Influence of the support composition on the hydrogenation of methyl acetate over Cu/MgO-SiO2 catalysts

Article abstract of DOI:10.1016/j.molcata.2015.07.013

A series of Cu/MgO-SiO₂ catalysts with different support compositions of MgO and SiO₂ were prepared using the ammonia-evaporation method and evaluated for methyl acetate hydrogenation reaction to synthesize ethanol. Physicochemical properties of these catalysts were investigated by N₂ physisorption, N₂O chemisorptions, X-ray diffraction, H₂-temperature programmed reduction, CO₂-temperature programmed desorption and X-ray photoelectron spectroscopy. It was found that the MgO content significantly influenced the chemical properties, then affected catalytic activities of Cu/xMgO-SiO₂ catalysts. The optimal catalytic performance was obtained over Cu/9MgO-SiO₂ catalyst with MgO/SiO₂ mass ratio of 9 with the methyl acetate conversion of 80.3% and ethanol selectivity of 99.0%. The high catalytic performance of Cu/9MgO-SiO₂ catalyst was attributed to the fine copper dispersion and large amount of weakly basic sites and Cu⁺ species.

Full text of DOI:10.1016/j.molcata.2015.07.013

Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
Contents lists available at ScienceDirect
Journal of Molecular Catalysis A: Chemical
journal homepage: www.elsevier.com/locate/molcata
Influence of the support composition on the hydrogenation of methyl
acetate over Cu/MgO-SiO catalysts
2
∗
Hongyun Qin, Cuili Guo , Chengwei Sun, Jinli Zhang
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of Cu/MgO-SiO2 catalysts with different support compositions of MgO and SiO2 were prepared
using the ammonia-evaporation method and evaluated for methyl acetate hydrogenation reaction to
synthesize ethanol. Physicochemical properties of these catalysts were investigated by N2 physisorp-
tion, N2O chemisorptions, X-ray diffraction, H2-temperature programmed reduction, CO2-temperature
programmed desorption and X-ray photoelectron spectroscopy. It was found that the MgO content sig-
nificantly influenced the chemical properties, then affected catalytic activities of Cu/xMgO-SiO2 catalysts.
The optimal catalytic performance was obtained over Cu/9MgO-SiO2 catalyst with MgO/SiO2 mass ratio
of 9 with the methyl acetate conversion of 80.3% and ethanol selectivity of 99.0%. The high catalytic per-
formance of Cu/9MgO-SiO2 catalyst was attributed to the fine copper dispersion and large amount of
Received 25 November 2014
Received in revised form 9 July 2015
Accepted 10 July 2015
Available online 17 August 2015
Keywords:
Ethanol
Methyl acetate
Hydrogenation
Magnesium oxide
+
weakly basic sites and Cu species.
©
2015 Elsevier B.V. All rights reserved.
1
. Introduction
[7] studied the activities of Cux-Zny-O catalysts for hydrogena-
tion of methyl acetate and found that the catalytic activities were
dependent on the Cu/Zn ratio. The methyl acetate conversion of
72.6% could be obtained on Cu0.4-Zn0.6-O catalyst, better than other
catalysts with other Cu/Zn ratio. Some of new and highly effective
catalysts were also found during the hydrogenation of dimethyl
oxalate [8–11]. These studies show that Cu-based catalysts are
active in the hydrogenation of acetate esters to ethanol. However,
the catalytic activity and stability still need to improve.
Cu-MgO catalysts are widely applied in many catalytic reaction
processes such as low-temperature methanol synthesis from syn-
gas [12,13], hydrogenation of furfural to furfuryl alcohol [14–15]
and selective hydrogenolysis of glycerol to 1,2-propanediol [16].
These reports showed that Cu/MgO catalysts could exhibit excel-
lent catalytic performance for hydrogenation reactions. Tu and
Chen [17] reported the catalytic activities of different alkaline-earth
Ethanol, one of the most widely used chemical raw materials,
is applied to diverse industries, such as chemical, pharmaceutical,
coating food industries, etc. In particular, ethanol as an alter-
native energy source will hold great promise [1–4]. Ethanol is
commercially produced via two routes, fermentation of sugars and
hydration of ethylene. However, fermentation of sugars and hydra-
tion of ethylene will face great challenges owing to the lack of
food supplies and the worldwide oil crisis. Hence, it is necessary
to explore new methods that can supplement these resources to
meet the increasing demands of ethanol in the future. At present,
one of ethanol productive processes arising significant interest is
the hydrogenation of methyl acetate (MeOAc), since the process can
solve acetic acid (AcOH) overcapacity and avoid the requirement for
expensive equipment comparing with AcOH hydrogenation.
