Construction of activated carbon-supported B3N3doped carbon as metal-free catalyst for dehydrochlorination of 1,2-dichloroethane to produce vinyl chloride

Article abstract of DOI:10.1039/d0ra10037d

Dehydrochlorination of 1,2-dichloroethane (1,2-DCE) is an important oil-based way for the industrial production of vinyl chloride monomer (VCM), but has proved to be plagued by a high operating temperature and low efficiency. Therefore, environmentally friendly and metal-free catalysts are in high demand for green chemical processes. In view of the stronger electronegativity of borazine (B₃N₃) and convenience of constructing a two-dimensional structure because of the coplanarity of B₃N₃, the acetenyl group, and the benzene ring, herein, we report a novel controllable B₃N₃doped activated carbon (B,N-ACs) synthesized using B₃N₃-containing arylacetylene resin for dehydrochlorination of 1,2-DCE. The result is activated carbon loaded with B₃N₃-doped carbon nanosheets on the surface due to the B₃N₃-containing arylacetylene resin grown on the surface of activated carbons. The B,N-ACs deliver excellent catalytic performance, with a 1,2-DCE conversion of ～92.0% and VCM selectivity over 99.9% at 250 °C, significantly higher than that of the current catalysts in the industry. The results further verified that pyridinic-N and the internal B₃N₃play significant roles in this catalysis. The new green, metal-free B,N-ACs with excellent catalytic efficiency make it a promising catalyst for dehydrochlorination of 1,2-DCE to produce VCM.

Full text of DOI:10.1039/d0ra10037d

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PAPER
Construction of activated carbon-supported B N
3
3
doped carbon as metal-free catalyst for
dehydrochlorination of 1,2-dichloroethane to
produce vinyl chloride†
Cite this: RSC Adv., 2021, 11, 183
Chen Chen,‡ Zhaobing Shen,‡ Yaping Zhu, Fan Wang, Biao Jiang *bc
a
bc
a
a
a
and Huimin Qi
*
Dehydrochlorination of 1,2-dichloroethane (1,2-DCE) is an important oil-based way for the industrial
production of vinyl chloride monomer (VCM), but has proved to be plagued by a high operating
temperature and low efficiency. Therefore, environmentally friendly and metal-free catalysts are in high
demand for green chemical processes. In view of the stronger electronegativity of borazine (B
convenience of constructing a two-dimensional structure because of the coplanarity of B
acetenyl group, and the benzene ring, herein, we report a novel controllable B doped activated
carbon (B,N-ACs) synthesized using B -containing arylacetylene resin for dehydrochlorination of 1,2-
DCE. The result is activated carbon loaded with B -doped carbon nanosheets on the surface due to
the B -containing arylacetylene resin grown on the surface of activated carbons. The B,N-ACs deliver
3 3
N ) and
3 3
N , the
3 3
N
3
N
3
3
N
3
3 3
N
excellent catalytic performance, with a 1,2-DCE conversion of ꢀ92.0% and VCM selectivity over 99.9% at
Received 27th November 2020
Accepted 14th December 2020
ꢁ
2
50 C, significantly higher than that of the current catalysts in the industry. The results further verified
3 3
that pyridinic-N and the internal B N play significant roles in this catalysis. The new green, metal-free
DOI: 10.1039/d0ra10037d
B,N-ACs with excellent catalytic efficiency make it a promising catalyst for dehydrochlorination of 1,2-
rsc.li/rsc-advances
DCE to produce VCM.
2,5
may cause severe environmental problems. Recently, a lot of
work has been done on the catalysts to increase the conversion
1
. Introduction
Polyvinyl chloride (PVC) is one of the ve most commonly used of 1,2-DCE and the selectivity of VCM at low reaction tempera-
6
–11
engineering plastics in many elds. A common technique of ture.
Though they have drawn considerable interest in this
12
producing vinyl chloride monomer (VCM) in industry is the eld, until now, they are still far from industrialization.
1
thermal dehydrochlorination of 1,2-dichloroethane (1,2-DCE).
Therefore, efforts are ongoing to produce metal-free, environ-
This process is operated industrially at a temperature of 450– mentally friendly, and more efficient materials as catalysts for
ꢁ
50 C and pressure of 1–2 MPa, with a conversion of 1,2-DCE of industrial green chemical processes to date.
5
2–4
about 50–60%, and selectivity of VCM of about 95–99%.
