Acetylene hydrochlorination over boron-doped Pd/HY zeolite catalysts

Article abstract of DOI:10.1039/c9ra05576b

A novel boron-doped Pd/HY zeolite catalyst for acetylene hydrochlorination was prepared and exhibited an outstanding catalytic performance (the acetylene conversion was maintained at >95% for about 30 h). The boron species can stabilize catalytically active Pd²⁺ species and weaken carbon deposition and Pd²⁺ reduction during the reaction, thus improving the catalytic stability.

Full text of DOI:10.1039/c9ra05576b

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Acetylene hydrochlorination over boron-doped
Pd/HY zeolite catalysts†
Cite this: RSC Adv., 2019, 9, 30335
ab
a
a
a
Jide Wang, *a
Lu Wang,
Chao Yang
*
Lizhen Lian, Haijun Yan, Feng Wang,
and Lida Ma
a
b
Received 19th July 2019
Accepted 16th September 2019
A novel boron-doped Pd/HY zeolite catalyst for acetylene hydrochlorination was prepared and exhibited an
outstanding catalytic performance (the acetylene conversion was maintained at >95% for about 30 h). The
DOI: 10.1039/c9ra05576b
2+
2+
boron species can stabilize catalytically active Pd species and weaken carbon deposition and Pd
rsc.li/rsc-advances
reduction during the reaction, thus improving the catalytic stability.
The coal-based acetylene hydrochlorination process is a major new supports were prepared Pd/HY catalysts applied for
route for the production of vinyl chloride monomer (VCM) in acetylene hydrochlorination and the catalysts stabilities
China, which is essential for polyvinyl chloride (PVC) produc- could be enhanced aer modication with NH
tion. However, this process is restricted by the application of aniline.
4
F or poly-
While the carbon deposition and the active
toxic and scarce mercury chloride, which is used as the active component reduction is the major obstacle to improve
1
4–17
1,2
ingredient of catalysts in the industrial process. Hence, it is activity and stability of catalysts. It reported that heteroatom
imperative to explore environmentally friendly catalysts for doping of support materials was effective for the improve-
2
5
acetylene hydrochlorination.
ment of the catalytic performance of metal catalysts and
Since Hutchings et al. suggested that the activities of few reports were studied on the B-doped zeolite-based
metal catalysts were associated with the standard electrode catalysts for acetylene hydrochlorination at present. In
3
potentials of the related metal ions, numerous studies have this work, a novel boron-doped Pd/HY zeolite-based catalyst
been carried out to develop non-mercury catalysts for effi- for acetylene hydrochlorination was prepared and its
cient and sustainable hydrochlorination of acetylene in outstanding catalytic performance was further studied.
4
–11
12–19
20
21
22
23,24
recent years, such as Au,
Pd,
Pt, Ru, Bi, Cu,
The boron-doped HY zeolites supports were prepared using
3
etc. Based on the detailed study by Hutchings' team, metal boron oxide (B2) as the boron source. The boron oxide aqueous
chloride/activated carbon catalysts (including Pd , Hg
Cu , Cu , Ag ) had superior catalytic activity and the order 3.0%, 5.0%, 7.0%, 9.0%) added into HY zeolites (purchased by
2
+
2+
,
solution was quantitatively (the weight percentage of B2 is 1.0%,
2
+
+
+
2
+
2+
2+
+
+
of their activities was Pd > Hg > Cu > Cu > Ag . Nankai University, Si/Al ¼ 9, 5.0 g) under stirring for 4 h, then
Therefore, palladium-based catalysts were reported to be washed with distiller water to pH about 7 and water was evap-
1
2–19
ꢀ
active for acetylene hydrochlorination.
Wang et al. orated at 80 C for 10 h, the B-doped HY zeolites supports were
prepared Pd-based/C catalysts via impregnation method obtained. The Pd/B2-HY catalysts were prepared via ultrasonic-
and suggested that the Pd loss and the carbon deposition assisted impregnation using the B-doped HY or the original HY
14–17
were main reasons for the catalyst deactivation, and the supports, as described in our previous work.