For ester hydrogenation, chromium oxide modified Cu-based
catalysts exhibit excellent catalytic activities and are widely
used. However, the environmental hazard caused by the loss of
chromium limits its practical applications. Therefore, it is essential
to explore efficient chromium-free catalysts for ester hydrogena-
tion reactions. Recently, Zhu et al. [5,6] reported Cu-Zn/SiO2 and
Cu-Zn/Al O catalysts for the hydrogenation of ethyl acetate, and
oxide modified Cu/SiO catalyst for the dehydrogenation of ethanol,
2
the magnesium oxide modified Cu/SiO catalyst exhibited excellent
2
activity and stability, better than other alkaline-earth oxide modi-
fied catalysts. Till now, a detailed study on Cu/MgO-SiO2 catalysts
for methyl acetate hydrogenation to ethanol is yet to be published.
In this paper, the MgO-modified Cu/SiO2 catalysts with
different magnesium oxide content were prepared using an
ammonia-evaporation method, and their catalytic performances
for hydrogenation of methyl acetate were evaluated in fixed-bed
reactor. In addition, several characterization techniques includ-
ing N2 physisorption, N2O titration, X-ray diffraction (XRD),
H2-temperature programmed reduction (TPR), CO2-temperature
2
3
the ethanol yields were 76.5% and 63.2%, respectively. Wang et al.
∗ Corresponding author. Fax: +86 22 2270 4495.
E-mail address: gcl@tju.edu.cn (C. Guo).
http://dx.doi.org/10.1016/j.molcata.2015.07.013
1
381-1169/© 2015 Elsevier B.V. All rights reserved.

8
0
H. Qin et al. / Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
programmed desorption (CO -TPD), and X-ray photoelectron spec-
2.3.2. N O chemisorption
2
2
troscopy (XPS) were performed to investigate the influence of
magnesium oxide content on the physical properties and chemical
properties of the catalysts.
The copper surface area and dispersion of calcined samples were
measured by a pulse titration method using the adsorption and
decomposition of N O on a Micromeritics AutoChem 2910 [18–20].
2
2.3.3. X-ray diffraction
The powdered X-ray diffraction (XRD) profiles were collected on
2
. Material and methods
a D/MAX-2500 X-ray diffractometer operated at 40 kV and 40 mA,
◦
with CuK␣ as the radiation source. The scanned range was from 10
2.1. Catalyst preparation
◦
◦
−1
to 90 , with a scanning step of 5 min . The Cu species crystallite
size was calculated by the Scherrer equation.
A series of Cu/xMgO-SiO2 catalysts with the copper loading of
3
0 wt% were manufactured via the ammonia-evaporation method.
2
.3.4. H -temperature programmed reduction
H -temperature programmed reduction (H -TPR) patterns
2
2
The ammonia aqueous solution, Mg(NO ) ·6H O, Cu(NO ) ·3H O,
3
2
2
3
2
2
2
silica sol were purchased from Tianjin Guangfu Fine Chemical Insti-
tute, China. The preparation procedures were as follows. Dissolving
were obtained on the Micromeritics AutoChem 2910 chemisorp-
tion apparatus. Prior to the measurement, the catalysts were
pretreated at the temperature of 373 K for 1 h using argon gas. Then
the catalysts were reduced by 5 vol.% H /Ar from 373 K up to 1173 K,
by a heating rate of 10 K min
5
.66 g of Cu(NO ) ·3H O and a certain amount of Mg(NO ) ·6H O
3
2
2
3
2
2
in deionized water under the continuous stirring at room temper-
ature. Then the silica sol with amount of 30 wt% was added and
mixed for 10 min. Afterwards, a certain amount of 30 wt% ammonia
aqueous solution was added and mixed for 3 h. The pH of suspen-
sion was kept about 11. Then the suspension was placed in the 368 K
water bath to remove the excess ammonia. This progress was ter-
minated at a pH of around 6. The precipitate was aged for 3 h under
the room temperature, then calcined at 723 K for 3 h after drying
at 393 K for 12 h. The prepared catalyst was named Cu/xMgO-SiO2
2
−
1
.
