The direct transformation of ethanol to ethyl acetate over Cu/SiO 2 catalysts that contain copper phyllosilicate

Article abstract of DOI:10.1007/s12039-014-0659-z

Cu/SiO₂ catalysts that contain copper phyllosilicate, were successfully prepared using the ammonia-evaporation method. The catalysts were characterized via XRD, ICP, BET, FTIR, TPR, XPS, NH₃-TPD and FTIR of Pyridine Adsorption techniques. The results demonstrated that the formation of the copper phyllosilicate species significantly affected the structural properties and caused the CuO nanoparticles to become highly dispersed, and the copper phyllosilicate would provide access to the Lewis acidic Cu⁺ species. It was found that the catalyst with a 23.7 wt% copper loading exhibited the best ethanol conversion and ethyl acetate selectivity. When compared to a catalyst with the same copper loading which was prepared with the impregnation method, the higher activity and selectivity of catalysts might be ascribed to the homogenous distribution of copper nanoparticles, which was the active site for the dehydrogenation, and the amount of Lewis acidic Cu⁺ sites active for esterification. The synergetic effect between the Cu⁰ and Lewis acidic sites was the key factor to achieve direct transformation of ethanol to ethyl acetate.

Full text of DOI:10.1007/s12039-014-0659-z

J. Chem. Sci. Vol. 126, No. 4, July 2014, pp. 1013–1020. ꢀc Indian Academy of Sciences.
The direct transformation of ethanol to ethyl acetate over Cu/SiO2
catalysts that contain copper phyllosilicate
a
c
a
a
a
XUE YU , SHUBO ZHAI , WANCHUN ZHU , SHUANG GAO , JIANBIAO YAN ,
a
a
b
a
HONGJING YUAN , LILI CHEN , JIAHUAN LUO , WENXIANG ZHANG and
ZHENLU WANG
Key Laboratory of Surface and Interface Chemistry of Jilin Province, College of Chemistry, Jilin University,
a,∗
a
Changchun 130021, People’s Republic of China
b
State Key Laboratory of Inorganic Synthesis and Preparative Chemistry, College of Chemistry,
Jilin University, Changchun 130012, People’s Republic of China
c
First Hospital of Jilin University, Changchun 130021, People’s Republic of China
e-mail: wzl@jlu.edu.cn
MS received 13 November 2013; revised 16 February 2014; accepted 24 April 2014
Abstract. Cu/SiO2 catalysts that contain copper phyllosilicate, were successfully prepared using the
ammonia-evaporation method. The catalysts were characterized via XRD, ICP, BET, FTIR, TPR, XPS,
NH3-TPD and FTIR of Pyridine Adsorption techniques. The results demonstrated that the formation of the
copper phyllosilicate species significantly affected the structural properties and caused the CuO nanoparticles to
+
become highly dispersed, and the copper phyllosilicate would provide access to the Lewis acidic Cu species.
It was found that the catalyst with a 23.7 wt% copper loading exhibited the best ethanol conversion and ethyl
acetate selectivity. When compared to a catalyst with the same copper loading which was prepared with the
impregnation method, the higher activity and selectivity of catalysts might be ascribed to the homogenous dis-
tribution of copper nanoparticles, which was the active site for the dehydrogenation, and the amount of Lewis
+
0
acidic Cu sites active for esterification. The synergetic effect between the Cu and Lewis acidic sites was the
key factor to achieve direct transformation of ethanol to ethyl acetate.
Keywords. Ethanol; ethyl acetate; copper phyllosilicate; lewis acid sites.
1
. Introduction
with another equivalent of ethanol or ethoxide to form
a hemiacetal, which was then dehydrogenated to fur-
nish ethyl acetate. Moreover, Wang et al. studied the
formation of ethyl acetate from ethanol with Cu/ZrO2
catalysts which were prepared via the co-precipitation
method. They proposed that the molar ratio of copper
and zirconium had a significant effect on the catalytic
performance, and the addition of zirconium improved
the selectivity to favour ethyl acetate.
6
Ethyl acetate is an important environment-friendly sol-
vent which is used industrially across a wide range of
applications. The direct transformation of ethanol to
ethyl acetate has been afforded a significant amount
of attention because both components are simple, non-
corrosive, and relatively non-toxic. Several studies
detailing the direct transformation of ethanol to ethyl
acetate using Cu-based catalysts have been published.
