A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl Benzoate to Benzyl Alcohol in Methanol Solution

Article abstract of DOI:10.1007/s10562-019-02721-x

The Cu/ZnO/Al₂O₃ catalysts prepared by co-precipitation method were used for the hydrogenation of methyl benzoate to benzyl alcohol. These catalysts were characterized at various stages of preparation by nitrogen adsorption–desorptio

Full text of DOI:10.1007/s10562-019-02721-x

Catalysis Letters
https://doi.org/10.1007/s10562-019-02721-x
A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl
Benzoate to Benzyl Alcohol in Methanol Solution
Ye Jiang1 · Qiang Bao1 · Wenying Gui1 · Yifan Wu1 · Xiaofei Liu1 · Li Zhang1 · Bin Zheng2 · Zhenlu Wang1
Received: 11 October 2018 / Accepted: 20 February 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The Cu/ZnO/Al2O3 catalysts prepared by co-precipitation method were used for the hydrogenation of methyl benzoate to
benzyl alcohol. These catalysts were characterized at various stages of preparation by nitrogen adsorption–desorption, X-ray
diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), and X-ray photoelectron spectroscopy (XPS).
The experimental results show that the addition of ZnO to the catalyst greatly improves the selectivity of benzyl alcohol.
When the Cu/Zn/Al molar ratio is 2:2:1 and the calcination temperature of the catalyst is 650 °C, the catalyst exhibits very
highly catalytic performance. In addition, the effects of reaction temperature, pressure and time were also investigated during
the hydrogenation of methyl benzoate to benzyl alcohol. When the methyl benzoate was hydrogenated over this catalyst at
160 °C and 7 MPa of H2 for 10 h, the conversion of methyl benzoate can reach 93.89% and the selectivity of benzyl alcohol
is 88%. This effectively catalytic performance can be attributed to the presence of highly dispersed and stable metallic cop-
per nanoparticles, and the weak acidity of the catalyst surface. Besides, the reaction pressure and temperature play a crucial
role in the conversion of methyl benzoate and the selectivity of benzyl alcohol.
Graphical Abstract
Application of Cu/ZnO/Al2O3 catalyst in hydrogenation of methyl benzoate to benzyl alcohol.
Keywords Cu/ZnO/Al2O3 catalysts · Liquid-phase hydrogenation · Methyl benzoate · Benzyl alcohol · Weak acidity
1 Introduction
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02721-x) contains
Benzyl alcohol is an important chemical solvent for inks,
supplementary material, which is available to authorized users.
paints, varnishes, and used as a precursor for various esters
* Zhenlu Wang
in the cosmetics and coatings industry [1]. As early at the
1940s, Adkins pioneered the development of a series of
wzl@jlu.edu.cn
Extended author information available on the last page of the article
Vol.:(0123456789)
1 3

Y. Jiang et al.
Cu/Cr/Ba oxide-containing catalysts for hydrogenation of
lactate-hydrogenated α-amino and hydroxy esters and hydro-
genation of methyl and butyl hexanoate for preparing the
corresponding alcohols. Due to the inherent resistance of
the ester, especially for the reduction reaction [2, 3], the
current heterogeneous catalytic process is usually carried
out under extremely harsh conditions. At the same time,
Mozingo and Folkers [4] began to study the reaction of Cu/
CrO3/BaO catalysts for the hydrogenation of aromatic esters
to prepare the corresponding alcohols in methanol. In the
past decade, a series of strategies have been developed to
prepare aromatic alcohols from corresponding esters. The
inorganic metal hydride (such as LiAlH4 and NaBH4) was
used as a catalyst to reduce the ester, but it suffered poor
compatibility with functional groups, low atomic utilization,
and wastes producing [2, 5]. The benzyl chloride hydrolysis
method was also used to prepare benzyl alcohol. However,
the inevitable introduction of free chloride ions cannot sat-
isfy the high quality of benzyl alcohol which is applied in the
food and pharmaceutical industries. Therefore, developing
highly efficient and environmentally friendly catalysts is a
long-term goal for researchers.
important role in the hydrogenation of methyl benzoate to
benzyl alcohol. Besides, the effect of reaction condition of
catalysts on their catalytic performances were discussed. The
Cu/ZnO/Al2O3 catalyst exhibits high catalytic activity and
benzyl alcohol selectivity in this reaction, which may be
applied to the hydrogenation of methyl benzoate to produce
benzyl alcohol in industry.
