Promotional effect of copper(ii) on an activated carbon supported low content bimetallic gold-cesium(i) catalyst in acetylene hydrochlorination

Article abstract of DOI:10.1039/c5ra22807g

The synthesis of a vinyl chloride monomer (VCM) from acetylene hydrochlorination is a highly attractive coal-based route using mercury chloride (HgCl₂) as the catalyst. On reducing the use of mercury and with increasing concerns about environmental issues, searching for alternative catalysts has gained interest in recent years. However, to achieve high yield and stability using a mercury-free catalyst in this reaction is a substantial challenge. We approach this question by probing a Cu-added AuCs/AC catalyst working as a highly active, stable and cost-effective catalyst for this reaction. Introducing Cu into the catalyst significantly increased the activity and stability compared to a bicomponent AuCs/AC catalyst, underscoring a remarkable synergistic effect of the three metals. The particularly remarkable enhancement of activity was observed for the catalyst with a Au/Cu/Cs weight ratio of 1: 1: 4 (Au = 0.25 wt%), which provided a high turnover frequency of 73.8 min^-1 based on Au. Further experiments showed that the AuCuCs/AC catalyst delivered a stable performance during a 600 h test with the conversion of acetylene maintaining more than 98.8% at a C₂H₂ gas hourly space velocity of 50 h^-1 and the estimated lifetime exceeding 6540 h. After a careful characterization of the AuCuCs/AC catalyst and additional catalytic tests, we concluded that the observed enhanced catalytic performance could be associated with the enhanced dispersion of Au particles, the stabilization of Au in the state of Au³⁺ and facile substrate C₂H₂ molecule desorption. Compared with the commercial high content HgCl₂ catalyst (Hg = 12 wt%), this low content AuCuCs/AC catalyst (Au = 0.25 wt%) has similar activity, higher stability, relative low cost and environmental friendliness, meaning it has potential as an alternative to the HgCl₂ catalyst for commercial production of VCM.

Full text of DOI:10.1039/c5ra22807g

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PAPER
Promotional effect of copper(II) on an activated
carbon supported low content bimetallic gold–
cesium(I) catalyst in acetylene hydrochlorination
Cite this: RSC Adv., 2015, 5, 101427
Jia Zhao,a Shanchuan Gu,a Xiaolong Xu,a Tongtong Zhang,a Xiaoxia Di,a Zhiyan Panb
a
*
and Xiaonian Li
The synthesis of a vinyl chloride monomer (VCM) from acetylene hydrochlorination is a highly attractive
coal-based route using mercury chloride (HgCl2) as the catalyst. On reducing the use of mercury and
with increasing concerns about environmental issues, searching for alternative catalysts has gained
interest in recent years. However, to achieve high yield and stability using a mercury-free catalyst in this
reaction is a substantial challenge. We approach this question by probing a Cu-added AuCs/AC catalyst
working as a highly active, stable and cost-effective catalyst for this reaction. Introducing Cu into the
catalyst significantly increased the activity and stability compared to a bicomponent AuCs/AC catalyst,
underscoring
a remarkable synergistic effect of the three metals. The particularly remarkable
enhancement of activity was observed for the catalyst with a Au/Cu/Cs weight ratio of 1 : 1 : 4 (Au ¼
0.25 wt%), which provided a high turnover frequency of 73.8 minꢀ1 based on Au. Further experiments
showed that the AuCuCs/AC catalyst delivered a stable performance during a 600 h test with the
conversion of acetylene maintaining more than 98.8% at a C2H2 gas hourly space velocity of 50 hꢀ1 and
the estimated lifetime exceeding 6540 h. After a careful characterization of the AuCuCs/AC catalyst and
additional catalytic tests, we concluded that the observed enhanced catalytic performance could be
associated with the enhanced dispersion of Au particles, the stabilization of Au in the state of Au3+ and
facile substrate C2H2 molecule desorption. Compared with the commercial high content HgCl2 catalyst
(Hg ¼ 12 wt%), this low content AuCuCs/AC catalyst (Au ¼ 0.25 wt%) has similar activity, higher stability,
relative low cost and environmental friendliness, meaning it has potential as an alternative to the HgCl2
catalyst for commercial production of VCM.
Received 30th October 2015
Accepted 17th November 2015
DOI: 10.1039/c5ra22807g
www.rsc.org/advances
and stability for the hydrochlorination of acetylene is highly
desirable.
1. Introduction
Among the numerous metal chlorides including Au,4–10
The acetylene hydrochlorination reaction (C2H2 + HCl /
CH2]CHCl, DH ¼ ꢀ124.8 kJ molꢀ1) has received signicant
attention as an alternative route to the manufacture of vinyl
chloride monomers (VCM).1,2 Industrially, the hydro-
chlorination of acetylene is performed at temperatures
between 130 and 180 ꢁC over an activated carbon supported
mercuric chloride (HgCl2) catalyst.3 However, it suffers from
high toxicity and sublimation under the reaction conditions in
spite of the high conversion. This not only leads to deactiva-
tion of the catalyst, but also contaminates the product, and
may cause severe environmental problems and threats to
human health. From a sustainable point of view, the devel-
opment of efficient non-mercury catalysts with high activity
Pt,11,12 Pd,13,14 Ru,15–17 Cu,18,19 Bi20 etc., AuCl3 is widely used as
catalyst because of its high activity, but Au3+ is readily reduced
to Au0 under reaction conditions and consequently loses its
activity.21,22 Although its catalytic stability can be improved by
alloying with a second metal component such as LaCl3,23
CoCl3,24 NiCl2,25 BaCl2,26 CsCl27,28 or TiO2,29 this type of Au-based
catalysts still deactivates continuously with increasing time on
stream. Additionally, current state-of-the-art hydrochlorination
catalysts employ Au or Au-based catalysts with total Au loading
levels of 1.0 wt%, making the catalysts too expensive to use for
large scale production. Ru-based catalyst is a good candidate
due to its environmental friendship, cheapness, and high
activity.17 However, the abundance of Ru is about 0.001 ppm,
which is much smaller than that of other precious metals
(Fig. 1). It is worthwhile to note that we should keep in mind the
difference in their abundance and annual output when we
attempt to design such noble metal industrial catalysts. For
another, non-precious metals catalysts (e.g., BiCl3 (ref. 20) or
aIndustrial Catalysis Institute of Zhejiang University of Technology, State Key
Laboratory Breeding Base of Green Chemistry-Synthesis Technology, Hangzhou,
310014, P.R. China. E-mail: xnli@zjut.edu.cn; Tel: +86 571 88320002
bDepartment of Environmental Engineering, Zhejiang University of Technology,
Hangzhou, 310014, P.R. China
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stability which make it possible to be widely applied in indus-
trial hydrochlorination of acetylene.
