fe catalysts operate via
oxidation of formiate because of the partial oxidation of Fe cations [128].
It could be concluded that the WGS kinetics under FT synthesis still
requires additional research. Also, the knowledge about the dynamic posi-
tions for FT synthesis with WGS reaction could provide more informa-
tion for the kinetic modeling of FT synthesis process. Several studies on
kinetics focused on empirical rate equations, which are known for CO
conversion; a popular one utilized a simple first order in CO [102,122].
In general, two WGS mechanisms are applied for kinetic reaction, which
convert CO through formiate reaction [128].
In the first model developed by Bohlbro [34], which was established
on straight CO conversion process, CO reacted with adsorbed oxygen
from gas phase, the reaction formed by water decomposition with H 2