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CHEMICAL ENGINEERING TRANSACTIONS

VOL. 45, 2015

A publication of

The Italian Association

of Chemical Engineering

www.aidic.it/cet
Guest Editors: Petar Sabev Varbanov, Jiří Jaromír Klemeš, Sharifah Rafidah Wan Alwi, Jun Yow Yong, Xia Liu

ISBN 978-88-95608-36-5; ISSN 2283-9216 DOI: 10.3303/CET1545179

Please cite this article as: Lin J.-Y., Fang C.-M., Chein R.-Y., 2015, Kinetics of ultrahigh temperature water-gas shift reaction

catalysts using simulated coal-derived syngas, Chemical Engineering Transactions, 45, 1069-1074

DOI:10.3303/CET1545179

1069

Kinetics of Ultrahigh Temperature Water-Gas Shift Reaction

Catalysts Using Simulated Coal-Derived Syngas

Jhih-Yan Lin, Chien-Min Fang, Rei-Yu Chein*

Department of Mechanical Engineering, National Chung Hsing University, Taichung Taiwan.

rychein@dragon.nchu.edu.tw

H2 is currently being widely recognized as a possible energy carrier because of its high energy content and

environmental compatibility. H2 production from coal gasification has gained renewed interest because it is

recognized as the most abundant fossil fuel. The coal-derived syngas consists mainly of CO and H2. The

CO can be further reacted with steam via the water-gas shift reaction (WGSR) to increase the H2

concentration in the syngas. Development of catalyst that can be used at temperature higher than the

traditional WGSR operating temperatures is an alternative way to enhance the overall coal-to-H2 thermal

efficiency and cost-effective design. With this high temperature catalyst two-stage shift reactors can be

reduced to a single reactor and connected at the gasifier exit without the need for syngas cooling. In this

study, catalyst performance of WGSR operated in ultrahigh temperature region (750 - 850 °C) was

examined experimentally. Using syngas with various compositions and S/C ratios as feedstock, the

chemical reaction kinetics of WGSR using 2.5 wt%Pt - 2.5 wt%Ni/5 wt%CeO2/Al2O3 as catalyst can be

established based on the experimental data and simple power law. It was found that the prepared catalyst

promotes the rate of WGSR when the syngas consists of higher CO concentration and lower CO2

concentration for the operation temperature range studied.

1. Introduction

The coal-derived syngas consists mainly of CO and H2. The CO can be further reacted with steam via the

water-gas shift reaction (WGSR) to increase the H2 concentration in the syngas. At the same time, this

reaction produces a concentrated CO2 stream that can be sequestered to mitigate the greenhouse effect

once the H2 is removed.

The WGSR is an exothermic reaction limited by thermodynamic equilibrium,

, molkJH
K

/2.41
298

 (1)

That is, the conversion to H2 and CO2 decreases with increasing temperature (Fogler, 2006). However, a

fast chemical reaction rate can be achieved at high temperatures. Moreover, for the case of coal-derived

syngas where the CO concentration is relatively high (40 - 60 %), considerably higher degree of shifting is

required. For these reasons the WGSR is carried out in two stages in practical applications: a high

temperature (350 - 450 °C) shift reaction using Fe-Cr catalyst to increase the chemical reaction rate and

low temperature (200 - 250 °C) shift reaction using Cu-Zn catalyst to increase the conversion efficiency. In

general, the syngas produced from a gasifier has a higher temperature in comparison to the operating

temperature range of practical reactors. The syngas must be cooled to perform the two-stage WGSR,

which is capital intensive and incurs a loss of power production. Moreover, the traditional WGSR process

is likely to deliver CO2 at reduced pressure, which will have to be re-compressed for sequestration and

storage.

To enhance the overall coal-to-H2 thermal efficiency and cost-effective design, recent efforts have been

devoted to develop catalysts that can be used at temperatures higher than the traditional high-temperature

shift reactor and also exhibits high CO conversion capability. With this high temperature catalyst two-stage

reactors can be reduced to a single reactor and connected at the gasifier exit without the need for syngas

222
HCOOHCO 

1070

cooling. However, relatively few WGSR catalysts for operating temperatures higher than 450 °C were

reported in the literature. Valsamakis and Flytzani-Stephanopoulos (2011) reported a high activity and

stability of lanthanide oxysulphides catalyst for WGSR. With temperature higher than 750 °C, CO

conversion can reach the equilibrium value. Aranifard et al. (2014) performed an analysis on the

mechanism of WGSR at the three-phase boundary of Pt/CeO2 catalysts. They showed that both the redox

pathway and the associative carboxyl pathway with redox regeneration could operate on Pt/CeO2 catalysts.

