Kinetic studies of vapor-phase hydrogenolysis of butyl butyrate to butanol over Cu/ZnO/Al2O3 catalyst

Article abstract of DOI:10.1016/j.apcata.2010.08.009

Kinetic investigations on the hydrogenolysis of butyl butyrate to butanol over a commercial Cu/ZnO/Al₂O₃ catalyst were conducted. The catalytic measurements at atmospheric pressure showed that the rate of hydrogenolysis was approximately 0.67 order with respect to butyl butyrate and had a positive effect for hydrogen. The activation energy of this reaction was measured to be about 62 kJ/mol, and D₂ isotope studies corroborated that the hydrogenolysis of butyl butyrate proceeds via dissociative adsorption of ester producing C₃H₇CO and C₄H₉O fragments. In addition, kinetic studies, interpreted by applying the basis of the Langmuir-Hinshelwood model, suggested that the rate-determining step involves the dissociative adsorption of butyl butyrate. Finally, the rate expression derived in this study provided precise and reasonable fitting results, and an activation energy close to the value obtained from the power law equation.

Full text of DOI:10.1016/j.apcata.2010.08.009

Applied Catalysis A: General 387 (2010) 100–106
Contents lists available at ScienceDirect
Applied Catalysis A: General
journal homepage: www.elsevier.com/locate/apcata
Kinetic studies of vapor-phase hydrogenolysis of butyl
butyrate to butanol over Cu/ZnO/Al2O3 catalyst
In Bum Jua,b, Wonjin Jeona, Myung-June Parkc, Young-Woong Suha,∗, Dong Jin Suha, Chang-Ha Leeb
a Clean Energy Center, Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea
b Department of Chemical and Biological Engineering, Yonsei University, Seoul 120-749, Republic of Korea
c Department of Chemical Engineering, Ajou University, Suwon 443-749, Republic of Korea
a r t i c l e i n f o
a b s t r a c t
Article history:
Kinetic investigations on the hydrogenolysis of butyl butyrate to butanol over a commercial Cu/ZnO/Al2O3
catalyst were conducted. The catalytic measurements at atmospheric pressure showed that the rate of
hydrogenolysis was approximately 0.67 order with respect to butyl butyrate and had a positive effect
for hydrogen. The activation energy of this reaction was measured to be about 62 kJ/mol, and D2 isotope
studies corroborated that the hydrogenolysis of butyl butyrate proceeds via dissociative adsorption of
ester producing C3H7CO and C4H9O fragments. In addition, kinetic studies, interpreted by applying the
basis of the Langmuir–Hinshelwood model, suggested that the rate-determining step involves the dis-
sociative adsorption of butyl butyrate. Finally, the rate expression derived in this study provided precise
and reasonable fitting results, and an activation energy close to the value obtained from the power law
equation.
Received 18 January 2010
Received in revised form 2 August 2010
Accepted 9 August 2010
Available online 14 August 2010
Keywords:
Kinetics
Hydrogenolysis
Butyl butyrate
Butanol
© 2010 Elsevier B.V. All rights reserved.
Cu/ZnO/Al2O3
1. Introduction
tanol production can be developed such that 1 mol of butyric acid
is esterified with 1 mol of butanol to form butyl butyrate which
Since the first description of the catalytic hydrogenolysis of
esters (R1COOR2) to two alcohols (R1CH2OH and R2OH) by Flok-
ers and Adkins in 1931 [1], this reaction has been of considerable
industrial importance. In particular, many researchers includ-
ing Trimm and co-workers in the 1980s thoroughly investigated
the hydrogenolysis reaction mechanisms of methyl formate and
ethyl acetate over copper-based catalysts [2–6]. Since then, little
attention has been paid to this reaction owing to the relatively
well-established reaction scheme.
is subsequently hydrogenated to 2 mol of butanol, where one part
of butanol may be recycled for the esterification of butyrate while
the other part of butyric acid will come out through the product
stream.