Based on the
adding of K and La could improve the stability and regen- weight percentage of the boron oxide, the obtained B-doped Pd/
1
8
eration of Pd/C catalysts. Mitchenko et al. reported that HY catalysts were named as Pd/1B2-HY, Pd/3B2-HY, Pd/5B2-HY,
1
9
Pd(II) chloro complexes were the active sites of catalysts
and the (NH PdCl complex could stabilize the Pd species catalysts was 0.9 wt%.
resulted in improving the catalytic performance over X-ray diffraction (XRD) data were collected using
carbon-based materials. In our previous study, zeolites as a M18XHF22-SRA diffractometer with Cu–K irradiation at 50 kV
Pd/7B2-HY and Pd/9B2-HY, respectively. The Pd loading in all
4
)
2
4
1
3
ꢀ
ꢀ
and 100 mA in the scan range of 2 between 10 –80 . Scanning
electron microscopy (SEM) and energy dispersive X-ray (EDX)
analyses were performed using a LEO1450VP detector to
a
Key Laboratory of Oil and Gas Fine Chemicals of Education, Xinjiang Uyghur
Autonomous Region, College of Chemistry and Chemical Engineering, Xinjiang
University, Urumqi, PR China, 830046. E-mail: wanglu_4951@163.com; awangjd@ determine the morphology. High-resolution transmission elec-
1
26.com; Fax: +86 991 8581018; Tel: +86 991 8581018
tron microscopy (HRTEM) experiment was performed using
a JEM-2100F (JEOL, Japan) working at 200 kV. BET surface areas
analysis was performed by JW-BK Brunauer–Emmett–Teller
b
Xinjiang De'an Environmental Protection Technology Co. Ltd, Urumqi, 830026, PR
China
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c9ra05576b
(BET) equipment. Thermogravimetric (TG) tests were detected
1
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2 2
by a NETZSCH SAT 449F3 multifunctional thermal analyzer in displayed the optimal catalytic performance with the C H
ꢁ
1
an air atmosphere at a ow rate of 50 mL min . The nature of conversion of 96% and the VCM selectivity of 98% aer 10 h and
carbon deposition was determined by an Agilent 7890A/5975C its activity kept over 95% within 30 h (Fig. S2†). It is suggested
gas chromatography-mass spectrometry (GC-MS). Palladium that the appropriate amount of B doping can improve the
contents were detected using an inductively coupled plasma activity and stability of Pd-based catalysts for acetylene
(ICP-6300) instrument. X-ray photoelectron spectroscopy (XPS) hydrochlorination.
data were recorded by AXIS ULTRA spectrometer (Kratos It is obvious that no other diffraction peaks of Pd species were
Analytical Ltd) and binding energies were referred to the C 1s detected, except the strongest characteristic peak of HY zeolites,
line at 284.8 eV. Fourier transform infrared spectrometer (FTIR) which could be attributed to the low concentration or high disper-
2
6,27
was used EQUINOX-55 (Bruker Company, Germany) in trans- sion of Pd species
(Fig. 2a). For the fresh Pd/7B2-HY catalyst,
ꢁ
1
mittance (%) mode in the range 4000–400 cm and tempera- numerous Pd-based particles with the size about 2.81 nm were
ture programmed decomposition (TPD) was determined using distributed uniformly on the HY support (Fig. 2b and d), which was
a
TP-5080 adsorption instrument with ammonia over slight bigger than that of the average pore width (by BET results,
ꢀ
ꢀ
ꢁ1
a temperature ramp of 0–900 C, rate ramp of 10 C min and 2.49 nm) of the 7B2-HY zeolites, deducing that most Pd species
ꢁ
1

ow of 100 mL min
The catalytic performances of catalysts were evaluated in the Pd species on the HY zeolite were visualized with well-dened
a xed bed with 10 mm-diameter a quartz tube micro reactor. fringes, which was ascribed to the (111) plane of face-centered
.
involved in reaction might be on the support surface. In addition,
28
The reactor temperature was calibrated by a CKW-110 cubic Pd with a d spacing of 0.23 nm (Fig. 2c). The characteriza-
temperature controller (Chaoyang automation instrument tion of HRTEM veries that XRD pattern is reasonable and suggests
factory, Beijing, China) and the gas ow during the reaction that the Pd species are highly dispersed in the fresh Pd/7B2-HY
was regulated by a D08-1F mass ow controller (Sevenstar catalyst (Table 1).