For example, Colley et al. reported that the forma-
tion of ethyl acetate from ethanol could be achieved
over a Cu/Cr O catalyst. They proposed that the metal-
lic copper species are the major active components in
the catalyst and that the Brønsted acid site on the sur-
Recently, metal-silica hybrid nanostructures have
been investigated widely because silica has a high ther-
mal stability that does not alter the physical nature of
the metal components when used as a support. In some
cases, silica reacts with metals to form metal phyl-
losilicates (or metal silicate hydroxides), which make
the supported metal nanoparticles more stable, highly
1
2
3
face of Cr O facilitates the selectivity for ethyl acetate.
2
2
3
–4
5
7
,8
Inui et al. and Zonetti et al. used Cu-Zn-Zr-Al-O
multi-component catalysts in a dehydrogenation pro-
cess and the results indicated that ethanol was first
dehydrogenated to form acetaldehyde before reacting
dispersed and less crystalline.
Silica-supported
phyllosilicates have been formed during the prepa-
9
,10
11,12
ration of Ni phyllosilicate,
Mg phyllosilicate,
13,14
15
Co phyllosilicate,
Zn phyllosilicate, Cu phyllo-
Copper phyllosilicate, which is also called
chrysocolla, is a copper silicate with a lamellar structure
16,17
silicate.
∗
For correspondence
1013

1014
Xue Yu et al.
that consists of layers of SiO tetrahedra sandwiched entailed the following: ammonia solution added drop-
4
between discontinuous layers of CuO octahedra. wise to a known amount of aqueous Cu(NO ) solu-
6
3 2
16
Toupance et al. were the first to note that the copper tion (0.2 mol/L) and stirred for 30 min. An appropriate
phyllosilicate formed in Cu/SiO samples that were amount of silica sol (30 wt %) was added to the copper-
2
prepared by using cationic exchange, and they investi- ammonia solution (pH of the solution was 12) before
gated the formation conditions of copper phyllosilicate the mixture was stirred for another 4 h. Subsequently,
17
when using the selective adsorption method. Huang the solution was stirred in oil bath at 363 K to evaporate
18
et al. prepared silica-supported, dispersed copper the ammonia until the pH = 6–7. Next, the product was
nanomaterials via the precipitation-gel method. They filtered, washed with distilled water (the pH of preci-
noted that the copper phyllosilicate was rather stable pitation was held at 6–7), and dried in the vacuum oven
and affected both the structure and thermal stability at 373 K for 4 h before being calcined in air at 673 K
of the samples profoundly. Many studies have inves- for 2 h. The obtained catalysts were named CuSi-1
tigated the activity of CuSiO catalysts that contain (7.5 wt %), CuSi-2 (23.7 wt %), and CuSi-3 (36.6 wt
2
copper phyllosilicate in some reactions. For example, %). For comparison, a Cu/SiO catalyst with a 23.9 wt
2
8
,19–21
several authors
reported that certain Cu/SiO2 % copper loading was prepared by impregnating the
catalysts, which were prepared by ammonia- silica with an aqueous solution of Cu(NO ) ·3H O. The
3
2
2
evaporation method and urea hydrolysis deposition- impregnation method (IM) was followed by drying at
precipitation method, could hydrogenate dimethyl 393 K for 4 h with stirring and calcination at 673 K for
oxalate to form ethylene glycol. They suggested that 4 h in flowing air. This catalyst was named CuSi-IM.
copper phyllosilicate species were formed in the
+
Cu/SiO catalysts. Additionally, the Cu from the
2
2
.2 Catalyst characterization
copper phyllosilicate participated in hydrogenation of
dimethyl oxalate to ethylene glycol and cooperated
Powder X-ray diffraction (XRD) patterns were recorded
with a Shimadzu Lab XRD-6000 X-ray Diffractome-
ter with nickel-filtered Cu Kα radiation. Inductively
Coupled Plasma Atomic Emission Spectroscopy (ICP-
AES) analysis was conducted with a Perkin Elmer
emission spectrometer. The BET specific surface areas
of the samples were measured by using N as the adsor-
bate on a Micromeritics ASAP 2010 system at liquid-
N temperature. IR spectra were recorded with a Nicolet
0
with the Cu to enhance the catalytic performance.
22
Gong et al. used a Cu/SiO catalyst that was pre-
2
pared by using the ammonia evaporation method to
0
+
produce ethanol. They demonstrated that Cu and Cu
0
coexisted within the Cu/SiO catalysts; the Cu and
Cu originated from well-dispersed CuO nanoparticles
and copper phyllosilicate; and the Cu was primarily
2
+
0
2
responsible for the catalytic activity in the active site.
