Hydrogenation Performance of Acetophenone to 1-Phenylethanol on Highly Active Nano Cu/SiO2 Catalyst

Article abstract of DOI:10.1007/s10562-019-02908-2

Abstract: In this work, highly active nano Cu/SiO₂ catalysts with various copper content were prepared by urea homogeneous precipitation method. The catalysts were characterized by N₂ adsorption, XRD, H₂-TPR, XPS and TEM. It was found that the nano Cu/SiO₂ catalyst displayed excellent catalytic performance for the selective hydrogenation of acetophenone (AP) to 1-phenylethanol (PhE) when copper content was 25?wt%. The Cu/SiO₂ catalyst had well dispersed copper species, small particle size, high BET surface area (ca. 540?m²/g) and abundant pore structure. The influence of different reaction conditions on the hydrogenation process were also discussed. AP conversion and the PhE selectivity reached 99.8% and 99.08%, respectively, under the optimal reaction conditions (Temperature: 353?K; Pressure: 2.0?MPa, LHSV: 1.0?h^?1 and the molar ratio of H₂/AP:15). Besides, the above catalyst maintained a high catalytic performance in the duration of 500?h operation. The synergistic effect between Cu⁺ and Cu⁰ improved the activity and stability of Cu/SiO₂ catalyst. The research indicated that the catalyst had a wide industrial prospect. Graphic Abstract: The Cu/SiO₂ catalyst showed a good performance for AP hydrogenation. The reduced Cu/SiO₂ catalyst contains both Cu⁺ and Cu⁰ consistent with XPS. Cu⁺ sties stabilize the methoxy and acyl species and Cu⁰ facilitates the decomposition of H₂. Phenyl in AP and Cu had electrostatic repulsion, which was favorable for desorption of PhE.[Figure not available: see fulltext.].