2 Experimental
2.1 Catalyst Preparation
The precursor of Cu/ZnO/Al2O3 catalysts were synthe-
sized by the co-precipitation method. Cu(NO3)2·3H2O,
Zn(NO3)2·6H2O and Al(NO3)3·9H2O (A.R., Sinopharm
Chemical Reagent Ltd.) were used as the iron source and
Na2CO3 was the precipitation. Typically, 1.0 M Cu(NO3)2,
1.0 M Zn(NO3)2, 1.0 M Al(NO3)3 and 0.5 M Na2CO3 were
prepared respectively. The 1.0 M Cu(NO3)2 and 1.0 M
Zn(NO3)2 solution was introduced into a precipitation ves-
sel at 70 °C. At the time, an aqueous of Na2CO3 (0.5 M)
was dripped into the vessel until the pH at 7.5 under con-
stant stirring. Also, the Al(NO3)3·9H2O was dripped by the
same method described above. Then, the above two samples
were mixed under the same condition. This synthesis solu-
tion was aged under constantly stirring for 2 h at 70 °C and
cooled maintaining for 30 min. The precipitate was filtered
and washed with deionized water until the filtrate appears to
be neutral. Then the precursor material was dried at 100 °C
for 12 h. The catalyst was obtained after heated to 450 °C
at 5 °C min−1 and calcined at 450 °C for 4 h in a flow of air
atmosphere.
In general, catalysts for ester hydrogenation are prepared
by mixing a hydrogenation metal (e.g., Fe, Co, Ni, Cu, Zn)
with various oxides (e.g., ZrO2, V2O5, Cr2O3, WO3) [6].
Especially the copper-based catalysts exhibit excellent per-
formance in the hydrogenation of esters to the corresponding
alcohols [7–12]. Among them, Cu/ZnO/Al2O3 is widely used
as a highly efficient and environmentally friendly catalyst
due to their excellent activity and selectivity for the hydro-
genation of C=O bands [13, 14]. The studies hold various
views on the rule of ZnO in the reaction of ester hydrogena-
tion to produce the corresponding alcohol, such as storing
hydrogen, activating hydrogen [15–17], and also increasing
the dispersion of Cu particles. However, to our knowledge-
ment, no detailed and in-depth study of the effects of Cu-
based catalysts has been reported in the hydrogenation of
esters to produce the corresponding alcohols [18].
2.2 Catalytic Reaction
The catalytic hydrogenation of benzoate to benzyl alcohol
was performed in a 100 stainless steel under constant stir-
ring at a speed of 500 rpm. Before testing the activity of
the catalyst, the calcined CuO/ZnO/Al2O3 (1 g) sample was
reduced in a 10% H2/Ar atmosphere at 250 °C for 4 h at a
heating rate of 5 °C min−1. The autoclave was charged with
1 g of the freshly reduced catalyst, 0.5 g of methyl benzo-
ate (≥ 99.0%) and 25 mL of methanol solution. Then the
autoclave was sealed, purging three times with hydrogen to
replace the air. The autoclave was pressured at 3 MPa with
hydrogen at room temperature, and the reaction temperature
was maintained at 200 °C. Finally, reactants and products
were analyzed by Shimadzu GC-14B gas chromatography
equipped with flame ionization detector and Agilent DB-
WAX capillary column.
In view of cost and practical application, the hydrogena-
tion of benzoate to benzyl alcohol is an essential industrial
reaction and will be widely used in the industrial production
of benzyl alcohol. Because benzoic acid methyl ester can
be obtained by direct esterification with benzoic acid and
methanol, the cost of the substrate and industrial produc-
tion can be greatly reduced. Therefore, the hydrogenation
of benzoic acid methyl ester to produce benzyl alcohol will
be a great practical significance in industry.
In this work, The Cu/ZnO/Al2O3 catalyst synthesized
by the co-precipitation method was first used in the hydro-
genation of methyl benzoate to benzyl alcohol. Their
physic-cochemical and catalytic properties for hydrogena-
tion of methyl benzoate were investigated. We have found
that highly dispersed Cu and weakly acidic sites play an
1 3

A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl Benzoate to Benzyl…
Table 1 Physisorption results of the Cu/ZnO/Al2O3 catalysts pre-
2.3 Catalyst Characterization
pared by co-precipitation method at a series of different Cu/Zn/Al
ratio
The specific surface areas of the Cu/ZnO/Al2O3 catalysts
were analyzed and measured by Nitrogen adsorption–des-
orption at −196 °C on a Micromeritics ASAP 2020M ana-
lyzer, was calculated the porous volume and pore size using
the Barrett–Joyner–Halenda (BJH) method.
Samples Molar ratio
S
BET ( m2 g−1) Pore
Pore sizea (nm)
of Cu/Zn/
Al
volumeb
(cm3 g−1
)
CZA-0 2:0:1
CZA-1 2:1:1
CZA-2 2:2:1
CZA-3 2:3:1
61.2
40.4
37.1
51.0
0.071
0.056
0.075
0.120
3.88
5.81
6.99
8.47
The power X-ray diffraction (XRD) patterns of catalysts
were collected on a Rigaku D max-2550 diffractometer with
nickel-filtered Cu K radiation (λ=1.54 Å).