2. Experimental
2.1. Catalyst preparation
A commercially activated carbon (AC) NORIT ROX 0.8 (pellets of
0.8 mm diameter and 5 mm length) was selected for the prep-
aration of supports. The activated carbon was rst pretreated
with HNO3 (65 wt%) at room temperature for 1 h to remove Na,
Fe, and Al contaminants.6 The pretreated activated carbon was
ltered, washed with deionized water until pH ¼ 7 and then
dried at 110 ꢁC for 12 h.
Fig. 1 Crustal abundance and annual output of the metals that are
used for constructing acetylene hydrochlorination catalysts.
Trimetallic AuCuCs/AC catalysts were prepared using incip-
ient wetness impregnation (IWI) technique. The catalyst
precursors containing HAuCl4$4H2O, CuCl2$2H2O and CsCl
were weighted separately ca. 0.25, 0.25 wt% and 1.00 wt% to the
mass of AC and then dissolved in aqua regia solution. Aer the
solution was homogeneously mixed, the pretreated AC support
was then added into the solution with continuous stirring. Then
the system was aged at 40 ꢁC for 4 h, followed by drying at 110 ꢁC
for 12 h for use. The same procedure was also followed to
prepare the corresponding Au/AC (0.25 wt% Au), AuCu/AC (0.25
wt% Au and 0.25 wt% Cu), AuCs/AC (0.25 wt% Au and 1.00 wt%
Cs), Cu/AC (1.00 wt% Cu), and Cs/AC (1.00 wt% Cs) catalysts for
comparison.
SnCl2 (ref. 30)) with low cost also suffer the twin disadvantages
of poor activity and fast deactivation, leading to limited
production capacity and difficult purication. In addition, N-doped
carbon materials are also known to catalyse this reaction.31–35
However, low conversion efficiency and high energy demand
preclude the wider commercial applicability of these catalysts.
As reported previously, with N-doped carbon materials no
complete conversion could be achieved, which are far from the
satisfactory level. Thus, Au-catalyzed hydrochlorination reac-
tion is still recognized as the most promising acetylene hydro-
chlorination technology currently, provided that the Au-based
catalysts used are sufficiently stable and cheap.
2.2. Catalyst characterization
Extensive efforts have been made to reduce the Au loading
and further improve the activity and stability of Au-based cata-
lysts. For example, it demonstrated that the addition of CuCl2
(ref. 36) or BiCl3 (ref. 37) to Au can reduce the Au loading down
to 0.5 wt% and 0.3 wt%, respectively. Although signicant
improvement has been achieved, it is still a signicant chal-
lenge to maintain or improve catalyst activity and stability when
the Au catalyst loading is reduced or eliminated. In our recent
study, 1Au–4Cs/AC catalyst demonstrates considerably higher
catalytic activity and stability than monometallic Au-based
catalyst.27 The issue facing Au-based hydrochlorination cata-
lysts is typically to create and maintain the oxidation state of the
AuCl3 species during preparation and reaction. Most impor-
tantly, the ability of CuCl2 to stabilize the cationic Au(III) in
many gold(III)–CuCl2 catalyst systems (e.g., AuCl3–CuCl2) has
been reported before.38–43 Inspired by the ndings in literatures
mentioned above, we proceeded to modify this catalyst herein
by the addition of controlled amounts of Cu (0.25 wt%) to a low
content AuCs/AC catalyst (Au ¼ 0.25 wt%) and evaluate the
properties of AuCuCs/AC material by several characterisation
techniques (TEM, XRD, H2-TPR, ICP-MS, TPD, TPO, TGA and
FTIR) comparing to monometallic Au/AC and bimetallic AuCs/
AC catalysts as reference. We originally demonstrate that the
trimetallic AuCuCs/AC catalyst preserves a high turnover
frequency of 73.8 minꢀ1 based on Au, and an estimated lifetime
exceeding 6540 h with the conversion of acetylene and the
selectivity of vinyl chloride reaching more than 98.1% and
99.9%, respectively. This catalyst has the advantages of low cost
of preparation and use, high catalytic activity and excellent
The textural properties of the prepared Au-based catalysts were
obtained from the N2 adsorption–desorption isotherms at ꢀ196
ꢁC measured with a Micromeritics ASAP 2020 apparatus. Prior
to the measurements, samples were outgassed at 100 ꢁC and
10ꢀ4 mbar overnight. Surface areas were determined by using
the Brunauer–Emmet–Teller (BET) equation and a nitrogen
˚
molecule cross section of 16.2 A. The total pore volume was
calculated from the adsorption isotherm at P/P0 ¼ 0.95.
XRD measurements of the catalyst samples were performed
on a PANalytical-X0Pert PRO generator with Cu Ka radiation (l ¼
0.1541 nm) that was operated at 60 kV and 55 mA. Dꢀiff1 raction
patterns were recorded at a scanning rate of 2ꢁ min and at
a step of 0.02ꢁ.
TEM analysis was conducted using a transmission electron
microscope (TEM, Tecnai G2 F30 S-Twin), operating at an
acceleration voltage of 300 keV. The solid samples were nely
ground. The resultant ne powders were dispersed ultrasoni-
cally in the ethanol and then two drops of the solution were
transferred to a carbon/Ni grid (Beijing Zhongjingkeyi Tech-
nology Co., Ltd). Grids were allowed to dry before TEM char-
acterization. The sizes of particles on samples were also
observed by a transmission electron microscope. The number
weighted average Au diameter (dTEM) was determined from
a count of 300 nanoparticles (NPs).
TPD experiments were performed in a tubular quartz reactor.
The samples (100 mg) were rst treated in situ at 180 ꢁC for 0.5 h
using pure C2H2 and then the sample was swept with pure Ar at
a ow rate of 30 mL minꢀ1 for 1 h to remove physisorbed and/or
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weakly bound species. TPD was performed by heating the the carbon balance values based on these products are above
sample from room temperature to 850 ꢁC at a ramp rate of 10 ꢁC 95%.The conversion of acetylene and the selectivity to VCM
minꢀ1 in pure Ar, and the TPD spectra were recorded by were calculated by eqn (1) and (2), as follows:
ꢀ
ꢁ
a quadrupole mass spectrometer (QMS 200 Omnistar).
