CO hydrogenation over K-Co-MoSx catalyst to mixed alcohols: A kinetic analysis

Article abstract of DOI:10.1002/kin.21453

Higher alcohol synthesis (HAS) from syngas is one of the most promising approaches to produce fuels and chemicals. Our recent investigation on HAS showed that potassium-promoted cobalt-molybdenum sulfide is an effective catalyst system. In this study, the intrinsic kinetics of the reaction were studied using this catalyst system under realistic conditions. The study revealed the major oxygenated products are linear alcohols up to butanol and methane is the main hydrocarbon. The higher alcohol products (C₃+) followed an Anderson-Schultz-Flory distribution while the catalyst suppressed methanol and ethanol formation. The optimum reaction conditions were estimated to be at temperature of 340°C, pressure of 117?bar, gas hourly space velocity of 27?000?mL?g^–1h^–1 and H₂/CO molar feed ratio of 1. A kinetic network has been considered and kinetic parameters were estimated by nonlinear regression of the experimental data. The results indicated an increasing apparent activation energy of alcohols with the length of alcohols except for ethanol. The lower apparent activation energy of alcohols compared with hydrocarbon evidenced the efficiency of this catalyst system to facilitate the formation of higher alcohols.

Full text of DOI:10.1002/kin.21453

Received: 30 July 2020
DOI: 10.1002/kin.21453
Revised: 25 October 2020
Accepted: 27 October 2020
A RT I C L E
CO hydrogenation over K-Co-MoS catalyst to mixed
x
alcohols: A kinetic analysis
Leila Negahdar1,3
Hero Jan Heeres2
Xiaoying Xi2
Feng Zeng1
J. G. M. Winkelman2
Regina Palkovits1
1 Heterogeneous Catalysis and Technical
Chemistry, RWTH Aachen University,
Aachen 52074, Germany
2 Green Chemical Reaction Engineering,
Engineering and Technology Institute
Groningen, University of Groningen,
Nijenborgh 4, Groningen 9747AG, The
Netherlands
Abstract
Higher alcohol synthesis (HAS) from syngas is one of the most promising
approaches to produce fuels and chemicals. Our recent investigation on HAS
showed that potassium-promoted cobalt-molybdenum sulfide is an effective cat-
alyst system. In this study, the intrinsic kinetics of the reaction were studied using
this catalyst system under realistic conditions. The study revealed the major oxy-
genated products are linear alcohols up to butanol and methane is the main
hydrocarbon. The higher alcohol products (C3+) followed an Anderson-Schultz-
Flory distribution while the catalyst suppressed methanol and ethanol forma-
tion. The optimum reaction conditions were estimated to be at temperature of
340◦C, pressure of 117 bar, gas hourly space velocity of 27 000 mL g–1 h–1 and
H2/CO molar feed ratio of 1. A kinetic network has been considered and kinetic
parameters were estimated by nonlinear regression of the experimental data. The
results indicated an increasing apparent activation energy of alcohols with the
length of alcohols except for ethanol. The lower apparent activation energy of
alcohols compared with hydrocarbon evidenced the efficiency of this catalyst
system to facilitate the formation of higher alcohols.
3 Department of Chemistry, UCL, London
WC1H 0AJ, UK
Correspondence
HeroJan Heeres, Green ChemicalReac-
tionEngineering, EngineeringandTech-
nologyInstitute Groningen, University of
Groningen, Nijenborgh4, Groningen, AG
9747, The Netherlands.
Email:h.j.heeres@rug.nl
Regina Palkovits, Chairof Heterogeneous
CatalysisandTechnical Chemistry, RWTH
Aachen University, Worringerweg 2,
Aachen52074, Germany.