Using Pt/TiO2 as catalyst for WGSR, Panagiotopoulou and Kondarides (2011) showed that activity of

alkaline earth metal-promoted catalysts depends appreciably on the nature and loading of the promoter, as

well as on the calcination temperature employed for the preparation of doped TiO2 supports. In the study of

Palma et al. (2014), they focused on the preparation and testing of differently-supported Pt-based catalysts

for WGSR and found that the Pt/CeO2/ZrO2 had a great potential for use in single-stage WGSR.

The objective of this study is to carry out the WGSR with reaction temperature at 750 °C which closes to

the syngas temperature at gasifier outlet. Bimetal catalyst will be prepared and used for WGSR

performance test using syngas with various compositions. Kinetics of WGSR will be established based on

the measured experimental data.

2. Experimental

The 2.5 wt%Pt - 2.5 wt%Ni/5 wt%CeO2/Al2O3 catalyst was prepared and used for WGSR in this study. The

procedures for the catalyst preparation was in a similar way as that described in the study of Haryanto et al.

(2007) except that spherical Al2O3 particles with an average diameter of 0.5 - 1.2 mm and specific surface

area of 220 m
2
/g were used as the catalyst support instead of alumina ceramic foam monoliths. A

schematic diagram of the experimental setup is shown in Figure 1. The reactor was placed horizontally in

a temperature-controlled furnace. The simulated syngas was made by mixing four gaseous species as

shown in Figure 1. All the gaseous species flow was metered and regulated by a mass flow controller

(Brooks 5850E, USA) and water was pumped through a HPLC pump (Simadzu LC-20AT, Japan) with the

flow rate at designated steam to carbon (S/C) ratio. A preheater was used to vaporize the water before it

mixed with the simulated syngas flow.

The WGSR was carried out using a conventional catalytic packed-bed tubular reactor operated

isothermally at atmospheric pressure. A quartz tube with a diameter of 4 mm was used as the reactor in

which the catalyst was loaded in the central section with two ends fixed using quartz wool. The catalyst

with weight of 0.5 g was used and this results in a reaction zone length of 4.2 cm. Accordingly the ratio of

catalyst bed length to catalyst particle size and the ratio of the inside diameter of the reactor to particle size

are in the ranges of 35 - 84 and 3 - 8. This ensures that the back mixing and channelling effects can be

minimized in the packed-bed reactor (Froment and Bischoff, 1990).

Figure 1: Experimental setup for WGSR test.

The experiments were carried out with reaction temperature at 750 °C. The reaction temperature was

monitored by a K-type thermocouple placed at the top of the catalyst bed. Each experiment was carried

Temperature

controlled oven

Catalyst

bed

HPLC pump (Shimadzu LC-20AT)

CO2

2
H2

MFC

Quartz cotton

Gas flow

meter

water

condensing
cooling

Moisture trap

H2S

MFC

Mixing

chamber

1071

out in 6 h after the reaction becomes steady. After removing the unused water by a condenser, the product

gas was collected every 2 h to ensure stable performance of the catalyst under specified operating

conditions. The product gases were analysed by gas chromatograph (Agilent 6890, USA). In this study,

CO conversion rate is defined as,

FF
R

outCOinCO

,,
 

 (2)

where
inCO

F
,

 and
outCO

F
,

 are the CO molar flow rate at reactor inlet and outlet. W is the catalyst weight

used in the test.