2.3.5. CO -temperature programmed desorption
2
CO -temperature programmed desorption (CO -TPD) tech-
2
2
nique was used to analyze the basicity of catalysts on
Micromeritics AutoChem 2910 instrument. The main steps were
as follows. (1) Hundred milligram catalyst sample was reduced for
a
4
h by 5 vol.% H /Ar at 723 K and then cooled to 373 K. (2) The gas
2
(
x = 1, 3, 9 and 20), where x stands for MgO/SiO2 mass ratio. For
was switched to CO2 for 1 h. (3) Using pure Ar sweeped to remove
weakly adsorbed CO2 at room temperature. (4) CO -TPD was per-
formed from 300 K to 1173 K by 10 K min under an atmosphere
of Ar.
comparsion, MgO and SiO2 suported catalysts were also prepared
with the same method.
2
−
1
2.2. Catalytic activity tests
2.3.6. X-ray photoelectron spectroscopy
X-ray photoelectron spectroscopy (XPS) and Auger electron
The catalytic performances were assessed using a fixed-bed
tubular reactor (the tube’s inner diameter of 10 mm). Typically,
.5 g catalyst (60–80 meshes) precursor was mixed with a certain
spectroscopy (XAES) were recorded on the PHI5000 Versa Probe
spectrometer equipped with a electron energy analyzer and a
monochromated Al K␣ X-ray radiation source (hv = 1486.6 eV).
All binding energies were referenced to contaminant carbon
1
amount of quartz sand (40–60 meshes) and placed in the tubular
reactor. The two thermocouples were inserted into the gasification
chamber and reactor respectively, for better controlling the tem-
perature. The catalysts were activated at the temperature of 623 K
(
C1s = 284.8 eV). To investigating the catalysts surface states of Cu
species at the reaction conditions, XPS spectra were collected for
the reduced catalysts. There were ± 0.2 eV errors in the process of
experiment.
−
1
for 4 h by a heating rate of 5 K min in a hydrogen atmosphere
(
150 ml min−1). When cooling to the reaction temperature, methyl
acetate (purchased from Tianjin Guangfu Fine Chemical Institute of
China) was injected into the gasification chamber of 533 K using a
constant flow pump. Then the hydrogen and the methyl acetate
3
. Results and discussion
3.1. Catalytic performance of the catalysts
were mixed at the H /MeOAc molar ratio of 10 in the gasifica-
2
tion chamber. The mixture went into the reactor, and the reaction
pressure and temperature were controlled at 3.0 MPa and 613 K,
respectively. The products were collected and analyzed through a
gas chromatograph device (North Branch of Ruili SP-3200A) using a
flame ionization detector (FID), equipped with a HJ-WAX capillary
column.
The effects of magnesium oxide amounts on the catalytic activi-
ties of Cu/xMgO-SiO catalysts for hydrogenation of methyl acetate
2
are shown in Fig. 1a and b. The results show that the catalytic activ-
ities obtained by Cu/xMgO-SiO catalysts are better than that of the
2
Cu/SiO catalyst, which indicate that using the composite supports
2
to replace the single support is favorable for ethanol production.
When the MgO/SiO2 mass ratio is 9, the conversion of methyl
acetate reaches 80.3% and the selectivity of ethanol is above 99%,
which are considerably better than the results of the Cu/SiO2 and
Cu/MgO catalysts under the same reaction conditions. It can be seen
from Fig. 1a, there are obvious decline in the catalytic performance
2
2
2
.3. Catalyst characterization
.3.1. N2 physisorption
The N2 physisorption was carried out on Micromeritics Nova
200e device to analyze the textual properties of the catalysts. First,
curves for Cu/1MgO-SiO , Cu/20MgO-SiO2 and Cu/MgO catalysts
2
and obvious decline in the initial two hours for Cu/3MgO-SiO2 and
the samples were heated to 573 K and outgassed for 4 h at the con-
Cu/9MgO-SiO catalysts. The two reasons may account for this phe-
2
dition of vacuum. Then the N adsorption–desorption isotherms for
2
nomenon, the content of Cu on the catalyst surface decreased after
undergoing reactions and carbon deposition.
