Mesoporous carbon nitride as a basic catalyst in dehydrochlorination of 1,1,2-trichloroethane into 1,1-dichloroethene

Article abstract of DOI:10.1039/c5ra22214a

1,1-Dichloroethene has many applications in industrial production and it holds great promise in developing a vapor phase catalytic dehydrochlorination process. We synthesized a carbon nitride material by dissolving dicyandiamide in N,N-dimethylformamide (DMF) as a precursor and using SBA-15 as a template. A carbon nitride material with a mesoporous structure and textured pores has been obtained and then characterized by N₂-adsorption measurements, XRD, HRTEM, EDS and FT-IR. A mesoporous carbon nitride material with a surface area of 350 m² g^-1 and pore volume of 0.72 cm³ g^-1 was fabricated, which also possessed triazine N heterocycles with extra amino groups. It is an outstanding heterogeneous base catalyst in the selective catalytic dehydrochlorination of 1,1,2-trichloroethane into 1,1-dichloroethene reaction with a maximum 1,1,2-trichloroethane conversion of 23.96% and maximum 1,1-dichloroethene selectivity of 100%. A total of 110 h stability experiment of the catalyst was provided and the selectivity stayed above 99% all through the experiment and the conversion remained no less than 15% for 35 h.

Full text of DOI:10.1039/c5ra22214a

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ARTICLE
Mesoporous Carbon Nitride as Basic Catalyst in
Dehydrochlorination of 1,1,2-Trichloroethane into 1,1-
Dichloroethene
Received 00th January 20xx,
Cong Tian, Chunshan Lu, Bolin Wang, Xiangzhou Xie, Yangsen Miao, Xiaonian Li *
1,1-dichloroethene has many applications in industrial producing and it holds great promise in developing vapor phase
catalytic dehydrochlorination process. We synthesized the carbon nitride material by dissolving dicyandiamide in N,N-
dimethylformamide (DMF) as precursor and using SBA-15 as template. Carbon nitride material with mesoporous structure
and textured pores had been obtained and then characterized by N2-adsorption measurements, XRD, HRTEM, EDS and FT-
IR. The mesoporous carbon nitride material with surface area of 350m2/g and pore volume of 0.72cm3/g was fabricated,
which also possessed triazine N heterocycles with extra amino groups. It exhibited as an outstanding heterogeneous base
catalyst in selective catalytic dehydrochlorination of 1,1,2-trichloroethane into 1,1-dichloroethene reaction with a
maximum 1,1,2-trichloroethane conversion of 23.96% and maximum 1,1-dichloroethene selectivity of 100%. A total of 110
h stability experiment of the catalyst was provided and the selectivity stayed above 99% all through the experiment as well
as the conversion remained no less than 15% for 35 h.
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
5
ZSM-5 . None of them can avoid the fast deactivation of CsCl
6
Introduction
caused by hydrogen chloride. Heijden used La2O3 as catalyst
in dehydrochlorination of TCE reaction and resulted better
stability comparing with alumina and Cs supported catalysts.
1,1-dichloroethene (DCE) is a monomer of polyvinylidene
chloride (PVDC), for the production of packing films, synthetic
fibers, and also used for the production of 1,1,1-
trichloroethane 1.
But the deactivation caused by hydrogen chloride still could be
observed. Hence, developing a new basic catalyst with high
activity, selectivity and especially stability has become a rather
urgent necessity to advance the catalytic dehydrochlorination
of TCE.
Recently, carbon nitride (CN) materials have received more
and more attentions because of its unique characteristics such
as semiconductivity, energy storage, and basicity 7, 8. Owing to
these features, carbon nitride has been considered one of the
Currently, DCE was produced via the alkaline hydrolysis
process of the 1,1,2-trichloroethane (TCE) dehydrochlorination
in liquid phase. This method led to huge amount of waste
water and possessed rather low atomic efficiency from the
view of atom economy. The catalytic dehydrochlorination of
TCE over solid catalyst in gas phase should be an
environmentally friendly process, owing to the absence of
sodium hydroxide, no waste water needs to be disposed and
with the recycling of hydrogen chloride and almost 100%
effective atom utilization could be achieved. However, the
sharply deactivation of solid catalysts had been a great
challenge in the gas phase TCE dehydrochlorination. Mochida2
applied alumina as a solid basic catalyst into the vapor phase
catalytic dehydrochlorination of TCE using the pulse technique,
and the results exhibited rather high activity of selective
conversion of DCE. But the as produced hydrogen chloride can
strongly adsorb on the active site and converse alumina into
deactivate aluminum chloride. Further investigation had been
9
most promising candidates to complement carbon materials
and has been studied in the field of photocatalysis 10, fuel cells
11, heterogeneous catalysis 12, and gas storage 13. Attributing to