Email:palkovits@itmc.rwth-aachen.de
Fundinginformation
K E Y WO R D S
ChinaScholarshipCouncil;Excellence
Initiative of the German Federal andState
Governments
carbon chain growth, kinetics, mechanism, mixed alcohols, molybdenum disulfide, syngas
1
INTRODUCTION
The thermochemical conversion of biomass to synthe-
sis gas, followed by catalytic conversion of synthesis
gas to higher alcohols (HAs), offers an attractive and
promising source of renewable energy.1,2 HAs contain
two or more carbon atoms including primary and sec-
ondary alcohols of both linear and branched carbon
chains. HAs from C2 to C5 can be used directly as
transportation fuels, as octane and cetane enhancers and
Abbreviations: Fi, molar flow of component i (mol s–1); KWGS
,
equilibrium constant; yi, molar composition of component i; yn, mole
fraction of alcohol; Ai, pre-exponential factor
(kmol/(kg s bar∑reaction orders); CMears, Mears criterion; CWP
,
Weisz-Prater criterion; Ea, activation energy (kJ mol–1); GHSV, Gas
hourly space velocity (mL g–1 h–1); HAS, higher alcohols synthesis; k,
reaction rate constant (s–1); n, carbon number; P, pressure (bar); r,
reaction rate (mol m–3 s–1); T, temperature (K); W, mass of catalyst (kg);
α, chain-growth probability
This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium,
provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
© 2020 Wiley Periodicals LLC
Int J Chem Kinet. 2020;1–9.
wileyonlinelibrary.com/journal/kin
1

2
NEGAHDAR et al.
environmentally friendly fuel additives, as specialty sol-
vents in, for example, cleaning agents and paint industry,
and as intermediates for manufacture of pharmaceuticals
and plastics.3–6
sulfide was prepared by the sulfurization of cobalt-
molybdenum oxide with potassium thiocyanate (KSCN).
Typically, 0.648 g cobalt-molybdenum oxide, 0.875 g KSCN,
and 35 mL deionized water were mixed in an autoclave.
The autoclave was kept at 200◦C for 24 h. The autoclave
was cooled, and the precipitate was filtered and washed
with deionized water to remove the impurities. After dry-
ing at ambient conditions overnight, cobalt-molybdenum
sulfide (Co0.13Mo0.87S1.76) was determined by inductively
coupled plasma - optical emission spectrometry (ICP-
OES) analysis. The detailed characterization data of this
catalyst can be found elsewhere.16
A wide variety of heterogeneous catalysts have been
developed for the conversion of syngas into HA.2 Among
the various catalysts, Mo-based catalysts are considered
the most promising due to their high activity and selectiv-
ity for alcohol formation and being excellent catalysts for
the water–gas shift reaction. Particularly, MoS2-based cat-
alysts developed by Dow Chemical possess several advan-
tages such as high resistance to sulfur poisoning and
high selectivity to linear alcohols.7–10 However, the addi-
tion of alkali metals is required to suppress or minimize
the hydrogenation activity of surface alkyl species form-
ing alkanes and to enhance the performance of catalysts
toward HAs.7,11 Previous studies emphasized that addi-
tion of transition metals such as Co, Ni, and Fe to the
alkali-promoted MoS2 enhances the selectivity of HA,9,12,13
among which Co is the most effective promoter for higher
yield of HAs.14 The major oxygenated products over these
catalysts include linear alcohols also carbon distribu-
tions usually follow the Anderson-Schultz-Flory (ASF)
distribution.14,15
Our recent investigation also showed that cobalt-
molybdenum sulfide promoted by potassium is an effective
catalyst system for HA synthesis.16 Detailed study on the
role of potassium and cobalt in K-modified CoMoSx cata-
lysts and their promotional effects on the selectivity of HAs
have been reported by our group.17 In this study, we aimed
to analyze the kinetics of mixed alcohol synthesis over this
catalyst system enabling an insight into the reaction and
providing information applicable for reactor design and
process optimization. The effects of operating conditions
such as temperature, pressure, gas hourly space velocity,
and H2/CO molar feed ratio on HA selectivity have been
investigated. Further, the reaction kinetic parameters were
estimated to explain the catalytic activity of CO hydrogena-
tion over potassium promoted cobalt molybdenum disul-
fide.
