Effect of acidity and ruthenium species on catalytic performance of ruthenium catalysts for acetylene hydrochlorination

Article abstract of DOI:10.1039/c8cy01677a

Carbon-supported ruthenium catalysts are promising mercury-free catalysts for acetylene hydrochlorination, due to their high activity and relatively low price. However, ruthenium catalysts often suffer from serious deactivation. Herein, a stable RuCl₃-A/AC catalyst was prepared by applying a simple ammonia treatment during the impregnation process. The fresh and used ruthenium catalysts were comprehensively characterized using N₂ sorption, NH₃-temperature-programmed desorption (NH₃-TPD), H₂ temperature-programmed reduction (H₂-TPR), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The results show that the RuCl₃ species is identified as the active species, and the surface acidity of the RuCl₃/AC catalyst is generated mainly from supported RuCl₃ species, which can easily cause coke deposition. The enhancement of the stability of the RuCl₃-A/AC catalyst is attributed to the formation of RuO_x species and the decrease of the surface acidity.

Full text of DOI:10.1039/c8cy01677a

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Effect of acidity and ruthenium species on
catalytic performance of ruthenium catalysts for
acetylene hydrochlorination†
Cite this: Catal. Sci. Technol., 2018,
8, 6143
*
Xiaolong Wang, Guojun Lan, Huazhang Liu, Yihan Zhu
and Ying Li
Carbon-supported ruthenium catalysts are promising mercury-free catalysts for acetylene hydro-
chlorination, due to their high activity and relatively low price. However, ruthenium catalysts often suffer
from serious deactivation. Herein, a stable RuCl3-A/AC catalyst was prepared by applying a simple ammo-
nia treatment during the impregnation process. The fresh and used ruthenium catalysts were comprehen-
sively characterized using N2 sorption, NH3-temperature-programmed desorption (NH3-TPD), H2
temperature-programmed reduction (H2-TPR), thermogravimetric analysis (TGA), and X-ray photoelectron
spectroscopy (XPS). The results show that the RuCl3 species is identified as the active species, and the sur-
face acidity of the RuCl3/AC catalyst is generated mainly from supported RuCl3 species, which can easily
cause coke deposition. The enhancement of the stability of the RuCl3-A/AC catalyst is attributed to the for-
mation of RuOx species and the decrease of the surface acidity.
Received 13th August 2018,
Accepted 22nd October 2018
DOI: 10.1039/c8cy01677a
rsc.li/catalysis
ever, the general activity of Ru-based catalysts is relatively lower
than that of Au-based catalysts. Therefore, many efforts have
1 Introduction
Vinyl chloride monomer (VCM) is a major chemical intermedi-
ate in the manufacture of polyvinyl chloride (PVC), which is the
third most important polymer in use today.1 At present, VCM is
generally synthesized via hydrochlorination of acetylene in re-
gions of the world where coal is abundant, especially in China.
However, production of VCM in acetylene hydrochlorination
units consumes about 1400 tons of mercury, which causes seri-
ous environmental problems. With the implementation of mer-
cury restrictions, the substitution of mercury is one of the key
challenges for vinyl chloride production via acetylene hydro-
chlorination.2 Therefore, mercury-free catalysts for acetylene
hydrochlorination have been extensively researched.3,4
Hutchings' group reported a relationship between the catalytic
performance and the standard electrode potential of a cationic
catalyst, and predicted that a gold catalyst would be a good can-
didate for acetylene hydrochlorination.5,6 Since then, Au cata-
lysts have been intensively studied.7–9 Although Johnson
Matthey technology has achieved the successful commercializa-
tion of gold catalysts with low loading in 2016,6 gold has not
been widely applied in chloride alkali plants due to its high
cost. Therefore, Ru-based catalysts, which are much less expen-
sive and possess high activity, are considered to be another
promising candidate for acetylene hydrochlorination.10 How-
been dedicated to enhancing their catalytic activity, such as
adding another metal or ionic liquids,11–17 using heteroatom-
doped carbon supports,18–23 and using other Ru salts rather
than RuCl3.24–26 RuO2, RuCl3 and Ru/RuOy species have been
