Catalytic synthesis of diethyl carbonate with supported Pd-Cu bimetallic nanoparticle catalysts: Cu(I) as the active species

Article abstract of DOI:10.1016/S1872-2067(15)60973-1

Cupric oxide (CuO) and copper-cuprous oxide (Cu-Cu₂O) nanoparticles were prepared by a simple hydrothermal method for the synthesis of diethyl carbonate (DEC) from ethanol. During these syntheses, varying NaOH and glucose concentrations were applied to explore and pinpoint the active species. It was found that PdCl₂/CuO and PdCl₂/Cu-Cu₂O both catalysts exhibited good thermal stability and morphology. The results of catalytic tests showed that the catalysts prepared with 5 mol/L NaOH show superior catalytic performances because of their lower extent of agglomeration. It is noteworthy that the PdCl₂/Cu-Cu₂O catalysts were the most active, especially the PdCl₂/Cu-Cu₂O catalyst prepared with 10 mmol glucose and having a higher Cu₂O concentration. In Pd(II)-Cu(II) (PdCl₂/CuO) catalysts, there is an induction period, during which Pd(II) is reduced to Pd(0), that must occur prior to electron transfer between Pd and Cu, and this can slow the catalytic reaction. To further pinpoint the active species, PdCl₂/Cu-Cu₂O catalysts with different Cu₂O contents were prepared by controlling the dosages of glucose. The maximum DEC yield obtained with these catalysts was 151.9 mg·g^-1·h^-1, corresponding to an ethanol conversion of 7.2% and 97.9% DEC selectivity on an ethanol basis. Therefore, it was concluded that Cu⁺ was the active species in this catalytic system, possibly because a higher proportion of Cu⁺ reduces the Pd²⁺ concentration and limits the CO oxidation side reaction, thus increasing DEC selectivity. In addition, Cu⁺ promotes electron transfer between Pd and Cu without an induction period, which could also promote the catalytic activity.

Full text of DOI:10.1016/S1872-2067(15)60973-1

Chinese Journal of Catalysis 36 (2015) 2036–2043
ava i l a b l e a t w w w. s c i e n c ed i r e c t . c o m
j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e /c h n j c
Article
Catalytic synthesis of diethyl carbonate with supported Pd‐Cu
bimetallic nanoparticle catalysts: Cu(I) as the active species
Pingbo Zhang, Yan Zhou, Mingming Fan*, Pingping Jiang
The Key Laboratory of Food Colloids and Biotechnology, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University,
Wuxi 214122, Jiangsu, China
A R T I C L E I N F O
A B S T R A C T
Article history:
Cupric oxide (CuO) and copper‐cuprous oxide (Cu‐Cu2O) nanoparticles were prepared by a simple
hydrothermal method for the synthesis of diethyl carbonate (DEC) from ethanol. During these
syntheses, varying NaOH and glucose concentrations were applied to explore and pinpoint the
active species. It was found that PdCl2/CuO and PdCl2/Cu‐Cu2O both catalysts exhibited good
thermal stability and morphology. The results of catalytic tests showed that the catalysts prepared
with 5 mol/L NaOH show superior catalytic performances because of their lower extent of
agglomeration. It is noteworthy that the PdCl2/Cu‐Cu2O catalysts were the most active, especially
the PdCl2/Cu‐Cu2O catalyst prepared with 10 mmol glucose and having a higher Cu2O concentration.
In Pd(II)‐Cu(II) (PdCl2/CuO) catalysts, there is an induction period, during which Pd(II) is reduced
to Pd(0), that must occur prior to electron transfer between Pd and Cu, and this can slow the
catalytic reaction. To further pinpoint the active species, PdCl2/Cu‐Cu2O catalysts with different
Cu2O contents were prepared by controlling the dosages of glucose. The maximum DEC yield
obtained with these catalysts was 151.9 mg·g−1·h−1, corresponding to an ethanol conversion of 7.2%
and 97.9% DEC selectivity on an ethanol basis. Therefore, it was concluded that Cu+ was the active
species in this catalytic system, possibly because a higher proportion of Cu+ reduces the Pd2+
concentration and limits the CO oxidation side reaction, thus increasing DEC selectivity. In addition,
Cu+ promotes electron transfer between Pd and Cu without an induction period, which could also
promote the catalytic activity.