+
2
Cu facilitates the conversion of intermediates.
4
10 FT-IR spectrometer. H -TPR analysis, NH -TPD
2 3
The effect of copper phyllosilicate species on an
ethanol dehydrogenation reaction that forms ethyl
acetate has not been reported. In this paper, silica-
supported copper catalysts, which contain a copper
phyllosilicate species, were successfully prepared and
applied to the dehydrogenation of ethanol to form ethyl
acetate. The catalyst’s properties were investigated
analysis and N O chemisorption were carried out on
2
a self-made instrument. The measurement process was
carried out according to previous literature reports.6
The X-ray photoelectron spectroscopy (XPS) measure-
ment was carried out with a VG ESCA LAB MK II
XPS spectrometer that used AlKα radiation. Pyridine
adsorption Fourier transform infrared spectrum was
,23
using XRD, ICP, BET, TPR, FTIR, XPS, NH -TPD and
3
24
performed according to literature.
FTIR of Pyridine Adsorption techniques. This research
studies the structure and active sites of a Cu/SiO
catalyst. The highly dispersed Cu and Lewis acid sites
2
0
2
.3 Catalytic activity
from the copper phyllosilicate are the active sites for the
dehydrogenation and esterification processes.
The activity of catalyst was studied with a conti-
nuous flow fixed-bed reactor under the following con-
ditions: P = 1 atm, T = 543 K, LHSV = 1 h . In each
experiment, 2 mL of the appropriate catalyst was used,
and the ethanol was fed into the reactor via a plunge
pump. Before the reaction, each catalyst was reduced
−1
2. Experimental
2.1 Catalyst preparation
in situ with a 10% H /Ar mixture. The temperature
2
The Cu/SiO catalysts were prepared by using the was increased at 5 K/min. until the temperature reached
2
ammonia-evaporation method (AE).1 The process 573 K, which was maintained for 2 h. The reactor was
9

Direct transformation of ethanol to ethyl acetate
1015
connected to gas chromatography using a six-port high to amorphous silica for catalyst CuSi-1.25 With an
temperature valve. The effluent streams from the reac- increased Cu loading, the peak attributed to the amor-
tions were analyzed with an online gas chromatograph phous silica disappeared at the same time correspond-
(
Shimadzu GC-14C) that was equipped with a flame ing to two weak peaks, which were attributed to copper
◦
◦
ionization detector (FID) and a 3 m PEG 20000 column. phyllosilicate (approximately 2θ = 31.2 and 35.8 ).
These data demonstrate that the copper phyllosilicate
8
,17
species was formed. However, severe aggregation of
the copper species occurred in the IM sample (CuSi-
IM), which was indicated by the strong diffraction
3
. Results and discussion
◦
◦ 25
peaks for CuO observed at 2θ = 35.5 and 38.9 .
3
.1 XRD analysis
This result suggests that the Cu/SiO catalysts that
2
were prepared by the AE method, formed copper phyl-
losilicate [Cu SiO (OH) ] and exhibited greater disper-
Figure 1 depicts the XRD patterns for the CuSi-x cat-
alysts. From the data for the calcined catalysts shown
in figure 1a, it was observed that no diffraction peaks
attributed to copper oxide species were detected on
the AE catalysts, and a broad and diffuse diffraction
2
5
2
sion than what was observed in the product of the IM
22
method.
In the XRD patterns of the reduced catalysts
(figure 1b), a broad and diffuse diffraction peak, which
◦
peak, which was centered at 2θ = 22.7 , was ascribed
◦
was centered at 2θ = 22.7 , was attributed to amor-
phous silica in the AE catalysts. This result suggests
that the copper phyllosilicate species had disappeared
and therefore the amorphous SiO species were formed
2
after the AE catalysts were reduced. The diffraction
0
◦
peaks of Cu , which were at approximately 43.3 and
5
◦
0.5 , on the CuSi-2 catalyst were broader and less
intense than those that were observed for the reduced
CuSi-IM catalyst with the same copper loading. This
result suggests that the presence of copper phyllosili-
cate could inhibit the sintering of the Cu particles of
0
the CuSi-2 catalyst during reduction. The Cu species
were markedly aggregated on CuSi-3 catalyst because
the copper loading was high. Notably, the CuSi-2
catalyst exhibited a different Cu O diffraction peak than
2
what was measured with the CuSi-IM catalyst. A por-
+
tion of copper exists as Cu , which is reduced from both
the ion exchange Cu-O-Si and copper phyllosilicate on
19
the AE catalyst that occurs after the reduction.