suggested to be the active species in ruthenium catalysts, as
reported by Li.27 Zhang et al. prepared a series of ruthenium–
cobalt catalysts, and found that the Co cobalt additive can
greatly influence the amount of ruthenium species, which re-
sults in good catalytic activity.12 Dai et al. reported the effect of
nitrogen functional groups on ruthenium catalysts and found
that the modified catalysts exhibited better catalytic activity.18
Han et al. prepared a Ru-based catalyst by using ammonium
hexachlororuthenate ((NH4)2RuCl6) as the ruthenium precur-
sor, and found that the resulting (NH4)2RuCl6/AC catalyst ex-
hibits superior catalytic activity.24
For industrial heterogeneous catalysts, especially those
used for acetylene hydrochlorination, the stability of the cata-
lyst is also very important. Hydrochlorination is a typical re-
action catalyzed by a Lewis acid; however, the strong acidic
sites at the surface of the catalyst can cause coke deposition,
especially for reactions involving acetylene and olefins. It is
known that the Lewis acidity of RuCl3 is much stronger than
that of AuCl3 and HgCl2 and the coke deposition phenome-
non could be more severe for Ru-based catalysts than Au and
Hg catalysts. In addition, according to the literature,12,15 the
main reason for the deactivation of ruthenium catalysts is
coke deposition. To inhibit coke deposition, Li et al.13 pre-
pared a series of ruthenium–potassium catalysts to study the
Institute of Industry Catalysis, Zhejiang University of Technology, 18 Chaowang
Road, Hangzhou 310014, PR China. E-mail: liying@zjut.edu.cn
† Electronic supplementary information (ESI) available: Fig. S1–S7, Tables S1
and S2, see ESI. See DOI: 10.1039/c8cy01677a
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effects of KCl on the performance of Ru-based catalysts. They
found that the addition of alkali metals inhibited coke depo-
sition. More importantly, with increasing amount of alkali
metal added, the carbon deposition of the catalyst decreased.
Li et al. studied the effect of ionic liquids on Ru-based cata-
lysts during acetylene hydrochlorination and found that ionic
liquids not only increased the amount of HCl adsorbed onto
the catalyst but also enhanced HCl activation, which could
inhibit self-polymerization of acetylene, which produces coke
deposition.16
Up to now, there have been no studies investigating the
surface acidity of RuCl3/AC catalysts for acetylene hydro-
chlorination. The present work studied the relationship be-
tween the surface acidity and stability of ruthenium catalysts,
and provides a simple method to solve the problem of ruthe-
nium catalyst stability by treating the as-prepared RuCl3/AC
catalyst with concentrated ammonia solution.
passed through concentrated sulfuric acid solution to remove
the trace impurities, and hydrogen chloride gas (99.9% pu-
rity) was dried using 5A molecular sieves. Acetylene (3.4 mL
min−1) and hydrogen chloride (3.7 mL min−1) were intro-
duced into a heated reactor containing catalyst (2.0 mL)
through a mixing vessel via calibrated mass flow controllers,
giving a C2H2 gas hourly space velocity (GHSV) of 100 h−1 at
180 °C. The pressure of C2H2 and HCl was 0.1 MPa and the
feed volume ratio of VHCl/VC H was 1.10. The microreactor
was purged with nitrogen to remove water and air before the
reaction. The catalyst was activated by passing HCl gas over it
at various times before C2H2 and HCl were mixed together.
The activation time was 4 hours if not otherwise stated. The
reactor effluent was passed through an absorption bottle
containing a sodium hydroxide solution to remove the
unreacted hydrogen chloride. The gas mixture was analyzed
by using a GC-1690F gas chromatograph (GC) equipped with
FID detector. The initial conversion of C2H2 was recorded af-
ter the reaction had proceeded for 1 hour.
2
2
2 Experimental
2.1 Materials
2.4 Characterization
Activated carbon (AC) (coconut carbon, 12–24 mesh) was pur-
chased from Hainan Yeqiu Co., Ltd. Ruthenium chloride
hydrate (RuCl3·3H2O) was purchased from Sino-Platinum
Metals Co. Ltd. NH3·H2O (25–28%) was purchased from Hang
Zhou Longshan Fine Chemical Co. Ltd. Other reagents were
obtained from Shanghai Chemical Reagent Inc. of the Chi-
nese Medicine Group. All materials except for AC were of ana-
lytical grade and were used without any further purification.