Metal-free nanocarbon-based materials have been widely
1
3,14
However, coke is likely to be deposited in the tubular reactor reported as an ideal sustainable catalyst.
The chemical
because of the high operating temperature. This not only leads activities and catalytic properties of nanocarbon-based mate-
15–17
to blocking the reactor, but also a waste of energy resources, and rials can be easily tuned by heteroatoms functionalization.
Doping with heteroatoms such as nitrogen, boron, sulfur, and
phosphorus increase active sites and enhance the physical and
18–21
a
chemical activities of nanocarbon-based materials.
For
Key Laboratory of Specially Functional Polymeric Materials and Related Technology of
Ministry of Education, School of Materials Science and Engineering, East China instance, Xu et al. prepared a nitrogen-doped ordered meso-
University of Science & Technology, Shanghai, P. R. China. E-mail: qihm@ecust.edu.cn
porous carbon (N-OMCs) as the catalyst for dehydrochlorina-
b
Green Chemical Engineering Research Centre, Shanghai Advanced Research Institute,
Chinese Academy of Sciences, No. 99 Haike Road, Zhangjiang Hi-Tech Park, Pudong,
Shanghai, P. R. China
ꢁ
22
tion of 1,2-DCE, with a 1,2-DCE conversion ꢀ80% at 300 C.
Furthermore, doping carbon with two elements has been found
to effectively enhance its properties over those of its singularly
doped counterparts, which is a result of the synergistic coupling
c
Shanghai Green Chemical Engineering Research Centre, Shanghai Institute of Organic
Chemistry, Chinese Academy of Sciences, No. 345 Lingling Road, Shanghai, P. R.
China. E-mail: jiangb@mail.sioc.ac.cn
23,24
effects between heteroatoms.
In particular, boron and
†
1
‡
Electronic supplementary information (ESI) available. See DOI: nitrogen have attracted great interest because B and N are
0.1039/d0ra10037d
adjacent to C in the periodic table and has similar atomic
These authors contributed equally.
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25–29
characteristics with the carbon atom.
Thus, the substitution based carbon) was purchased from Ningxia Guanghua Acti-
of the C–C units with B–N does not alter the structural features, vated Carbon Co., Ltd. ACs was pre-treated by a solution of HCl
but the strong polarity of B–N can create a unique electronic (2 M). The nitrogen (99.99%) gas were purchased from Shanghai
structure, which can change the catalytic performance of raw Air Liquide Co., Ltd.
30–34
materials.
3 3
Borazine (B N ), as a novel B–N compound with
a planar hexagonal structure, has equalized bond lengths to 2.2 Preparation of borazine-containing arylacetylene (PBSZ)
35
ꢀ
ꢀ
that of benzene (1.40 A for benzene and 1.44 A for borazine).
resin
Borazine has presented great potential in tailoring the elec-
tronic structure of carbon materials due to its electronegativity
All synthetic reactions described below were carried out in
a nitrogen atmosphere using Schlenk techniques. The B,B ,B -
0
00
(
5.04) as a doping unit being higher than that of boron (2.04)
trichloroborazine (TCB) was prepared by allowing BCl
3
to react
36
and nitrogen (3.04). For instance, B N doping in the graphene
ꢁ
3
3
with NH Cl in toluene at 110 C and puried by sublimation.
4
increase the HOMO–LUMO and optical gap, imparting strong
The PBSZ resin was obtained according to the following
procedure. EtMgBr (7.99 g, 0.06 mol) in 60 mL THF was added
in a 250 mL four-necked ask equipped with a condenser,
thermometer, mechanical agitation, and funnel. DEB (3.78 g,
37–39
UV-emitting absorption and electrical insulating.
It can be
used as good microwave-absorbing material, positive electrode
material, also can improve the catalytic performance of result-
40,41
ing materials like oxygen reduction reaction.
Inspired by this
0
.03 mol) in 30 mL THF was dropped into EtMgBr solution and
idea, we wonder if such B doping of carbon materials can
3
N
3
ꢁ
reacted at 70 C for 2 h to synthesis diethynylphenyl-
magnesium bromide (DEPM) as shown in Scheme 1. Then
cooling the solution to 0 C, TCB (1.84 g, 0.01 mol) in 70 mL
enhance the adsorption of 1,2-DCE and the catalytic perfor-
mance for dehydrochlorination of 1,2-DCE accordingly because
of an increased electron density near the B N . Therefore, it is
ꢁ
3
3
toluene was dropwise added. Aer that, the mixture was allowed
quite clear that the further study of preparing B
3
N
3
doped
ꢁ
31
to heat up to 50 C and stirring for an additional 4 h. The
solution was cooled to room temperature and dioxane was
added to the solution at last until no more precipitation was
produced and then standing for 6 h. Subsequently, the
suspension was centrifuged, then PBSZ resin was obtained by
carbon materials and using them as a kind of potential catalysts
for dehydrochlorination of 1,2-DCE to produce VCM will be
essential and inspiring.