Received 29 August 2015
Accepted 16 September 2015
Published 20 November 2015
Keywords:
Cupric oxide
Copper‐cuprous oxide
Diethyl carbonate
Sodium hydroxide concentration
Dosages of glucose
Active species
© 2015, Dalian Institute of Chemical Physics, Chinese Academy of Sciences.
Published by Elsevier B.V. All rights reserved.
1. Introduction
developed for the synthesis of DEC, including; (i) the reaction of
highly toxic phosgene gas with EtOH [5], (ii) the oxidative
Diethyl carbonate (DEC) is a fuel oxygenate additive with
the potential to replace methyl tert‐butyl ether (MTBE), and is
currently thought to be superior to other alternative additives
such as dimethyl carbonate (DMC) and ethanol (EtOH) [1]. DEC
has also been considered for applications as a solvent [2] and
as a component of a lithium cell electrolyte mixture because of
its low toxicity [3,4]. Several commercial processes have been
carbonylation of EtOH in the liquid phase [6], (iii) the
transesterification reaction of DMC and EtOH [7], (iv) the gas
phase oxidative carbonylation of EtOH [1,8], (v) the reaction
between carbon monoxide and ethyl nitrite (C2H5ONO) [9], (vi)
the reaction of EtOH with urea over organotin catalysts [10]
and (vii) the activation of carbon dioxide [11]. Among these, the
oxidative carbonylation of EtOH in the gas phase is the most
* Corresponding author. Tel: +86‐510‐85917090; Fax: +86‐510‐85917763; E‐mail: fanmm2000@126.com
This work was supported by the National Natural Science Foundation of China (21106054).
DOI: 10.1016/S1872‐2067(15)60973‐1 | http://www.sciencedirect.com/science/journal/18722067 | Chin. J. Catal., Vol. 36, No. 11, November 2015

Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
2037
attractive method because it is environmentally benign by
nature [1,8,12].
mixture stirred vigorously at 50 °C for 1 h, after which the
reaction mixture was sealed in a stainless steel pressure
container and held at 140 °C for 24 h. The resulting product
was collected, washed several times with distilled water
followed by absolute EtOH and then dried under vacuum to
obtain black CuO powder. Different NaOH concentrations (2.5,
5 and 10 mol/L) were used during the preparation. In addition,
while employing the optimized NaOH concentration, different
concentrations of glucose were added during the preparation
process after adding the CTAB so as to prepare brick‐red
Cu‐Cu2O nanoparticles containing various Cu2O species. In our
previous work, the special roles of Pd and Cu in PdCl2/Cu‐HMS
catalysts were investigated in detail [16,18]. Therefore, in the
present work, catalysts were also prepared by impregnating
the CuO or Cu‐Cu2O with a methanol solution of palladium
chloride (PdCl2). The total palladium concentration in the final
products was 0.25 wt% based on the mass of CuO or Cu‐Cu2O.
There have been numerous reports concerning the
application of chlorine‐containing copper catalysts to the
synthesis of DEC via the oxidative carbonylation of EtOH
[13–18]. Various catalysts have been investigated for this
purpose, all of which are prepared by dispersing CuCl2 or CuCl2
and PdCl2 onto supports. Early studies showed that activated
carbon (AC) [9,12,14], metal oxides [19] and zeolites [20] may
all be used as the support. Subsequently, to reduce problems
with equipment corrosion, chlorine‐free catalysts were
prepared by a solid‐state ion exchange method for the
synthesis of DEC [21,22]. However, uncertainties regarding the
active species in these catalysts still remain. Thus, in early work
with DMC catalytic systems, chlorine‐free catalysts were
prepared by solid‐state ion exchange to explore the issues of
equipment corrosion and the uncertainty of the active species
[23,24]. Cu+ ions were studied as the active species through
experimental observations [23–25] as well as theoretical
investigations [26,27]. Later, Cu2O supported on carbon‐based
materials was also applied as a chlorine‐free catalyst to address
the above challenges [28,29]. More recently, nanoscale metal
oxides have attracted much attention because of their unique
size‐ and dimensionality‐dependent physical and chemical
properties [30,31]. Cupric oxide (CuO) and cuprous oxide
(Cu2O) nanostructures are of particular interest because of
their interesting properties and promising applications, such as
in lithium‐ion batteries [32], catalysis [33,34] and CO oxidation
[35]. Therefore, copper‐based oxides with different valence
states might be efficient supports to catalyze the synthesis of
DEC in the gas phase, and studies using these material could
also assist in elucidating the active species.