Huachuang electronics. co. Ltd, Beijing, China). Aer N
2
ow
Aer B doping, the 7B2-HY specic surface areas reduced
and the decrease could result from the abundant presence of B
ꢁ1
ꢁ1
(
20 mL min ) purged, hydrogen chloride (12.6 mL min
)
ꢁ1
and acetylene (10.1 mL min ) were fed through a mixing species introduced on the surface (Table S1†), which possibly
29
vessel containing catalyst (3.0 g), giving a temperature at block the small pores in the zeolite-based support. Compared
ꢀ
1
60 C, feed volume ratio V
: VC2H2 ¼ 1.25 and the C H gas with the corresponding supports, the specic surface areas of
HCl
2
2
ꢁ1
hourly space velocity (GHSV) of 110 h . The exit gas mixture the fresh catalysts showed a certain decrease because of the
26
from the reactor was passed through an absorption bottle blocking of pores as a result of Pd addition. Aer reaction, the
lled with sodium hydroxide solution and then set into a gas specic surface areas and total pore volumes of the catalysts
chromatography (GC 2010, Shimadzu) to analyse the acety- were reduced and the decrease of catalysts BET surface area

1
3–17
lene conversion and the VCM selectivity immediately.
(DSBET%) order was Pd/HY (93.7%) > Pd/7B2-HY (91.7%). The
Fig. 1 and S1† display the catalytic performance of undoped
and B-doped catalysts. The undoped Pd/HY catalyst exhibited
a poor catalytic stability and its C H conversion dropped
2
2
dramatically from 93% to 13% in 3 h. Aer B doping, the C H
2
2
conversion was signicantly enhance from 93% of the undoped
Pd/HY catalyst to 96% of the B-doped Pd/B2-HY catalyst under
the same conditions. It was clear that the Pd/7B2-HY catalyst
Fig. 2 The characterization on the fresh catalysts: (a) XRD patterns of
Pd-based catalysts. (b and c) HRTEM images of Pd/7B2-HY catalyst. (d)
Fig. 1 The catalytic performances of the B-doped Pd/B2-HY catalysts. Pd particle size distribution of Pd/7B2-HY catalyst.
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Table 1 Porous structure parameters of samples
a
2
ꢁ1
b
3
ꢁ1
c
Samples
HY
S
BET (m g
)
V (cm g
)
D (nm)
505
379
333
21
217
18
0.11
0.12
0.23
0.07
0.10
0.09
1.03
2.49
1.24
2.92
2.74
2.98
7
B2-HY
Fresh Pd/HY
Used Pd/HY
Fresh Pd/7B2-HY
Used Pd/7B2-HY
a
b
c
Specic surface area. Total pore volume. Average pore diameter.
carbon deposition, the agglomeration of Pd species and the
collapse of zeolite framework are the possible reasons for
clogging pores, covering the active sites and decreasing catalyst
30,31
activity.
SEM results (Fig. S3†) showed that the deactivated
catalyst surface was aggregated more seriously and the carbon
32
deposition was supposed to the main reason. To further testify
the results, the TG analysis of the fresh and used Pd/HY and Pd/
7B2-HY catalysts were showed in Fig. 3. The result indicated
that the actual amount of carbon deposited on the Pd/7B2-HY
catalyst could be calculated as 3.00%, which was about
29.41% less than that in the Pd/HY catalyst (4.25%). It is sug-
gested that the B doping to Pd/HY catalysts can inhibit the
formation of the carbon deposition to some extent, thus
33
improving the catalytic stability of catalyst. In addition, the
GC-MS results (Table S2†) showed that the carbon deposition is
probably ascribed to some hydrocarbon compounds (such as
benzene, 1,1-dichloroethane, chlorobenzene, 1-chlorobutylene
and so on), which is also the main reason for the undesirable
Fig. 4 XPS Pd 3d profiles of the fresh and used Pd-based catalysts.
Combination with the activity of catalysts (Fig. 1), the fresh Pd/
7B2-HY catalyst with the enhanced catalytic performance is
attributed to the presence of B (wide-scan spectra are shown in
31,34
VCM selectivity of Pd/B2-HY catalysts.
XPS analysis (Fig. 4) was carried out to investigate the valence
state and relative amount of Pd species in the fresh and used
Pd/HY and Pd/7B2-HY catalysts. It should be noted that all of
the Pd (3d) signals had been divided into two components
2
+
0
Fig. S4†), which can inhibit the less reduction of Pd to Pd in
the reaction process (Table 2). Moreover, only one B species
3
+
(
B ) were detected in the fresh and used Pd/7B2-HY catalyst.