FA
Acetylene conversionð%Þ ¼ 1 ꢀ
ꢂ 100%
(1)
(2)
H2-TPR experiments were performed in the same apparatus
as the TPD experiments. The weight of the tested samples was
75 mg. The temperature was linearly increased from 30 to 850
ꢁC at a rate of 10 ꢁC minꢀ1. The hydrogen consumption was
measured using a thermal conductivity detector (TCD).
FA0
FVCM
VCM selectivityð%Þ ¼
1 ꢀ FA
ꢂ 100%
where FA0, FA, and FVCM represents the volume fraction of
acetylene in the raw gas, the volume fraction of remaining
acetylene, and the volume fraction of vinyl chloride in the
product mixture gas, respectively.
TPO experiments were also performed in the same apparatus
as the TPR experiments. Each sample (100 mg) was previously
heated in Ar ow at 200 ꢁC for 1 h to remove the volatile
compounds and cooled to room temperature in the same ow of
Ar. Then the gas ow was switched to 5% O2/Ar and the
ꢀ1
ꢁ
ꢁ
temperature was raised to 850 C at a rate of 10 C min
.
3. Results and discussion
3.1. Catalytic activity of trimetallic AuCuCs/AC catalyst
A thermogravimetric analysis (TGA) of the samples was performed
using a NETZSCH STA 449 F3 Jupiter thermogravimetric-differential
scanning calorimetry (TG-DSC) simultaneous thermal analyzer
in an air atmosphere at a ow rate of 30 mL minꢀ1. The
Table 1 compared the catalytic performances of the different
Au-based catalysts as well as Cu/AC and Cs/AC for acetylene
hydrochlorination under the same reaction conditions. The Cu/
AC catalyst gave rather low but stable activity with only 8.6%
C2H2 conversion and more than 99.9% VCM selectivity in 24 h.
Controlled tests of the Cs/AC catalyst showed that only a small
amount of VCM is observed in the gas phase (<6.0% based on
C2H2). Hydrochlorination of acetylene over 1Au/AC catalyst
provided high activity with an initial conversion of 72.4%. It
should be note that the C2H2 conversion on pure AC support
was below 5%. The activity of the activated carbon can arise
from the presence of trace amounts of K+ and Al3+ in the carbon
matrix, as these metals can display some activity to the hydro-
chlorination reaction of acetylene.8
ꢁ
temperature was increased from 30 to 850 C at a rate of 10 ꢁC
minꢀ1
.
2.3. Gas phase hydrochlorination of acetylene
Catalysts were tested for acetylene hydrochlorination in
a xed-bed glass micro-reactor (i.d. 10 mm). Acetylene (5.0 mL
minꢀ1, 1 bar) and hydrogen chloride (6.0 mL minꢀ1, 1 bar)
were fed though a mixing vessel via calibrated mass ow
controllers to a heated glass reactor containing catalyst (200 mg)
with a total GHSV (C2H2) of 740 hꢀ1. The long-term stability
experiment was performed in the same apparatus with acety-
lene (24.3 mL minꢀ1, 1 bar) and hydrogen chloride (29.2 mL
minꢀ1, 1 bar) fed though a mixing vessel via calibrated mass
ow controllers to a heated glass reactor containing the catalyst
(1.0 g) with a total GHSV (C2H2) of 720 hꢀ1. A reaction
It has been reported that 1.00 wt% Au loading was an
appropriated compromise for Au/Carbon catalyst.5–7,36 However,
with such an amount of Au loading, Au/AC still deactivated
continuously from 72.4% to 57.7% with about 14.7% C2H2
conversion loss aer 24 h. The observation was in line with
ꢁ
temperature of 180 C was chosen. Blank tests using an empty
reactor lled with quartz wool did not reveal any catalytic
activity, and quartz sand was used to extend the bed length,
above and below the catalyst itself, separated by quartz wool.
The gas phase products were passed through an absorption
bottle containing NaOH solution to remove excess HCl rst and
then analyzed on-line by GC equipped with a ame ionization
detector (FID). Chromatographic separation and identication
of the products was carried out using a Porapak N packed
column.
The composition of the reactor outow (dissolve in the N- 1Cu/AC
methylpyrrolidone solution) was determined using a Waters
GCT Premier chromatograph equipped with a HP-5 capillary
column.44 Product mass fractions were obtained using an
internal standard. The main product of acetylene hydro-
chlorination was vinyl chloride, a small amount of the by- AuCuCs/AC 0.25 wt% Au 84.1
products 1,1-dichloroethane and 1,2-dichlorethane were also
produced. The gas-phase products of acetylene hydro-
chlorination were quantied using the peak area normalization
method. Given that hydrogen chloride is absorbed by the
absorption liquid aer the reaction, the volume of the reaction
system can be considered constant during the calculations, and
Table 1 Screening of non-mercury catalyst active componentsa
C2H2
VCM
Chemical
composition
conversion selectivity Deactivation
Catalyst
(%)
(%)
rateb (% hꢀ1
)
1Au/AC
Au/AC
1.00 wt% Au
0.25 wt% Au
1.00 wt% Cu
1.00 wt% Cs
0.25 wt% Au
0.25 wt% Cu
0.25 wt% Au
1.00 wt% Cs
72.4
13.9
8.6
5.2
57.9
>99.9
>99.9
>99.9
99.7
0.61
0.24
—
—
1.6
1Cs/AC
AuCu/AC
99.8
AuCs/AC
42.2
>99.9
>99.9
0.19
0.17
0.25 wt% Cu
1.00 wt% Cs
a
Reaction conditions: T ¼ 180 ꢁC, V(HCl)/V(C2H2) ¼ 1.2 : 1, GHSV ¼ 740 hꢀ1
,
t ¼ 24 h. b Deactivation rate was dened as (the initial maximum C2H2
conversion – the nal C2H2 conversion)/(deactivation period, h),
deactivation period ¼ 24 h.
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previous studies.23–29,36,37 However, when Au loading decreased
from 1.00 wt% to 0.25 wt%, the conversion shapely decreased
from 72.4% to less than 14.0%, indicating that high conversions
required high Au loading, as reported before.37 For the bime-
tallic AuCs/AC catalyst, the C2H2 conversion increases to
approximately 42.2%, which represents a signicant improve-
ment compared with the Au/AC catalyst.
Table 1 showed that the activity can be further enhanced
by adding Cu species to the bimetallic AuCs/AC catalyst.
Indeed, AuCuCs/AC exhibited a much higher activity (84.1%)
compared to monometallic Au/AC and bimetallic AuCs/AC
and also delivered a fairly stable catalytic performance for
more than 24 h. A comparable experiment with AuCu/AC
catalyst revealed high catalytic activity (57.9%) and selectivity
(>99.9%), but this enhancement was lost rapidly, demon-
strating that the coexistence of Cu and Cs species is essential
for the observed catalyst modication effects for an active low
content Au-based catalyst.