Activated carbon (AC) was washed with a 1 mol L−1 HCl solu-
tion at 70 °C for 5 hours to remove impurities, followed by
washing with water to neutral pH and drying at 120 °C for 5
hours. The dried AC was stored in a desiccator for further use.
X-ray powder diffraction (XRD) measurements were performed
by using a Rigaku D/Max-2500/pc powder diffraction system
using Cu Kα radiation (40 kV and 100 mA) over the range 10°
≤ 2θ ≤ 80°.
Transmission electron microscope (TEM) images of the
samples were obtained using a FEI Tecnai G20 instrument.
The samples were mounted and ultrasonically dispersed in
ethanol, and then a few droplets of the suspension were de-
posited on a copper grid coated by a carbon film, followed by
drying under ambient conditions.
Nitrogen adsorption isotherms were determined at −196
°C on a Quantachrome Autosorb-IQ apparatus. The samples
were outgassed at 350 °C for 3 hours before the adsorption
measurements. The specific surface area was obtained by
using the Brunauer–Emmett–Teller (BET) model for adsorp-
tion data in the relative pressure range of 0.05–0.30. The total
pore volume was determined from the aggregation of N2 va-
por adsorbed at a relative pressure of 0.99. The pore size dis-
tribution was acquired from the desorption branches of the
isotherms using the DFT model.
Hydrogen temperature-programmed reduction (H2-TPR) of
Ru catalysts was carried out with a self-made TPD/TPR instru-
ment. The mass spectra were collected using an online Hiden
gas analyzer (QIC 20). Prior to analysis, the samples (ca. 50
mg) were placed in a fixed bed U-shaped quartz tubular reac-
tor located inside an electrical furnace. Then each sample
was purged at 110 °C for 2 hours in an argon stream to re-
move the adsorbed water and other impurities on the surface
of the sample. After cooling down to room temperature, each
sample was heated to 850 °C at a ramp rate of 10 °C min−1
under 5 vol% H2/Ar with a flow rate of 30 mL min−1. The fol-
lowing mass signals were monitored simultaneously on a
quadrupole mass spectrometer: m/z = 2, 17, 18, 28, 35, 36, 37,
40 and 44 amu.
2.2 Catalyst preparation
The RuCl3/AC catalyst was prepared using RuCl3·3H2O as the
precursor via an incipient impregnation technique. The nom-
inal ruthenium loading was 2 wt%, which was calculated
based on Ru metal. The detailed procedure is as follows: 0.29
grams of RuCl3·3H2O was first dissolved in 8 mL of water,
then 5 grams of the activated carbon was added to an aque-
ous solution of RuCl3 at room temperature. The impregna-
tion was kept at room temperature for 24 hours and then the
catalyst was dried at 120 °C for 10 hours. The as-prepared cat-
alyst was denoted as RuCl3/AC. RuCl3/AC was reduced by H2
with a flow rate of 30 mL min−1 at 400 °C for 2 hours. The re-
duced catalyst was denoted as Ru/AC.
The as-prepared undried RuCl3/AC catalyst was put directly
in 8 mL of concentrated NH3·H2O solution and kept at room
temperature for another 24 hours. Then it was dried at 120 °C
for 10 hours. The obtained catalyst was denoted as RuCl3-A/AC.