In order to further illustrate the promoted behavior of modified
Cu/SiO2 catalyst, a long-term stability for Cu/9MgO-SiO2 catalysts
are carried out and displayed in Fig. 1c. It is evident that during 50 h
longterm test, methyl acetate conversion shows a slight decrease
the catalysts were measured at the temperature of 77 K. The spe-
cific surface area was calculated according to the isotherms using
the BET method, and the pore volume and pore size were calcu-
lated by BJH method on the basis of the desorption branches of the
nitrogen isotherms.

H. Qin et al. / Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
81
Fig. 1. (a–c) Catalytic performance of Cu/xMgO-SiO2 catalysts. Reaction conditions: P = 3 MPa, T = 613 K, H2/MeOAc = 10 (mol/mol), LHSV = 2.0 h−1; (d) Effect of the H2/MeOAc
−
1
on the catalytic performance of the Cu/9MgO-SiO2catalyst. Reaction conditions: P = 3 MPa, T = 613 K, GHSV = 1800 h
.
from 80 to 76%; In the meantime, ethanol selectivity remains at
about 97%. The results indicate that Cu/9MgO-SiO2 catalyst per-
forms a better catalytic performance.
The influence of H /MeOAc molar ratio on the performance of
2
the Cu/9MgO-SiO catalyst was also studied. The results are showed
2
in Fig. 1d. As shown in Fig. 1d, the conversion of MeOAc increases
with increasing molar ratio of H /MeOAc, while the selectivity to
2
ethanol remains unchanged. When the H /MeOAc molar ratio is 50,
2
the MeOAc conversion reaches 96.7%, with the ethanol selectivity
of 99.0%. The Reaction (1) describes the hydrogenation of methyl
acetate to ethanol process.
CH COOCH + 2H ꢀ C H5OH + CH OH
(1)
3
3
2
2
3
It can be found that the chemical equilibrium shifts to posi-
tive direction with the increase of the H2 molar contents, so the
Cu/9MgO-SiO2 catalyst can exhibit a much better catalytic activ-
Fig. 2. Copper surface area and dispersion versus support composition.
ity with increasing H /MeOAc molar ratio at constant LHSV (liquid
hour space velocity).
2
the primary factors that determine the catalytic performance. The
key factors which mainly influence the catalytic performance may
be more chemical properties than physical properties.
3.2. Catalyst characterization
The copper dispersion and surface area of Cu/SiO and Cu/xMgO-
2
SiO2 catalysts measured by N O adsorption are shown in Table 1
2
3
.2.1. Textural properties of catalysts
The textural properties of different composite MgO-SiO2 sup-
and Fig. 2. The copper dispersion and surface area increase with
the increased magnesium oxide content and maximize when the
MgO/SiO2 mass ratio is 9, and then decline with further increas-
ing in magnesium oxide content. The various copper dispersion
and surface area may be caused by different content of magne-
sium oxide which is used as a kind of isolating agent to suppress
aggregation of copper species during the activation of catalysts
and hydrogenation of MeOAc. The Cu/9MgO-SiO2 catalyst demon-
strates a best catalytic activity that may be due to the acquired
maximum copper dispersion and surface. In dimethyl oxalate
hydrogenation, Yin et al. [21] reported that 20 wt% Cu catalyst
exhibited a best catalytic performance while it possessed a max-
ported Cu-based catalysts are summarized in Table 1. The Cu/SiO
sample possess relatively large pore volume of 0.79 cm g and
relatively high BET surface area of 356.6 m g , whereas those
for Cu/MgO are only 30.0 m g and 0.16 cm g . The pore vol-
ume and BET surface area of Cu/xMgO-SiO2 are between Cu/SiO2
and Cu/MgO, and gradually decrease with the increased content
of magnesium oxide. The Cu/9MgO-SiO2 catalyst exhibits the best
catalytic activity, however, the pore volume and surface area of this
catalyst are ordinary. It can be concluded from the above facts that
textural properties, such as surface area and pore volume, are not
2
3
−1
2
−1
−1
2
−1
3

8
2
H. Qin et al. / Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
Table 1
Physicochemical properties of Cu/xMgO-SiO2 catalysts.