Full text of DOI:10.1007/s10562-019-02908-2

Catalysis Letters
https://doi.org/10.1007/s10562-019-02908-2
Hydrogenation Performance of Acetophenone to 1‑Phenylethanol
on Highly Active Nano Cu/SiO2 Catalyst
Bing Wang1 · Manman Jin1 · Hao An1 · Zhenmei Guo2 · Zhiguo Lv1
Received: 23 January 2019 / Accepted: 15 July 2019
© Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
In this work, highly active nano Cu/SiO2 catalysts with various copper content were prepared by urea homogeneous pre-
cipitation method. The catalysts were characterized by N2 adsorption, XRD, H2-TPR, XPS and TEM. It was found that the
nano Cu/SiO2 catalyst displayed excellent catalytic performance for the selective hydrogenation of acetophenone (AP) to
1-phenylethanol (PhE) when copper content was 25 wt%. The Cu/SiO2 catalyst had well dispersed copper species, small
particle size, high BET surface area (ca. 540 m2/g) and abundant pore structure. The infuence of diferent reaction condi-
tions on the hydrogenation process were also discussed. AP conversion and the PhE selectivity reached 99.8% and 99.08%,
respectively, under the optimal reaction conditions (Temperature: 353 K; Pressure: 2.0 MPa, LHSV: 1.0 h−1 and the molar
ratio of H2/AP:15). Besides, the above catalyst maintained a high catalytic performance in the duration of 500 h operation.
The synergistic efect between Cu+ and Cu0 improved the activity and stability of Cu/SiO2 catalyst. The research indicated
that the catalyst had a wide industrial prospect.
Graphic Abstract
The Cu/SiO2 catalyst showed a good performance for AP hydrogenation. The reduced Cu/SiO2 catalyst contains both Cu+
and Cu0 consistent with XPS. Cu+ sties stabilize the methoxy and acyl species and Cu0 facilitates the decomposition of H2.
Phenyl in AP and Cu had electrostatic repulsion, which was favorable for desorption of PhE.
Keywords Nano Cu/SiO2 catalyst · Urea · AP hydrogenation · Cu+ and Cu0
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s10562-019-02908-2) contains
supplementary material, which is available to authorized users.
1 Introduction
The catalytic hydrogenation of acetophenone (AP) is of
increasing importance because of the growing demand of
1-phenylethanol (PhE). Indeed, PhE is a simple aromatic
alcohol which is an important raw material of spices,
* Zhiguo Lv
lvzhiguo@qust.edu.cn
Extended author information available on the last page of the article
Vol.:(0123456789)
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B. Wang et al.
aromatic agents and intermediates, such as the nonsteroidal
anti-infammatory Ibuprofen [1–3]. However, there are many
by-products of the reaction, such as ethylbenzene (EB) and
ethylcyclohexane (CHE). Therefore, it is crucial to improve
the yield of PhE by adopting appropriate catalysts.
around 7 after heating for 1 day. The fltrate was washed with
200 ml of deionized water three times and dried at 383 K for
8 h. The calcination temperature of the catalysts precursors
was 723.15 K for 4 h. Then Cu/SiO2 catalyst was crushed and
sieved to 20–40 mesh. The catalyst samples were denoted as
x-Cu/SiO2, where x represents the copper content.
The hydrogenation of AP has been studied in the cata-
lytic systems of noble metal catalysts [4–12]. But they are
extremely expensive and have low selectivity of PhE. So it
is inevitable to look for a kind of efcient and cheap catalyst
to replace the traditional noble metal catalysts. The Ni-based
catalysts have been reported to the hydrogenation of AP, but
they can lead multiple by-products, such as EB and CHE [13,
14]. Cu-based catalysts have been found to exhibit excellent
performance for hydrogenation of alcohol and ester because
of the selective hydrogenation of C–O bonds and relatively
inactive in C–C bond hydrogenolysis [15–20], which is con-
ducive to improve the selectivity of AP for PhE. But there
are few studies on Cu-based catalysts for hydrogenation of
AP [1, 20–23]. Zaccheria etc. prepared Cu/Al2O3 catalyst by
the ammonia-evaporation method. The reaction conversion
of AP and the selectivity of PhE is 96% and 98% under the
condition of 363 K and 1 MPa in batch reaction [21]. Tarsarti
studied the infuence of solvent on the hydrogenation of AP
over silica-supported Ni, Co and Cu catalysts. The solvent
had weak efect on the activity of Cu/SiO2 catalyst [1].
The Cu/SiO2 catalysts has excellent performances: high
low-temperature activity, safety in use, cheap and material
availability [24]. Besides, the catalyst supported by silica has
large specifc surface area, which benefts the dispersion of
copper species [25, 26].
2.2 Catalysts Characterization
The X-ray difraction (XRD) patterns were recorded on a
RINT2000 vertical goniometer X-ray difractometer using
CuKα radiation (λ=0.15418 nm) in the range of 10°–80°,
at a speed of 5° min−1.
The reducibility of the calcined samples was determined
by H2 temperature-programmed reduction (TPR) on a
Micromeritics Autochem II 2920 instrument. The content of
hydrogen was detected by the thermal conductivity detector.
Nitrogen adsorption–desorption isotherms at 77 K
were measured with the ASAP 2020 chemical adsorption
of Micromeritics company. The samples were outgassed
at 573 K. The quality of the samples after degassing was
recorded, respectively.
IR spectra were recorded on a Nicolet 6700 spectrometer.
The samples were fnely grounded, dispersed in KBr, and
then pelletized. The spectral resolution was 4 cm−1, Scan-
ning range of 4000–400 cm−1 and 32 scans were recorded
for each spectrum.
X-ray photoelectron spectroscopy (XPS) and Auger elec-
tron spectroscopy (XAES) were carried out on a Quantum
2000 Scanning ESCA Microprobe instrument (Physical
Electronics) equipped with an Al Kα X-ray radiation source
(hv=1486.6 eV).
Herein, nano Cu/SiO2 catalysts with diferent Cu con-
tent were prepared by the urea homogeneous precipitation
method. The catalytic performances of the catalysts were
tested. The Cu/SiO2 catalyst had dispersed copper spe-
cies, small particle size (4.5 nm), high specifc surface area
(540 m2/g) and abundant pore structure, when the Cu load-
ing was 25%. Besides, the catalyst showed high activity and
stability after continuously running for 500 h under the opti-
mal conditions.
The morphology of the catalysts was studied by ultra-high
resolution transmission electron microscopy (TEM) using
FEI-Tecnai G2 F20 S-Twin 200 kV equipment.
2.3 Activity Test and Product Analysis
The catalytic performance were evaluated using a fxed-bed
micro-reactor (East China University of Science and Tech-
nology, China). The reactor tube diamteter is 16 mm and
the catalyst loading quantity was 6 ml. 20–40 mesh quartz
sandon was added to fx catalyst. The catalyst was reduced
under 30% H2/N2 fow (200 ml/min) at 543.15 K at a pres-
sure of 1.5 MPa maintained for 4 h. The temperature and
the pressure were then changed into desired reaction condi-
tions (353–423 K and 1–3 MPa). The liquid AP (30 wt%,
0.06–2.0 ml/min) was pumped into the reactor to react with
the preheated hydrogen. The reaction products were analyzed
by gas chromatography (GC-122 chromatograph) with a cap-
illary column (30 m×0.25 mm). AP hydrogenation comprise
several continuous reactions, and the reaction scheme for AP
hydrogenation over mental catalysts was shown in Scheme 1.
2 Experimental
2.1 Catalyst Preparation
Calculated amounts of Cu(NO3)2·3H2O and urea (A.R.,
Shanghai national medicine company) were dissolved in
deionized water, respectively. The silica sol (Qingdao Hai-
yang Chemical Co., Ltd., China) was added and acidized
to pH 2–3 with dilute nitric acid. The above three solutions
were mixed and stirred at room temperature for 1 h. Then the
mixed solutions heated at 363 K to accelerate the decompo-
sition of urea. The fnal pH value of the mixture remained
1 3