To prove the outstanding performance of this catalyst
system, the AuCuCs/AC catalyst was compared with a wide
range of other catalyst materials reported in literature (note that
the experimental conditions are not necessarily identical),
including ones based on different monometallic catalysts as
well as bimetallic and trimetallic Au-based catalysts, and the
result is shown in Fig. 2. It is clear the AuCuCs/AC catalyst is
one of the best catalysts reported in terms of offering a high
TOF (73.8 minꢀ1) at a relatively high GHSV. To the best of our
knowledge, this value is much higher than those reported
previously for the state-of-the-art Au catalyst (max TOF ¼ 49.3
minꢀ1, all TOF values were calculated with respect to the total
Au content of the catalyst), further highlighting the excellent
catalytic performance of the AuCuCs/AC catalyst.
Fig. 3 Catalytic performance of AuCuCs/AC with different Au/Cu
weight ratio. Reaction conditions: T ¼ 180 ꢁC, V(HCl)/V(C2H2) ¼ 1.2 : 1,
GHSV ¼ 740 hꢀ1
.
formulation. Thus, based on the results of our catalysis exper-
iments, it is clear that a Au/Cu ratio of 1 : 1 was considered
optimized in terms of catalytic activity, selectivity and stability.
To evaluate whether there was also a chemical effect of Cu and
Cs on the structure of Au which may responsible for the improved
catalyst performance, four different synthesis routes of Au–Cu–Cs
series catalysts were investigated (Fig. 4a). All four catalysts con-
tained equal amounts of Au (0.25 wt%), Cu (0.25 wt%) and Cs
(1.00 wt%) and evaluated under identical reaction conditions.
For the bimetallic AuCs/AC, the maximum acetylene conversion is
42.2% during a reaction time of 24 h. However, all trimetallic
In order to determine the optimized ratio of Au and Cu, the
ratio of Au/Cu was varied from 1 : 0.5 to 1 : 5 (weight ratio),
whilst maintaining a constant Au (0.25 wt%) and Cs (1.00 wt%)
loadings of the catalysts, as shown in Fig. 3. As the ratio of
Au/Cu increased from 1 : 0.5 to 1 : 3, the initial conversion
increased; as the ratio was further increased, there was little
increase in the conversion. Besides that, the catalysts having
higher Cu content show a signicant rate of deactivation. The
results of the present study demonstrated that the activity
and stability of Au-based catalyst are highly sensitive to their
Fig. 2 (a) The TOF value for the different catalysts: Au/AC,5 Pt/AC,45
Pd/AC,5 Ru/AC,15 Rh/AC,5 Ir/AC,45 Bi/AC,20 Ag/AC,5 Cu/AC,18 Cd/AC,5 Fig. 4 (a) Schematic diagrams four different routes to synthesize Au–
Zn/AC,5 and Hg/AC.5 (b) The TOF value for the Au-based catalysts: Cu–Cs/AC catalyst. (b) Catalytic performance of Au–Cu–Cs series
AuBa/AC,26 AuLa/AC,23 AuCo/AC,24 AuCuCo/AC,44 Au/Ni,25 AuCs/AC,28 catalysts prepared by different synthesis method. Reaction conditions:
AuTiO2/AC,29 AuInCs/AC,46 AuCuK/AC,47 AuBi/AC37 and AuCuCs/AC.
T ¼ 180 ꢁC, V(HCl)/V(C2H2) ¼ 1.2 : 1, GHSV ¼ 740 hꢀ1
.
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catalysts with the different synthesis method showed higher component during the reaction and carbon deposition. To gain
catalytic activity than the bimetallic AuCs/AC catalyst. These an insight into the cause of the performance improvement
results show that the presence of CuCl2 species promoted the observed we have analyzed the catalysts using STEM, XRD, ICP,
initial activity of the AuCs/AC catalyst. The highest activity was H2-TPR, BET, TPO and TPD analysis.
obtained on the catalyst named as AuCuCs/AC synthesized via
The TEM of fresh and used Au/AC, AuCs/AC and AuCuCs/AC
route 4 by co-impregnation of an aqueous solution of HAuCl4, catalysts was performed to evaluate possible sintering of NPs
CuCl2 and CsCl onto AC, with the initial conversions being 84.1%. aer the reaction. Fig. 6 shows exemplary TEM images of
Besides that, the AuCuCs/AC catalyst also displayed optimal selected Au-base catalysts. The small bright dots represent the
catalytic stability for the hydrochlorination reaction of acetylene metal NPs. As can be seen, the fresh Au/AC (Fig. 6a), AuCs/AC
with only 4.0% C2H2 conversion loss aer 24 h, as shown in (Fig. 6c) and AuCuCs/AC (Fig. 6e) catalysts are made up of
Fig. 4b. These results show that the different method can largely small metal NPs ranging from 1 to 8 nm in diameter, indicating
affect the catalytic performance of the trimetallic Au–Cu–Cs the particles are highly dispersed. However, monometallic Au/
series catalysts. We have observed that the optimal catalytic AC catalysts are not resistant to sintering and show a large
performance using the AuCuCs/AC catalyst only occurs when particle size distribution ranging from 2 to 12 nm in diameter
the metal precursor is co-impregnated onto AC. We originally aer reaction for 50 h (Fig. 6b). This indicates that the size
considered that the formation of trimetallic Au–Cu–Cs distribution for Au NPs in this sample is quite heterogeneous
complex structured during the preparation is essentially and that the agglomeration of Au occurs easily. In contrast,
responsible for the special catalytic behaviour of the sample. particles below 5 nm are dominant in used AuCs/AC catalyst,
However, we cannot provide direct evidence of this phenom- though some are found up to 6 nm in diameter (Fig. 6d). For the
enon currently, and further efforts for accurately character- sample using used AuCuCs/AC catalyst, most of the particles
ising the catalyst surface structure should be carried out.
had particle sizes below 4 nm, with a small fraction between
To further prove the outstanding performance of this catalyst 4 and 6 nm (Fig. 6f). The order of average particle was AuCuCs/
system, the AuCuCs/AC catalyst was compared with the most active
1Au/AC catalyst (1.00 wt% Au), as well as a commercial high
content 12Hg/AC catalyst (12.00 wt% Hg). Compared to the
commercial 12Hg/AC catalyst, AuCuCs/AC catalyst has a slightly
lower initial conversion, but the value is signicantly higher
than the 1Au/AC, as shown in Fig. 5. More importantly, the
AuCuCs/AC catalyst is also highly stable catalyst, in the gas
phase hydrochlorination of acetylene. For the 24 h running,
the values of acetylene conversion have dropped for all three
catalysts. However, the deactivation is the least severe for this
trimetallic AuCuCs/AC catalyst. The high activity together with
the extraordinary stability, support the possible applicability
of this catalyst in industry.