Cu dispersiona
(%)
SCu
(m
a
dCuOb
(nm)
dMb(nm)
Catalyst
SBET
VP
(cm
dP
(nm)
2
−1
3
−1
2
−1
g cat)
(m
g
)
g
)
Cu/SiO2
356.6
222.9
110.7
64.7
52.7
30.0
0.79
0.53
0.20
0.22
0.21
0.16
20.2
16.1
14.6
13.9
16.1
21.1
18.3
22.8
29.8
32.6
30.4
15.5
30.6
38.2
49.8
54.5
50.9
26.0
20.9
19.0
14.5
–
–
–
20.9
18.8
13.2
–
–
–
Cu/1MgO-SiO2
Cu/3MgO-SiO2
Cu/9MgO-SiO2
Cu/20MgO-SiO2
Cu/MgO
a
Cu dispersion and surface area of Cu determined by N2O titration.
CuO and Cu crystallite sizes calculated using the Scherrer formula.
b
imum copper dispersion and surface, and identified that copper
dispersion and surface may promote its catalytic performance.
of larger CuO clusters. For Cu/SiO2 catalyst, the 576 K reduced
peaks may be ascribed to collective action of the reduction of
above mentioned Cu species. The Cu/MgO sample exhibits a broad
reduction peak at 739 K along with a shoulder peak at 677 K, indi-
3.2.2. Crystalline phase
cating that the sample is reduced in two stages, i.e., CuO → Cu O
The XRD patterns of all the samples after calcination are shown
2
0
and Cu O → Cu . The broad peak may be ascribed to collective
in Fig. 3a. When MgO to SiO mass ratio is lower than 3, the charac-
2
2
+
0
◦
◦
action of reducing Cu and CuO clusters to Cu . A similar behav-
ior was reported by Nagaraja et al. [23] for Cu/MgO catalyst
prepared by co-precipitation method that Cu/MgO sample was
reduced in two steps. For Cu/xMgO-SiO2 samples, the reduction
peak is shifted to higher temperature with increasing magnesium
oxide amount. However, it lies between Cu/SiO2 and Cu/MgO. A
similar result was also reported by Tu and Chen [17] that the
reduction temperature of Cu-MgO/SiO2 was higher than that of
teristic peaks at 2ꢀ of 35.6 and 38.7 (JCPDS 05-0661) are ascribed
to CuO, indicating that some copper species are agglomerated on
the surface of the support. With the continuous increasing of mag-
◦
◦
nesium oxide content, new diffraction peaks at 2ꢀ of 36.9 , 42.9 ,
◦
and 62.2 (JCPDS 43-1022) attributed to magnesium oxide become
apparent, whereas CuO diffraction peaks disappear, indicating the
copper species are highly dispersed in MgO-SiO2 support. The CuO
particle sizes calculated by Scherrer equation are shown in Table 1.
Since the crystalline sizes of copper species are quite small, the
diffraction peak can not be detected. The peak intensity and sharp-
ness increase along with the increasing particle sizes. According to
this situation, the CuO crystallite sizes of the Cu/xMgO-SiO2 cata-
lysts are much smaller than the Cu/SiO2 catalyst, which illustrate
Cu/SiO . This result is possibly due to the addition of MgO into
2
Cu/SiO2 catalyst, which essentially improves the dispersion of
cupreous species during the preparation of catalysts, strengthens
the interaction between active components of copper ions and
catalyst support. The enhanced interaction makes catalysts more
0
difficult to be reduced to Cu , and alters Cu valence states distribu-
that the employ of composite MgO-SiO support can reduce particle
2
tion on catalyst surface.
size to promote copper particles dispersed.
Temperature programmed desorption (TPD) of CO is a common
The XRD patterns of reduced catalysts are presented in Fig. 3b.