2.2
Experimental procedure
The catalytic reactions were carried out in a high-pressure
fixed bed reactor (10 mm inner diameter). The gas mixture
with a H2/CO/N2 volume ratio of 55:36.7:8.3 and H2/CO
of 1.5 was mixed and pressurized by a high-pressure com-
pressor before entering the reactor. The flow rate of gas
mixture was controlled using a high-pressure mass flow
controller. The reactor was placed in an oven to keep
the reaction temperature constant. The exit stream from
the reactor was cooled and separated by a double walled
condenser at −5◦C. Cobalt-molybdenum sulfide (0.394 g)
and 0.056 g K2CO3 were mixed and grinded in a mor-
tar, and 0.4 g of the mixture was diluted with 3.0 g SiC
before loading in the reactor. Before syngas reaction exper-
iment, the catalyst mixture was pretreated in H2 flow of
50 mL min–1 at 450◦C and for 8 h. The stability of the opti-
mal catalyst was tested at 340◦C, 117 bar, H2/CO = 1.5,
and 4 500 mL g–1 h–1 and the result showed that stable
CO conversion and product selectivity could be obtained
after an induction period of 20 h. Therefore, samples were
collected after 20 h and analyzed by average of 6 h run-
time, to ensure that reactor was operated at steady-state
conditions. The gas products were analyzed by an online
gas chromatograph (Compact GC; Interscience BV, Breda,
the Netherlands). The liquid products were analyzed by
an offline gas chromatograph (Finnigan TRACE GC Ultra;
Thermo Scientific, Eindhoven, the Netherlands). Details
regarding product analysis are described in our previous
publication.16 The following ranges of operating condi-
tions were explored: temperature 340-380◦C; total pres-
sure, 87-147 bar; gas hourly space velocity (GHSV) 4 500-
27 000 mL g–1 h–1 and H2/CO molar feed ratio of 1–2.
2
EXPERIMENTAL
2.1
Catalyst preparation
The cobalt-molybdenum oxide precursor was pre-
pared by dissolving 2.83 g Co(NO3)2⋅6H2O and 17.170 g
(NH4)6Mo7O24⋅4H2O in 50 mL deionized water, followed
by heating at 120◦C to evaporate the water. After that, the
obtained mixture was calcined in air at 500◦C for 3 h to
form cobalt-molybdenum oxide. The cobalt-molybdenum
For all experiments, a carbon balance closure higher than
95% was obtained and the selectivity of all products is
mole (carbon) based. Several duplicate experiments were
performed (Table S1) confirming the reproducibility ( 5%
relative) of results. The CO conversion (XCO) and the

NEGAHDAR et al.
3
80
70
60
50
40
30
20
10
0
80
CO Conversion
(A)
(B)
70
60
50
40
30
20
10
0
Liquid Oxygenate
Selectivity
CO Conversion
Liquid Oxygenate
Selectivity
2 000
7 000
12 000
17 000
22 000
27 000
280
300
320
340
360
380
400
Temperature (°C)
GHSV (mL g-1 h-1)
60
60
(C)
(D)
50
40
30
20
10
0
50
40
30
20
10
0
CO Conversion
CO Conversion
Liquid Oxygenate
Selectivity
Liquid Oxygenate
Selectivity
75
85
95
105
115
125
135
145
155
0.8
1
1.2
1.4
1.6
1.8
2
2.2
Pressure (bar)
H2/CO (-)
F I G U R E
1
Effects of reaction conditions on CO conversion and liquid oxygenate selectivity; reaction conditions: (A) P = 117 bar,
H2/CO = 1, GHSV = 4 500 mL g–1 h–1; (b) P = 117 bar, T = 360◦C, H2/CO = 1; (C) GHSV = 4 500 mL g–1 h–1, T = 380◦C, H2/CO = 1; (D)
GHSV = 4 500 mL g–1 h–1, T = 380◦C) P = 117 bar
product selectivity (Si) were calculated using Equations (1)
and very small amounts of acetaldehyde. The liquid
oxygenate selectivity exhibits a maximum at reaction
temperature of 300◦C and decreases with increasing
reaction temperature (Figure 1A). This indicates that
CO hydrogenation becomes less selective toward liquid
oxygenates with increasing reaction temperatures and it
favors the formation of alkanes. However, the increase
in GHSV has a positive effect on the selectivity of liquid
oxygenates (Figure 1B). Higher GHSV means shorter
contact time between reacting species and catalyst. With
longer contact time, liquid oxygenates might be further
converted to hydrocarbons. Therefore, the selectivity of
liquid oxygenates increases with higher GHSV. The effect
of pressure indicates that pressures below and at 117 bar
are the most effective to maximize the liquid oxygenate
selectivity and pressure above 117 bar favors hydrocarbon
formation (Figure 1C).
and (2):
moles of COinfluent − moles of COeffluent
ꢀCO
ꢁi =
=
× 100%
moles of COinfluent
(1)
moles of product i × number of carbons in product i
moles of COinfluent − moles of COexfluent
×100%
(2)
3
RESULTS AND DISCUSSION
3.1
Effects of reaction conditions on CO
conversion and liquid oxygenate selectivity
The effects of reaction conditions on CO conversion and
liquid oxygenate selectivity were investigated (Figure 1).