In our previous work, we successfully prepared B
3 3
N doped
31
carbon nanosheets using B N -containing arylacetylene resin.
3
3
removing the solvent from the clear superstratum solution by
2
The hybridization of atoms in the arylacetylene resin, sp for
1
rotary evaporation. Anal.: NMR (CDCl ): ( H, ppm) ¼ 7.20–7.80
3
2
boron in B N , sp for carbon in the benzene ring, and sp for
3
3
(m, Ar), 3.11 (s, –C^CH), 5.60 (brs, –NH).
carbon in the acetenyl group, ensures the two-dimensional (2D)
structure of the resultant. However, their limitation of low
surface area for practical applications is also recognized. In this
respect, activated carbons may provide a solution by serving as
a support for nanostructured carbon, which could afford a large
2
3 3
.3 Preparation of B N doped activated carbons (B,N-ACs)
B,N-ACs were prepared by an incipient wetness vacuum
impregnation technique using ACs and PBSZ resin solution
shown in Scheme 2. The PBSZ resin was congured to 11 wt%,
42,43
surface area,
meanwhile, it also can provide a base plane for
1
3 wt%, 15 wt% and 17 wt% using THF solvent, respectively.
the two-dimensional growth of polymer. In light of the infor-
mation above, in this study, B N doped activated carbons (B,N-
PBSZ resin solution with a certain concentration was added
quantitatively into 5 g ACs powder. Having been solvent
extraction for 2 h and desiccated at 120 C for 12 h, the dried
PBSZ@ACs was calcined in a tubular furnace at 700 C for 2 h
under N atmosphere with a heating rate of 2.6 C min . The
PBSZ resin solution loading changed according to the mass
ratio with constant ACs. The obtained B,N-ACs samples were
labelled as shown in Table 1.
3
3
3 3
ACs) by using B N -containing arylacetylene resin (PBSZ) was
ꢁ
prepared for dehydrochlorination of 1,2-DCE. The effect of
concentration and proportion of the PBSZ precursor was
determined. Morphology and thermogravimetric analysis were
performed to investigate the formation and deactivation
mechanism of the catalysts. The catalytic performance of
prepared materials and the main active sites of the catalysts
were discussed.
ꢁ
ꢁ
ꢂ1
2
ꢁ
As a comparison, the ACs was calcined at 700 C without the
addition of PBSZ solution, and the obtained sample was deno-
ted as AC.
2. Experimental
2.1 Materials
Boron trichloride was purchased from Beijing Multi Technology
Co. Ltd. Diethynylbenzene (DEB) was supplied by Fine Chem-
ical Institute of East China University of Science and Tech-
nology and distilled on a vacuum line before using. Ammonium
chloride, ethylmagnesium bromide (EtMgBr), 1,2-DCE, hydro-
chloric acid, toluene, and tetrahydrofuran (THF) were
purchased from Taitan Technology Co., Ltd. Tetrahydrofuran
and toluene were reuxed over sodium and freshly distilled in
nitrogen before using. Activated Carbons (ACs) (neutral, coal- Scheme 1 Schematic representation of the synthesis of PBSZ.
184 | RSC Adv., 2021, 11, 183–191
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ꢂ1
velocity (LHSV) of 0.67 h by a microinjection pump at a rate of
ꢂ1
1
mL h . The effluent of the reactor was condensed to separate
the unreacted 1,2-DCE and then passed into an absorption
bottle containing water to remove HCl, followed by the
composition analysis using a gas chromatograph (Shimadzu
GC-2014) with a hydrogen ame ionization detector (FID).
The conversion of 1,2-DCE (X) and the selectivity to VCM (S)
as the criteria of catalytic performance were dened as the
following equations, respectively:
Scheme 2 Schematic representation of the synthesis of B,N-ACs.