3.2 Textural properties of the catalysts
The physicochemical properties of the CuSi-x cata-
lysts are summarized in table 1. The BET surface area
2
−1
increased from 302 to 460 m g when the Cu load-
ing was increased for catalysts generated with the AE
method, it should be attributed to the copper phyllosili-
cate species of the AE catalysts. As observed, the BET
surface area of the AE catalyst was higher than the
IM catalyst, which might be due to the copper species
aggregated on the IM catalyst. The copper dispersion of
the catalysts obtained from N O chemisorption for AE
2
catalysts was decreased with increasing copper loading,
and they were higher than the IM catalyst. This is in
agreement with XRD.
Figure 1. XRD patterns of the CuSi-x catalysts, (a)
calcined, (b) reduced.

1016
Xue Yu et al.
0
Table 1. (a) Cu loading conducted by ICP; (b) Cu dispersion determined by N2O chemisorption; (c) Cu crystallite size
calculated by the Scherrer formula.
Cu loading (wt %)a
SBET(m2g
−1
)
Vp(cm3g
−1
)
dp(nm) Cu Dispersion (%)b
Cu particle size (nm)c
0
Sample
CuSi-1
CuSi-2
CuSi-3
CuSi-IM
7.5
302
453
460
206
0.61
0.81
0.54
0.52
6.3
5.7
4.1
7.2
44
–
9.8
21.5
25.9
23.7
36.6
23.9
40.2
22.3
18.2
3.3 FTIR analysis
of the highly dispersed CuO. The higher temperature
reduced peaks at 653 K and 614 K were ascribed to
FTIR spectra of the CuSi-x catalysts are displayed in
figure 2. The formation of copper phyllosilicate was
the reduction of larger particles of CuO on the SiO
2
26,27
surface.
These results suggest that the Cu species
−1
supported by the appearance of an δ band at 670 cm
OH
were poorly dispersed on the surface of Cu/SiO cata-
2
−1
and a νSiO shoulder at 1042 cm on the low-frequency
side of the asymmetric stretching ν band of SiO at
lyst which was prepared with the IM method. For the
AE catalysts with different copper loadings, only one
broad and asymmetric reduction peak was observed
SiO
2
−1 16
1
100 cm . The magnitudes of these resonances grew
19
as the copper loading increased. These resonances were
not observed with the CuSi-IM catalyst, which was pre-
pared by the impregnation method. The relative amount
of supported phyllosilicate in these samples could be
(
520 K - 526 K). Chen et al. reported that the main
reduction peak for the Cu/SiO catalysts that are pre-
2
pared via ammonia evaporation is attributed to the
0
reduction of the well-dispersed CuO to Cu , as well as
evaluated by dividing the integrated intensity of the δ
OH
the reduction of the ion-exchanged Cu-O-Si and copper
−1
+
28
band at 670 cm by the integrated intensity of the
phyllosilicate to form Cu . Marchi et al. determined
−
1
symmetric νSiO band of amorphous silica at 800 cm ,
that the reduction of the ion-exchanged Cu-O-Si species
16
+
which can be written as I /I . Copper phyllosili-
6
70 800
to Cu overlapped with the reduction peak of the well-
0
cate could be formed during the AE method of prepara-
tion. This species was more abundant when the copper
loading was increased.
dispersed CuO to Cu . Therefore, under our conditions,
0
+
the results suggested that Cu and Cu coexist in the
AE catalysts.
3.4 TPR analysis
3.5 XPS analysis
The TPR profiles of CuSi-x catalysts are depicted in
figure 3. For the IM catalyst, three reduction peaks were
observed. The lower temperature reduced peak, which
was centered at 513 K, was attributed to the reduction
The chemical state of CuSi-x catalysts were investi-
gated by XPS (figure 4). As displayed in figure 4a,
the binding energy of the Cu2p3/2 peak, which was
Figure 2. FTIR spectra of calcined CuSi-x catalysts.
Figure 3. TPR spectra of calcined CuSi-x catalysts.

Direct transformation of ethanol to ethyl acetate
1017
+
0
For the BE values of Cu and Cu are almost iden-
tical, the distinction between these two species present
on the catalyst surface is feasible only by their differ-
ent kinetic energies in the XAES Cu LMM line position
ꢁ
or the modified Auger parameters α . It was reported
ꢁ
0
+ 19
that α is 1851.0 eV for Cu and 1847.0 eV for Cu .