The overall reaction for the catalytic hydrogenolysis of butyl
butyrate (BB) is as follows:
C3H7COOC4H9 + 2H2 → 2C4H9OH
(1)
However, the ester hydrogenolysis has attracted much indus-
trial interest in recent years, because ester, which is a raw material
for bio-alcohols such as bioethanol and biobutanol, can be produced
from organic acids available in fermentation broths. This process is
named “indirect fermentation”. Eggeman and Verser in Zeachem
Inc. [7,8] and Holtzapple at Texas A&M University [9] proposed
that the energy ratio, defined as the ratio of renewable energy pro-
duced divided by the fossil fuel energy input, would be higher in
this process than that in the conventional ethanol fermentation
process. From this point of view, the process scheme for the biobu-
and the reaction was carried out in the vapor phase over a
commercial Cu/ZnO/Al2O3 catalyst. Although numerous catalytic
studies on the hydrogenolysis reaction of methyl formate or ethyl
acetate were conducted previously [2–6,10–12], no research work
has been reported regarding BB hydrogenolysis. Thus, this study
addressed the kinetic mechanism of the vapor-phase hydrogenoly-
sis of butyl butyrate to butanol. In order to investigate if elementary
steps include a dissociative adsorption of butyl butyrate, we uti-
lized D2 instead of H2 for the reaction, and we characterized the
resulting D-labeled compounds by 1H nuclear magnetic resonance
(NMR) spectroscopy and gas chromatography–mass spectrometry.
In addition, a kinetics model was developed, on the basis of the
mechanism proposed by the experimental study, to determine the
rate-determining step.
∗
Corresponding author. Tel.: +82 2 958 5193; fax: +82 2 958 5209.
E-mail address: ywsuh@kist.re.kr (Y.-W. Suh).
0926-860X/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apcata.2010.08.009

I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
101
Fig. 1. Schematic diagram of the reaction system for the hydrogenolysis of butyl butyrate with H2 or D2.
2. Experimental
2.2. D2 isotope study
2.1. Reaction kinetic study
The hydrogenolysis experiment of BB with D2 was performed
in a fixed-bed SUS reactor (9 mm i.d. and 445 mm). In this case,
the reaction pressure was 10 atm in order to obtain a relatively
high conversion of BB. After the same pretreatment as explained
above, the catalytic tests were done in the temperature range of
497–533 K. To measure the conversion of BB, we analyzed the liq-
uid products using the same GC as mentioned above. Besides, the
D-labeled liquid products were characterized by 1H nuclear mag-
netic resonance (1H NMR) spectroscopy in a Varian Unity Plus 300
analyzer (300 MHz) and gas chromatography coupled with mass
spectrometry (GC–MS) in an Agilent 6890 Gas Chromatograph by
DB-XLB column (25 m, 0.200 mm, 0.33 ␮m).
Commercial CuO/ZnO/Al2O3 catalyst designated as ICI 83-3M
was employed in this study; the copper surface area measured by
N2O chemisorption is 9.85 m2/g. Its BET surface area is 78 2 m2/g
with a type II isotherm, and its t-plot showed a straight line with
an intercept of almost zero (micropore area = 4.5 m2/g), which is
indicative of a nonporous material. Thus, the effect of internal mass
transfer was negligible. Moreover, the catalyst pellet was crushed
into the size of less than 90 ␮m since the BB conversion remained
constant under different values of the flow rate as the amount of
catalyst loading changed to keep the space velocity constant at
120,000 h−1 [13]. The criterion suggested by Madon and Boudart
[14] also guaranteed that the effect of external diffusion is mini-
mized. Prior to the reaction, the catalyst was reduced in a flow of
20% H2/N2 at 573 K for 6 h. Reaction kinetic studies were carried
out in a quartz reactor (4 mm i.d. and 450 mm length) at ambi-
ent pressure with the space velocity of 120,000 h−1. Using He as
a diluent, we varied the molar ratio of H2 and BB while the par-
tial pressure of BB (PBB) was 4–7 kPa and that of H2 (PH2 ) was
75–90 kPa. BB was vaporized in the controlled evaporator mixer
(CEM, Hi-TEC Corp.) operating at 473 K and then fed to the reac-
tor maintained at a desired temperature in the range of 546–575 K.
The liquid products collected in the separator were finally analyzed
using a gas chromatograph (GC) equipped with flame ioniza-
tion detector (FID) by HP-INNOWAX column (30 m, 0.053 mm,
1.00 ␮m). The reaction system is schematically illustrated
in Fig. 1.