The H2-temperature-programmed reduction (H2-TPR)
was performed on a conventional flow system equipped with
a thermal conductivity detector (TCD) as follow: sample was
loaded in a quartz U-tube reaction, was treated at 120 °C for
1 h under flow of argon (30 mL min−1). After it was cooled
to 50 °C under flow Nitrogen, it was changed to 10% H2/Ar
(30 mL min−1), and TPR of the catalyst was heated from 50
to 400 °C.
aBJH desorption pore size
bBJH desorption average pore diameter
indicates a significant sintering of the catalyst at high calci-
nation temperature.
From the patterns of CZA-X-450 catalysts in Fig. 1a, it
can be seen five obvious peaks at 35.52°, 35.45°, 35.55°,
38.73°, 38.92°, which are the characteristic peaks of CuO
(JCPDS 05-0661). As shown in Fig. 1b, the XRD patterns
of the reduced CZA-X-450 catalysts present clearly three
strong diffraction peaks at 43.3°, 50.4° and 74.1°, which
correspond to the (111), (200) and (116) planes of metallic
copper phase (JCPD 65-9743). This indicates that the Cu2+
transferred to Cu0 after the reduction process. In addition,
the diffraction peaks at 2θ=31.77°, 34.42° 36.25°, 47.54°,
56.60°, 62.86° and 67.96° can be found in the unreduced
and reduced CZA-X-450 catalysts, which are characteris-
tic peaks of ZnO (JCPDS 36-1451). Besides, no diffraction
peaks of Al2O3 can be observed in the XRD patterns of all
catalysts, which indicates that the Al2O3 were amorphous
or highly dispersed in the unreduced and reduced CZA-
X-450 catalysts. From the XRD results, we can found that
the reduction treatment can change the valence state of Cu,
while the Al and Zn states were unchanged.
The NH3-temperature-programmed desorption
(NH3-TPD) of the catalyst were carried out using a conven-
tion flow system which was connected with thermal con-
ductivity detector (TCD). The calcined CuO/ZnO/Al2O3
sample (50 mg) was place in a quartz U-tube reaction that
was pretreated at 450 °C for 30 min under a Nitrogen flow
atmosphere (30 mL min−1) at a rate of 10 °C min−1. Then
the sample was cooled to 100 °C at the same condition that
followed by treatment with the 10% NH3/N2 (30 mL min−1)
for 30 min.
The X-ray photoelectron spectroscopy (XPS) was per-
formed on a Thermo ESCALB 250 system with a Mg Kα
source (1254.6 ev). The XPS spectra were calibrated by
adjusting the position of the C 1 s peak to 284.6 eV.
The transmission electron microscope (TEM) observation
were carried out on a TECNAI F20 electron microscope
with on an operating voltage of 200 kV.
The XRD patterns of CZA-2-T catalysts are shown in
Fig. S1c. It is evident that CuO and ZnO diffraction peaks
were observed in the patterns. The intensity of CuO and
ZnO diffraction peaks gradually increase with the treatment
temperature increasing. It may be caused by the Cu spe-
cific area loss of the CZA-2-T catalysts reduced [20]. At
the same time, the XRD patterns of the reduced CZA-2-T
catalysts were performed in Fig. S1d. No CuO diffraction
peaks can be observed in the XRD patterns of all catalysts,
which indicates that CuO has been completely reduced to
metallic copper. With increasing the calcination temperature,
the average crystallite size of metallic copper particles esti-
mated by the Scherrer formula according to the (111) plane
decreases gradually (Table S3). Besides, the XRD patterns
of the used CZA-2-650 catalyst are shown in Fig. S3. It is
clear that Cu and ZnO diffraction peaks remains unchanged.
The reducibility of the unreduced CZA-X-450 catalysts
was measured by H2-TPR (Fig. 2). It shows that reduction
3 Results and Discussion
3.1 Textural and Structural Properties of Catalysts
The physicochemical and surface properties of CZA-X (X
mean the different molar ratio of Cu, Zn and Al) catalysts
calcined at 450 °C are shown in the Table 1. It can be clearly
seen that with the addition of ZnO to Cu/Al2O3, the BET
surface area of the CAZ-X-450 catalyst has dropped sig-
nificantly from 61.2 to 40.4 m2 g−1. However, the surface
area of the catalysts also increases with the increase of the
Zn contents. CZA-2-T catalysts (CZA-T, T mean the calci-
nation temperature) exhibit decrease tendency of the area
from 50.5 to 29.8 m2 g−1 with the treatment temperature
increasing (Table S1). Especially, CZA-2-750 sample shows
the dramatically decreased surface area at 9.1 m2 g−1, which
1 3