In figure 5, it was obvious that each Cu LMM spec-
trum possessed the broad and asymmetrical peak shape,
0
+
implying the coexistence of Cu and Cu on the cata-
lysts surface. Deconvolution of the original Cu LMM
peaks was performed, obtained two symmetrical peaks
centered at near 914.6 and 918.0 eV, corresponding
+
0
to Cu and Cu species, respectively. The deconvolu-
tion results are listed in table 2. For AE method, the
+
+
0
Cu /(Cu +Cu ) intensity ratio derived by fitting the
Cu LMM peak increased with the copper loading, and
the intensity ratio reached maximum for CuSi-2 sample
of 49.3%. It was attributed to the hindered reduction
2
+
of Cu in ion exchanged Cu-O-Si species and copper
+
phyllosilicate. For IM method, the Cu species also
+
+
0
existed on the catalyst surface, but the Cu /(Cu +Cu )
intensity ratio was lower than the CuSi-2 catalyst; the
reason might be the weak interaction between copper
species and support.
3
.6 NH -TPD analysis
3
The NH -TPD profiles of the reduced CuSi-x catalysts
3
are displayed in figure 6. CuSi-2 and CuSi-3 catalysts
exhibited a broad peak, which began at approximately
3
88 K with a long tail that extended to 673 K, and
Figure 4. XPS spectras of CuSi-x catalysts (a) calcined
b) reduced.
(
the CuSi-1 and CuSi-IM catalysts showed two NH
3
desorption peaks between the same temperature range.
This result indicated that a large distribution of acid
9
35.0 eV–935.4 eV with a shake-up feature at approxi-
mately 943.5 eV, provided conclusive evidence that the
2+ 29
copper species on the catalyst surface was Cu . The
higher BE of CuSi-AE catalyst, which contained cop-
per phyllosilicate, might be caused by a strong interac-
tion between the Cu2 and the support. This observa-
tion was in agreement with the FTIR and XRD data.
After reduction (figure 4b), the satellite peak disap-
peared, and a simultaneous shift in the Cu2p3/2 peak
toward lower binding energy (BE) occurred. These phe-
nomena provided conclusive evidence that the copper
+
30
0
+ 31
species on the catalyst’s surface were Cu or Cu ,
which was because the binding energies for these Cu
+
0
species typically overlap with those of the Cu species
in Cu 2p XPS analysis.3
2,33
After combining these data
with those of the XRD and TPR, we concluded that
0
the main Cu species on the reduced catalysts was Cu ,
+
although a small portion of Cu was formed during the
Figure 5. Cu LMM XAES spectra of the reduced CuSi-x
reduction.
catalyst.

1018
Xue Yu et al.
Table 2. (a) Kinetic energy (b) Auger parameter (c) Mole ratio of Cu to Si of the catalysts after reduction determined by
+
+
+
0
XPS (d) X % = Cu /(Cu +Cu )× 100% by deconvolution of Cu LMM XAES spectra.
Cu
K.E.(eV)a
α (eV)
ꢁ
b
B.E. of Cu 2p3/2
+
Cu0
+
Cu0
c
d
Catalyst
Cu
Cu
(eV)
R
XCu+%
Cu/Si
CuSi-1
CuSi-2
CuSi-3
CuSi-IM
915
915
915
915
918
918
918
918
1847
1847
1847
1847
1851
1851
1851
1851
932.7
932.7
932.7
932.6
0.1
0.3
0.4
0.1
38
49.3
39.9
36.5
sites that varied from weak to medium were present was due to a combination band associated with
on the catalysts surface.3
4–36
It can be observed from Brønsted acid sites, while the band at about 1480 cm
−1
the data in figure 6 that the areas of reduced CuSi-x could be attributed to Lewis acid and Brønsted acid
desorption peaks increased in size as follows: CuSi- sites. As shown in figure 7, the main acid type was
1
<CuSi-IM<CuSi-3<CuSi-2. The number of acid sites Lewis acid site, and the trend of the mount of acid
on the AE catalysts increased when the copper loading sites was consistent with NH -TPD. This result further
3
+
increased to peak with the CuSi-2 catalyst. This effect confirmedthattheCu could beusedasLewisacidsites.
occurred because the amount of copper phyllosilicate
species grew with higher copper loading, and a portion
3
.8 Catalytic tests
of the copper phyllosilicate could be reduced to highly
+
dispersed Cu species, which were regarded as Lewis
The direct transformation of ethanol to ethyl acetate
was carried out to study the catalytic properties of
the CuSi-x catalysts. The catalytic performances are
listed in table 3. The catalyst with low copper con-
tent demonstrated lower activity to achieve only a
37
acid sites. However, when the copper loading was
increased further, the copper species aggregated, which
influenced the reduction of Cu2+ to Cu . For the IM
+
+
catalyst, the acid sites also came from the Cu species.