3. Results and discussion
3.1. Kinetic study
Since the main reaction presented in Eq. (1) is unfavor-
able at high temperatures due to its exothermic characteristics
(ꢀHrxn,298.15 K = −24.9 kJ/mol), equilibrium BB conversions (Xe)
were calculated under various H2/BB ratios and reaction tem-
peratures in which no side reactions occur. For the calculation
of thermodynamic values for given conditions spe◦cified in this
study, the constants of heat capacity (Cp) and ꢀGf for butanol
and butyl butyrate were taken from the database available in the
Unisim Design Suite (Honeywell Inc.), and the equilibrium con-
version was obtained by solution of the cubic expression for the
equilibrium constant. As a result, the values of Xe were in the range

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I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
Table 1
Extent of deutration of each proton in butyl butyrate and butanol.a
% deutration (mol%)
Compound
Proton
Butyl butyrate
Butanol
ab
bc
c
d
ec
fd
gb
hb
id
jc
k
le
Condition Af
Condition Bg
0
n.a.
0
n.a.
0
n.a.
74
n.a.
0
n.a.
0
n.a.
0
n.a.
0
0
0
3.7
15
83
97
97
95
97
a
Each proton in butyl butyrate and butanol was assigned as shown in Fig. 5.
b
c
d
e
f
Protons a, g, and h were found at ca. 0.9 ppm in 1H NMR spectra.
Proton j was found at ca. 1.5 ppm while protons b and e were found at 1.5–1.7 ppm in 1H NMR spectra, both of which were overlapped.
Protons f and i were found at ca. 1.35 ppm in 1H NMR spectra.
Condition A: BB LHSV 0.15 h−1, D2/BB = 22.5, 497 K, 7.5 bar.
Condition B: BB LHSV 0.15 h−1, D2/BB = 35, 553 K, 7.5 bar.
of 34–51%, while the experimental conversions were less than 3% of
the equilibrium values. These observations indicate that the kinetic
measurements in this study were carried out far from equilibrium.
For kinetic study, an empirical power law equation (cf. Eq. (2))
considering the normal Arrhenius temperature dependence was
used to fit the experimental data obtained at the fixed-bed flow
reactor:
−r = kPBBPˇ = Ae−E
P
PHˇ
(2)
˛
/RT
˛
BB
a
H
2
2
where
k is the apparent rate constant in the power law
model in mol/h/gcat/kPa−(␣+␤), A is the pre-exponential factor in
mol/h/gcat/kPa−(␣+␤), Ea is the activation energy in kJ/mol, Pi is the
partial pressure of species i in kPa, and ˛ and ˇ represent the reac-
tion orders of BB and H2, respectively.
The influence of two reactants was investigated by changing
the partial pressure of one reactant at a fixed partial pressure of
the other, where the total pressure was maintained at the same
in all catalytic tests using the diluent gas. The plots used to deter-
mine reaction orders with respect to butyl butyrate and hydrogen
over Cu/ZnO/Al2O3 catalyst are shown in Fig. 2. Both BB and H2
had positive effects on the reaction, where the reaction orders of
BB (˛) and H2 (ˇ) (cf. Eq. (2)) were determined to be 0.67 0.2
and 0.25 0.2, respectively, indicating that the hydrogenolysis rate
depends more on the concentration of butyl butyrate than on the
H2 partial pressure. Besides, the Arrhenius plot of the reaction
rates, presented in Fig. 2, shows that the activation energy calcu-
lated for BB hydrogenolysis over Cu/ZnO/Al2O3 catalyst is about
62 0.5 kJ/mol, which is lower than the hydrogenolysis of ethyl
acetate over Cu/SiO2 (88 kJ/mol) [4] and that of methyl formate
over copper chromite (83 1 kJ/mol) [5]. Through this determina-
tion of the reaction orders and the activation energy, the values
of the pre-exponential factor (A) and the apparent rate constants
(k) in Eq. (2) could be calculated as A = 94.8 mol kPa−(␣+␤)/h gcat and
k = 1.11, 1.42, 1.93 and 2.31 mol kPa−(␣+␤)/h·gcat at 546, 555, 564
and 575 K, respectively.
When the calculated rates of Eq. (2) using the above values of
the kinetic parameters were compared with the observed rates,
it is obvious that the power law expression fits the experimen-
tal data very well for commercial Cu/ZnO/Al2O3 catalyst (Fig. 3).
However, in spite of some useful information discussed above, a
power law model still fails to provide the detailed procedure for
the heterogeneous hydrogenolysis reaction.