2.3 Measurement of catalytic activity
The catalytic performance was investigated using a fixed-bed
glass reactor (i.d. of 10 mm). Acetylene (99.9% purity) was
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Ammonia temperature-programmed desorption (NH3-
TPD) of various Ru catalysts was carried out using a self-
made TPD instrument. The mass spectra were collected on
an online Hiden gas analyzer (QIC20). Prior to ammonia ad-
sorption, the samples (50 mg) were activated at 120 °C for 1
hour in an argon stream. Subsequently, ammonia was intro-
duced by a stream of 10 vol% NH3/He at 100 °C. The physi-
cally adsorbed NH3 was removed by purging with an argon
steam at 100 °C until the baseline was flat. After cooling
down to room temperature, the sample was heated to 500 °C
at a ramp rate of 10 °C min−1 under argon with a flow rate of
30 mL min−1. The following mass signals were monitored si-
multaneously using a quadrupole mass spectrometer: m/z =
2, 14, 15, 16, 17, 18, 28, 40 and 44 amu. The quantification of
the acidic sites was done by using (NH4)2CO3 as a standard
compound to calibrate the area of the MS signals.28
Thermogravimetric analysis (TGA) was performed using a
TG–DTG simultaneous thermal analyzer (NETZSCH STA 449F3)
under air at a flow rate of 30 mL min−1. The temperature was
increased from 30 °C to 850 °C at a rate of 10 °C min−1.
X-ray photoelectron measurements (XPS) were conducted
on a Kratos AXIS Ultra DLD instrument using 300 W Al Kα.
The binding energies were calibrated using the contaminant
carbon (C 1s 284.6 eV).
Table 1, the surface area and pore volume of activated carbon
are 1235 m2 g−1 and 0.53 cm3 g−1, respectively. The surface
area and the pore volume of RuCl3/AC are decreased to 1094
m2 g−1 and 0.47 cm3 g−1. The decrease of the surface area
and pore volume of the AC after impregnation of RuCl3 salts
indicates that parts of the pores of AC are filled by RuCl3.
Furthermore, the surface area and pore volume of RuCl3-A/
AC and Ru/AC are not very different compared to RuCl3/AC.
The ruthenium loading values of RuCl3/AC, Ru/AC and
RuCl3-A/AC are 2.01%, 2.01% and 2.04%, respectively, as
measured using ultraviolet spectrophotometry. This is nearly
the same as the theoretical ruthenium loading, indicating
that there is no loss of ruthenium during impregnation.
Fig. 1A and B give the catalytic performances of these Ru-
based catalysts for acetylene hydrochlorination. The initial
acetylene conversion of RuCl3-A/AC is 82.5%, and acetylene
conversion reaches the maximum value of 95.8% after the reac-
tion has proceeded for 8 hours. Meanwhile, the initial acety-
lene conversion for the RuCl3/AC catalyst reaches the maxi-
mum value of 94.0% at the very beginning of the reaction. This
existence of an induction period for a catalyst may indicate that
the active ruthenium species are formed during the reaction.
To further identify the induction period of the RuCl3-A/AC
catalyst, Fig. S1A† shows the effect of HCl activation time on
the catalytic performance of RuCl3-A/AC. The induction period
was greatly suppressed when the activation time was 6 hours.
The initial acetylene conversion for RuCl3-A/AC increased up
to the maximum value of 97.2%. This indicates that the active
species was generated during pre-treatment with HCl. This re-
sult indicates that the active ruthenium species for the ruthe-
nium catalysts is ruthenium chloride. To further identify the
active species, Ru/AC (in situ reduction of RuCl3/AC in fixed-
bed glass reactor) was tested as a comparison and the results
are given in Fig. 1B. The initial activity for Ru/AC was only
10%, which is close to the catalytic performance of the carbon
support (shown in Fig. 1B). This indicates that metallic Ru is
not the active species. The acetylene conversion increased up
to 30% in 20 hours and stabilized at 30% after 20 hours. This
indicates that the active species was formed during the reac-
tion. The stabilized activity of Ru/AC is still much lower than
that of RuCl3/AC and RuCl3-A/AC, although they have similar
Ru loadings. This could be due to the fact that Ru nano-
particles are formed during reduction by hydrogen. The Ru
dispersion of Ru/AC was determined via CO chemisorption to
be only 35%, and only the surface Ru atoms could be acti-
vated into the active species (RuCl3). Meanwhile for RuCl3/AC,
3 Results and discussion
3.1 Textural properties and catalytic performance of various
Ru catalysts
An incipient impregnation method was used for the prepara-
tion of the various carbon-supported catalysts, as shown in
Scheme 1. There are three main catalysts studied in this
work: RuCl3/AC (as-prepared); Ru/AC (reduced); and RuCl3-A/
AC (ammonia pre-treated). For the detailed preparation
methods of the catalysts, see the Experimental section.