Y. Jiang et al.
a
a
CuO
ZnO
234
CZA-3
CZA-2
CZA-1
CZA-3
235
234
245
CZA-2
CZA-1
251
272
CZA-0
CZA-0
100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
10
20
30
40
50
60
70
80
Temperature (°C)
2θ (degree)
b
b
Cu
ZnO
245
235
333
CZA-750
CZA-3
CZA-2
246
CZA-650
CZA-550
241
251
CZA-1
235
245
CZA-450
CZA-350
282
291
CZA-0
100 120 140 160 180 200 220 240 260 280 300 320 340 360 380
10
20
30
40
50
60
70
80
Temperature (°C)
2θ (degree)
Fig. 2 H2-TPR profiles of CZA-X-450 catalysts (a) and CZA-2-T cat-
alysts (b)
Fig. 1 XRD patterns of CZA-X-450 catalysts unreduced (a) and
reduced (b)
CuO. With the increasing of Zn/Al molar ratio, the reduction
temperature of CZA-3-450 catalyst gradually shifts towards
the low temperature, which indicates that CuO is highly dis-
persed in the catalyst.
peak of CZA-X-450 catalysts located at about 210–320 °C.
Compared to unreduced CZA-0-450 catalyst, a much lower
temperature (234 °C) peak was observed of CZA-1-450,
CZA-2-450 and CZA-3-450 catalysts. In addition, two
reduction peaks could be observed in the profiles of CZA-
0-450 and CZA-2-450. The lower temperature peak can be
attributed to the reduction of highly dispersed CuO particles
and high temperature peak belongs to the reduction of bulk
CuO particles [19, 20]. It is clearly shown that the reduction
peak of the CZA-X-450 catalysts shift towards to the low
temperature when ZnO is introduced into the catalyst. It is
well-known that the presence of ZnO can promote the reduc-
tion of CuO by the hydrogen spillover [21, 22]. In addition,
ZnO and Al2O3 cannot be reduced at below 500 °C [23, 24].
In the previous article [18], it was reported that the addition
of ZnO to Cu/Al2O3 can form a Cu–Zn–O solid solution
which can be reduced at a lower temperature compared to
In order to further investigate the reducibility of CZA-2-T
catalysts treated at different temperature, the TPR characteri-
zation was performed as shown in the Fig. 2b. Two peaks
can be observed in Fig. 2b. Copper species in CZA-2-T cata-
lysts are reduced at different temperatures. The CZA-2-350
catalysts exhibits a higher reduction temperature in the range
of 270–310 °C, which could be assigned to the reduction
of bulk CuO particles [25]. With the calcination tempera-
ture increasing, the CZA-2-450 and CZA-2-650 catalysts
exhibit lower reduction temperatures. Especially, the CZA-
2-650 catalyst exhibits the lowest reduction temperature at
235 °C, with a smallest shoulder peak at 246 °C, suggesting
that the electronic interaction exists in catalyst. This may
change the electronic environment around CuO and make
1 3

A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl Benzoate to Benzyl…
the CZA-2-650 catalyst more easily reduced [26]. In addi-
tion, it may be attributed to the presence of highly dispersed
CuO nanoparticles, which could be easily reduced [7].
In the previous report, toluene and benzene were formed
by catalytic hydrogenolysis of benzyl alcohol [8]. And
acidic center of the catalyst surface affects the efficiency
of C–O hydrogenolysis [27–29]. Therefore, NH3-TPD was
performed to evaluate the surface acidity of the CZA-X-450
catalysts. As shown in the Fig. 3a, four similar broad peaks
can be observed obviously. It can be divided into two peaks
(α and β). The α peak center is located at approximately
210–215 °C, which can be ascribed to weak acid sites.
The β peak center is located at approximately 300–325 °C,
which can be ascribed to medium acidic sites. The acidic
sites of the CZA-X-450 catalyst are provided by ZnO, CuO,
and Al2O3, but largely contributions are derived from the
Al2O3 support [30]. With the Zn/Al molar ratio increasing,
the intensities of the α and β peaks gradually decreased,
which can be attributed to the reduction of the weaker and
medium-strong acid site amount. The CZA-2-450 catalysts
had the smallest amount of acid sites among the CZA-X-
450. However, the catalyst acidity gradually increases as the
ZnO content increase, which may be due to the increase in
specific surface area of the catalyst [31].