3.2. D2 isotope study
In order to get insight into the hydrogenolysis mechanism of
butyl butyrate, D2 instead of H2 was utilized, and the expected reac-
tion scheme would be expressed as Eq. (3), under the assumption
in the previous reports that dissociative adsorption initially occurs
in the hydrogenolysis of ester [2,3,5,10]. In this case, two n-butanol
molecules having different m/z values could be produced by the
Fig. 2. Log–log plots of the BB consumption rate in [mol/h/gcat] vs. partial pressure
of BB (top) or H2 (middle) in [kPa] and Arrhenius plot of the BB consumption rate
(bottom) for hydrogenolysis of butyl butyrate over Cu/ZnO/Al2O3 catalyst.

I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
103
m/z of the main butanol fragment was 56, due to the McLafferty
rearrangement and subsequent cleavage [15,16]. When BB was
reacted with D2, the fragment of deutrated butanol showed m/z
of 58 (left-hand side in Fig. 4b), implying that two D atoms are
attached to the C atom next to O atom. From this result, we can
conclude that the dissociative adsorption of BB would be clearly
involved in the elementary steps for the hydrogenolysis reaction.
Besides, the following features were observed in the D2 isotope
study: Among the fragments of butyl butyrate obtained at 80% con-
version, there was the fragment corresponding to m/z of 58 (cf.
right-hand side in Fig. 4b), while the deutrated butanol obtained at
nearly 100% conversion showed m/z of 60 (cf. Fig. 4c). This indicates
that another reaction would proceed along with the hydrogenolysis
reaction.
The deutrated liquid samples were also analyzed by 1H NMR
spectroscopy. Fig. 5 shows the 1H NMR spectrum of the sample
obtained at 497 K with the pressure of 7.5 atm. After integration
of each proton peak, the degree of deutration at each proton of
butyl butyrate and butanol assigned in Fig. 5 was calculated, and
this could be extended to liquid samples deutrated under differ-
ent conditions. Table 1 summarizes such deutration degrees of the
above sample and the sample obtained at 553 K and 7.5 atm. Under
a relatively mild condition (condition A in Table 1), the protons j, k
and l of butanol were deutrated at the extent of 15%, 97% and 95%,
respectively. The deutration extent of the proton l was close to the
predicted value, but the other protons were deutrated to the extent
greater than the predictions (0% and 50% for protons j and k, respec-
tively) based on Eq. (3). This observation might be explained by the
mechanism in the previous reports on the deutrolysis of methyl or
ethyl acetate [3], i.e., the mechanism via alcohol–aldehyde equi-
librium (Eqs. (4)–(7)) and keto-enol tautomerism (Eqs. (8)–(11)),
even though the exchange between butanol and deuterium may
occur under the condition employed in the isotopic labeling exper-
iments. Also, the deuterium exchange with the proton j of butanol
Fig. 3. Comparison of the calculated rates using the power law model with the
observed rates for hydrogenolysis of butyl butyrate over Cu/ZnO/Al2O3 catalyst.
addition of D2.
C3H7COOC4H9 + 2D2 → 2C3H7CD2OD + C4H9OD
(3)
D2 experiment, initially performed under the reaction con-
ditions employed in the kinetic study (cf. Table 1), resulted in
extremely low BB conversion, and multiplicity of butanol and BB
protons could not lead to clear quantification on the extent of
deutration of each proton in the reactants and products. Thus, to
produce a large amount of deutrated butanol (i.e., high BB conver-
sion) as well as to minimize the formation of side products, we
carried out the hydrogenolysis experiment with D2 at 7.5–10 atm
and 497–533 K, where the maximum conversions were in the range
of 80–99%. The resulting liquid samples obtained under three dif-
ferent reaction conditions were then characterized by GC–MS, as
shown in Fig. 4. In the sample obtained with BB and H2 (Fig. 4a),
Fig. 4. Mass spectra of butanol (left) and butyl butyrate (right) GC peaks in liquid product samples obtained at different reaction conditions: (a) H2, 497 K, 10 bar, (b) D2,
497 K, 7.5 bar, and (c) D2, 553 K, 7.5 bar.

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I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
Fig. 5. 1H NMR spectrum of the liquid product sample obtained in the hydrogenolysis of butyl butyrate with D2 at 497 K and 7.5 bar.