44.5% conversion of ethanol and a 34.4% selecti-
vity for ethyl acetate. The catalytic activities increased
with greater copper content and peaked with the CuSi-2
catalyst, which yielded an approximately 65.3% con-
version of ethanol and a 48.9% selectivity for ethyl
acetate. Further increasing copper content causes
decrease in ethanol conversion and ethyl acetate
selectivity. For the IM catalyst with the same copper
3
.7 FTIR of pyridine adsorption
FTIR spectra of pyridine adsorbed reduced CuSi-x cat-
alysts are displayed in figure 7. According to the pub-
lished work,
36,38,39
the spectra of pyridine adsorbed on
−
1
various catalysts displaying bands around 1595 cm ,
−1
−1
1611 cm and 1445 cm were assigned to pyridine
−
1
coordinated to Lewis acid sites. The band at 1540 cm
Figure 7. FTIR of Pyridine Adsorption spectra of reduced
CuSi-x catalysts.
Figure 6. NH3-TPD spectra of reduced CuSi-x catalysts.

Direct transformation of ethanol to ethyl acetate
1019
Table 3. Catalytic performance during the direct transformation of ethanol to ethyl acetate over CuSi-x catalysts.
Conversion of
Ethanol (%)
Selectivity to Ethyl
acetate (%)
Selectivity to
Acetaldehyde (%)
Yield to Ethyl
acetate (%)
Catalysts
CuSi-1
CuSi-2
CuSi-3
CuSi-IM
44.5
65.3
52.9
49.3
34.4
48.9
36.7
32.5
54.5
17
35.5
48.9
15.3
31.9
19.4
16
loading as CuSi-2, the conversion of ethanol reached catalyst. These traits might be because the copper
9.3% and the selectivity for ethyl acetate was 32.5%, phyllosilicate could inhibit the sintering of the Cu par-
both of which were lower than the values for the CuSi-2 ticles during reduction, and made the copper species
catalyst. highly dispersed on the catalyst surface. This result
4
Metallic Cu phases act as active centers for the dehy- suggested that the Cu/SiO catalyst, which was pre-
2
drogenation of alcohols. However, both copper parti- pared by AE method and contained the copper phyl-
cle size and metal dispersion affect the dehydrogenation losilicate, was more effective for the conversion of
40
activity. Tonner et al. studied copper catalysts during a ethanol.
methanol dehydrogenation for the formation of methyl NH -TPD and FTIR of Pyridine Adsorption analy-
3
formate. They proposed that both the degree of disper- ses indicated that the number of acid sites increased in
sion and the metallic surface area of the copper were the following order: CuSi-1<CuSi-IM<CuSi-3<CuSi-
important during the selection of the most active cata- 2, and the main type of acid site is Lewis acid. The
41
lyst. Crivello et al. investigated the reaction of n-octyl selectivity to ethyl acetate demonstrated a similar trend.
alcohol dehydrogenation over copper catalysts, and the After reduction, the XRD of the AE catalyst exhib-
0
Cu sites were discovered to be the active ones. The ited a small diffraction peak for Cu O when the cop-
2
addition of magnesium into copper catalyst increased per loading was increased. This peak became weaker
4
,6
its stability and dispersion. The previous reports pro- when the copper loading increased further. The XAES
0
+
posed that the direct transformation of ethanol to ethyl spectra showed that both Cu and Cu coexisted on
+
+
0
acetate required the active centers for dehydrogenation the surface of reduced catalysts. The Cu /(Cu +Cu )
0
(
Cu ) and esterification (acid site). First, the ethanol intensity ratio of AE catalysts increased with the cop-
was dehydrogenated to produce acetaldehyde, which per loading, and maximized for CuSi-2 sample. The
+
+
0
was adsorbed on the acid sites to form a hemiacetal. Cu /(Cu +Cu ) intensity ratio of the IM catalyst was
37
Finally, the hemiacetal was dehydrogenated rapidly to lower than the AE catalyst. Zhang et al. and Zhu
42
produce ethyl acetate.
et al. proposed that the electropositive copper species,
The reduced XRD results of AE catalysts indicated which are generated by strong interactions between the
0
that the number of Cu sites increased with the copper copper and the SiO surface, might be strong Lewis acid
2
0
43
44
loading to a point, but the Cu species were seriously sites. Gong et al. and Benaliouche et al. discovered
aggregated with too high of a copper loading. It could that the number of Lewis acid sites increased on zeo-
+
+
be observed from table 3 that the conversion of ethanol lites after Cu and Ag were exchanged, which may
over CuSi-2 was highest of all of the AE catalysts, the be because the metal cations are the electron acceptors.