The liquid oxygenates include alcohols (mainly C1-C4)
The influence of the H2/CO molar feed ratio on the
selectivity of liquid oxygenates indicates that the selectiv-
ity decreases linearly with higher H2/CO molar feed ratios

4
NEGAHDAR et al.
F I G U R E 2 3D Plot of reaction conditions (liquid temperature, pressure, H2/CO ratio, and GHSV) [Color figure can be viewed at wileyon-
linelibrary.com]
as shown in Figure 1D. At higher H2/CO molar ratio, the
rate of chain growth by CO insertion decreases and higher
hydrogen partial pressures supports the hydrogenation of
intermediates to hydrocarbons.17 As such, the selectivity of
liquid oxygenates decreases at higher H2/CO molar ratio.
The increase in the reaction temperature, pressure, and
H2/CO molar feed ratio has positive effects on CO conver-
sion but higher GHSV does not favor the CO conversion
due to short contact time between reactants and catalyst.
To investigate the optimum reaction conditions for
higher selectivity of liquid oxygenate, the selectivity of
liquid oxygenates with respect to the reaction conditions
has been plotted in Figure 2. The 3D plot indicates that
the optimum conditions become evident at reaction tem-
F I G U R E 3 ASF distribution of alcohols for C3+, at 340, 360, and
perature around 340◦C, pressure of 117 bar, GHSV above
380◦C, 117 bar, GHSV of 27 000 mL g–1 h–1 and H2/CO = 1.5
27 000 mL g–1 h–1, and H2/CO molar feed ratio of 1.
In this study, alcohol product distribution followed the
so-called ASF distributions. Based on ASF distribution,18 if
with an ASF distribution. The chain growth probabilities
the hydrocarbon chain is formed step-wise by insertion or
addition of C1 intermediates with constant growth proba-
bility then the chain length distribution can be defined as
Equations (3) and (4)19:
for alcohols were estimated to be 0.13, 0.11, and 0.09 at
temperatures of 340, 360, and 380◦C, respectively, which
were obtained based on C3+ alcohols. The chain growth
probabilities decrease with increasing reaction tempera-
ture, implying that HAS is unfavorable at higher temper-
ature. This is in line with our experimental analysis of
effects of reaction temperature on selectivity of liquid oxy-
genates.
ꢃ−1
ꢂꢃ = 1 − ꢄ ꢄ
(3)
(4)
(
)
(
)
1
Ln ꢂ = ln
− 1 + ꢃln ꢄ
(
)
( )
ꢃ
ꢄ
where yn is the mole fraction of alcohol or hydrocarbon,
n is the carbon number, and α is the chain-growth prob-
ability. Figure 3 illustrates the ASF distributions of alco-
hols at the operating conditions of 340, 360, and 380◦C,
117 bar, GHSV of 27 000 mL g–1 h–1, and a H2/CO ratio of
1.5. Experimental observations show that the formation of
alcohols except for methanol and ethanol, decreases expo-
nentially with increasing carbon number, in agreement
3.2
Internal and external diffusion
effects
The Weisz-Prater criterion (CWP) was used to determine
possible internal mass transfer limitations. In general,
internal mass-transfer limitations can be neglected in case
the CWP ≪ 1.20 The value of CWP was calculated to be 0.142,
considering an average particle diameter of 105 μm and a

NEGAHDAR et al.
5
S C H E M E 1 Parity plot of the experimental and model flow
rates for the different components
ious kinetic models and mechanistic proposals have been
made regarding HAS.19,24–28 The widely accepted mech-
anism for alcohol formation over MoS2 catalysts is the
CO insertion mechanism proposed by Santiesteban et al,14
which was verified by isotopic labeling studies. The pro-
posed mechanism comprehends the insertion of CO to
F I G U R E 4 Effect of GHSV on boundary layer thickness around
catalyst particle (δ) at 360◦C, 117 bar, H2/CO = 1
*
the surface alkyl group (CH3 ) to form an acyl interme-
CO/H2 molar ratio of 1, indicating that internal diffusion is
negligible (Supporting Information). External mass trans-
fer limitations were verified experimentally by varying the
GHSV at constant reaction conditions.21,22 The external
mass transfer diffusion can be eliminated by decreasing the
mass-transfer boundary layer thickness (Supporting Infor-
mation), which will disappeared at high GHSV.22 GHSV of
4 500, 9 000, 18 000, and 27 000 mL g–1 h–1 were used at
360◦C, 117 bar of syngas with a H2/CO ratio of 1, and an
averaged catalyst particle size of 105 μm to test the pres-
ence of external mass transfer limitation. At low GHSV,
the boundary layer across which the reactant diffuses is
thick, and it takes a long time for reactants to diffuse to
the surface of the catalyst. Therefore, mass transfer across
the boundary layer is slow and limits the rate of the overall
reaction. On the other hand, when the GHSV increases, the
velocity over the pellet increases which results in a thin-
ner boundary layer and the mass transfer rate increases.