Table 1 gives the textural properties of the various cata-
lysts prepared by the incipient impregnation method. From
Scheme 1 The preparation process of various ruthenium catalysts.
Table 1 Textural properties of activated carbon and various fresh and used ruthenium catalysts
Fresh
Used
Ru
(wt%)
S.A.
P.V.
Ru
(wt%)
S.A.
P.V.
Amount of coke
deposition (%)
Acid content
Deactivation
Samples
(m2 g−1
)
(cm3 g−1
)
(m2 g−1
)
(cm3 g−1
)
(mmol g−1
)
rate (% h−1
)
AC
∼
1235
1094
1102
1105
0.53
0.47
0.47
0.47
—
22
340
946
—
—
11.6
9.1
—
—
RuCl3/AC
RuCl3-A/AC
Ru/AC
2.01
2.04
2.01
1.80
1.88
2.00
0.02
0.17
0.41
6.34
2.66
None
1.64
0.14
None
Not detected
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Fig. 1 The conversion of acetylene in acetylene hydrochlorination
over (A) RuCl3/AC and RuCl3-A/AC and (B) AC and Ru/AC catalysts.
Reaction conditions: T = 180 °C, GHSVIJC2H2) = 100 h−1 and VHCl/VC H
2
2
Fig. 2 XRD patterns of RuCl3/AC, RuCl3/AC-used, RuCl3-A/AC and
RuCl3-A/AC-used catalysts.
= 1.10.
monolayer RuCl3 can be easily formed on the surface of the
activated carbon support according to the spontaneous dis-
persion phenomenon reported by Xie et al.29,30 From Fig. 1A,
it can be clearly seen that the deactivation rate is obviously de-
creased for RuCl3-A/AC compared with RuCl3/AC. The acety-
lene conversion of the RuCl3-A/AC catalyst is still above 90.5%
after the catalyst has been used for 50 h. The deactivation
rates for RuCl3-A/AC and RuCl3/AC are 0.14% h−1 and 1.64%
h−1 respectively. This result indicates that the ammonia pre-
treatment of the as-prepared RuCl3/AC catalyst can greatly im-
prove the stability. To identify the role of ammonia pre-
treatment and the deactivation mechanism of the ruthenium
catalysts, a detailed characterization of the textural properties
and statuses of the Ru species in these two catalysts are given
and discussed below.
no aggregation of RuCl3 occurs even after the reaction has
proceeded for 50 hours.
The STEM and HRTEM images are also provided in Fig. 3
and S3,† respectively. There are no Ru nanoclusters or parti-
cles observed at high resolution mode. Even after the reac-
tion, there are still no Ru nanoparticles to be observed. How-
ever, from the scanning transmission electron mode, the
distribution of Ru element is clearly observed. This might in-
dicate a monolayer distribution of RuCl3 salts on the surface
of the activated carbon.
Fig. 4 shows hydrogen temperature-programmed reduc-
tion profiles of the fresh and used Ru-based catalysts. Com-
pared with the Ru catalysts, activated carbon shows very weak
H2 consumption (see ESI† Fig. S4†). For RuCl3/AC, there are
two peaks of H2 consumption located at 140 °C and 235 °C.
Combined with a signal at m/z = 18 corresponding to H2O, it
is concluded that the consumption of H2 is related to the re-
duction of RuCl3 and RuOx. However, no peaks correspond-
ing to HCl are detected due to the re-adsorption of HCl on
the carbon support. For RuCl3-A/AC, there are two peaks of
H2 consumption located at 180 °C and 270 °C that corre-
spond to RuCl3 and RuOx. Obviously, the temperature of the
Ru reduction peak is shifted to high temperature and the
amount of ruthenium oxide is increased. This indicates that
the treatment with ammonia solution can change the status
of RuCl3 species and increase the amount of ruthenium ox-
ides. For both the used RuCl3/AC and RuCl3-A/AC catalysts,
the H2 consumption peak shifts to 325 °C and there is an
3.2 Characterization of the fresh and used RuCl3/AC and
RuCl3-A/AC catalysts
Fig. S2A and B† show the isotherms and pore size distribu-
tions of the fresh and used Ru catalysts. The isothermal
curves for the fresh RuCl3/AC and RuCl3-A/AC catalysts are
type IV with an H4 hysteresis loop in a high relative pressure
range, which indicates that these samples have mesoporous
structures in addition to a micropore structure. The pore size
distributions of all the samples calculated via DFT methods
are given in Fig. S2B.† All the samples have main pore size
distributions in the range of 0.5–5.0 nm. For RuCl3/AC-used,
the isothermal curve becomes flat without any hysteresis
loops, indicating that both micropores and mesopores have
been blocked. For RuCl3-A/AC-used, the isothermal curve is
also changed. However, from the pore size distribution, the
main micropores and mesopores still exist. The textural prop-
erties of the fresh and used catalysts are summarized in
Table 1. The specific surface area and pore volume of RuCl3/
AC-used and RuCl3-A/AC-used are greatly decreased.