On the basis of the above explanation on GC–MS and 1H NMR
results, it can be suggested that BB hydrogenolysis proceeds dom-
inantly via the dissociative adsorption of ester and the subsequent
hydrogenation of the C3H7CO and C4H9O fragments so formed,
though several concomitant reactions occur under severe con-
ditions. Moreover, the C3H7CO species would be present on the
adsorption sites for a longer time, followed by insertion of H atoms
to produce butanol via butyraldehyde, whereas the hydrogenation
of butoxy species is rapid.
was more dominant under more D2-fed conditions (condition B in
Table 1). Therefore, the combination of these results and several
reaction pathways could lead to the proton j of butanol being deu-
trated, due to the keto-enol tautomerism of butyraldehyde which
would be absorbed for a longer period. This explanation is consis-
tent with the mechanism proposed for the hydrogenolysis of ethyl
acetate [10].
C4H9OD → C3H7CHO + HD
(4)
(5)
(6)
(7)
(8)
C3H7CHO + D2 → C3H7CHDOD
3.3. Mechanistic consideration
C3H7CD2OD → C3H7CDO + D2
C3H7CDO + D2 → C3H7CD2OD
C3H7CHO → C2H5CH CHOH → C2H5CH CHO∗ + H∗
To achieve a proper kinetic model with the experimental data
of BB hydrogenolysis over Cu/ZnO/Al2O3 catalyst, we developed
a mechanistic consideration based on the Langmuir-Hinshelwood
mechanism. According to the rationale explained above, five ele-
mentary reaction steps were set up as follows:
C2H5CH CHO ∗ +D∗ → C2H5CH CHOD → C2H5CHDCHO →
C2H5CHDCHDOD
(9)
k
1
Step 1 : C3H7COOC4H9 + 2 ∗ ꢀ C3H7C ∗ O + C4H9O∗
(13)
(14)
(15)
(16)
(17)
k
−1
C3H7CDO → C2H5CH CDOH → C2H5CH CDO ∗ +H∗
(10)
k
2
Step 2 : C3H7C ∗ O + H ∗ ꢀ C3H7CHO + 2∗
k
−2
C2H5CH CDO ∗ +D∗ → C2H5CH CDOD → C2H5CHDCDO →
k
3
C2H5CHDCD2OD
(11)
Step 3 : C3H7CHO + H ∗ ꢀ C3H7CH2O∗
k
−3
where * denotes the adsorbed surface species. Additionally, the pro-
ton d of butyl butyrate was deutrated to 74%, presumably as a result
of trans-esterification as follows:
k
4
Step 4 : C4H9O ∗ +H ∗ ꢀ C4H9OH + 2∗
k
−4
C3H7COOC4H9 + C3H7CD2OD → C3H7COOCD2C3H7 + C4H9OD
k
5
Step 5 : H2 + 2 ∗ ꢀ 2H∗
(12)
k
−5
Table 2
Langmuir-Hinshelwood model kinetic parameters for hydrogenolysis of butyl butyrate to butanol over Cu/ZnO/Al2O3 catalyst.a
T (K)
k (mol/h/gcat/kPa)
K2 (kPa)
K3 (kPa−1
)
K4 (kPa)
K5 (kPa−1
)
Ea (kJ/mol)
555
565
575
1.57 × 10−3
1.89 × 10−3
2.50 × 10−3
2.69
0.38
0.35
4.03
0.32
0.09
0.13
2.01
1.99
8.19 × 10−3
8.35 × 10−3
8.84 × 10−3
61.5 8.0
a
Reaction condition same as shown in Table 1.

I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
105
Four rate expressions were derived by assuming each step as the
rate-determining step (RDS), except the adsorption of hydrogen (cf.
step 5 in Eq. (17)), as follows:
for the estimation at 555 and 575 K), compared to the other mod-
els. All kinetic parameters in the RDS 1 model are summarized in
Table 2.