Hydrogenation Performance of Acetophenone to 1-Phenylethanol on Highly Active Nano Cu/SiO2…
Scheme 1 Reaction scheme for
AP hydrogenation over metal
OH
O
catalysts
H2
H2
H2
H2
H2
OH
O
H2
H2
Table 1 Catalytic performance
of Cu/SiO2 with diferent
copper content
Cu content
(wt%)
Reaction conditions
Catalytic performance
T (K)
P (MPa)
LHSV (h−1
)
H2/AP
AP conversa-
tion (%)
PhE selec-
tivity (%)
10
25
35
45
353.15
353.15
353.15
353.15
2.0
2.0
2.0
2.0
0.8
1.0
1.5
1.5
15
15
15
15
97.81
99.52
99.12
99.03
98.9
99.09
97.93
96.79
weak in the spectra, indicating that the crystalline sizes in
the catalyst were small and evenly dispersed [24]. The peak
at 22.0° corresponded to the phase of SiO2, while the peak
at 32.6° and 35.6° corresponded to the copper phyllosillicate
and CuO phases, respectively [27]. The copper phyllosilli-
cate showed poor crystallinity. The phase of CuO was rarely
observed when the copper loading was at 10 wt%. As the
copper loading increased, the peak of CuO phase became
apparent, indicating that copper species was in good disper-
sion [28].
3 Results and Discussions
3.1 Efect of Cu/SiO2 with Diferent Copper Content
for AP Hydrogenation
3.1.1 Catalytic Performance of Cu/SiO2 with Diferent
Copper Content
The copper loading (TCL) was calculated according to
Eq. (1):
mCu
TCL =
3.1.3 FT‑IR Spectra of Cu/SiO2 with Diferent Copper
(1)
mCuO + m
SiO2
Content
Catalytic performance of Cu/SiO2 catalysts with diferent
copper content for AP hydrogenation to PhE was listed in
Table 1. It could be seen from Table 1 that the hydrogenation
of AP still remained high conversation when the Cu content
was low. It was indicating that the Cu/SiO2 catalyst had excel-
lent activity for AP hydrogenation, even though the copper
content was low. When the Cu content was 25 wt%, AP hydro-
genation exhibited high AP conversion and selectivity to PhE.
Infrared spectra diagram of Cu/SiO2 catalysts with difer-
ent copper loading were shown in Fig. 2. The absorption
band at 670 cm−1 was assigned to OH scissoring vibra-
tion, and the band at 1110 cm−1 was assigned to Si–O–Si
asymmetric stretching vibrations. It was reported that the
characteristic peak of copper pllosillicate was supported
by the appearance of the δOH band at 670 cm−1 and the
νSiO shoulder peak at 1040 cm−1 [24]. When the copper
loading increased, the band at 1110 cm−1 was instead by
1040 cm−1. This could be ascribed to a strong interaction
between copper species and SiO2 [27]. The relative con-
tent of the copper phyllosillicate could be estimated by
the strength of the band at 670 cm−1 and 800 cm−1, which
3.1.2 XRD Patterns of Cu/SiO2 with Diferent Copper
Content
The XRD patterns of diferent copper loading on Cu/SiO2
catalysts were shown in Fig. 1. The peaks were small and
1 3