2.2. Catalyst characterization
The composition and phase of each sample was identified by
powder X‐ray diffraction (XRD) with a D8 X‐ray diffractometer
(Bruker AXS, German) using Cu Kα radiation (λ = 1.5406 Å) at a
scanning rate of 2°/min from 2θ
=
10° to 80°.
Thermogravimetric analysis (TGA) of the samples was
performed using a Mettler TGA/SDTA 851E analyzer over the
temperature range 25 to 800 °C at a heating rate of 10 °C/min
under O2. The morphologies of products were examined by
scanning electron microscopy (SEM) with an S‐4800 (Hitachi,
Japan) scanning electron microscope at an accelerating voltage
of 2.0 kV. Inductively couple plasma (ICP) spectrometry using a
PE 5300DV was employed to determine the concentrations of
metallic palladium in the catalysts. X‐ray photoelectron
spectroscopy (XPS) was performed with a multifunctional
imaging electron spectrometer (Thermo ESCALAB 250XI) as a
means of analyzing the various metallic species and their
valence states.
In the present work, the goal was to synthesize DEC from
EtOH, CO and O2 in the gas phase over PdCl2‐loaded CuO and
Cu‐Cu2O prepared with different NaOH concentrations.
Unfortunately, the initial results did not identify the active
species for the synthesis of DEC. To further investigate such
species, PdCl2‐loaded Cu‐Cu2O catalysts having a variety of
Cu2O contents were investigated by tuning the glucose
concentration. By comparing the catalytic performances of
catalysts incorporating different copper species, the active
species involved in the gas phase synthesis of DEC were clearly
identified.
2.3. Catalytic performance measurements
Catalytic activities were measured with a computer‐
controlled continuous micro‐reactor system incorporating a
stainless steel tubular reactor with an inner diameter of 8 mm.
The reaction conditions were as follows: 3 mL catalyst, 0.1
mL/min liquid EtOH, 10 mL/min O2, 80 mL/min CO, 50
mL/min N2, reaction temperature of 150 °C and reaction
pressure of 0.64 MPa. The analytical methods used during
these trials have been previously reported in detail [16,18].
2. Experimental
2.1. Catalyst preparation
Copper chloride (> 99%), sodium hydroxide (98%),
hexadecyl trimethyl ammonium bromide (> 99%), ethanol (>
99%), PdCl2 (> 99%) were obtained from Sinopharm Chemical
Reagent Co, Ltd, China.
CuO and Cu‐Cu2O nanoparticles were prepared by
hydrothermal synthesis based on literature methods [36,37]. In
a typical synthesis, 20 mL of a 1 mol/L CuCl2·2H2O solution was
added dropwise into 80 mL NaOH and stirred vigorously at 50
°C. Subsequently, 40 mL CTAB (0.25 mol/L) was added and the
3. Results and discussion
The catalytic performances during the oxidative
carbonylation of EtOH with CO and O2 over PdCl2/CuO and
PdCl2/Cu‐Cu2O catalysts prepared with different NaOH
concentrations (2.5, 5 or 10 mol/L) are summarized in Table 1.
From these data, it is evident that the product of the catalytic
reaction was primarily DEC, together with lesser amounts of

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Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
Table 1
The catalytic performances of PdCl2/CuO and PdCl2/Cu‐Cu2O catalysts
synthesized using various NaOH concentrations.