3. Results and discussion

A power-law rate model is used to describe the kinetics of the catalyst. The power-law expression for the

WGSR is generally of the form (Adams and Barton, 2009),

)1(
222


d

COCO
PPPkPR (3)

In Eq(3), RCO is the CO reaction rate (mol gcat
-1

s
-1

), Pi is the partial pressure of gas component i (kPa), a, b,

c, and d are the reaction orders of CO, H2O, CO2, and H2. k is the rate constant defined as,

)/exp( RTEAk  (4)

Where A is pre-exponential factor, E is the activation energy (kJ mol
-1

), and T is the reaction temperature

(K).  is the extent of the reverse reaction defined as,

OHCO

HCO

eq
PP

K
2

22
1

 (5)

Where
eq

K is the chemical equilibrium constant given as (Moe, 1962),

1)/000,1(  Tz
(6)

The simulated syngas compositions investigated in this study was chosen based on the study of Murgia et

al. (2012) in which they reported a syngas produced from an air-blown updraft coal gasifier has the

composition of 30 % CO, 18 % H2, 22 % CO2, and 30 % N2. In this study, this syngas composition was

used as the base syngas composition. To investigate the effect of CO, H2O, CO2, and H2 concentrations, a

syngas composition variation based on this base syngas composition was selected. Steam was added to

syngas with S/C ratio varied from 3 to 5. The kinetic data measured for the WGSR at 750 °C was

presented in Table 1. Experimental runs to examine the effects of CO, H2O, CO2 and H2 were carried out

by varying the composition of one component by replacing it with N2 while all other components were held

as close to constant as possible. The minor variations in these other gas compositions were caused by

fluctuations in the total pressure of the system between each run. In Table 1, the value of β varied in

0.0188-0.1399 range indicating that the reaction was far from equilibrium.

Figure 2 presents plot of ln [RCO/(1-β)] versus log of partial pressure of each component for WGSR at 750

°C. It is clear that all plots in Figure 2 are nearly linear, indicating that the kinetics of the WGSR can be

expressed by using the empirical power-law model. The slope of each straight line is used to determine

the reaction order with respect to the individual species and these values are also shown in Figure 2. As

expected, Figure 2 shows that CO conversion rate increases with CO partial pressure under the conditions

investigated. The reaction order for CO at 750 °C is found to be 0.8932. Figure 2 also shows that the

reaction rate significantly depends on the H2O concentration with reaction order of 1.7329 which is quite

different from that obtained using Fe-Cr catalysts at 450 °C reported by Hla et al. (2009). The reaction

order for CO2 at 750 °C was found to be -0.2561 indicating that reaction rate decreases with the increase

in CO2 amount in syngas. A similar observation was also reported by Bohlbro (1961) and Hla et al. (2009)

for their studies for the effect of CO2 concentration on CO conversion rate over an Fe-Cr based catalyst in

}31688.0]1778.4)29353.063508.0([exp{  zzzK
eq

1072

a temperature range of 380 - 500 °C. A small positive effect of H2 concentration on CO conversion rate

with reaction order of 0.1072 is observed, as shown in Figure 2 which is also different from that report by

Hla et al. (2009). Further studies are needed to investigate the variation trend with H2 concentration at

other temperature for realizing the reason for this observation.

Table 1: Kinetic data for WGSR over 2.5 wt%Pt - 2.5 wt%Ni/5 wt%CeO2/Al2O3 catalyst with simulated coal-

derived syngas at 750°C.

CO
P

(kPa)

OH
P

(kPa)

2CO
P

(kPa)

2H
P

(kPa)

2N
P

(kPa)

β
CO

(x10
-5

mol gcat
-1

s
-1

)

CO varied (S/C=5)
8.22 61.07 8.74 6.99 16.32 0.0973 0.94
12.31 60.99 8.6 7.01 12.4 0.0644 1.28
16.68 61.6 8.91 7.05 7.09 0.0489 1.88

H2O varied (S/C=3, 4, 5)
12.85 36.28 8.9 6.57 36.73 0.1002 0.5
12.46 47.1 8.69 6.41 26.67 0.0758 0.61
12.31 60.99 8.62 7.01 12.4 0.0644 1.28

CO2 varied (S/C)=5
12.36 60.54 2.44 7.19 18.8 0.0188 1.73
12.31 60.99 8.62 7.01 12.4 0.0644 1.28
12.32 60.87 14.73 6.96 6.46 0.1094 0.97

H2 varied (S/C=5)
12.31 60.99 8.62 7.01 12.4 0.0644 1.28
12.35 60.96 8.66 11.04 8.32 0.1015 1.27
12.41 60.66 8.73 15.08 4.45 0.1399 1.28

Figure 2: Determination of power-law rate model reaction orders: Log-log plots for the effect of CO, H2O,

CO2 and H2 partial pressure on reaction rates over 2.5 wt%Pt - 2.5 wt%Ni/5 wt%CeO2/Al2O3 catalyst at

750 °C.