B. Wang et al.
Fig. 3 H2-TPR patterns of Cu/SiO2 with diferent copper content (a)
Fig. 1 XRD patterns of Cu/SiO2 with diferent copper contents (a)
10%-Cu/SiO2, (b) 25%-Cu/SiO2, (c) 35%-Cu/SiO2, (d) 45%-Cu/SiO2
10%-Cu/SiO2, (b) 25%-Cu/SiO2, (c) 35%-Cu/SiO2, (d) 45%-Cu/SiO2
indicates that Cu/SiO2 catalyst corresponded to diferent
types of copper species. The low copper content benefted
to good dispersion of copper species. The reduction peak
of 10%-Cu/SiO2 catalyst was 445 K, and there was also a
shoulder peak at 457 K. The reduction peaks of 25%-Cu/
SiO2 catalyst were 453 K and 523 K, respectively. The
low temperature reduction peak was symmetrical, corre-
sponded to the high dispersible CuO reduced to Cu0 and
copper phyllosillicate reduced to Cu+. The copper phyl-
losillicate was hard to reduce directly to Cu0 due to the
strong interaction between copper species and support. It
was documented that reduction of copper species with H2
involved the processes as following: Cu2+ to Cu0, Cu2+ to
Cu+, and Cu+ to Cu0 [27]. The high temperature reduction
peak corresponded to Cu+ reduced to Cu0 or the reduction
of amorphous bulk CuO [20]. With the increase of copper
content, copper species tend to aggregate into larger par-
ticles, making the reduction of catalysts difcult. The high
temperature reduction peak corresponded to the reduction
peak of Cu+ reduced to Cu0 or the reduction peak of large
CuO particles forming in the process of calcination [30].
Fig. 2 FT-IR patterns of Cu/SiO2 with diferent copper loading (a)
45%-Cu/SiO2, (b) 35%-Cu/SiO2, (c) 25%-Cu/SiO2, (d) 10%-Cu/SiO2
3.2 Catalytic Performance of the 25%‑Cu/SiO2
defned as I670/I800 [29]. It was obvious that the copper
phyllosillicate contents were more abundant as the copper
loading increased. Besides, it had been reported that the
copper phyllosillicate had formed before calcining.
Catalyst
3.2.1 Physicochemical Properties of 25%‑Cu/SiO2 Catalyst
Highly initial copper surface area on support was considered
as a key factor to obtain good catalytic activity [31]. The N2
adsorption–desorption isotherms and pore size distribution
of 25%-Cu/SiO2 catalyst were plot in Fig. 4. It demonstrated
that the isotherms were the type IV isotherms, which was
corresponded to the capillary cohesion system of porous
3.1.4 Reduction Behavior of 25%‑Cu/SiO2 Catalyst
H2-TPR patterns of Cu/SiO2 catalysts with diferent cop-
per content were shown in Fig. 3. All the Cu/SiO2 cata-
lysts appeared two reduction peaks in the spectrum, which
1 3

Hydrogenation Performance of Acetophenone to 1-Phenylethanol on Highly Active Nano Cu/SiO2…
Fig. 4 N2 adsorption–desorption isotherms and pore size distribution curves of 25%-Cu/SiO2 a fresh catalyst, b reduced cata
Table 2 Surface area and pore structure of the fresh catalyst and
than the fresh catalyst, which might be due to the partial
reduced catalysts
sintering of copper species in the reduction process.
Catalyst
SBET/m2/g
Vp/cm3/g
Dp/nm
3.2.2 Surface Chemical States of 25%‑Cu/SiO2 Catalyst
Fresh Cu/SiO2
Reduced Cu/SiO2
540
500
0.7166
0.5565
5.7543
5.1816
XPS and XAES spectra of reduced Cu/SiO2 catalyst was
illustrated in Fig. 5. The Cu2p3/2 and Cu2p1/2 peaks cen-
tered at binding energies of 933.3 and 952.5 eV, conven-
tionally assigned to Cu+ or Cu0 species [24]. Generally,
the binding energy for Cu0 and Cu+ species was similar,
and their diference could be distinguished by the XAES
adsorbent. As was shown in Table 2, the pore size of the
reduced catalyst was resembled to the fresh catalyst. The
BET surface area of the reduced catalyst was a little smaller
Fig. 5 Cu2p XPS (a) and Cu LMM XAES (b) spectra of reduced 25%-Cu/SiO2 catalyst
1 3