(1)
(2)
NaOH
Conversion
STY of
DEC
Selectivity (%)
DEC AH EA
Catalyst
concentration of EtOH
(mol/L)
(3)
(%)
3.0
4.5
2.7
4.5
6.5
3.2
(mg∙g−1∙h−1)
63.2
PdCl2/CuO
2.5
5
10
2.5
5
90.8 6.2 3.0
92.1 5.2 2.7
91.4 6.5 2.1
94.2 3.8 2.0
93.8 2.2 4.0
91.9 6.1 2.0
91.7
53.8
93.7
133.9
65.1
(4)
(5)
PdCl2/Cu‐Cu2O
10
Reaction conditions: 150 °C, 0.64 MPa, O2 10 mL/min, CO 80 mL/min,
N2 50 mL/min.
(6)
100 200 300 400 500 600 700 800
acetaldehyde (AH) and ethyl acetate (EA). In comparison with
other NaOH concentrations, the catalysts prepared with 5
mol/L NaOH showed better catalytic performances. Neupane et
al. [36] pointed out that the use of a strong base in the
precipitation reaction played a vital role during the catalyst of
synthesis. Both low and high NaOH concentrations could lead
to free electrons on the surfaces of the CuO and Cu‐Cu2O,
possibly resulting in some powder agglomeration and partial
coverage of the active sites. In addition, at the same NaOH
concentration, the PdCl2/Cu‐Cu2O exhibits better catalytic
performance than the PdCl2/CuO. As previously reported [8], in
the case of Pd(II)‐Cu(II) (PdCl2/CuO) catalysts, an induction
period during which Pd(II) is reduced to Pd(0) is required prior
to electron transfer between Pd and Cu, which might slow the
catalytic reaction. Thus the presence of either Cu0 or Cu+ is
beneficial with regard to improving the catalytic performance.
The phase compositions and structures of the catalysts were
evaluated by XRD, with the results shown in Fig. 1. In Fig. 1(a),
the diffraction peaks seen in the XRD patterns can be ascribed
Temperature (oC)
Fig. 2. TG patterns of PdCl2/CuO (1‒3) and PdCl2/Cu‐Cu2O (4‒6)
catalysts synthesizing using different NaOH concentrations. (1, 4) 2.5
mol/L; (2, 5) 5 mol/L; (3, 6) 10 mol/L.
42.30°, 61.34° and 73.53° and these are assigned to the (111),
(200), (220) and (311) reflections of cubic Cu2O (JCPDS
05‐0667). Even when employing different NaOH
concentrations, the PdCl2/CuO catalysts exhibit similar XRD
patterns, as do the PdCl2/Cu‐Cu2O materials, suggesting that
the same crystal structures are present, with major crystal
planes diffracting at essentially the same 2θ angles.
To assess the thermal stability of the catalysts throughout
the reaction, TG analysis was performed under O2 and the
resulting data are summarized in Fig. 2. It is evident that there
were no mass changes associated with any temperature for the
PdCl2/CuO catalysts, while the PdCl2/Cu‐Cu2O catalysts exhibit
obvious mass increases beginning at 500 °C. Combined with the
XRD analysis, these results indicated that the former materials
were composed of pure CuO while the latter were a
combination of Cu and Cu2O.
–
to pure CuO, and the principal peaks are indexed to the (111),
–
(111) and (202) reflections, corresponding to the crystal
structure of CuO (JCPDS 48‐1548). In Fig. 1(b), prominent
peaks appear at 43.30°, 50.43° and 74.13° corresponding,
respectively, to the (111), (200) and (220) reflections of cubic
Cu (JCPDS 04‐0836). Weaker features are also seen at 36.42°,
The morphologies of the catalysts were observed by means
of SEM and EDS, and the results are shown in Fig. 3. These
images demonstrated that CuO nanorods with rectangular
CuO
(b)
◆ Cu
★ Cu2O
(a)
◆
◆
★
◆
★
★
(1)
(2)
(3)
★
(1)
(2)
(3)
10
20
30
40
2/( o )
50
60
70
80
10
20
30
40
2/(o )
50
60
70
80
Fig. 1. XRD patterns of PdCl2/CuO (a) and PdCl2/Cu‐Cu2O (b) catalysts synthesized using various NaOH concentrations. (1) 2.5 mol/L; (2) 5 mol/L; (3)
10 mol/L.

Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
2039
(b)
(a)
(d)
(c)
2 µm
2 µm
2 µm
(e)
(f)
10 µm
10 µm
10 µm
Fig. 3. SEM images of PdCl2/CuO (a‒c) and PdCl2/Cu‐Cu2O (d‒f) catalysts synthesized at various NaOH concentrations. (a, d) 2.5 mol/L; (b, e) 5 mol/L;
(c, f) 10 mol/L.
sections (a‒c) were present in the PdCl2/CuO catalysts, while
the PdCl2/Cu‐Cu2O catalysts show sphere‐like morphologies
that might allow greater contact areas during the catalytic
reaction. This result suggests one factor affecting the catalytic
performance. In conclusion, the PdCl2/Cu‐Cu2O exhibited better
catalytic performance than the PdCl2/CuO series of catalysts
when the synthesis parameters were identical. It has been
reported that copper atoms form the main active site during
the synthesis of DEC by oxidative carbonylation of EtOH in the
gas phase [38‒40], although PdCl2 also plays an important role
such that its presence can improve the space time yield (STY)
of DEC by a factor of three compared with catalysts without
PdCl2 [12]. For this reason, ICP analyses were performed to
assess the PdCl2‐loadings. The resulting data showed that the
PdCl2/CuO and PdCl2/Cu‐Cu2O catalysts both had similar PdCl2
concentrations, at 0.15% and 0.16%, respectively.
Based on the above analysis, it was concluded that the
PdCl2/Cu‐Cu2O catalyst exhibited better catalytic performance
than the PdCl2/CuO, although the main factors responsible for
the differing catalytic performance between Cu0 and Cu+
remained unknown. Therefore, catalysts with different Cu0 and
Cu+ contents were prepared for comparison purposes by
varying the glucose concentration applied during synthesis.
The catalytic performances over the PdCl2/Cu‐Cu2O catalysts
are summarized in Table 2. From these data, it is evident that
the PdCl2/Cu‐Cu2O prepared with 10 mmol glucose showed
high catalytic performance. The STY for DEC obtained with this
material was 151.9 mg·g−1·h−1, corresponding to an EtOH
conversion of 7.2% and DEC selectivity of 97.9% on an EtOH
basis. Additionally, it is worth noting that the selectivity for AH
based on EtOH increased with the amount of glucose added.
Cu0 is the main active center during the synthesis of AH, and so
these results could imply that the catalyst prepared with 10
mmol glucose had less Cu0. Ding et al. [25] has reported that a
higher ratio of Cu+ can reduce the Pd2+ concentration and limit
the CO oxidation side reaction, thus increased the DEC
selectivity. This could explain the higher catalytic performance
of the PdCl2/Cu‐Cu2O catalyst, which had
a greater
concentration of Cu+ species. From the above results, it can be
concluded that the active species in the synthesis of DEC is Cu+.
Figure 4 displays the XRD patterns of the PdCl2/Cu‐Cu2O
catalysts. It is well known that glucose is a strong reducing
agent, and so Cu2O can be expected to be further reduced to Cu
in the presence of an excess of glucose, such that a two phase
composition is produced. The diffraction peaks at 2θ values of
43.30°, 50.43° and 74.13° be assigned to Cu(111), (200) and
◆ Cu
★ Cu2O
★
◆
★
◆
★
★
◆
Table 2
Catalytic performances of PdCl2/Cu‐Cu2O catalysts synthesized with
varying concentrations of glucose (5 mol/L NaOH).
Selectivity (%)
Dosage of
glucose (mmol)
10
15
20
Conversion of STY of DEC
EtOH (%)
(mg∙g−1∙h−1)
DEC AH
97.9 0.7
96.5 1.2
93.8 2.2
EA
7.2
151.9
1.4
2.3
4.0
10
20
30
40 50
2/(o )
60
70
80
6.8
140.8
6.5
133.9
Fig. 4. XRD patterns of PdCl2/Cu‐Cu2O catalysts synthesized with
varying amounts of glucose. (1) 10 mmol; (2) 15 mmol; (3) 20 mmol.