1073

Figure 3: Arrhenius plot for the WGSR based on Eq(6) for temperature in the range of 750- 850°C.

Using the reaction rate orders obtained from the slopes of the plots in Figure 2, the rate constant can be

calculated by rearranging Eq(3) as

)exp(
)1(

222
RT

E
A

PPPP

R
k

CO 





(7)

Taking log on Eq(6), the Arrhenius plot can be generated and the activation energy can be evaluated. To

be able to generate the Arrhenius plot, at least three points are needed. In addition to 750 °C, the CO

conversion rates at 800 °C and 850 °C with base syngas composition and S/C=5 were also measured.

Figure 3 shows the Arrhenius plot using the measured CO conversion rates for these three temperatures.

Using the slope of the Arrhenius straight line in Figure 3, the value of -E/R is found to 22,771, which results

in the activation energy of 183.322 kJ/mol. The corresponding pre-exponential factor A can also be

determined from Arrhenius plot and has the value of 10
1.063

. Based on these calculated values, the power-

law reaction rate under the operation conditions can be expressed,

)1()
322,183

exp(10
1072.02156.07329.18932.0063.1

222




HCOOHCOCO
PPPP

RT
R (8)

Comparison between reaction rates calculated using Eq(8) and experimental results are shown in Figure 4.

It can be seen that the calculated rates correlate with experimental data very well. This power-law rate

expression can be regarded as an intrinsic WGSR rate equation for 2.5 wt%Pt - 2.5 wt%Ni/5

wt%CeO2/Al2O3 which can be used in reactor design to calculate either the amount of catalyst required to

achieve a certain degree of CO conversion or the level of conversion that can be obtained with a given

amount of catalyst at ultra-high temperature.

4. Conclusion

In this study, water-gas shift reaction performance at temperature of 750 °C with 2.5 wt%Pt - 2.5 wt%Ni/5

wt%CeO2/Al2O3 as catalyst was tested using simulated coal-derived syngases. A power-law reaction

kinetics was established based on the experimental data. At this high temperature, it was found that the

reaction rate increases with the amounts of CO, H2O, and H2 while increasing the CO2 amount results in

decrease in CO reaction rate. Further studies will be needed to obtain more accurate rate constant and H2
concentration dependence with more temperature variations.

1/T (1/K)

ln
k

8.5E-04 9.0E-04 9.5E-04 1.0E-03
-22

-21.5

-21

-20.5

-20

-19.5

-19

E/R=-22771

1074

Figure 4: Measured reaction rate vs. calculated CO reaction rate for WGSR over 2.5wt%Pt-

2.5wt%Ni/5wt%CeO2/Al2O3 catalyst at 750°C under selected inlet gas compositions.

Acknowledgments

Financial support from Ministry of Science and Technology of Taiwan (MOST 103-3113-E-042A-002) is

acknowledged.

References

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502-520.

Fogler H.S., 2006, Elements of Chemical Reaction Engineering, 4th Ed., Prentice Hall, Upper Saddle River,

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Froment G.F., Bischoff K.B., 1990, Chemical Reactor Analysis and Design, Wiley, New York, US.

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chemisorptive properties and water-gas shift activity of supported platinum catalysts, Applied Catalysis

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Valsamakis I., Flytzani-Stephanopoulos M., 2011, Sulfur-tolerant lanthanide oxysulfide catalysts for the

high-temperature water–gas shift reaction, Applied Catalysis B: Environmental, 106, 255-263.

Measured R
CO

(x10
-5

mol g
cat

-1
s

-1
)

C
a

lc
u

la
te

d
R

C
O

(x
1

0
-5

m
o

l
g

c
a

t-1
s

-1
)

0 0.5 1 1.5 2 2.5
0

0.5

1.5

2.5