The NH3-TPD is also performed to evaluate the surface
acidity of the CZA-2-T catalyst in the Fig. 3b. It is clearly
seen that the CZA-2-350, CZA-2-450, CZA-2-550 and CZA-
2-650 have a similar broad peak located at 150–430 °C. It
can be also deconvoluted into two peaks (α and β). With the
increase of calcination temperature at 350–650 °C, the CZA-
2-650 had the smallest amount of acid sites, which may be
due to decrease in the specific surface area of the catalyst
[32]. As for CZA-2-750 catalyst, the peaks in the figure can
hardly be observed. Considering the higher calcination tem-
perature, the dramatic decrease should be correlated with the
sintering of the catalyst, in which a large number of surface
acidic sites have been lost [33, 34].
X-ray photoelectron spectroscopy (XPS) was employed to
investigate the surface chemical states and compositions of
the reduced Cu/ZnO/Al2O3 catalysts. As shown in Fig. 4, the
peaks centered at 932.6 and 952.9 eV should be assigned to
the binding energy of Cu 2p3/2 and Cu 2p1/2. Meanwhile, the
absence of “shakeup” peaks of the binding energy (BE) at
940–945 eV may indicate that Cu2+ was completely reduced
to metallic copper (Cu0) and/or Cu+ for the reduced Cu/
ZnO/Al2O3 composites [35–38]. In addition, In addition,
the atomic concentration of related elements is shown in
Table S3.
a
CZA-3
CZA-2
CZA-1
β
Figure 5 shows the HRTEM images of reduced CZA-
2-650 and ZCA-2-750 catalysts. It is apparent that the
15–17 nm copper nanoparticles are uniformly dispersed on
the surface of the support and with a few agglomeration for
α
CZA-0
100
200
300
400
500
Temperature (°C)
b
932.6(eV)
952.9(eV)
CZA-750
CZA-750
CZA-650
CZA-550
CZA-650
CZA-550
CZA-450
CZA-450
CZA-350
CZA-350
100
200
300
400
500
925
930
935
940
945
950
955
960
965
Temperature (°C)
Binding energy (eV)
Fig. 3 NH3-TPD profiles of CZA-X-450 catalysts (a) and CZA-X-T
catalysts (b)
Fig. 4 The Cu2p X-ray photoelectron spectra of reduced CZA-2-T
catalysts
1 3

Y. Jiang et al.
Fig. 5 TEM and HRTEM images of reduced CZA-2-650 and CZA-2-750 catalysts
100
Table 2 Effect of Zn/Al ratio on catalytic properties of Cu/ZnO/
Al2O3 catalysts in the reaction of hydrogenation of methyl benzoate
to benzyl alcohol
80
Catalysts T (°C) Time (h) Conversion (%) Selectivity (%)
BAOL Toluene
60
Conversion of MB (%)
Selectivity of BAOL (%)
Selectivity of Toluene (%)
CZA-0
CZA-1
CZA-2
CZA-3
200
200
200
200
8
8
8
8
73.13
51.21
62.45
32.17
24.40
81.94
81.00
84.12
75.60
18.06
19.00
15.88
40
20
0
Reaction conditions: methyl benzoate=0.5 g; methanol=25 mL,
T=200 °C; P=3 MPa; n=500 rpm (the speed is shown on the panel
in the reactor of speed control); mCu/ZnO/Al2O3 =1 g (catalysts cal-
cined 4 h at 450 °C, reduced 4 h at 250 °C with 10% H2/Ar)
150
160
170
180
190
200
210
220
230
Temperature (°C)
the CZA-2-650 catalyst (Fig. 5b, c). As for the CZA-2-750
catalyst (Fig. 5a) some irregular large black copper particles,
which should be mainly attributed to the sintering of copper
particles.
Fig. 6 Influence of reaction temperature on reaction of hydrogenation
of methyl benzoate to benzyl alcohol
catalyst and increases the dispersion of Cu, inhibiting the
formation of toluene by-products.
3.2 Catalytic Performance of Cu/ZnO/Al2O3
Table 2 summarize the results of hydrogenation of methyl
benzoate to benzyl alcohol over as-synthesized CZA-X-450
catalysts with different Cu/Zn/Al molar ratio, the yield of
benzyl alcohol decreases in the following order for the cata-
lysts: CZA-2-450>CZA-1-450>CZA-3-450>CZA-0-450.
It is clear that CZA-0-450 catalyst exhibits the lower yield
of benzyl alcohol, while the selectivity of the correspond-
ing toluene by-product was as high as 75.6%. This result
indicates that the excessive acidity is more conducive to the
hydrogenolysis of C–O to produce a large amount of by-
product toluene in this reaction condition. However, with
the addition of Zn, the selectivity of benzyl alcohol has been
greatly improved. When the molar ratio of Zn/Al is 2, the
conversion of methyl benzoate is 62.45%, and the selectivity
of benzyl alcohol is 81%. This may be due to the fact that the
addition of Zn reduces the surface acidity of the CZA-X-450
3.3 Effect of Reaction Conditions
on the Hydrogenation of Methyl Benzoate
Based on the above results, the CZA-2-450 is an optimized
catalyst for the hydrogenation of methyl benzoate to ben-
zyl alcohol. Therefore, the CZA-2-450 catalyst was used to
investigate the influence of the reaction conditions, including
reaction pressure, temperature and time.