2
◦
◦
◦
technique to determine the basicity of solid catalysts. The basicity
Some diffraction peaks at 2ꢀ of 43.3 , 50.4 , and 74.1 attributed to
0
0
of Cu/SiO2 and Cu/xMgO-SiO2 catalysts obtained by CO -TPD and
Cu (JCPDS 04-0836) are observed. The intensities of Cu diffraction
2
the profiles are displayed in Fig. 4b. Cu/SiO2 sample exhibits two
CO2 desorption peaks, a low-temperature peak of 550–700 K and
a high desorption peaks of 750–950 K, which can be identified as
moderate and strong basic sites, respectively. For Cu/xMgO-SiO2
catalysts, added magnesium oxide can lead to the appearance of
weak basic sites with a CO2 desorption peak at 300–500 K and the
disappearance of the moderate basic sites with a CO2 desorption
peak at 550–700 K. Strong basic sites with a CO2 desorption peak
at 950–1050 K gradually disappears when the content of magne-
sium oxide increases. Tu and Chen [17] found that the addition of
magnesium oxide to Cu/SiO2 catalyst could increase the content of
peaks weaken or even disappear with an increasing MgO/SiO mass
2
ratio, but the diffraction peaks are very distinct for Cu/MgO sam-
0
ple. The Cu crystallite size estimated as shown in Table 1 by the
Scherrer equation decreases along with the increased magnesium
oxide when the MgO/SiO2 mass ratio is lower than 20. Obviously,
the results demonstrate that adding moderate magnesium oxide to
catalysts is beneficial for inhibiting growth of metallic copper parti-
◦
cles. Moreover, a weak peak at 2ꢀ of 36.6 attributed to Cu O (JCPDS
2
0
5-0667) is observed when MgO /SiO mass ratio is above 1, and the
2
peak becomes apparent with an increasing MgO/SiO2 mass ratio,
and Cu/MgO catalyst sample exhibits the most obvious Cu O char-
2
weak basic site of catalyst and Cu-MgO/SiO catalyst exhibited bet-
acteristic peak. The results indicate that the metallic Cu and Cu O
2
2
0
+
+
ter catalytic stability than Cu/SiO in the dehydrogenation reaction
coexist in the working catalysts, and the ratio of Cu /(Cu + Cu )
significantly change with increasing magnesium oxide content. It
can be concluded that the catalytic activity may be associated with
the Cu valence states distribution and other chemical properties.
2
process, which was mainly attributed to beneficial effects of weakly
basic sites on Cu species, while the strong basic sites could damage
the stabilities of the catalysts. It can be found that Cu/9MgO-SiO2
catalyst exhibits more weak basic sites, so the excellent catalytic
activity may be associated with it.
3.2.3. Reducibility and surface base properties
To evaluate the reduction behavior of the catalysts, the cal-
cined Cu/SiO , Cu/MgO and Cu/xMgO-SiO samples were examined
2
2
by H -TPR and the result are presented in Fig. 4a. In Cu/SiO2
3.2.4. Surface chemical states
2
catalyst, the reduction peak centered at 576 K can be identified
XPS and XAES were recorded to analyze the chemical state and
surface composition of activated catalysts. The XPS curves of acti-
vated Cu/xMgO-SiO2 are shown in Fig. 5a. Generally, the peak at
binding energy of around 934 eV and the 2p → 3d satellite peak at
942–944 eV are the proofs of existing Cu2+ [24]. However, the above
two peaks can not be found and the peak at 932 eV is observed,
which may be due to the reduction of Cu2+ to Cu+ or Cu0 species.
In addition, the tiny chemical shift of binding energy for Cu2p3/2
0
as CuO → Cu . In many open literatures, this reduction peak is
ascribed to the process of reducting small CuO clusters. Wang
et al. [22] reported Cu/SiO2 catalyst prepared by impregnation
method presented three different temperature of TPR peaks (518 K,
5
60 K, and 629 K). The two lower reduced peaks can be tenta-
tively ascribed to small CuO clusters and highly dispersed copper
species; The reduced peak at 629 K may be caused by reduction

H. Qin et al. / Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
83
Fig. 3. (a) XRD patterns of the calcined Cu/xMgO-SiO2 catalysts; (b) XRD patterns of the reduced Cu/xMgO-SiO2 catalysts.
(
A) Cu/SiO2; (B) Cu/1MgO-SiO2; (C) Cu/3MgO-SiO2; (D) Cu/9MgO-SiO2; (E) Cu/20MgO-SiO2; (F) Cu/MgO.
Fig. 4. (a) H2-TPR profiles of the calcined Cu/xMgO-SiO2 catalysts. (b) CO2-TPD patterns of Cu/xMgO-SiO2 catalysts.