kPBB
RDS1 :
− r =
(18)
2
(1 + K2−1K3−1K4−1K5−3/2PH
P
+ K−1K5−1/2PH
P
BuOH
+ K1/2PH1/2
)
2
−3/2
−1/2
BuOH
4
5
2
2
kK1K4K5PH PBBPB−u1OH
2
RDS2 :
− r =
(19)
2
(1 + K1K4K1/2PH1/2
P
PBB + K−1K5−1/2PH
P
BuOH
+ K1/2PH1/2
)
2
−1/2
−1
5
BuOH
4
5
2
2
kK1K2K4K3/2PH3/2
P
BB
P
−1
5
BuOH
2
RDS3 :
RDS4 :
− r =
− r =
(20)
(21)
1 + K1K4K1/2PH1/2
P
PBB + K−1K5−1/2PH
P
+ K1/2PH1/2
−1/2
−1
BuOH
5
BuOH
4
5
2
2
2
kK11/2K21/2K31/2K5PH
P
BB
1/2
2
2
−1/2
(1 + K11/2K2−1/2K3−1/2K5−1/2PH
P
1/2 + K11/2K21/2K31/2K51/2PH1/2PB1B/2 + K51/2PH1/2
)
2
BB
2
2
where the RDS1 denotes the reaction rate with step 1 (Eq. (13))
that is assumed to be the RDS, while the assumption of the rapid
equilibrium is made to the other steps. The equilibrium constant Kn
is defined as the ratio of the rate constant of the forward reaction to
that of the backward reaction, and Pi denotes the partial pressure
of species i.
After deriving the rate expressions, we determined the kinetic
parameters (k and Kn) to fit the data obtained at the tempera-
tures of 555, 564, and 575 K, using the nonlinear regression analysis
with the POLYMATH 5.1 (Polymath Software). Since experiments at
each temperature produced 8 data points (cf. Fig. 2), a total of 24
points were used in the nonlinear data-fitting procedure. The aim
of the data-fitting procedure is to minimize the mean-square dif-
ferences between calculated values of the rate and the rate values
obtained directly from the experimental data using the differen-
tial method. Mathematically this can be expressed by the following
equation:
It is very meaningful to compare the hydrogenolysis reaction
mechanism of ethyl acetate with that of butyl butyrate inves-
tigated in this study. In the proposed reaction scheme for the
reduction of ethyl acetate on silica-supported Cu catalyst [10], both
the dissociative adsorption of ethyl acetate and the hydrogenation
of acyl species are important in controlling the overall reduction
rate of esters. In partial accordance with the previous report, the
hydrogenolysis reaction of butyl butyrate proceeds via its disso-
ciative adsorption, which is considered to be the rate-determining
step in this study, to form surface C3H7CO and C4H9O fragments.
Furthermore, the former fragment is hydrogenated via butyralde-
hyde to butanol and the latter is directly hydrogenated, where both
reaction rates are relatively faster than those reported previously
for the hydrogenolysis reaction of ethyl acetate.
It should be noted that the temperature dependence of the equi-
librium constants, K2 and K4 in Table2, maybepoor, since thevalues
at 565 and 575 K are close. This feature may come from the quality
of data or from the estimation performance. The values of R2 for the
estimation at 555 and 575 K are higher than 95%, while the value at
565 K is relatively low although the average error at the tempera-
ture is still within the allowable limits. However, since the average
error for RDS1 model is still lowest at 575 K and the purpose of
the present study is to find the best fit model and to determine
the detailed mechanism for the hydrogenolysis reaction, relatively
poor performance of estimation at higher temperature exerts no
effect on our conclusion. It is recommended for readers to be careful
when the developed model with the estimated kinetic parame-
ters is used for quantitative analysis, especially when the correct
temperature dependence of equilibrium constants is required.
ꢀ
2
minꢁ =
(rcalc − rexp
)
(22)
p
all data samples
To find the best fit model and thus, the rate-determining step
which describes the kinetics of the hydrogenolysis reaction,
the value of R2 (the coefficient of determination) is calculated
ꢁ
ꢁ
as [1 −
(rexp − rcalc)2/ (rexp − rexp,avg)2]. The calculated rates
obtained at each RDS were compared with the experimental data,
as shown in Fig. 6. As a result, the rate expression model, whose RDS
was specified with the dissociative adsorption of butyl butyrate, i.e.,
Eq. (13), showed the most precise and reasonable results (R2 = 0.96
4. Conclusions
The kinetic study for the vapor-phase hydrogenolysis of butyl
butyrate to butanol over a commercial Cu/ZnO/Al2O3 catalyst was
carried out. The catalytic experiment was conducted far from equi-
librium, and several experimental conditions, such as the partial
pressures of two reactants, BB and H2, and the reaction tempera-
ture, were varied. In the empirical power law equation, the rate
of hydrogenolysis had a positive effect with respect to both BB
and hydrogen, and was dependent more on the BB concentra-
tion due to inhibited adsorption of ester on the Cu/ZnO-based
catalysts. In order to investigate the hydrogenolysis mechanism,
we conducted D2 isotopic labeling experiments. The analyses of
the resulting D-labeled liquid samples by GC–MS and 1H NMR
confirmed that the hydrogenolysis of butyl butyrate proceeds via
dissociative adsorption of ester, producing C3H7CO and C4H9O frag-
ments. The kinetics for the BB hydrogenolysis was interpreted on
Fig. 6. Comparison of the calculated rates using four different rate-determining
steps (Eqs. (13)–(16)) based upon the Langmuir-Hinshelwood model with the
observed rate for hydrogenolysis of butyl butyrate over Cu/ZnO/Al2O3 catalyst.