The effect of reaction temperature on the reaction is
shown in the Fig. 6. The results show that the conversion rate
of methyl benzoate is increased with the reaction tempera-
ture. When the temperature is 200 °C, the conversion rate
of methyl benzoate and benzyl alcohol selectivity reaches a
better value. Therefore, the appropriate reaction temperature
is 200 °C. However, when the reaction temperature increases
to 220 °C, the selectivity of benzyl alcohol drops rapidly.
1 3

A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl Benzoate to Benzyl…
Table 3 Effect of Cu/ZnO/Al2O3 catalysts with different calcination
temperatures on hydrogenation of methyl benzoate to benzyl alcohol
That implies that the high temperature is not favorable for
the selectivity of benzyl alcohol.
Figure 7 shows the effect of hydrogen pressure on this
reaction. It is clearly seen that the conversion of methyl ben-
zoate increases with improving hydrogen pressure. When the
hydrogen pressure is 3 MPa, the conversion rate of benzoic
acid methyl ester and benzyl alcohol selectivity reaches an
optimal value. Therefore, when the reaction temperature is
200 °C, the appropriate reaction pressure is 3 MPa.
Effect of catalyst calcination temperature on the yield
of benzyl alcohol was investigated at 350–750 °C, and the
result was shown in the Table 3. The CA-2-650 catalyst
exhibits the highest catalytic activity among the CA-2-T
catalysts. At the same time, the H2-TPR results show that
the CZA-2-650 catalyst could be reduced at a lower tempera-
ture, which could be attributed to the presence of highly dis-
persed and easily reduced CuO nanoparticles [9]. Besides,
the NH3-TPD results suggest that the catalyst calcined at
650 °C has a weaker acidity. Therefore, it can be inferred
that weaker acid sites is another important factor in increas-
ing catalyst activity [29].
Catalysts
T (°C) Time (h) Conversion (%) Selectivity (%)
BAOL Toluene
CZA-2-350 200
CZA-2-450 200
CZA-2-550 200
CZA-2-650 200
CZA-2-750 200
5
5
5
5
5
48.61
49.39
44.85
70.85
25.84
85.93 14.07
90.11 9.89
86.23 13.77
72.00 28.00
88.83 11.17
Reaction conditions: methyl benzoate=0.5 g; methanol=25 mL,
T=200 °C; P=3 MPa; n=500 rpm (the speed is shown on the panel
in the reactor of speed control); mCu/ZnO/Al2O3 =1 g (catalysts cal-
cined 4 h at 350 °C, 450 °C, 550 °C, 650 °C, 750 °C, reduced 4 h at
250 °C with 10% H2/Ar)
140–200 °C, and the reaction results are shown in Table 4.
It is clear that the CZA-2-650 catalyst exhibits a better
selectivity of benzyl alcohol (86%) at 160 °C, which can
be served as the optimum reaction temperature. However,
the conversion of methyl benzoate is lower in this reaction
condition. In the previous article [4], the high pressure has a
good catalytic efficiency in the hydrogenation of methyl ben-
zoate to benzyl alcohol. Then, the effect of reaction pressure
was investigated from 3 to 8 MPa (Table 5). It can be seen
that the CZA-2-650 catalyst exhibits superior performance
with increasing pressure. At a pressure of 7 Mpa, the conver-
sion rate of methyl benzoate is 93.89%, and correspondingly
selectivity of benzyl alcohol is 88%, which indicates that
CZA-2-650 catalyst has excellent catalytic performance in
this reaction condition (Scheme 1).
3.4 Effect of Reaction Pressure and Temperature
on Catalytic Efficiency of CZA‑2‑650 Catalyst
Under the above conditions, CZA-2-650 catalyst exhibits the
highest catalytic activity. The conversion of methyl benzo-
ate is up to 25.41% in the first hour (Fig. S2). However, the
toluene by-product also increases rapidly with the increase
of reaction time. It is obvious that further hydrogenation
of benzyl alcohol could favorably occur under this reaction
condition. Therefore, the condition of catalytic reaction
should be continuously optimized based on the above results.