Accordingly, external mass transfer no longer limits the
rate of reaction (Figure 4).21
diate (CH3CO*), which is then hydrogenated to the cor-
responding alcohol or to a longer alkyl group. Hydrocar-
bons are then formed by hydrogenation of the alkyl group.
The overall reaction network for linear alcohols from syn-
gas based on the CO insertion mechanism is shown in the
Scheme 1.
Kinetic models for HAS over MoS2 catalysts are lim-
ited and some of them require complex formulations,19,27
which might not be practical for the process design.
Accordingly, in this study, the reaction schemes and rate
expressions were simplified and CO insertion mechanism
proposed by Santiesteban et al14 is assumed. The reaction
steps are summarized in Equations (5)−(10):
ꢅ
CH OH
3
⟶
CO + 2H2
CH3OH
(5)
(6)
ꢅ
CH
4
5
H
H
⟶
CH3OH + H2
CH4 + H2O
ꢅ
An alternative criterion to determine the influence of
external diffusion on the overall kinetics is the Mears cri-
terion (CMears).23 External mass transport limitations are
absent when the value of CMears ≪ 0.15. The Mears crite-
rion was calculated to be 1.95 × 10−5 (at equal molar ratio
of CO and H2), which indicates that external mass transfer
limitation can be excluded, which is in line with the exper-
imental data obtained by variation of the GHSV (Support-
ing Information).
C
H
OH
2
⟶
CH3OH + CO + 2H2
C2H5OH + CO + 2H2
C3H7OH + CO + 2H2
C2H5OH + H2O (7)
C3H7OH + H2O (8)
C4H9OH + H2O (9)
ꢅ
C
OH
OH
7
9
3
⟶
ꢅ
C
4
⟶
ꢅ
↔
CO + H2O CO2 + H2
(10)
3.3
Reaction network and kinetic
Higher alcohol (C2+) formation is assumed to proceed
by a stepwise chain growth of alcohols by CO insertion
into a lower molecular weight alcohol, whereas methanol
is formed directly from syngas. The water–gas shift reac-
tion (Equation 10) is known to be reversible and the other
model development
The mechanism of synthesis gas conversion over Mo-based
catalysts has been the subject of debate in recent years. Var-

6
NEGAHDAR et al.
dꢋPr
dꢌ
reactions are assumed to be irreversible under high CO
conversion. It is assumed that the hydrocarbons are formed
by hydrogenation of the corresponding alcohols. Note
that in the product mixture, mostly linear alcohols, small
amount of branched propanol and butanol, methane, car-
bon dioxide, un-reacted carbon monoxide, and hydrogen
were observed. It should be mentioned that the water
concentration was about 10% of the overall liquid prod-
ucts, which is negligible. For kinetic model development,
a power-law approach was applied.19,27,30–32 Reaction rates
of the individual compounds are expressed as follows:
= ꢆPr
(23)
(24)
(25)
(26)
dꢋBu
dꢌ
= −ꢆPr
dꢋCH
4
= ꢆCH
4
dꢌ
dꢋCO
2
= ꢆCO
2
dꢌ
where W is the mass of catalyst and Fi is the molar flow of
component i. The parameter estimation was performed by
minimizing the objective function (Q), which is defined as
the sum of the squares of the residuals (Equation 27):
a
b
ꢆCH OH = ꢅCH OH ꢇCO ꢇH
(11)
(12)
(13)
(14)
(15)
3
3
2
e
c
d
ꢆCH = ꢅCH ꢇCH OH ꢇH
4
4
3
2
ꢎ
ꢐ
∑ ∑
f
g
m
(
)
2
ꢆC H OH = ꢅC H OH ꢇCH OH ꢇCO ꢇH
2
5
2
5
3
2
ꢍ =
ꢋꢏꢑ model − ꢋꢏꢑ experiment
(27)
(
)
(
)
ꢏ=1 ꢑ=1
h
i
j
ꢆC H OH = ꢅC H OH ꢇC H OH ꢇCO ꢇH
3
7
3
7
2
5
2
2
k
l
ꢆC H OH = ꢅC H OH ꢇC H OH ꢇCO ꢇH
4
9
4
9
3
7
where Fij is the molar flow of compound i at the outlet
of the reactor for experiment number j, N is the num-
ber of experiments, and M the number of compounds.