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I.B. Ju et al. / Applied Catalysis A: General 387 (2010) 100–106
the basis of the Langmuir-Hinshelwood model, and it appears that
the rate-determining step involves dissociative adsorption of butyl
butyrate. Moreover, the surface C3H7CO fragment produced by this
adsorption step is hydrogenated via butyraldehyde to butanol and
the counterpart fragment (C4H9O) is directly hydrogenated The
rate expression derived in this study also showed precise fitting
performance and an activation energy (61.5 8.0 kJ/mol) close to
the value obtained from the power law equation (about 62 kJ/mol).
In conclusion, the kinetic information presented in this study is
expected to provide valuable insight into the design of large-scale
butanol production processes, particularly indirect fermentation
processes.
[2] T. Turek, D.L. Trimm, N.W. Cant, Catal. Rev.—Sci. Eng. 36 (1994)
645–683.
[3] A.K. Agarwal, N.W. Cant, M.S. Wainwright, D.L. Trimm, J. Mol. Catal. 43 (1987)
79–92.
[4] J.W. Evans, M.S. Wainwright, N.W. Cant, D.L. Trimm, J. Catal. 88 (1984)
203–213.
[5] X. Juang, N.W. Cant, J.W. Evans, M.S. Wainwright, Catal. Today 93–95 (2004)
113–119.
[6] K.M. Kim, H.C. Woo, M. Cheong, J.C. Kim, K.H. Lee, J.S. Lee, Y.G. Kim, Appl. Catal.
A: Gen. 83 (1992) 15.
[7] T. Eggeman, D. Verser, Appl. Biochem. Biotechnol. 121–124 (2005)
605–618.
[8] T. Eggeman, D. Verser, Appl. Biochem. Biotechnol. 129–132 (2005)
361–381.
[9] C.B. Granda, L. Zhu, M.T. Holtzapple, Environ. Prog. 26 (2007) 233–250.
[10] M.A. Natal Santiago, M.A. Sánchez-Castillo, R.D. Cortright, J.A. Dumesic, J. Catal.
193 (2000) 16–28.
[11] C.J.G. van der Grift, A.F.H. Wielers, B.P.J. Joghi, J. van Beijnum, M. de Boer, M.
Versluijs-Helder, J.W. Geus, J. Catal. 131 (1991) 178–189.
[12] F.Th. Van de Scheur, L.H. Staal, Appl. Catal. A: Gen. 108 (1994) 63–83.
[13] F.M. Dautzenberg, in: S.A. Bradley, M.J. Gattuso, R.A. Bertolacini (Eds.), Char-
acterization and Catalyst Development: An Interactive Approach, American
Chemical Society, Washington, 1989, pp. 99–119.
[14] R.J. Madon, M. Boudart, Ind. Eng. Chem. Fundam. 21 (1982) 438–447.
[15] A.N. Zavilopulo, O.B. Shpenik, V.A. Surkov, Anal. Chim. Acta 573–574 (2006)
427–431.
Acknowledgment
The authors would like to acknowledge funding from Korea
Ministry of Environment as “Converging Technology Project
(202–101–006)”.
References
[16] E. de Hoffmann, V. Stroobant, Mass Spectrometry: Principles and Applications,
third ed., John Wiley & Sons Ltd., Singapore, 2007.
[1] H. Adkins, K. Folkers, J. Am. Chem. Soc. 53 (1931) 1095–1097.