Firstly, the effect of reaction temperature was investigated at
Based on the above experimental results, a possible reac-
tion mechanism of hydrogenation of methyl benzoate could
be concluded (Scheme 2). Firstly, Cu0 should be an effective
active center for the dissociation of H2 in the hydrogenation
of methyl benzoate. Then surface acid sites of catalysts can
100
90
80
70
60
50
Table 4 Effect of Cu/ZnO/Al2O3 catalysts with different reaction
temperatures on hydrogenation of methyl benzoate to benzyl alcohol
Catalysts
T (°C) Time (h) Conversion (%) Selectivity (%)
BAOL Toluene
Conversion of MB (%)
40
Selectivity of Toluene (%)
Selectivity of BAOL (%)
30
20
10
0
CZA-2-650 140
CZA-2-650 160
CZA-2-650 180
CZA-2-650 200
5
5
5
5
31.11
57.58
66.21
70.85
92.08
7.92
86.02 13.98
70.20 29.80
72.00 28.00
0
1
2
3
4
5
Reaction conditions: methyl benzoate=0.5 g; methanol=25 mL,
T=140–200 °C; P=3 Mpa; n=500 rpm (the speed is shown on the
panel in the reactor of speed control); mCu/ZnO/Al2O3 =1 g (cata-
lysts calcined 4 h at 650 °C reduced 4 h at 250 °C with 10% H2/Ar)
Reaction pressure (MPa)
Fig. 7 Influence of reaction pressure on hydrogenation of methyl ben-
zoate to benzyl alcohol
1 3

Y. Jiang et al.
Table 5 Effect of Cu/ZnO/Al2O3 catalysts with different H2 pressure
which facilities the nucleophilic attack of H to the carbon
bearing a positive charge [39].
on hydrogenation of methyl benzoate to benzyl alcohol
Catalysts
MPa Time (h) Conversion (%) Selectivity (%)
BAOL Toluene
4 Conclusion
CZA-2-650
CZA-2-650
CZA-2-650
CZA-2-650
CZA-2-650
CZA-2-650
3
4
5
6
7
8
10
10
10
10
10
10
80.67
82.01
90.68
94.85
93.89
86.94
68.78 31.22
80.58 19.42
83.56 16.44
76.92 23.08
88.00 12.00
In summary, the preparation of Cu/ZnO/Al2O3 catalyst by
co-precipitation method was used to investigate in the liquid-
phase hydrogenation of methyl benzoate to benzyl alcohol.
The CZA-2-650 catalysts exhibit the highest catalytic activ-
ity and selectivity. When the methyl benzoate was hydrogen-
ated over this catalyst at 160 °C and 7 MPa of H2 for 10 h,
the conversion of methyl benzoate can reach 93.89%, and the
selectivity of benzyl alcohol is 88%. The activity of Cu/ZnO/
Al2O3 catalysts is not only related to highly dispersing cop-
per nanoparticles, but also inextricably linked to the acidity
of the catalysts and reaction temperature. Besides, we have
found that higher reaction pressures effectively inhibit the
hydrogenolysis of C–O. Therefore, the conversion of methyl
benzoate and the selectivity of benzyl alcohol are greatly
improved.
93.26
6.74
Reaction conditions: methyl benzoate=0.5 g; methanol=25 mL,
T=160 °C; P=3–8 Mpa; n=500 rpm (the speed is shown on the
panel in the reactor of speed control); mCu/ZnO/Al2O3 =1 g (cata-
lysts calcined 4 h at 650 °C reduced 4 h at 250 °C with 10% H2/Ar)
intimately absorb the reactant, which facilitates the activa-
tion of the reactant by virtue of the metallic Cu0. Finally,
it interact with the π* acceptor orbital of the C=O group,
Scheme 1 Reaction pathway
COOCH3
CH3
CH2OH
for the of methyl benzoate to
benzyl alcohol
Cu/ZnO/Al2O3
Cu/ZnO/Al2O3
R1
R2
Scheme 2 Possible reaction
mechanism of hydrogenation
of methyl benzoate to benzyl
alcohol catalyzed by Cu/ZnO/
Al2O3
1 3

A Highly Effective Cu/ZnO/Al2O3 Catalyst for Hydrogenation of Methyl Benzoate to Benzyl…
19. Twigg MV, Spencer MS (2001) Appl Catal A 212:161–174
Acknowledgements This work was supported by the technology
institute of Shanghai Huayi (Group) Company, Jilin Province Science
and Technology research plan (key scientific research project) (No.
20150204020GX).