A) Cu/SiO2; (B) Cu/1MgO-SiO2; (C) Cu/3MgO-SiO2; (D) Cu/9MgO-SiO2; (E) Cu/20MgO-SiO2; (F) Cu/MgO.
(
Fig. 5. (a) Cu2p XPS spectra of the reduced Cu/xMgO-SiO2 catalysts; (b) Cu LMM XAES spectra of the reduced Cu/xMgO-SiO2 catalysts.
(
A) Cu/SiO2; (B) Cu/1MgO-SiO2; (C) Cu/3MgO-SiO2; (D) Cu/9MgO-SiO2; (E) Cu/20MgO-SiO2; (F) Cu/MgO.
Table 2
occurs, which may be caused by the interaction of Cu species and
support.
Surface Cu component of the reduced catalysts based on Cu LMM XAES spectra.
0
a
b
c(%)
The binding energy distinction is very minimal between Cu and
Catalyst
KE (eV)
AP (eV)
Cu2p3/2
BE (eV)
XCu
+
+
Cu . Thus, the kinetic energy of the Cu LMM and the binding energy
Cu+
Cu0
Cu+
Cu0
of the Cu2p3/2 together make up an Auger parameter ␣ ı´ , which
is used to distinguish Cu+ and Cu that existing on the catalyst
0
Cu/SiO2
915.8
915.6
915.2
915.6
915.3
915.0
916.6
917.0
917.6
917.4
917.2
917.0
1848.4
1848.5
1848.1
1848.5
1847.7
1847.9
1849.2
1849.9
1850.5
1850.3
1849.6
1849.9
932.6
932.9
932.9
932.9
932.4
932.9
44.4
50.4
52.6
63.9
56.1
45.9
Cu/1MgO-SiO2
Cu/3MgO-SiO2
Cu/9MgO-SiO2
Cu/20MgO-SiO2
Cu/MgO
0
surface. In general, ␣ ı´ is ca. 1849.0 eV for Cu and ca. 1847.0 eV for
+
Cu [21,25,26]. In the Cu LMM XAES spectra of activated catalysts
(
Fig. 5b), Auger kinetic energy peaks ranging from 905 to 925 eV
are observed, strongly indicating the Cu and Cu+ are coexisting
0
on the catalysts surface. The results of the Cu+ molar content esti-
mated from the deconvolution are shown in Table 2. The addition
a
Kinetic energy.
b
Auger parameter.
c
+
+
0
+
XCu = Cu /(Cu + Cu ) × 100%.

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H. Qin et al. / Journal of Molecular Catalysis A: Chemical 409 (2015) 79–84
displayed the best catalytic performance. The characterization
analysis show that, adding magnesium oxide to Cu/SiO2 catalyst
can improve Cu surface area and dispersion, on the other hand,
can increase content of surface Cu+ sites through strengthening
the interaction between copper species and support. The maximum
+
0
+
molar ratio of Cu /(Cu + Cu ) obtained by tuning the magnesium
oxide content can lead to the highest catalytic performance. There-
fore, the large Cu surface area, Cu dispersion, amount of weakly
basic sites and Cu+ species are believed to the main reasons for
improving catalytic performance in the hydrogenation of methyl
acetate to ethanol.
Acknowledgements
Fig. 6. Yield of ethanol and Cu /(Cu0 + Cu ) versus support composition.
+
+
We gratefully acknowledge the financial supports from Major
State Basic Research Program of China (2012CB720300), and Pro-
gram for Changjiang Scholars and Innovative Research Team in
University (IRT1161).
+
+
0
of magnesium oxide results in a change of the Cu /(Cu + Cu )
molar content on the catalyst surface, following the order:
Cu/9MgO-SiO2 (63.9%) > Cu/20MgO-SiO2 (56.1%) > Cu/3MgO-
SiO2 (52.6%) > Cu/MgO-SiO2 (50.4%) > Cu/MgO (45.9%) > Cu/SiO2
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2
+
+
0
+
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between copper species and support is strong, which hinders the
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4
. Conclusions
A series of Cu/MgO-SiO2 catalysts with different support
compositions of MgO and SiO2 were prepared by the ammonia-
evaporation method and evaluated for methyl acetate hydrogena-
tion to ethanol. Among all catalysts tested, Cu/9MgO-SiO2 catalyst