+
CuSi-3 was in a middle position, and the CuSi-1 was Therefore, after reduction, the Cu sites could func-
at the lowest position. Simultaneously, the selectivity tion as Lewis acidic sites to absorb the acetaldehyde,
toward acetaldehyde displayed an inverse trend. The thus improving the esterification. The high ethyl acetate
catalytic activity results suggested that the metallic Cu selectivity compared with IM catalyst was attributed to
+
phase acted as an active center for the dehydrogenation the abundant Cu species.
of alcohols. Interestingly, the conversion of ethanol over
Therefore, after considering all the above results, we
the CuSi-2 catalyst was higher than was observed with propose that the presence of copper phyllosilicate can
0
the CuSi-IM catalyst with the same copper loading. improve the dispersion of Cu , as well as generate a
+
From the reduced XRD results, we determined that the Lewis acidic Cu species. The catalytic performance,
0
Cu species on CuSi-2 catalyst were highly dispersed (which is higher that observed for the AE catalyst), is
and had a small particle size, and the results (table 2) superior because of the synergistic effect between the
0
showed that the content of surface copper species on highly dispersed Cu and Lewis acid sites which are
+
the CuSi-2 catalyst was higher than that on the IM generated from Cu .

1020
Xue Yu et al.
4
. Conclusions
14. Loaiza-Gil A, Arenas J, Villarroel M, Imbert F,
del Castillo H and Fontal B 2005 J. Mol. Catal. A: Chem.
28 339
2
A series of Cu/SiO catalysts have been synthesized
2
15. Schlegel M L and Manceau A 2006 Geochim. Cos-
mochim. Acta 70 901
via the ammonia-evaporation method. The formation
of copper phyllosilicate had wide effects on the tex-
ture and structure of the materials. Compared to the IM
16. Toupance T, Kermarec M and Louis C 2000 J. Phys.
Chem. B 104 965
catalyst, the AE catalysts exhibited a much higher dis- 17. Toupance T, Kermarec M, Lambert J-F and Louis C
2
002 J. Phys. Chem. B 106 2277
persion, a smaller copper particle size and a larger
surface area, in addition to the formation of copper
phyllosilicate, which could be reduced to Cu . The
1
8. Huang Z, Cui F, Xue J, Zuo J, Chen J and Xia C 2010 J.
Phys. Chem. C 114 16104
9. Chen L-F, Guo P-J, Qiao M-H, Yan S-R, Li H-X,
Shen W, Xu H-L and Fan K-N 2008 J. Catal. 257 172
+
1
AE catalysts exhibited superior ethanol conversion and
selectivity for ethyl acetate formation when enacting 20. Zhao L, Zhao Y, Wang S, Yue H, Wang B, Lv J and
the direct transformation of ethanol to ethyl acetate.
Ma X 2012 Ind. Eng. Chem. Res. 51 13935
21. Yin A, Guo X, Dai W-L and Fan K 2011 Catal. Com-
mun. 12 412
0
The synergistic effect of Cu and appropriate amount of
+
Lewis acidic sites generated from Cu cause this effect.
2
2
2
2
2
2. Gong J, Yue H, Zhao Y, Zhao S, Zhao L, Lv J, Wang S
and Ma X 2012 J. Am. Chem. Soc. 134 13922
3. Pu Z-Y, Liu X-S, Jia A-P, Xie Y-L, Lu J-Q and Luo M-F
2008 J. Phys. Chem. C 112 15045
Acknowledgements
4. Zhu X, Li X, Jia M, Liu G, Zhang W and Jiang D 2005
Appl. Catal., A 282 155
5. Su W G, Wang S G, Ying P L, Feng Z C and Li C 2009
J. Catal. 268 165
6. Chen C-S, You J-H, Lin J-H and Chen Y-Y 2008 Catal.
Commun. 9 2381
This work was supported by the Natural Science
Foundation of Science and Technology Department
of Jilin Province (20130101015JC), the open project
supported by State Key Laboratory of Inorganic
Synthesis and Preparative Chemistry of Jilin University, 27. Zhu Y-Y, Wang S-R, Zhu L-J, Ge X-L, Li X-B and
Luo Z-Y 2010 Catal. Lett. 135 275
the Innovation Project for the Frontiers of Science and
the new interdisciplinary project of Jilin University.