Table 1 Details of the sample
Q ꢃ r ꢃ t ꢂ m
X ¼
ꢃ 100%
Q ꢃ r ꢃ t
Concentration
of PBSZ solution
Mass ratio
with ACs
Samples
S ¼ 4 ꢃ 100%
ꢂ1
PBSZ–AC-1#
PBSZ–AC-1*
PBSZ–AC-1
PBSZ–AC-1
PBSZ–AC-2
PBSZ–AC-3
11 wt%
13 wt%
15 wt%
17 wt%
15 wt%
15 wt%
1 : 1
1 : 1
1 : 1
1 : 1
2 : 1
3 : 1
where, Q is the volume ow rate of 1,2-DCE (Q ¼ 1 mL h ), r is
the mass density of 1,2-DCE, t is the time of reaction time. m is
the collection mass of 1,2-DCE, 4 is the mole fraction of VCM in
the gas mixture of which composition is analysed by gas
chromatograph.
0
3
. Results and discussion
2.4 Characterization and instrumentation
3.1 Synthesis of the B,N-ACs
The structures of PBSZ were analysed using Fourier transform
infrared spectroscopy (Nicolet-6700, Thermo Fisher Scientic The PBSZ resin solution was prepared through the condensa-
1
Company) and H NMR spectroscopy (Bruker Avance 400). tion reaction of TCB and DEPM, its structure was conrmed by
1
Morphological features characterization of the sample was the FTIR and H NMR as shown in Fig. S1.† The PBSZ solution
performed using a high-resolution transmission electron was used as a precursor to impregnate ACs, which could supply
microscope (HR-TEM, JEM-2100, JEOL Company, USA) and eld the boron and nitrogen source simultaneously. The hybridiza-
2
2
emission scanning electron microscope (FE-SEM, S-4800, Hita- tion of atoms in the PBSZ resin, sp for boron in B N , sp for
3 3
chi Company, Japan). The XPS spectra were performed on X-ray carbon in the benzene ring, and sp for carbon in the acetenyl
photoelectron spectroscopy (EscaLab 250Xi, Thermo Fisher group, enabled the 2D structure of the PBSZ. Among all kinds of
Scientic Company, USA). The X-ray diffraction (XRD) patterns the PBSZ solution concentration, when the concentration was
were determined by the Bruker D8 Advance X-ray powder lower than 13 wt%, it can be obviously found that the resin
ꢁ
ꢁ
diffraction instrument with 2q between 5 to 80 . Thermogra- cannot be completely impregnated with the pore surface of the
vimetric analysis (TGA) was conducted with a TGA/DTA system ACs from the catalytic performance as shown in Fig. S2†
ꢁ
(
SDT Q600, TA Company, USA) at room temperature to 900 C because the resin content was too low, the impregnating effect
ꢁ
ꢂ1
with the air ow of 10 C min in air atmosphere. Raman became worse. And when the concentration was higher than
spectra were acquired using a micro-Raman spectroscopy 15 wt%, the viscosity became higher. It was obvious that the
system (inVia reex, Renishaw Company, US, with excitation PBSZ solution was difficult to uniformly impregnate on the pore
energy of 2.41 eV, 514 nm). Brunauer–Emmett–Teller (BET) surface of activated carbons, which also reduced the impreg-
surface area data were collected by obtaining nitrogen adsorp- nating effect. This also can be demonstrated by the catalytic
tion-desorption isotherms at 77 K using a Micromeritics ASAP performance shown in Fig. S2.† Because of the poor impreg-
0
2
020 analyzer.
nating effect, the performance of PBSZ–AC-1# and PBSZ–AC-1
was far lower than that of PBSZ–AC-1* and PBSZ–AC-1. There-
fore, the concentration limit of PBSZ solution has a great
inuence on the nal catalytic performance.