Reaction conditions: 150 °C, 0.64 MPa, O2 10 mL/min, CO 80 mL/min,
N2 50 mL/min.

2040
Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
(a)
(d)
(1)
13.89%
(2)
10 µm
16.62%
(b)
(3)
23.14%
(e)
Cu(111)
d = 0.18 nm
10 µm
100 200 300 400 500 600 700 800
Temperature (oC)
Cu2O(111)
d = 0.24 nm
(c)
Fig. 5. TG data for PdCl2/Cu‐Cu2O catalysts synthesized with varying
amounts of glucose. (1) 10 mmol; (2) 15 mmol; (3) 20 mmol.
(220) (JCPDS 04‐0836). While the peaks at 36.42°, 42.30°,
61.34°, 73.53° and 77.32° are attributed to the (111), (200),
(220), (311) and (222) reflections of Cu2O (JCPDS 05‐0667),
respectively. The relative intensities of the Cu2O diffraction
peaks are seen to decrease with increasing glucose amounts,
indicating that the PdCl2/Cu‐Cu2O catalyst prepared with 10
mmol glucose contained more of the Cu2O, in accordance with
its improved catalytic performance (Table 2). That is to say, the
PdCl2/Cu‐Cu2O catalyst prepared with 10 mmol glucose had a
higher Cu2O content showed better catalytic performance.
Accordingly, Cu+ was the more active species in comparison
with Cu0.
The thermal stability of each PdCl2/Cu‐Cu2O catalyst was
assessed by TG between 25 and 800 °C in under O2, with the
results shown in Fig. 5. These data allowed the comparison of
experimental and theoretical mass gain rates, assuming that
the theoretical mass gain rates were limited by the amounts of
Cu and Cu2O, respectively. That is to say, supposing that the
catalyst was composed purely of Cu2O, the theoretical mass
gain rate can be calculated by the chemical equation 2Cu2O + O2
→4CuO with the same holding true for Cu, in which case the
equation is 2Cu+O2→2CuO. Theoretical weight gain rate of Cu
is 25.11% and that of Cu2O is 11.12%. If the theoretical mass
gain rate based on Cu2O is closer to the actual rate, this
suggests that the catalyst contained a greater proportion of
Cu2O. The PdCl2/Cu‐Cu2O catalyst prepared with 10 mmol
glucose had an experimental mass gain rate of 13.89% which
was closer to the calculated rate based on Cu2O of 11.12%,
compared with the other catalysts. Thus, the PdCl2/Cu‐Cu2O
catalyst prepared with 10 mmol glucose had more Cu2O, which
resulted in better catalytic performance, as further confirmed
by the XRD analysis.
10 µm
Fig. 6. SEM images of PdCl2/Cu‐Cu2O catalysts synthesized with varying
amounts of glucose. (a) 10 mmol; (b) 15 mmol; (c) 20 mmol. TEM (d)
and HRTEM (e) images of the PdCl2/Cu‐Cu2O catalyst synthesized using
10 mmol glucose.
that the plane spacings of 0.24 and 0.18 nm correspond to the d
spacings of Cu2O(111) and Cu(111), respectively.
The entire XPS spectrum of the PdCl2/Cu‐Cu2O catalyst
made with 10 mmol glucose is shown in Fig. 7(a), in which both
Cu 2p and O 1s peaks are observed. Fig. 7(b) shows a high
resolution view that emphasizes the main Cu 2p3/2 and Cu 2p1/2
peaks of the catalyst. The broad Cu 2p3/2 peak has been divided
into two peaks, attributed to Cu [41] and Cu2O [42],
respectively. It has been reported that PdCl2 plays an important
role in catalytic reactions [12], although a metallic Pd peak is
not clearly observed in Fig. 7(a) because of the low PdCl2
concentration in the catalyst. Hence, high resolution XPS
spectra of the Pd 3d (Fig. 7(d)) and Cl 2p (Fig. 7(e)) regions of
the catalyst are presented to illustrate the presence of PdCl2.