2
8. Marchi A J, Fierro J L G, Santamaría J and Monzón A
996 Appl. Catal., A 142 375
1
2
9. Ghodselahi T, Vesaghi M A, Shafiekhani A, Baghizadeh
A and Lameii M 2008 Appl. Surf. Sci. 255 2730
References
30. Huang Z, Cui F, Xue J, Zuo J, Chen J and Xia C 2012
Catal. Today 183 42
1
. Colley S W, Tabatabaei J, Waugh K C and Wood M A 31. Ji D H, Zhu W C, Wang Z L and Wang G 2007 Catal.
2
005 J. Catal. 236 21
. Inui K, Kurabayashi T and Sato S 2002 Appl. Catal., A
37 53
Commun. 8 1891
3
3
2. Matter P H and Ozkan U S 2005 J. Catal. 234 463
3. Agrell J, Birgersson H, Boutonnet M, Melián-Cabrera I,
Navarro R M and Fierro J L G 2003 J. Catal. 219 389
4. Chen X R, Ju Y H and Mou C Y 2007 J. Phys. Chem. C
2
2
3
4
. Inui K, Kurabayashi T and Sato S 2002 J. Catal. 212 207
. Inui K, Kurabayashi T, Sato S and Ichikawa N 2004
J. Mol. Catal. A: Chem. 216 147
. Zonetti P C, Celnik J, Letichevsky S, Gaspar A B and
Appel L G 2011 J. Mol. Catal. A: Chem. 334 29
. Wang L X, Zhu W C, Zheng D F, Yu X, Cui J, Jia M,
3
3
3
111 18731
5. Turco M, Bagnasco G, Cammarano C, Senese P,
Costantino U and Sisani M 2007 Appl. Catal., B 77 46
6. Zhang Y Q, Wang S J, Wang J W, Lou L L, Zhang C and
Liu S X 2009 Solid State Sci. 11 1412
5
6
Zhang W X and Wang Z L 2010 Reac. Kinet. Mech. Cat. 37. Zhang B, Zhu Y, Ding G, Zheng H and Li Y 2012 Appl.
101 365
Catal., A 443 191
7
8
9
. Ji Chan Park H J L, Jung Up Bang, Kang Hyun Park and 38. Chen L F, Noreña L E, Navarrete J and Wang J A 2006
Hyunjoon Song 2009 Chem. Commun. 7345
. Zhang B, Hui S, Zhang S, Ji Y, Li W and Fang D 2012
J. Nat. Gas Chem. 21 563
. Che M, Cheng Z X and Louis C 1995 J. Am. Chem. Soc.
Mater. Chem. Phys. 97 236
3
4
4
9. Jia A Z, Li J, Zhang Y Q, Song Y J and Liu S X 2008
Mater. Sci. Eng., C 28 1217
0. Tonner S P, Trimm D L, Wainwright M S and Cant N W
1984 Ind. Eng. Chem. Prod. Res. Dev. 23 384
1
17 2008
0. Burattin P, Che M and Louis C 1997 J. Phys. Chem. B
01 7060
1. Fonseca M G and Airoldi C 2000 Thermochim. Acta
59 1
1. Crivello M E, Pérez C F, Mendieta S N, Casuscelli
S G, Eimer G A, Elías V R and Herrero E R 2008 Catal.
Today 133 787
1
1
1
1
1
42. Zhu W C, Wang L X, Liu S Y and Wang Z 2008 React.
Kinet. Catal. Lett. 93 93
3
2. Lagadic I L, Mitchell M K and Payne B D 2001 Environ.
Sci. Technol. 35 984
43. Gong Y, Dou T, Kang S, Li Q and Hu Y 2009 Fuel
Process. Technol. 90 122
3. Mhamdi M, Marceau E, Khaddar-Zine S, Ghorbel A, 44. Benaliouche F, Boucheffa Y and Thibault-Starzyk F
Che M, Taarit Y and Villain F 2004 Catal. Lett. 98 135
2012 Microporous Mesoporous Mater. 147 10