0
2+
The binding energy observed at 193.5 eV for the fresh Pd/7B2-
HY catalyst was typically referred to as boron–oxygen bond,
while the lower binding energy (193.2 eV) was detected in the
used Pd/7B2-HY catalyst, indicating that the weakened inter-
action between boron and the support in the reaction. From ICP
responding to metallic Pd (335.5 eV and 340.6 eV) and Pd
35–37
(
337.1 eV and 342.3 eV) species
employed to analyse the ratio of Pd and Pd species (the
results were calculated in Table 2). The relative Pd content is
2.5% presented in the fresh Pd/HY catalyst and the relative
Pd content of is decreased to 30.72% in the fresh Pd/7B2-HY
catalyst. However, the relative Pd content in the used Pd/HY
and Pd/7B2-HY catalyst is 26.90% and 29.54%, respectively. It
is established that Pd was reduced into Pd during the reac- catalysts determined by XPS, and the actual Pd content determined by
and curve tting were
0
2+
2
+
4
2
+
2
+
Table 2 The relative content of Pd species in the fresh and used
2
+
0
1
3–17
tion, contributing to the deactivation of Pd-based catalysts.
ICP
0
2+
Catalysts
Pd (area%)
Pd (area%)
Fresh Pd/HY
Used Pd/HY
Fresh Pd/7B2-HY
Used Pd/7B2-HY
57.50
73.10
69.28
70.46
42.50
26.90
30.72
29.54
Total Pd (wt%)
Loss ratio
of Pd (%)
Catalysts
Fresh
Used
Pd/HY
Pd/7B2-HY
0.59
0.75
0.17
0.45
71.2
40.0
Fig. 3 TG profiles of Pd-based catalysts.
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results (Table 2), the total Pd content in the used catalyst is
much less than that in the fresh one. The loss of ratio of Pd in
Conclusions
the Pd/HY catalyst is 71.2% and that in the Pd/7B2-HY catalyst is The boron-doped Pd/HY catalyst was prepared and assessed for
0.0% aer reaction. The less Pd loss in the Pd/7B2-HY catalyst acetylene hydrochlorination reaction. It is exhibited that B
also suggests that the B doping in the Pd-based catalysts can additive can improve the activity and stability of Pd-based/HY
4
stabilize Pd species.
FT-IR (a) and NH
catalysts during the reaction. The obtained Pd/7B2-HY catalyst
-TPD (b) results shown in Fig. 5 and S5† shows the best catalytic performance with the acetylene
3
were investigated the surface functional groups and acidic conversion and the VCM selectivity over 95% more than 30 h.
properties of Pd-based catalysts. For the HY zeolites, the region The results indicated that the presence of boron can make the
ꢁ
1
from 3800 to 3000 cm was attributed to the hydroxyl groups Pd species dispersed well and partly weaken carbon deposition
2
+
(
including Si–OH, Al–OH and H-bonded hydroxyl groups) and and Pd reduction, thus improving the catalytic stability.
ꢁ
1
the region from 1300 to 400 cm was indicated the framework
vibration of lattice cell (T-O-T unit: T is coordinated Si or Al
atoms). Compared with the HY support, there was slight band
38
Conflicts of interest
position shi in the B-doped samples but they remained kept
There are no conicts to declare.
ꢁ
1
the zeolite framework. However, the band at 3550–3410 cm
the hydroxyl groups) were disappeared in the used Pd/7B2-HY
(
catalyst, which was suggested the existence of catalytic activity Acknowledgements
that originated from the acidic sites on Y zeolite. Moreover,
This work was nancially supported by the Natural Science
Founds of General Programs of Xinjiang Uygur Autonomous
Region (2017D01C034).
NH -TPD results could further provide evidence to analyse the
3
changes of acidic properties on the fresh Pd/HY catalyst aer B
doping. Based on the desorption temperature, acid sites were
ꢀ
identied to possess weak (ꢂ115 C), medium strength (300–
ꢀ
ꢀ
5
00 C) and strong strength (750–850 C) in the Pd/HY catalyst,
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14–17
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doping, the range of peak corresponds to weak acid sites shied
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