4. Conclusions
Both CuO and Cu‐Cu2O nanoparticles were successfully
synthesized by
a
simple hydrothermal method and
subsequently used as supports to prepare catalysts for the gas
phase synthesis of DEC. The results of this work show that
catalysts prepared with 5 mol/L NaOH exhibit better catalytic
performances because of their low extent of powder
agglomeration. It is noteworthy that the PdCl2/Cu‐Cu2O
showed better catalytic performance than PdCl2/CuO made at
the same NaOH concentration. In Pd(II)‐Cu(II) (PdCl2/CuO)
catalysts, there is an induction period, during which Pd(II) is
reduced to Pd(0), that must occur prior to electron transfer
between Pd and Cu, and this can slow the catalytic reaction. To
further pinpoint the active species, PdCl2/Cu‐Cu2O catalysts
with different Cu2O contents were prepared by controlling the
dosages of glucose. XRD, TG and catalytic performance data all
SEM images (Fig. 6(a−c)) of PdCl2/Cu‐Cu2O catalysts made
with varying amounts of glucose were acquired, and all the
catalysts displayed
a
sphere‐like morphology. The
low‐magnification TEM image in Fig. 6(d) shows the
morphology of PdCl2/Cu‐Cu2O nanoparticles generated using
10 mmol glucose. Fig. 6(e) is a high‐resolution TEM (HRTEM)
image taken from the red sphere region in Fig. 6(d), showing

Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
2041
Cu 2p
Cu 2p3/2
(b)
(a)
Cu
Cu2O
Cu 2p3/2
940 938 936 934 932 930 928 926
Binding energy (eV)
O 1s
Cu 2p1/2
C 1s
1000
800
600
400
200
960
955
950
945
940
935
930
Binding energy (eV)
Binding energy (eV)
Pd 3d (d)
(c)
(e)
Cl 2p
O 1s
545
540
535
530
345
340
335
330
210
205
200
195
Binding energy (eV)
Binding energy (eV)
Binding energy (eV)
Fig. 7. (a) The complete XPS spectrum and the high‐resolution XPS spectra for the (b) Cu 2p, (c) O 1s, (d) Pd 3d and (e) Cl 2p regions for
PdCl2/Cu‐Cu2O catalysts made with 10 mmol glucose.
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indicate that the PdCl2/Cu‐Cu2O catalyst prepared with 10
mmol glucose had more Cu+ and also showed better catalytic
performance. The selectivity for DEC based on EtOH reached
97.9%, together with an EtOH conversion value of
approximately 7.2% and a STY for DEC of 151.9 mg∙g–1∙h–1. The
higher concentration of Cu+ in the PdCl2/Cu‐Cu2O catalyst
evidently lowered the Pd2+ concentration and limited the CO
oxidation side reaction, thus DEC selectivity was increased and
catalytic performance was enhanced. From the above results, it
can be concluded that the active species in the synthesis of DEC
is Cu+. However, it would still be beneficial to study PdCl2/Cu2O
catalysts without Cu in the future to obtain a more complete
understanding of this catalyst system.
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2042
Pingbo Zhang et al. / Chinese Journal of Catalysis 36 (2015) 2036–2043
Graphical Abstract
Chin. J. Catal., 2013, 34: 2036–2043 10.1016/S1872‐2067(15)60973‐1
Catalytic synthesis of diethyl carbonate with supported
Pd‐Cu bimetallic nanoparticle catalysts: Cu(I) as the active
species
PdCl2/CuO catalyst
Pingbo Zhang, Yan Zhou, Mingming Fan*, Pingping Jiang
Jiangnan University
STY of DEC = 91.7 mg·g-1·h-1
O
CH3–CH2–OH + CO + O2
CH3
O
O
CH3
STY of DEC = 151.9 mg·g-1·h-1
The catalytic performances of PdCl2/Cu‐Cu2O materials were
found to be superior to those of CuO catalysts. The primary
reason is believed to be that Cu+ promotes electron transfer
between Pd and Cu without the requirement for an induction
period, which could potentially enhance the catalytic reaction.
PdCl2/Cu-CuO catalyst
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Page numbers refer to the contents in the print version, which include
both the English version and extended Chinese abstract of the paper. The
online version only has the English version. The pages with the extended
Chinese abstract are only available in the print version.