Our objective is to find the rate constants such that the
molar flow obtained by integrating the differential equa-
tions (Equations 18–26) resembles the experimental molar
flow as closely as possible. This is accomplished through an
optimization procedure that we implemented in MATLAB
using a general-purpose finite difference solver combined
with MATLAB’s native optimization routines. These rou-
tines are based on the method of least squares, employing
a trust region reflective search algorithm. Figure 5 shows
the fit between experimental and the predicted model val-
ues. The R2 values of the models emphasize a good fit with
the experimental results. Table 1 summarizes the estimated
kinetic parameters for the different reactions. The results
indicate the activation energy increases with the length of
alcohols except for ethanol. The lower value of apparent
activation energy of ethanol compared with those for other
alcohols was also reported by Gunturu et al,19 which was
attributed to the ethanol conversion to products such as
esters and ethers at higher reaction temperature. Methane
and carbon dioxide have higher activation energy than
alcohols. This also explains that the potassium promoted
cobalt-molybdenum sulfide catalyst system favors the HAs
formation compared with hydrocarbons as a result of lower
activation energies of alcohols. In other words, this cat-
alyst system facilitates the formation of HAs. Overall, a
good agreement between the estimated kinetic parameters
in this study and the reported range of data in the literature
can be seen. Nevertheless, the estimated kinetic param-
eters can provide information required for simulation of
commercial reactor, which will be addressed in future
studies.
First-order reversible kinetics are assumed for the for-
mation of CO2 by the water–gas shift reaction (Equa-
tion 16)33,34
:
(
)
ꢅ
ꢆCO = ꢅꢈCO
−
ꢈCO
(16)
2
2
ꢉWGS
where k is reaction rate constant and KWGS is the equilib-
rium constant that can be calculated from Equation (17)33:
[(
)
]
4577.8
ꢊ
ꢉWGS = exp
− 4.33 .
(17)
3.4
Reactor modeling
It is assumed that reactor follows the ideal plug-flow condi-
tions and operates isothermally. With these assumptions,
the mole balances for the individual components can be
derived (Equations 18–26).
(
)
dꢋCO
dꢌ
= − ꢆMe + ꢆEt + ꢆPr + ꢆCO
(18)
2
dꢋH
(
)
2
= − 2ꢆMe + 2ꢆEt + 2ꢆPr + ꢆCH + ꢆCO (19)
4
2
dꢌ
dꢋH O
2
= ꢆEt + ꢆPr + ꢆCH − ꢆCO
(20)
(21)
(22)
4
2
dꢌ
dꢋMe
dꢌ
= ꢆMe − ꢆEt − ꢆCH
4
dꢋEt
dꢌ
= ꢆEt − ꢆPr

NEGAHDAR et al.
7
0.25
0.2
0.15
0.1
0.05
0
Carbon monoxide
Hydrogen
0.15
0.1
0.05
0
R² = 0.9839
R² = 0.9209
0
0.05
0.1
0.15
0.2
0
0.05
0.1
0.15
0.2
Experimental (mol h-1)
Experimental (mol h-1)
0.004
0.003
0.002
0.001
0
Carbon dioxide
Methane
0.012
0.008
0.004
0
R² = 0.8421
R² = 0.8745
0
0.001
0.002
0.003
0.004
0
0.004
0.008
0.012
Experimental (mol h-1)
Experimental (mol h-1)
Methanol
Ethanol
0.006
0.004
0.002
0
0.003
0.002
0.001
0
R² = 0.939
R² = 0.9349
0
0.001 0.002 0.003 0.004 0.005 0.006
Experimental (mol h-1)
0
0.001
0.002
0.003
Experimental (mol h-1)
Propanol
0.005
0.0006
0.0004
0.0002
0
Butanol
R² = 0.8182
R² = 0.9003
0.004
0.003
0.002
0.001
0
0
0.0001 0.0002 0.0003 0.0004 0.0005
Experimental (mol h-1)
0
0.001
0.002
0.003
Experimental (mol h-1)
F I G U R E 5 The overall reaction mechanism over alkali/MoS2 catalysts14,29

8
NEGAHDAR et al.