Fig. 2 displays the XRD patterns of the fresh and used cat-
alysts. There are only two diffraction peaks at 26.5° and 45°
for all the fresh and used catalysts, which can be assigned to
the (002) and (101) diffraction peaks of amorphous carbon.
No discernible reflection is detected for all the fresh and
used Ru catalysts, indicating that the ruthenium species are
highly dispersed and the particle size is less than 4 nm and
Fig.
catalyst.
3
STEM images and element mapping for the RuCl3-A/AC
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X-ray photoelectron spectroscopy (XPS) was used to char-
acterize the status of the ruthenium species on the catalysts.
Because the binding energy of the Ru 3d orbital overlaps with
that of C 1s, the Ru 3p orbital was chosen for the analy-
sis.31,32 The high-resolution Ru 3p spectra for the fresh and
used RuCl3/AC, RuCl3-A/AC and Ru/AC catalysts are given in
Fig. 5A. The deconvolution results, including the binding en-
ergy and relative content of different peaks, are shown in
Table 2. The photoelectron spectra of Ru 3p for fresh Ru/AC,
RuCl3/AC and RuCl3-A/AC catalysts clearly show two doublet-
peaks. The spin–orbit splitting of Ru 3p is 22.2 eV and inten-
sity ratio is about 2 : 1 (Ru 3p3/2 : Ru 3p1/2). For RuCl3/AC,
around 44% of the ruthenium is ascribed to Ru3+ species in
RuCl3 (463.4 eV)33 and around 55.9% of ruthenium is as-
cribed to Ruσ+ species in RuOx (465.0 eV).34 For RuCl3-A/AC,
around 32.5% of ruthenium was ascribed to Ru3+ species in
RuCl3 (463.4 eV) and around 67.5% of ruthenium was as-
cribed to Ruσ+ species in RuOx (464.8 eV). For Ru/AC, around
75.3% of ruthenium was ascribed to Ru0 species (462.2 eV)35
and around 24.7% of ruthenium was ascribed to Ruσ+ species
in RuOx (465.0 eV). The RuOx species is present in the Ru/AC
catalyst, which may be because the Ru/AC catalyst was ex-
posed to air and became oxidized. For the RuCl3/AC-used and
RuCl3-A/AC-used catalysts, the main peak of Ru 3p3/2 at 463.4
eV is attributed to Ru3+ species in RuCl3 and there are appar-
ently no Ru0 and RuOx species for both samples. However,
for the Ru/AC-used catalyst, around 72.2% of ruthenium was
ascribed to Ru0 species (461.7 eV) and around 27.8% of ru-
thenium was ascribed to Ru3+ species in RuCl3 (463.6 eV).
This indicates that some of Ru0 has been oxidized to RuCl3
under the reaction conditions and the RuCl3 species is the
active center of the Ru-based catalysts. This result is consis-
tent with the induction period for these catalysts as discussed
in a previous paragraph.
Fig. 4 H2-TPR profiles of (A) RuCl3/AC, (B) RuCl3-A/AC (C) RuCl3/AC-
used and (D) RuCl3-A/AC-used catalysts.