3.2. Characterization of AuCuCs/AC catalyst
It is known that Au-based hydrochlorination catalysts deactivate
due to sintering of the metal NPs, valence change of the active
Fig. 5 The comparison of the reactivity and stability of AuCuCs/AC, Fig. 6 Representative STEM images of (a) fresh Au/AC, (b) used Au/AC,
1Au/AC (Au ¼ 1.00 wt%) and 12Hg/AC (Hg ¼ 12.00 wt%) catalysts. (c) fresh AuCs/AC, (d) used AuCs/AC, (e) fresh AuCuCs/AC, and (f) used
Reaction conditions: T ¼ 180 ꢁC, V(HCl)/V(C2H2) ¼ 1.2 : 1, GHSV ¼ 740 hꢀ1
.
AuCuCs/AC, respectively.
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Table 2 Atomic compositions of Au-base catalysts derived from ICP
data
AC (4.0 nm) < AuCs/AC (4.6 nm) < Au/AC (6.8 nm). This is
indicative of the addition of Cs and Cu to the catalysts, so it can
effectively inhibit the catalyst sintering during the hydro-
chlorination reaction. It is well known that the particle size of
the active metal component of the catalyst has an important
inuence on the catalytic performance. For the hydro-
chlorination reaction of acetylene, catalytic activity was corre-
lated with Au content and the number of active sites. This is
because the activity was ascribed to Au3+ species at the perim-
eter of the Au NPs in contact with the support.48 AuCuCs/AC had
a stable conversion without signicant Au agglomeration
formation aer 24 h test, revealing the valuable improvement of
Au dispersion aer the introduction of Cu and Cs in Au/AC
catalyst.
Fig. 7 displays the XRD patterns of the fresh and used Au/AC,
AuCs/AC and AuCuCs/AC catalyst. The peak around 2q of 26ꢁ
corresponds to (002) planes of graphitized carbon from AC.
Apart from the amorphous diffraction peaks of the AC, no
discernible Au0 reection is detected in fresh Au-base catalysts.
This is indicative of extremely small Au-containing NPs on the
AC surface below the detection limit of this technique (smaller
than 4 nm) or most of the Au exists as non-crystalline Au3+
species.48 In the case of used Au/AC and AuCs/AC catalysts,
it shows diffraction peaks located at 2q values of 38.12ꢁ which
are assigned to Au (111) planes, indicating the big fraction of
Au3+ reduction to Au0 and/or a certain amount of catalyst sin-
tering. However, for used AuCuCs/AC catalyst, no sharp peaks
for Au0 can be observed, indicating that Au3+ NPs are still well
uniformly dispersed and their crystal size are very small, as
observed in the TEM images (Fig. 6f).
Fresh
Used
Au
Cu
Cs
Au
Cu
Cs
Catalysts
(wt%)
(wt%)
(wt%)
(wt%)
(wt%)
(wt%)
Au/AC
AuCs/AC
AuCuCs/AC
0.28
0.26
0.26
—
—
0.30
—
0.97
1.01
0.25
0.24
0.25
—
—
0.25
—
0.96
1.00
To check for exact loading amounts and thermal stability
of Au-based catalysts, ICP analysis was conducted and the
results are summarized in Table 2. As can be seen, the actual
content of Au, Cu and Cs element is almost identical to that of
the precursors. Due to the catalyst preparation procedure, no
ltrating of the carbon or catalyst washing was carried out. It
is reasonable that the metal loading is nearly equal to the
nominal amount of metal impregnated onto the support. For
Hg-based catalysts, it is apt to be reduced by acetylene and
sublimates during reaction, leading to deactivation of the
catalyst. However, Au-based catalysts are not particularly vola-
tile under the reaction conditions. And we did not observe
markedly loss of Au in this study, as previous studies reported,47
proving their good thermal stability.
Previous literature studies ascribed the activity of the Au-
based catalyst to the presence of Au3+ species, postulating
them to be active sites.5,7,8 In order to obtain a correlation on the
activity of VCM production with the amount of Au3+ species
clusters made on the catalyst surface, samples were carefully
analyzed by H2-TPR. Fig. 8 presents the H2-TPR proles of fresh
(Fig. 8a) and used (Fig. 8b) Au/AC, AuCu/AC, AuCu/AC, and
AuCuCs/AC catalysts. For all the catalysts, a distinguishable
hydrogen consumption peak in the range of 450–800 ꢁC can
be observed. This peak is a consequence of the reduction of
surface groups of activated carbon support.49,50 For all the Cu-
containing Au-based catalysts, the TPR prole shows a broad
ꢁ
band around 480 C, which corresponds to the reduction peaks
of the Cu2+ species. The analysis of Au/AC sample led to assign
the reduction band around 336 ꢁC to Au3+ to Au0. TPR proles of
the fresh AuCu/AC and AuCs/AC catalysts disclosed that the
CuCl2 and CsCl additives greatly affect the reducibility of Au3+
catalysts, a straightforward decrease of temperature in the
reduction band of Au3+ to 319 ꢁC and a straightforward increase
of temperature in the band of Au3+ to 350 ꢁC are observed,
respectively. These shis indicate strong interactions between Au
species and Cu2+ or Cs+ exist in AuCu/AC or AuCs/AC catalysts,
respectively. More specically, the reduction temperature of Au3+
may shi to lower or higher temperatures due to the presence of a
strong interaction between Au3+ and Cu2+ or Cs+ via the electron
transfer which in turn, facilitates or inhibits the reduction. In
fact, the Cu2+ species act as electron donors and transfer elec-
trons from Cu atom to the Au3+ species to facilitate electron
accumulation has been reported in many Au–Cu catalytic systems
before.43,44 This led to a easier reduction of active Au3+ species. In
contrast, the presence of Cs makes reducing Au3+ species the
Fig. 7 XRD patterns of fresh (a) and used (b) Au-based catalysts.
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estimations of ca. 12.1%, 32.0%, 33.9% and 47.1% for the
Au/AC, AuCu/AC, AuCs/AC and AuCuCs/AC catalysts,
respectively. As in the case of used Au-based catalysts, also
through comparing the TCD signals with a standard, this
allows an estimation of ca. 2.3%, 13.4%, 28.3% and 38.1%
for the used Au/AC, AuCu/AC, AuCs/AC and AuCuCs/AC
catalysts, respectively (Fig. 8c). This result showed that the
presence of Cu and Cs in the AuCuCs/AC catalyst efficiently
inhibited the reduction of Au3+, which can further stabilize
the catalytic active Au3+ species both in the preparation and
reaction process of AuCl3 catalysts. This result is consistent
with the higher activity and slower deactivation of the
AuCuCs/AC catalyst.