TA B L E 1 Kinetic parameters estimated based on model Equations (12)–(17)
Order of reaction species
Ea
Range of Ea reported in
Species
Methanol
Ethanol
Propanol
Butanol
Methane
Aa
(kJ/mol)
CO
1.85
0.75
1.0
H2
MeOH EtOH
–
0.24
–
–
PrOH
–
–
–
R2
literature (kJ/mol)b
0.0295
0.0102
0.419
5.201
5.812
63
54
82
104
126
146
0.44
1.39
0.28
0.08
0.6
–
–
1.22
–
0.82
0.83
0.81
0.88
0.81
0.82
36-83
38-83
92-159
107-148
112-118
57-97
0.63
0.59
0.83
–
Carbon dioxide 9.811
–
–
–
–
aUnits (kmol/(kg s bars∑reaction orders).
bSee Refs. 14, 19, 27, 28, 30, and 32.
catalyst active sites are more selective toward that reac-
tion pathway with lower activation energy and higher reac-
tion rate. The estimated activation energies and obtained
optimum reaction conditions can be further employed to
the design of an industrial reactor, optimizing the process
operating conditions and improving the chemical plant
economics.
4
CONCLUSION
Kinetic modeling is an important tool to study the reaction
kinetics, product distribution, and reactor performance.
The application of kinetic models ranges between the sim-
plest approach, such as power-law model and the high-
est degree of details, the microkinetic model. Models with
less complexity are practical for reactor design, scale-up
and process optimization. On the other hand, microki-
netic models are complicated, but they are useful in case
of design of new catalyst or improving the catalyst per-
formance by providing insight into intermediates and pre-
ferred reaction pathways. However, in this study, our focus
was on simplest approach providing information for reac-
tor design and scale-up as the insight into the role and
function of catalyst active sites was studied in our previous
report.17
In this study, the formation of HAs over a cobalt-
promoted MoS2 catalyst was evaluated. The formation
of both hydrocarbons and oxygenated products were
observed over this catalyst system. The major oxygenated
products were linear alcohols, such as methanol, ethanol,
n-propanol, and n-butanol. The main hydrocarbon prod-
uct was methane. Alcohol products (C3+) followed an ASF
distribution and alcohol chain growth occur via a CO inser-
tion mechanism. The results showed that liquid oxygenate
formation can be maximized under optimum reaction con-
dition: a temperature of 340◦C, a pressure of 117 bar, GHSV
of 27 000 mL g–1 h–1, and H2/CO molar feed ratio of 1.
A kinetic model based on the CO insertion mechanism
was developed and we successfully estimated the reaction
kinetics parameters within the range of reaction condi-
tions in this study. An increase in activation energy with
the length of alcohols was observed except for ethanol.
Lower apparent activation energies of alcohols in compar-
ison with hydrocarbon indicated that the catalyst is effec-
tive toward HAs formation. The lower activation energy
agrees with the higher reaction rate of the reaction path-
way, which means that reaction route is more efficient to
take place over surface of solid catalyst. In other words,
AC K N OW L E D G M E N T S
Feng Zeng and Xiaoying Xi acknowledge China Scholar-
ship Council (CSC) for financial support. Regina Palkovits
and Leila Negahdar acknowledge the project house P2F
(Competence Center Power to Fuel) of RWTH Aachen
University financed by the Excellence Initiative of the Ger-
man Federal and State Governments to promote science
and research at German universities.
Open access funding enabled and organized by Projekt
DEAL.
O RC I D
LeilaNegahdar https://orcid.org/0000-0002-9119-6445
ReginaPalkovits https://orcid.org/0000-0002-4970-2957
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How to cite this article: Negahdar L, Xi X, Zeng
F, Winkelman JGM, Heeres HJ, Palkovits R. CO
hydrogenation over K-Co-MoSx catalyst to mixed
alcohols: a kinetic analysis. Int J Chem Kinet.
2020;1-9. https://doi.org/10.1002/kin.21453