The XPS spectra of Cl 2p for fresh and used Ru-based cata-
lysts are given in Fig. 5B. The Cl 2p spectra could be split into
doublet-peaks (Cl 2p3/2 and Cl 2p1/2), with the energy separa-
tion being 1.6 eV and the intensity ratio being 2 : 1. There-
fore, the Cl 2p peaks are fitted into two peaks according to
the composition of the ruthenium catalyst. The peak located
at 197.7 0.1 eV is closer to the binding energy of Cl 2p spe-
cies in RuCl3.36 The peak at 200.2 0.1 eV is assigned to C–
Cl,37 which may be formed by the chemical adsorption of Cl−
anions produced by the hydrolysis of RuCl3 in aqueous solu-
tion (see ESI† Fig. S5†). The ratio of these two species is
42.4% and 57.6% for RuCl3/AC, and 16.3% and 83.7% for
Fig. 5 XPS spectra of (a) RuCl3/AC, (b) RuCl3/AC-used, (c) RuCl3-A/AC,
(d) RuCl3-A/AC-used catalysts, (e) Ru/AC, and (f) Ru/AC-used, for (A)
Ru 3p and (B) Cl 2p.
obvious HCl peak detected. This indicates that the Ru species
on the catalyst has been changed into RuCl3 species during
the reaction. The reduction temperature of the used catalyst,
which is shifted to a high temperature, is due to surface coke
deposition, which can inhibit the reduction of ruthenium.
Table 2 The XPS spectra fitting results of Ru 3p and Cl 2p for the fresh and used ruthenium catalysts
Ru 3p (area%)
Cl 2p (area%)
Samples
Ru (462.2 eV)
RuCl3 (463.4 eV)
RuOx (465.0 eV)
C : Cl (200.2 eV)
Ru : Cl (197.7 eV)
RuCl3/AC
—
—
—
—
75.3
72.2
44.1
100
32.5
100
—
55.9
—
67.5
—
24.7
—
42.4
73.8
16.3
48.4
100
57.6
26.2
83.7
51.6
0
RuCl3/AC-used
RuCl3-A/AC
RuCl3-A/AC-used
Ru/AC
Ru/AC-used
27.8
86.0
14.0
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Fig. 7 NH3-TPD profiles of AC, Ru/AC, RuCl3/AC, and RuCl3-A/AC
catalysts.
Fig. 6 TG and DTG curves of (A) RuCl3/AC and RuCl3/AC-used; (B)
RuCl3-A/AC and RuCl3-A/AC-used catalysts under air flow.
surface of the catalysts. The concentrations of acidic sites are
6.34 mmol g−1 for RuCl3/AC and 2.66 mmol g−1 for RuCl3-A/AC.
The treatment with ammonia solution can greatly reduce the
amount of surface acidic sites on the ruthenium catalysts. This
result explains the different deactivation rates of these catalysts.
To exclude the effect of the ammonia treatment on the acti-
vated carbon, an ammonia-treated activated carbon was used
as a reference to prepare a RuCl3/AC-A catalyst. The catalytic
performance and NH3-TPD results are provided in Fig. S6.† The
stability of the RuCl3/AC-A is slightly better than RuCl3/AC, but
it is still far lower than that of the RuCl3-A/AC catalyst. This can
be explained by the acidity difference between AC and RuCl3/
AC. Compared with RuCl3, the acidity of activated carbon is
quite low. The main acidity is generated by RuCl3. Therefore,
the ammonia treatment of the carbon support is not as obvious
as the treatment of the as-prepared catalysts.
RuCl3-A/AC, respectively. This indicates that the addition of
ammonia during impregnation greatly affected the hydrolysis
behavior of RuCl3. It should be noted that after the reaction
had proceeded for 50 hours, the C : Cl ratio greatly increased,
both for the RuCl3/AC-used and RuCl3-A/AC-used catalysts.
This indicates that the coke deposition occurs for the used
catalysts and is caused by vinyl chloride polymerization. How-
ever, it can be clearly seen that the coke deposition for
RuCl3/AC-used is much heavier than that of RuCl3-A/AC-used.
Comparing Ru/AC with Ru/AC-used, the Ru : Cl ratio for Ru/
AC-used increased to 14.0. This result is consistent with the
XPS spectra of Ru 3p for Ru/AC.