Previous studies have shown that the reduction of Au3+ to
Au0 is the main deactivation pathway at temperatures higher
ꢁ
than 120 C, while the deposition of coke/oligomers materials
on the catalyst is the predominant deactivation process occur-
ring at temperatures lower than 100 ꢁC.21 Recently, work by
Dai et al. indicated that coke/oligomers deposition is another
non-negligible reason for catalyst deactivation for the gas phase
hydrochlorination of acetylene even under the relative high
reaction temperatures (150–180 C).23–26,44 In general, the coke/
ꢁ
oligomers formation in hydrochlorination reaction includes
the adsorption of the hydrocarbons on the catalyst surface and
the spillovers of coke/oligomers species from the metal active
site to the support, which may result in covering some parts of
the active sites pore and clogging of the support and further
deactivation.
To provide direct evidence of coke/oligomers deposition,
N2 adsorption–desorption, TPO and TGA analysis were per-
formed. Table 3 shows the textural parameters of the
supports and the prepared Au-based catalysts. As expected,
no drastic changes in the textural properties of the materials
were observed. The slight decrease in AC surface area may be
caused by the phenomenon called the dilution effect, in
which the loading of the active component decreases the
ratio of the carriers in the catalysts. Aer the reaction, BET
analysis showed that the three catalysts' surface areas all
decreased, which may be caused by the coke/oligomers
deposition. The variation amplitude of the catalysts' SBET
follows the order: Au/AC (DSBET% ¼ 19.8%) > AuCs/AC
(DSBET% ¼ 9.8%) > AuCuCs/AC (DSBET% ¼ 3.0%). Thus, the
optimal AuCuCs/AC catalyst may have the least coke/
oligomers deposition and pore blocking compared to the
Fig. 8 H2-TPR patterns of fresh (a) and used (b) Au-based catalysts. (c)
The proportional content of Au3+ species for fresh and used Au-based
catalysts.
reduction temperature of Au3+ shows a slightly shi to a higher
temperature (356 ꢁC) as compared to the Au/AC sample. Such
a positive shi suggests that there are strong interactions
between the three components within the catalyst, and it is
reasonable to change the electronic structure of Au. However, the
presence of the Au–Cu–Cs complex or alloy cannot be excluded
for the AuCuCs/AC catalyst, which may inhibit the reduction
of Au3+ and increase the stability of the catalytically active
Au3+ species. Through comparing the TCD signals with
standard signals, the fractions of different Au species in
the fresh catalysts can be estimated (Fig. 8c). This allows
Table 3 Textural properties of the AC and the prepared Au-based
catalysts
Total pore volume
SBET (m2 gꢀ1
)
(cm3 gꢀ1
)
Sample
Fresh
Used
Fresh
Used
AC
Au/AC
AuCs/AC
AuCuCs/AC
1162
1139
1113
1016
—
0.63
0.64
0.62
0.58
—
913
1004
986
0.49
0.57
0.56
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Fig. 10 TPD profiles of acetylene on different Au-based catalysts.
Fig. 9 TPO spectra of the used Au/AC, AuCs/AC and AuCsCu/AC
catalysts.
The rst weak desorption peak covers the temperature range
of 50–180 ꢁC and corresponds to the acetylene desorption
from the support, which is consistent with our previous
report. For Au/AC, there is a obvious desorption peaks can be
observed higher than 180 ꢁC, suggesting that Au3+ species
favor the adsorption of C2H2. The desorption area of acetylene
of the bimetallic catalysts AuCs/AC is larger than that of
Au/AC catalysts. Furthermore, the desorption area of acety-
lene was further increased when both Cu and Cs was added to
the Au/AC catalysts, which is signicantly larger than that of
either of the monometallic and bimetallic catalysts, indi-
cating that addition of Cs and/or Cu improves the amounts
of active sites of the Au-based catalyst, which agrees well
with the activity sequence displayed in Table 1. Besides that,
by adding Cs and Cu species, the desorption temperature
of C2H2 shis to a lower temperature for AuCs/AC sample
(201 ꢁC) and AuCuCs/AC sample (179 ꢁC), respectively,
compared to the Au/AC sample (249 ꢁC). The shis in the
Au3+ peak to lower temperatures may be attributed to the
electronic modications on Au by Cs and Cu in trimetallic
catalysts. The presence of strong interactions between Au,
Cu and Cs is thus conrmed. Hence, the promotion of the
C2H2 activation should be one reason for the outstanding
catalytic performance of AuCuCs/AC catalyst for acetylene
hydrochlorination.
AuCs/AC and Au/AC catalysts. Therefore, AuCuCs/AC had
a better anti-coke ability.
TPO spectra of the used Au/AC, AuCs/AC and AuCuCs/AC
catalysts are presented in Fig. 9. It is not possible to apply
TPO analysis to identify the chemical nature of the coke/
oligomers species; however, we may use it to indicate where
the resulting coke/oligomers formed.51 According to Fig. 9, no
discernible oxygen consumption peak is detected in the
temperature region below 400 ꢁC in AC support. However, aer
the reaction, a distinct peak at around 200–350 ꢁC appeared for
the Au/AC, AuCs/AC and AuCuCs/AC catalysts, which could
conrm the presence of coke/oligomers species. In line with
the literature,52–54 this low temperature oxygen consumption
peak may associate with the coke/oligomers located on the
active metal sites, because the active metal could facilitate
the coke/oligomers decomposition. According to Fig. 9, the
intensity of oxygen consumption peak resulting from the
AuCuCs/AC catalyst is less signicant, when it is compared
with the Au/AC and AuCs/AC catalysts. The amount of coke/
oligomers deposited on the used catalysts was determined by
TGA measurements (gure not shown here). From the TGA
measurements, the amounts of coke/oligomers formed were
1.1 wt% (AuCuCs/AC), 2.5 wt% (AuCs/AC) and 4.7 wt% (Au/AC).
Based on this result, it is clear that the amount of carbon coke
species for the Au-based catalyst with addition of Cu and Cs
decreases, in good agreement with the results in Table 3.