B. Wang et al.
spectra. In the Cu LMM XAES spectrum (Fig. 5b), asym-
metry and broad Auger kinetic energy peaks were observed
and deconvoluted into two symmetrical peaks centered at
911.2 and 914.8 eV, corresponding to Cu0 and Cu+ species,
respectively. The ratio of Cu+/(Cu++Cu0) in 25%-Cu/SiO2
catalyst was ca. 57%. Cu+ was rooted in the reduction of
copper phyllosilicate, while Cu0 was rooted in the reduction
of CuO [16, 17].
low-temperature activity and PhE selectivity. The high tem-
perature led to low selectivity of PhE because of hydrogen-
olysis [8]. The contact time between AP and catalyst could be
increased by proper LHSV, which was benefcial to the con-
versation of AP. Besides, there were no byproducts of phe-
nyl group hydrogenation. It could be concluded that the AP
hydrogenation over 25%-Cu/SiO2 catalyst occurred mainly
in carbonyl groups. Under the following conditions: reaction
temperature, 353.15 K; H2 pressure, 2.0 MPa; LHSV, 1.0 h−1;
the molar ratio of H2/AP, 15, the conversion of AP and the
selectivity to PhE reached 99.8% and 99.08%, respectively.
3.2.3 Efect of Reaction Conditions on AP Hydrogenation
Efects of reaction temperature, H2 pressure, liquid hourly
space velocity (LHSV) and the molar ratio of H2/AP were
studied using fxed bed. It could be seen from Fig. 6 that the
temperature and LHSV had an obvious efect on the per-
formance of 25%-Cu/SiO2. The Cu/SiO2 catalyst had good
3.2.4 Stability of 25%‑Cu/SiO2
Conversion of AP and the selectivity to PhE with reaction
time were showed in Fig. 7. The activity was low at the
Fig. 6 Conditions of AP hydrogenation on 25%-Cu/SiO2 a efect of pressure, b efect of LHSV, c efect of temperature, d efect of molar ratio of
H2/AP
1 3

Hydrogenation Performance of Acetophenone to 1-Phenylethanol on Highly Active Nano Cu/SiO2…
initial stage, and the conversion rate of AP reached more
than 99% after 6 h. The catalytic activity decreased slightly
after 460 h. However, the AP conversion and PhE selectivity
remained above 98% in the duration of 500 h operation. It
was indicated that the catalyst had high stability and could
continuously operate for a long time.
3.2.4.1 XRD and TEM Analysis of 25%‑Cu/SiO2 Catalyst
Under Diferent Conditions The XRD spectrum diagrams
of 25%-Cu/SiO2 were shown in Fig. 8A. The peak of
reduced catalyst at 36.8° showed an obvious peak of Cu2O,
and there was a weak peak at 43° about the phase of Cu0
[30], which was consistent with the analysis of XPS. It was
reported that the feasible proportion of Cu+/(Cu++Cu0)
was benefcial to the activity and stability of AP hydro-
genation [32, 33]. The used catalyst showed a sharp peak
of Cu0 at 43°. It could be found that the Cu0 was agglomer-
ated to some extent after the reaction. The particle size of
reduced catalyst was 5.2 nm, while the used catalyst was
Fig. 7 Conversion of AP and selectivity to PhE in the duration of
500 h operation over 25%-Cu/SiO2 catalyst
Fig. 8 A: XRD patterns of Cu/SiO2 in a diferent state and B: The TEM of 25%-Cu/SiO2 catalyst operated for 500 h (a) fresh catalyst, (b)
reduced catalyst, (c) used catalyst
1 3

B. Wang et al.
stability of Cu/SiO2 catalyst. Besides, the catalyst had high
stability and operate continuously for 500 h without obvious
change. The research indicated that the catalyst had a wide
industrial prospect.
Acknowledgements This work was supported by grant from the Natu-
ral Science Foundation of Shandong Province (ZR2017ZC0632), the
Natural Science Foundation of National (NSFC21376128), the doctor
foundation of Shandong province (No. ZR2019BB010) and Qingdao
Applied Basic Research Program, Shandong Key Laboratory of Reac-
tions and Isolations of Multi-phase Liquid (2019MFRSE-B03).
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Publisher’s Note Springer Nature remains neutral with regard to
jurisdictional claims in published maps and institutional afliations.
Afliations
Bing Wang1 · Manman Jin1 · Hao An1 · Zhenmei Guo2 · Zhiguo Lv1
1
2
State Key Laboratory Base for Eco-chemical Engineering,
College of Chemical Engineering, Qingdao University
of Science and Technology, No. 53 Zhengzhou Road,
Qingdao 266042, China
College of Marine Science and Biological Engineering,
Qingdao University of Science and Technology, No. 53
Zhengzhou Road, Qingdao 266042, China
1 3