2.5 Catalytic activity evaluation
The catalytic performance of B,N-ACs and AC evaluation was
In the synthesis process of B,N-ACs, porous activated
performed in a xed bed microreactor (i.d. ¼ 6 mm). The carbons with large specic surface area as the support and base
temperature of the reactor was regulated using a temperature planar which can enhance the contact area for the formation of
controller (Y-Feng, Shanghai, China). The 1,2-DCE ow rate was active sites on the surface and 2D growth of PBSZ polymer,
regulated using a 2ZB-1L10 piston pump (Weixin, Beijing, respectively. At the initial phase, PBSZ resin was rstly adsorbed
China). Before each of the reaction, the reactor was cleaned with on the surface of activated carbons under the action of negative
nitrogen to remove moisture and air in the reaction system until pressure. Then, PBSZ resin began to grow up through the Diels–
ꢁ
the microreactor was heated to 250 C. Aerward, liquid 1,2- Alder reaction, coupling reaction and cycloaddition reaction
DCE was fed into a vaporizing chamber with liquid hourly space based on the carbon–carbon triple bond on the surface of
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ꢁ
ꢁ
activated carbons during carbonization at 700 C and formed a certain molecular weight during carbonation process at 700 C
a new molecular layer containing boron and nitrogen on the on the surface of ACs. Next, the boron and nitrogen co-doped
ꢁ
surface of activated carbons as shown in Scheme 2. 700 C was ACs with the coexistence of micropores and mesopores was
benecial to the growth of PBSZ on the one hand, and can also formed. As shown in Table 2, a certain dosage (ratio of PBSZ/
keep the high specic surface area of activated carbon as far as ACs) and concentration of PBSZ resin solution were very crit-
31
possible on the other hand. (In order to observe the growth ical to control the special surface area and total pore volume of
thickness of the PBSZ molecular layer, the PBSZ precursor was the catalyst which decided the amount and distribution of the
ꢁ
carbonized at 700 C, and the result was shown in Fig. S3,† active sites of the catalyst. It can be seen that with the increase
which was about 2.8 nm.)
of dosage of PBSZ, the specic surface area and total pore
volume were decreased, especially PBSZ–AC-3, mainly due to the
mesopores formed by the deposition of the polymer as dis-
cussed above. In addition, the PBSZ–AC-1* exhibited higher
special surface area and N atoms content than the PBSZ–AC-1,
due to the lower concentration of the PBSZ resin solution on
ACs. The very thin lm of PBSZ polymer formed on the surface
of ACs, which produced catalytic active structure, but not seri-
ously blocked the micropores of ACs.
3.2 Characterization of the B,N-ACs
Catalyst textural properties of the B,N-ACs. To investigate the
textural properties of the B,N-ACs, N2 adsorption–desorption
isotherms analysis was performed. As shown in Fig. 1, the B,N-
ACs catalysts exhibited a combination of type-I/IV adsorption–
desorption isotherms with strong N
sures (P/P < 0.1) and gradual adsorption at higher partial
pressures (0.1 < P/P < 1.0). The results demonstrated a strong
interaction between the catalysts and N , and indicated the
2
adsorption at low pres-
0
SEM and TEM studies of the B,N-ACs. To study the surface
morphology of the B,N-ACs catalysts, the SEM and HRTEM
technologies had been performed. The morphology and the
dispersion of boron and nitrogen atoms in the catalysts were
observed by means of SEM and EDS shown in Fig. 2 and S4–S8.†
In Fig. 2g, it was shown that nitrogen and boron elements were
doped in the ACs successfully and well distributed homoge-
neously in the catalysts. Compared to the HRTEM image of AC
in Fig. 2e, the HRTEM image of PBSZ–AC-1* could be clearly
observed that the polymer layer on the surface of AC in
0
2
coexistence of micropores (<2 nm) and small mesopores (2–5
nm). There was an obvious hysteresis loop caused by capillary
condensation at a wide relative pressure P/P ranging from 0.1–
0
1.0, which also indicated that there were mesopores in the
catalysts. The adsorption–desorption isotherms of PBSZ–AC-3
illustrated that with the increase of dosage (ratio of PBSZ/
ACs), there was much PBSZ resin coated on the ACs and the
textural character of the catalyst was completely supplied by the
growth of polymer, with the mainly sheet mesopores. As shown
in Table 2, the surface area and total pore volume of B,N-ACs
catalysts were lower than those of AC, mainly due to the pore
blocking resulted from the decomposition of PBSZ resin, in
agreement with the result of the adsorption–desorption
isotherms. This also demonstrated that the successful loading
of N and B atoms into the ACs surface, which usually could
increase the defects and active sites of ACs. Besides, the special
surface area and total pore volume of the PBSZ–AC-3 were lower
than PBSZ–AC-2 obviously, due to the main mesopores of the
PBSZ–AC-3 completely produced by the decomposition of the
polymer, with nothing to do with ACs.
44,45
Fig. 2f.
That also indicated the formation process of the B,N-
ACs catalyst. First, a very thin voile-like layer was formed on the
AC surface, and then the thin layer started to recombined to
produce C–N–B structure with the continuing process of calci-
nation, the textural structure and chemical composition of the
carbon layer can be nely modulated while the macro-
morphology of the material is retained, in consistent with the
isotherms and BET study.