In the acetylene hydrochlorination mechanism, previous
studies have shown that the reaction occurs via the formation
of a C2H2/Au due to C2H2 is easier to be adsorbed on the AuCl3
catalyst prior to HCl.6 However, it is a reverse order between
catalyst stability and C2H2 adsorption capacity, because C2H2
leads to deactivation.6 TPD is an effective technique providing
direct comparison of the adsorption and activation of reactants
on different catalysts. Specically, the desorption temperature
in the TPD proles reect the binding strength of the adsorbed
species with the catalyst surface and the peak area correlates
with the amount of active species.31 Fig. 10 presents the C2H2-
TPD proles for Au/AC, AuCs/AC and AuCuCs/AC catalysts.
3.3. Catalytic stability and lifetime estimation of the
trimetallic AuCuCs/AC catalyst
The important limiting factor for industrial acetylene hydro-
chlorination with supported Au-based catalysts is the long-term
stability under reaction conditions. To demonstrate the
superior performance of AuCuCs/AC, we further investigated
the stability of the catalysts for acetylene hydrochlorination
under the conditions of 180 ꢁC and 50 hꢀ1 of gas hourly space
velocity (GHSV, C2H2 based) over 600 h. The AuCuCs/AC
catalyst showed more than 98.8% conversion of C2H2 and
more than 99.9% selectivity to VCM during a 600 h test under
the upper limit of 50 hꢀ1 of industrial hydrochlorination space
velocity, as demonstrated in Fig. 11a. The results indicated
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hydrochlorination of acetylene. A maximum TOF of 73.8 minꢀ1
(based on total Au content) was obtained on the AuCuCs/AC
catalyst. Furthermore, the AuCuCs/AC catalyst remained
highly active and stable aer a 600 h test at C2H2 hourly space
velocity of 50 hꢀ1 and an estimated lifetime exceeding 6540 h.
The synergic catalysis derived from Au–Cu–Cs interaction
found in this work may be associated with the enhanced
dispersion of Au particles, the stabilization of Au in the state
of Au3+ and facile substrate C2H2 molecule desorption. The
optimized AuCuCs/AC catalyst featured in low cost, high
catalytic activity, good long-term stability and low toxicity,
demonstrating the potential for the replacement of Hg-based
catalysts for acetylene hydrochlorination.
Acknowledgements
The nancial support by the National Natural Science Foun-
dation of China (NSFC-21476207) is gratefully acknowledged.
References
1 M. W. Allsopp and G. Vianello, Ullmann's Encyclopedia of
Industrial Chemistry, Wiley-VCH, Weinheim, Germany, 2000.
2 J. Bing and C. Li, Polyvinyl Chloride, 2011, 39, 1–8.
3 G. J. Hutchings and D. T. Grady, Appl. Catal., 1985, 17, 155–
160.
4 G. J. Hutchings, J. Catal., 1985, 96, 292–295.
5 B. Nkosi, N. J. Coville and G. J. Hutchings, J. Chem. Soc.,
Chem. Commun., 1988, 1, 71–72.
Fig. 11 (a) Long-term stability test of AuCuCs/AC. Reaction condi-
tions: T ¼ 180 ꢁC, V(HCl)/V(C2H2) ¼ 1.2 : 1, GHSV ¼ 50 hꢀ1. (b) Lifetime
estimate for the AuCuCs/AC catalyst. Reaction conditions: T ¼ 180 ꢁC,
V(HCl)/V(C2H2) ¼ 1.2 : 1, GHSV ¼ 720 hꢀ1
.
6 M. Conte, A. F. Carley, C. Heirene, D. J. Willock, P. Johnston,
A. A. Herzing, C. J. Kiely and G. J. Hutchings, J. Catal., 2007,
250, 231–239.
7 M. Conte, C. J. Davies, D. J. Morgan, A. F. Carley, P. Johnston
and G. J. Hutchings, Catal. Lett., 2014, 144, 1–8.
8 M. Conte, C. J. Davies, D. J. Morgan, T. E. Davies, A. F. Carley,
P. Johnston and G. J. Hutchings, Catal. Sci. Technol., 2013, 3,
128–134.
9 M. Conte, A. F. Carley, G. Attard, A. A. Herzing, C. J. Kiely and
G. J. Hutchings, J. Catal., 2008, 257, 190–198.
10 W. Wittanadecha, N. Laosiripojana, A. Ketcong,
N. Ningnuek, P. Praserthdam and J. R. Monnier, Appl.
Catal., A, 2014, 475, 292–296.
11 S. A. Mitchenko, T. V. Krasnyakova, R. S. Mitchenko and
A. N. Korduban, J. Mol. Catal. A: Chem., 2007, 275, 101–108.
12 S. A. Mitchenko, E. V. Khomutov, A. A. Shubin and
Y. M. Shul'ga, J. Mol. Catal. A: Chem., 2004, 212, 345–352.
13 S. A. Mitchenko, T. V. Krasnyakova and I. V. Zhikharev,
Theor. Exp. Chem., 2010, 46, 32–38.
14 T. V. Krasnyakova, I. V. Zhikharev, R. S. Mitchenko,
V. I. Burkhovetski, A. M. Korduban, T. V. Kryshchuk and
S. A. Mitchenko, J. Catal., 2012, 288, 33–43.
that the low content AuCuCs/AC catalyst is stable under typical
acetylene hydrochlorination reaction conditions.
Furthermore, to preliminary estimate the lifetime of
AuCuCs/AC catalyst, high GHSV (720 hꢀ1) test was carried out
to accelerate the deactivate process of AuCuCs/AC catalyst. This
reaction under GHSV 720 hꢀ1 for 1 h is equivalent to a reaction
under GHSV 30 hꢀ1 for 24 h. The catalytic results are shown in
Fig. 11b. As shown, the conversion declines only by about 32%
from the initial 99% aer running for 270 h under conditions
of 180 ꢁC, GHSV(C2H2) ¼ 720 hꢀ1 and a feed HCl/C2H2 volume
ratio ¼ 1.2. This indicates that AuCuCs/AC is deactivated under
reaction conditions. At this point, the GHSV was adjusted to
30 hꢀ1. This change increases the acetylene conversion to 98.5%
within 20 h; at this GHSV, a high conversion is maintained, even
aer 40 h. This result suggests that the AuCuCs/AC catalyst can
maintain high catalytic activity at C2H2 hourly space velocity
30 hꢀ1 for at least 6540 h. Evidently, the high activity combined
with remarkable stability of this catalyst illustrates the potential
of low content trimetallic AuCuCs/AC catalyst for industrial
hydrochlorination of acetylene.
15 Y. Pu, J. Zhang, L. Yu, Y. Jin and W. Li, Appl. Catal., A, 2014,
488, 28–36.