20. Avgouropoulos G, Ioannides T, Matralis H (2005) Appl Catal B
56(1–2):87–93
21. Guo XM, Mao DS, Lu GZ, Wang S, Wu GS (2010) J Catal
271(2):178–185
22. Melian-Cabrera I, Granados ML, Fierro JLG (2002) J Catal
210(2):273–284
23. Bahmani M, Farahani BV, Sahebdelfar S (2016) Appl Catal A
520:178–187
References
24. Schumann J, Eichelbaum M, Lunkenbein T, Thomas N, Galván
MCÁ, Schlögl R, Behrens M (2015) ACS Catal 5(6):3260–3270
25. Li Z, Zheng HY, Xie KC (2008) Chin J Catal 29(5):431
26. Li W, Fan G, Yang L, Li F (2016) Catal Sci Technol
6(7):2337–2348
1. Jayesh TB, Itika K, Ramesh Babu GV, Rama Rao KS, .Keri RS,
Jadhav AH, Nagaraja BM (2018) Catal Commun 106:73–77
2. Dub PA, Ikariya T (2012) ACS Catal 2:1718–1741
3. Adkins HI, Pavlic AA (1947) J Am Chem Soc 69(12):3039–3041
4. Mozingo R, Folkers K (1948) J Am Chem Soc 70(1):229–231
5. Seyden-Penne J, Nguyen C, Burdett J (1997) J Organomet Chem
426(1):C22–C23
27. Perret N, Cárdenas-Lizana F, Keane MA (2011) Catal Commun
16(1):159–164
28. Zhu Y, Zhu Y, Ding G, Zhu S, Zheng H, Li Y (2013) Appl Catal
A 468(12):296–304
6. Santiago MAN, Sánchez-Castillo MA, Cortright RD, Dumesic JA
(2000) J Catal 193(1):16–28
29. Kusunoki Y, Miyazawa T, Kunimori K, Tomishige K (2005) Catal
Commun 6(10):645–649
7. Twigg M, Spencer M (2001) Appl Catal A 212:161–174
8. He L, Cheng H, Liang G, Yu Y, Zhao F (2013) Appl Catal A
452:88–93
30. Nakagawa Y, Ning X, Amada Y, Tomishige K (2012) Appl Catal
A 433–434(16):128–134
9. Sun Z, Chen X, Wang J, Zhao W, Shao Y, Guo Z, Zhang X, Zhou
Z, Sun T, Wang L, Meng H, Zhang H, Chen W (2018) J Catal
357:223–237
31. Shi Z (2016) Catal Sci Technol 6(10):3457–3467
32. Li T, Fu C, Qi J, Pan J, Chen S, Lin J (2013) React Kinet Mech
Cat 109(1):117–131
10. Zhu Y, Kong X, Zhu S, Dong F, Zheng H, Zhu Y, Li Y (2015)
Appl Catal B 166–167:551–559
33. Busca G (2014) Catal Today 226(1):2–13
34. Gao J, Jia C, Li J, Zhang M, Gu F, Xu G, Zhong Z, Su F (2013) J
Energy Chem 22(6):919–927
11. Hu Q, Fan G, Zhang S, Yang L, Li F (2015) J Mol Catal A Chem
397:134–141
35. Yang X, Xiang X, Chen H, Zheng H, Li Y-W, Zhu Y (2017)
ChemCatChem 9:3023–3030
12. Zhu Y, Kong X, Cao D, Cui J, Zhu Y, Li Y (2014) ACS Catal
4(4):3675–3681
36. Yang X, Chen H, Meng Q, Zheng H, Zhu Y, Li Y (2017) Catal
Sci Technol 7:5625–5634
13. Yang X, Meng Q, Ding G, Wang Y, Zhu Y, Li Y (2018) Appl
Catal A 561(5):78–86
37. Zhang B, Chen Y, Li J, Pippel E, Yang H, Gao Z, Qin Y (2015)
ACS Catal 5:5567–5573
14. Brands DS, Poels EK, Bliek A (1999) Appl Catal A
184(2):279–289
38. Zhang B, Zhu Y, Ding G, Zheng H, Li Y (2012) Appl Catal A
443:191–201
15. Scheur FTVD, Linden BVD, Mittelmeijer-Hazeleger MC,
Nazloomian JG, Staat LH (1994) Appl Catal A 111(1):63–77
16. Claus P, Lucas M, Lücke B, Berndt T, Birke P (1991) Appl Catal
A 79(1):1–18
39. Asao N, Nogami T, Takahashi K, Yamamoto Y (2002) J Am Chem
Soc 124(5):764–765
17. Frost J (1988) Nature 334(6183):577–580
18. Gao C, Xiao X, Mao D, Lu G (2013) Catal Sci Technol
3(4):1056–1062
Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional affiliations.
Affiliations
Ye Jiang1 · Qiang Bao1 · Wenying Gui1 · Yifan Wu1 · Xiaofei Liu1 · Li Zhang1 · Bin Zheng2 · Zhenlu Wang1
1
2
Key Laboratory of Surface and Interface Chemistry of Jilin
Province, College of Chemistry, Jilin University, Qianjin
Road 2699, Changchun 130012, People’s Republic of China
School of Chemistry and Chemical Engineering, Liaocheng
University, Liaocheng 252059, People’s Republic of China
1 3