Raman and XRD studies of the B,N-ACs. To further study the
surface properties of the B,N-ACs catalysts, Raman and XRD
technology were performed. It was shown in Fig. 3a, there were
ꢂ1
ꢂ1
two obvious peaks at ꢀ1350 cm and ꢀ1580 cm which cor-
responded to the D band originating from lattice distortion in
sp -hybridized carbon and G band arising from the tangential
stretching mode of sp -hybridized carbon, respectively. The
According to the investigation of the textural properties of
the catalyst, the formation process of the B,N-ACs catalyst was
deduced as follows. First, the PBSZ resin was uniformly absor-
bed on the surface of ACs. Then the resin started to grow up to
2
2
intensity ratio of D to G band (I /I ) was used to evaluate the
D
G
graphitization and defective degree of carbon materials. It was
noteworthy to mention that compared with the B,N-ACs, the
D G D G
PBSZ–AC-1* had the highest I /I ratio (1.03) and the I /I ratio
decreased with the increase of PBSZ dosage (0.95, 0.87 and 0.85
for PBSZ–AC-1, PBSZ-AC-2 and PBSZ-AC-3, respectively). It
indicated the PBSZ–AC-1* had the largest defect density in the
structure which could provide more adsorption sites and active
sites for the catalytic reaction.
Fig. 3b showed the XRD patterns of the fresh catalysts. Two
ꢁ
ꢁ
distinct diffraction planes with peak positions at 25 and 43
were detected in all catalysts, which correspond to the (002) and
(
46
101) diffraction planes of graphitic carbon. The peaks of
2
Fig. 1 (a) N adsorption–desorption isotherms of the B,N-ACs cata-
lysts; (b) the corresponding pore size distributions (PSD) on the surface
of the B,N-ACs catalysts.
magnesium salt were not detected in the material, indicating
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Table 2 Texture parameters and surface element content of the catalysts
c
c
N 1s content
(atom%)
B 1s content
(atom%)
a
2
ꢂ1
b
3
ꢂ1
S
BET (m g
)
V (cm g
)
Sample
AC/PBSZ
Fresh
Used
Fresh
Used
Fresh
Used
Fresh
Used
AC
1 : 0
1 : 1
1 : 1
1 : 2
1 : 3
965
678
531
441
199
920
542
524
399
47
0.49
0.36
0.29
0.26
0.19
0.47
0.28
0.28
0.24
0.09
—
—
—
—
PBSZ–AC-1*
PBSZ–AC-1
PBSZ–AC-2
PBSZ–AC-3
1.46
1.23
1.62
1.45
0.97
1.22
1.01
0.97
0.33
0.41
0.40
0.54
0.32
0.28
0.38
0.38
a
b
c
S
BET: special surface area. V: total pore volume. Surface element content determined by XPS.
3
98.3 eV, 398.8 eV, 400.3 eV and 401.2 eV, attributed to the
structure of NB C or NB in the interior site (that is B in the
interior site of the polymer layer), pyridinic-N, pyrrolic-N and
the N of amide groups (NB H) in the B (that means B at
the exterior site of the polymer layer), respectively.
Meanwhile, the impregnant discussed above was PBSZ (B N -
2
3
3 3
N
2
3
N
3
3 3
N
2
5,39,48–50
3
3
containing arylacetylene) resin solution, and the doping on the
ACs surface was mainly due to the growth of PBSZ through the
Diels–Alder reaction, coupling reaction and cycloaddition
ꢁ
reaction based on the carbon–carbon triple bond at the 700 C.
Therefore, above all, it can be explained that the doping struc-
ture in the B,N-ACs catalyst was mainly in the form of B N .
3 3
3.3 Catalytic performance of the B,N-ACs
To investigate the inuence of N and B on the catalytic perfor-
mance of dehydrochlorination of 1,2-DCE, the B,N-ACs and AC
were evaluated, respectively, as shown in Fig. 5. To reduce the
inuence of errors, the investigation of the catalytic perfor-
mance started when the reaction reached the restively stable
state. AC showed very low catalytic performance of the dehy-
drochlorination, with the conversion of 1,2-DCE only 19.8%,
Fig. 2 SEM micrograph of the (a and b) fresh PBSZ–AC-1* catalyst; (c
and d) used PBSZ–AC-1* catalyst; HRTEM images of (e) AC; (f) the
fresh PBSZ–AC-1* catalyst; (g) elemental distribution mapping of C,
B, N in fresh PBSZ–AC-1*.