4. Conclusions
In summary, we have shown that the addition of Cu as a third 16 J. Zhang, W. Sheng, C. Guo and W. Li, RSC Adv., 2013, 3,
metallic component to AC supported AuCs catalyst led to 21062–21068.
a reduction in the Au loading to about 0.25 wt% and enhanced 17 G. Li, W. Li, H. Zhang, Y. Pu, M. Sun and J. Zhang, RSC Adv.,
the activity and stability of Au-based catalyst in the
2015, 5, 9002–9008.
This journal is © The Royal Society of Chemistry 2015
RSC Adv., 2015, 5, 101427–101436 | 101435

View Article Online
RSC Advances
Paper
18 K. Zhou, J. Si, J. Jia, J. Huang, J. Zhou, G. Luo and F. Wei, RSC 37 K. Zhou, W. Wang, Z. Zhao, G. Luo, J. T. Miller, M. S. Wong
Adv., 2014, 4, 7766–7769. and F. Wei, ACS Catal., 2014, 4, 3112–3116.
19 J. Xu, J. Zhao, T. Zhang, X. Di, S. Gu, J. Ni and X. Li, RSC Adv., 38 A. S. K. Hashmi and G. J. Hutchings, Angew. Chem., Int. Ed.,
2015, 5, 38159–38163. 2006, 45, 7896–7936.
20 K. Zhou, J. Jia, X. Li, X. Pang, C. Li, J. Zhou, G. Luo and 39 A. S. K. Hashmi, Angew. Chem., Int. Ed., 2005, 44, 6990–6993.
¨
F. Wei, Fuel Process. Technol., 2013, 108, 12–18.
21 B. Nkosi, N. J. Coville, G. J. Hutchings, M. D. Adams, J. Friedl
and F. E. Wagner, J. Catal., 1991, 128, 366–377.
22 J. Zhang, Z. He, W. Li and Y. Han, RSC Adv., 2012, 2, 4814–
4821.
40 A. Hoffmann-Roder and N. Krause, Org. Biomol. Chem., 2005,
3, 387–391.
´
˜
´
41 E. Jimenez-Nuneza and A. M. Echavarren, Chem. Commun.,
2007, 333–346.
42 D. J. Gorin and F. D. Toste, Nature, 2007, 446, 395–403.
23 H. Zhang, B. Dai, X. Wang, L. Xu and M. Zhu, J. Ind. Eng. 43 X. Zhang and A. Corma, Chem. Commun., 2007, (29), 3080–
Chem., 2012, 18, 49–54. 3082.
24 H. Zhang, B. Dai, X. Wang, W. Li, Y. Han, J. Gu and J. Zhang, 44 H. Zhang, B. Dai, W. Li, X. Wang, J. Zhang, M. Zhu and J. Gu,
Green Chem., 2013, 15, 829–836. J. Catal., 2014, 316, 141–148.
25 Y. Pu, J. Zhang, X. Wang, H. Zhang, L. Yu, Y. Dong and W. Li, 45 B. Nkosi, M. D. Adams and G. J. Hutchings, J. Catal., 1991,
Catal. Sci. Technol., 2014, 4, 4426–4432. 128, 378–386.
26 H. Zhang, W. Li, X. Li, W. Zhao, J. Gu, X. Qi, Y. Dong, B. Dai 46 J. Zhao, T. Zhang, X. Di, J. Xu, S. Gu, Q. Zhang, J. Ni and X. Li,
and J. Zhang, Catal. Sci. Technol., 2015, 5, 1870–1877. Catal. Sci. Technol., 2015, 5, 4973–4984.
27 J. Zhao, J. Xu, J. Xu, J. Ni, T. Zhang, X. Xu and X. Li, 47 K. Zhou, J. Jia, C. Li, H. Xu, J. Zhou, G. Luo and F. Wei, Green
ChemPlusChem, 2015, 80, 196–201. Chem., 2015, 17, 356–364.
28 J. Zhao, J. Xu, J. Xu, T. Zhang, X. Di, X. Li, J. Ni and X. Li, RSC 48 M. Conte, C. J. Davies, D. J. Morgan, T. E. Davies, D. J. Elias,
Adv., 2015, 5, 6925–6931.
29 C. Huang, M. Zhu, L. Kang, X. Li and B. Dai, Chem. Eng. J.,
2014, 242, 69–75.
A. F. Carley, P. Johnston and G. J. Hutchings, J. Catal., 2013,
297, 128–136.
´
49 S. De Miguel, O. Scelza, M. Roman-Martınez, C. Salinas-
´
30 G. Deng, B. Wu and T. Li, Polyvinyl Chloride, 1994, 6, 5–9.
31 X. Li, X. Pan, L. Yu, P. Ren, X. Wu, L. Sun, F. Jiao and X. Bao,
Nat. Commun., 2014, 5, 3688–3694.
32 X. Li, Y. Wang, L. Kang, M. Zhu and B. Dai, J. Catal., 2014,
311, 28–294.
33 X. Wang, B. Dai, Y. Wang and F. Yu, ChemCatChem, 2014, 6,
2339–2344.
34 K. Zhou, B. Li, Q. Zhang, J. Huang, G. Tian, J. Jia, M. Zhao,
G. Luo, D. Su and F. Wei, ChemSusChem, 2014, 7, 723–728.
35 C. Zhang, L. Kang, M. Zhu and B. Dai, RSC Adv., 2015, 5,
7461–7468.
Martinez de Lecea, D. Cazorla-Amoros and A. Linares-
Solano, Appl. Catal., A, 1998, 170, 93–103.
50 J. Figueiredo, M. Pereira, M. Freitas and J. Orfao, Carbon,
1999, 37, 1379–1389.
51 E. Esmaeili, A. M. Rashidi, A. A. Khodadadi, Y. Mortazavi and
M. Rashidzadeh, Fuel Process. Technol., 2014, 120, 113–122.
52 R. Arasteh, M. Masoumi, A. M. Rashidi, L. Moradi, V. Samimi
and S. T. Mostafavi, Appl. Surf. Sci., 2010, 256, 4447–4455.
53 H. S. Oh, J. G. Oh, Y. G. Hong and H. Kim, Electrochim. Acta,
2007, 52, 7278–7285.
54 J. Jae, G. Tompsett, A. Foster, K. Hammond, S. Auerbach,
R. Lobo and G. Huber, J. Catal., 2011, 279, 257–268.
36 S. Wang, B. Shen and Q. Song, Catal. Lett., 2010, 134, 102–
109.
101436 | RSC Adv., 2015, 5, 101427–101436
This journal is © The Royal Society of Chemistry 2015