Fig. 6 gives the thermal gravimetric analysis results of the
fresh and used RuCl3/AC and RuCl3-A/AC catalysts under air
flow. For both the fresh RuCl3/AC and RuCl3-A/AC catalysts,
there are two weight loss peaks at 380 °C and 490/500 °C.
The first peak can be assigned to the combustion of carbon
species around Ru species, which can be catalyzed by ruthe-
nium. The second peak at the higher temperature (490–500
°C) is due to the combustion of the carbon support. A new
peak appears at 340 °C for the used RuCl3/AC and RuCl3-A/
AC catalysts. This can be assigned to the combustion of the
deposited carbon species. Therefore, the amount of coke de-
position is calculated based on the weight loss in the temper-
ature range of 150–380 °C. The amount of coke deposition
for the RuCl3/AC catalyst is about 11.6% and 9.1% for the
RuCl3-A/AC catalysts (listed in Table 1). The loadings of ru-
thenium for RuCl3/AC-used and RuCl3-A/AC-used catalysts
are 1.80% and 1.88% (given in Table 1). Considering the
weight increase caused by coke deposition of the used cata-
lyst, there was almost no loss of ruthenium. Therefore, the
main cause of catalyst deactivation is coke deposition.
To identify the differences between the RuCl3/AC and RuCl3-
A/AC catalysts, NH3 temperature-programmed desorption was
used to characterize the surface acidity of the catalysts. The re-
sults are given in Fig. 7. Both Ru/AC and AC were also charac-
terized for comparison. For RuCl3/AC and RuCl3-A/AC, there is
only a NH3 desorption peak at 170 °C. It also can be seen that
the peak area of the RuCl3-A/AC catalyst is smaller than that of
the RuCl3/AC catalyst. Furthermore, Ru/AC and activated car-
bon have no ammonia desorption peak. The above results indi-
cate that the acidic sites are generated by RuCl3 species on the
From the above analysis, we concluded that coke deposi-
tion, caused by the surface acidity of the RuCl3/AC catalyst, is
the main reason for the deactivation of the catalyst. Combined
with the TPR and XPS characterizations, RuOx may be formed
during the ammonia treatment. The following reaction may oc-
cur during the ammonia treatment of the as-prepared catalysts:
RuCl3 + NH3·H2O → RuIJOH)3↓ + NH4Cl. Ru ions can precipi-
tate in the form of hydroxide facilely because the KspIJRuIJOH)3)
is as low as 1 × 10−36 (25 °C). This has been fully discussed in
our previous reports.38 The existence and decomposition of
RuIJOH)3 results in the content of RuOx being greatly enhanced.
Therefore, the present study not only points out the deactiva-
tion mechanism of the carbon-supported ruthenium chloride
but also gives an easy and efficient approach to solve the prob-
lem of deactivation. However, as shown in the data in Table
S1,† the catalytic performance of the RuCl3-A/AC catalyst is not
the highest compared with the data reported by Li et al.,17 and
therefore needs to be improved in future. The improvement of
the catalytic activity can be done by increasing of the disper-
sion of ruthenium, such as trying to prepare single-atom cata-
lysts or by adjusting the metal support interaction to increase
the intrinsic activity of the active sites.
4 Conclusions
In summary, we prepared a stable RuCl3-A/AC catalyst by ap-
plying a simple ammonia treatment during an impregnation
process. From the catalyst characterization results, the RuCl3
species was identified as the active species, and the surface
6148 | Catal. Sci. Technol., 2018, 8, 6143–6149
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acidity of RuCl3/AC catalyst is generated mainly from RuCl3
species, which can easily cause coke deposition. The en-
hancement of the stability of RuCl3-A/AC is attributed to the
formation of RuOx species and the decrease of the surface
acidity. The present work identifies the deactivation mecha-
nism of ruthenium-based catalysts and offers a simple way to
prepare mercury-free catalysts with extraordinary stability for
acetylene hydrochlorination. However, the activity of the ru-
thenium catalyst needs to be further improved.
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22 B. Man, H. Zhang, J. Zhang, X. Li, N. Xu, H. Dai, M. Zhu and
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The financial support from Natural Science Foundation of
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