ꢁ
and the selectivity of VCM ꢀ92.9% at 250 C, due to almost no
active sites on AC. Compared with AC, the B,N-ACs all exhibited
excellent catalytic performance, with the 1,2-DCE conversion
6
9
1.7%, 71.4%, 75.2% and 92.0%, and the selectivity of VCM
9.0%, 99.5%, 99.7% and 99.9% over PBSZ–AC-3, PBSZ–AC-2,
PBSZ–AC-1 and PBSZ–AC-1*, respectively.
The result indicated that the B, N-dopant could greatly increase
the catalytic activity of ACs for 1,2-DCE dehydrochlorination. In
addition, it can be found that PBSZ–AC-1* has the best catalytic
performance, mainly because it has the highest specic surface
area and pore volume, giving it the highest defect density, which is
also consistent with the Raman results. The catalytic performance
of other catalysts also conrmed to this statement.
Fig. 3 (a) Raman spectra of the fresh catalysts; (b) XRD patterns of the
catalysts.
the magnesium salt have been disappeared by acid pickling,
and the catalytic performance had nothing to do with the metal.
Doping structure of the B,N-ACs. To further study the doping 3.4 The study on active sites of the B,N-ACs
structure of the B,N-ACs catalysts, the high-resolution N 1s
To study the active sites and mechanism of the dehydrochlori-
spectrum of the B,N-ACs catalysts were performed by XPS
analysis. As shown in Fig. 4, no obvious peak of B 1s was
observed and deconvoluted, which may be caused by the low
sensitivity factor and content of the boron. The N 1s of the
catalyst samples were clearly divided into four peaks around
nation, the high-resolution N 1s spectrum of the fresh and used
B,N-ACs catalysts were performed by XPS analysis. As shown in
Fig. 4 and Table 3. As shown in Table 3, PBSZ–AC-1* had the
47
highest content of the internal B
3
N
3
and pyridinic-N, while the
was the lowest
content of the pyrrolic-N and exterior B
3 3
N
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Fig. 4 The high-resolution N 1s spectrum of fresh catalysts.
pyridinic-N decreased, while the content of pyrrolic-N and
exterior B
tion concentration and dosage, the PBSZ formed a much thicker
lm by polymerization on the surface of ACs. Compared with
3 3
N increased. With the increase of PBSZ resin solu-

the thin lm, the chemical states of N atom were difficultly to
transform in the thicker polymer lm at the carbonization
condition. So, it is very crucial to control the dosage of the PBSZ
to increase the distribution of N and B atoms and the content of
3 3
the internal B N and pyridinic-N in the catalysts. As can be
Fig. 5 (a) The conversion of 1,2-DCE over the B,N-ACs catalysts; (b)
the selectivity of VCM over the B,N-ACs catalysts. Reaction conditions: seen from the catalytic performance of the dehydrochlorination
ꢁ
ꢂ1
.
temperature ¼ 250 C, 0.1 MPa, LHSV (1,2-DCE) ¼ 0.67 h
of 1,2-DCE over the B,N-ACs catalysts, PBSZ–AC-1* exhibited the
highest conversion of 1,2-DCE and selectivity to VCM, and with
the increase of PBSZ solution concentration and dosage, the
catalytic performance decreased gradually. The study showed
that the change rule of the catalytic performance over the B,N-
among all the catalysts. The catalysts soaked with a higher PBSZ
resin solution concentration was just the opposite. With the
increase of dosage of PBSZ, the content of internal B N and
3 3
Table 3 Quantitative N 1s analysis of the fresh and used catalysts determined by XPS
a
b
c
d
Catalysts
N
I
(%)
N
P
(%)
N
Pyr (%)
N
E
(%)
N
I
+ N
P
(%)
N
Pyr + N
E
(%)
PBSZ–AC-1*
PBSZ–AC-1
PBSZ–AC-2
PBSZ–AC-3
Used PBSZ–AC-1*
Used PBSZ–AC-1
Used PBSZ–AC-2
Used PBSZ–AC-3
13.50
9.84
8.33
7.50
9.40
8.90
6.90
6.45
20.90
19.12
16.67
13.33
18.70
12.33
12.41
12.90
22.00
24.59
25.00
27.50
22.60
27.40
28.98
29.03
43.60
46.45
50.00
51.67
49.30
51.37
51.72
51.62
34.40
28.96
25.00
20.83
28.10
21.23
19.31
19.35
65.60
71.04
75.00
79.17
71.90
78.77
80.69
80.65
a
b
c
d
Structure of NB
).
2
C or the NB
3
in the interior site (the internal B
3
N
3
). Pyridinic N. Pyrrolic N. The N of amide groups (NB
2
H) in the B
3
N
3
(the
3 3
external B N
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ꢁ
ACs catalysts was consistent with that of the N and B chemical 500 C, the weight loss of the used catalysts was higher than that
states. As shown in Table 3, line 7, with the increase of the of the fresh catalyst. The difference value of weight loss between
dosage and concentration of the PBSZ, the total content of the the fresh and used catalysts caused by the coke deposit and
internal B N3 and pyridinic-N decreased gradually, but the residual of reaction mass on the catalyst surface, indicating that
3
content of the pyrrolic-N and the exterior B
Therefore, it was concluded that the internal B
3
N
3
increased. the side reaction occurred on the catalysts surface during the
ꢁ
3
N
3
and dehydrochlorination of 1,2-DCE. While over 500 C, the mass
pyridinic-N were the active sites in the B,N-ACs catalysts, which loss of the catalysts was due to the burning of the ACs support in
play crucial roles in the dehydrochlorination of 1,2-DCE reac- an air atmosphere. The TGA results indicated that the coke
tion. In order to further verify this result, XPS was employed on deposition may be the main reason for the deactivation of the
the used catalyst and the high-resolution regional spectra of N
1
s as shown in Fig. 6. There are four obvious peaks on the used
catalyst like the fresh catalyst. As shown in Table 3, corre-
sponding to each fresh catalyst, the content of the internal B
and pyridinic-N in used catalysts decreased, and the content of
pyrrolic-N and the exterior B increased, which further
showed that compared with pyrrolic-N and the exterior B
the internal B and pyridinic-N were more likely active sites of
3 3
N
3 3
N
3 3
N ,
3 3
N
the dehydrochlorination of 1,2-DCE reaction. The pyridinic-N
and the internal B N species were partly covered by the coke-
3
3
deposition in the reaction. Therefore, the contents were rela-
tively decreased.
3.5 The study on deactivation of the B,N-ACs
To analyse the coke deposition of catalysts and clarify the
reason for the deactivation of the catalysts, TGA was performed
to demonstrate the analysis results as shown in Fig. 7. Below
ꢁ
1
00 C, the slight weight loss of the catalyst was due to the
Fig.
atmosphere of fresh and used catalysts, (a) PBSZ–AC-1*, (b) PBSZ–
adsorbed on the catalysts. In the temperature range of 100– AC-1, (c) PBSZ–AC-2, (d) PBSZ–AC-3.
7 Thermogravimetric analysis (TGA) curves recorded in air
moisture evaporation and other small molecules which were
Fig. 6 The high-resolution N 1s spectrum of fresh catalysts and used catalysts.
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catalysts. In addition, the amount of the coke deposition of Research Funds for the Central University (5032104918013,
PBSZ–AC-1*, PBSZ–AC-1, PBSZ–AC-2 and PBSZ–AC-3 was 3.87%, 5032104917001). The Key Laboratory of Specially Functional
2.99%, 2.43% and 1.31%, respectively, during the catalytic Polymeric Materials and Related Technology of Ministry of
reaction. The results indicated that coke deposition gradually Education, East China University of Science & Technology was
increased with the decreasing of the dosage and PBSZ resin responsible for the synthesis and characterization of the
solution concentration. Therefore, with a suitable content of samples, and Green Chemical Engineering Research Centre,
PBSZ precursor, the B,N-ACs catalysts had more potential to Shanghai Advanced Research Institute, Chinese Academy of
adsorb and activate the 1,2-DCE in the dehydrochlorination, Sciences, Shanghai Green Chemical Engineering Research
and at the same time, the much more micropores on the cata- Centre, Shanghai Institute of Organic Chemistry, Chinese
lyst caused the side reaction, due to the long dwell time.
Academy of Sciences was responsible for the catalytic activity
To further verify the deactivation of the catalyst due to coke evaluation of the samples.
deposition, N adsorption–desorption isotherms analysis and
2
SEM were performed on the used catalysts, as shown in Fig. S8,†
2
c, d and Table 2. The surface area and total pore volume of
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