the inbuilt basic site of nitrogen-contenting groups, the carbon
nitride materials were evaluated as a heterogeneous catalyst
in Friedel–Crafts Reaction of Benzene 9, CO2 activation14, water
splitting15
and
Knoevenagel
condensations
and
transesterification reactions 16. Li 17 investigated the catalytic
performance of carbon nitride for acetylene hydrochlorination
and the carbon nitride catalyst exhibited enhanced catalytic
activity. The result suggested carbon nitride catalyst is able to
adsorb and activate acetylene as well as hydrogen chloride
simultaneously. Meanwhile, these results indicated carbon
worked on CsCl/SiO2 3, CsNO3/SiO2 and Cs ion exchanged
4
nitride catalyst can be
dehydrochlorination reaction.
a
potential candidate for
Herein, we reported the catalytic performance of carbon
nitride materials, synthesized using dicyandiamide (DCDA)
dissolved into N,N-dimethylformamide (DMF) as precursor, in
The Industrial Catalysis Institute of College of Chemical Engineering of Zhejiang
University of Technology, State Key Laboratory Breeding Base of Green Chemistry-
Synthesis Technology, Hangzhou, 310032, PR China
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the selective catalytic dehydrochlorination of TCE into DCE
reaction.
Results and Discussion
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DOI: 10.1039/C5RA22214A
The XRD patterns of the carbon nitride samples were
presented in Fig.1. Both patterns can be the illustration of
graphite carbon nitride. The intense diffraction peaks at
around 2θ=27° displayed on both patterns corresponded to
the (002) planes, characteristic of interplanar stacking peak of
conjugated aromatic system 15. A slightly broadening and
decreasing of intensity in the (002) peak was observed in CN-
Experimental
Preparation of CN Material
10g of DCDA was dissolved into 35mL of DMF (the sample DMF when comparing with CN-water, which indicated the
dissolved in DMF was labeled as CN-DMF and the sample crystallinity is lowered due to the better dispersion of
dissolved in deionized water was labeled as CN-water) under precursor with DMF. The pronounced additional peak detected
stir. The solution was then added onto pre-dried SBA-15 at around 2θ=13° can be attributed to an interlayer structural
9
dropwisely. After 6h of digestion, the mixture was handled by packing motif . These peaks exhibited in the patterns confirm
an ultrasonic treatment for 2h and then heated at 90
overnight. The resultant solid was ground in a mortar and
heated at 3 /min to 550 and kept at 550 for another 4 h.
℃
a structure of graphitic materials 9.
℃
℃
℃
The as synthesized brown powder was immersed in 4mol/L
aqueous solution of NH4HF2 (100mL) for 2 days to remove the
siliceous template. The dispersion was then filtered and
washed with distilled water and ethanol for several times.
After filtering, the as obtained yellow compound was dried
（002）
under vacuum at 100
℃ overnight.
（100）
Sample Characterization
a
X-ray diffraction (XRD) patterns of the samples were measured
with a Thermo X’TRA X-ray diffractometer using Cu Kα
radiation. N2 adsorption–desorption isotherms of the samples
at 77K were measured by using a Micrometrics instrument
(ASAP2020). Specific surface areas were calculated according
to the Brunauer–Emmet–Teller (BET) method and pore size
distribution curves were obtained from the adsorption
branches using the Barrett–Joyner–Halenda (BJH) method. The
surface area was calculated in P/P0 range of 0.05-0.3 and pore
volume was determined at P/P0 value of 0.995. The
morphology was observed by high-resolution transmission
electron microscopy (HRTEM) in a JEM-1200EX equipment.
The elemental composition of catalysts was determined by
energy dispersive spectrometer (EDS, Thermo Vantage ESI).
FTIR spectroscopy was performed in transmission mode on KBr
pellets of the samples at room temperature on a Thermo
scientific Nicolet is50 FT-IR spectrometer (resolution: 4cm-1, 64
scans per spectrum, 400–4000cm-1).
b
0
10
20
30
40
50
60
70
80
90
2θ (o)
Fig. 1 XRD patterns of CN-water (a) and CN-DMF (b)
N2-adsorption/desorption isotherms and BJH pore-size
distribution of the CN-DMF sample are showed in Fig.2. The
typical type IV curves along with H1 hysteresis loops can be
observed at 0.6-1P/P0. The results indicated the CN-DMF
sample possessed well-constructed mesoporous structure,
meanwhile suggesting the mesoporous structure of the
template SBA-15 had been successfully replicated. The pore
size distribution curves were obtained from the adsorption
branches using the Barrett–Joyner–Halenda (BJH) method. The
textural parameters were displayed in table 1.
Catalytic Tests
Catalytic tests were performed in a fixed-bed reactor. The
catalyst bed consisted of 2mL CN pressed in a 425–850μm
sieve fraction. The flow was generated by flowing N2 of
10mL/min through a bubbler containing the TCE liquid
reactant. Once stabilized, the flow was led over the reactor
bed. The reaction was conducted at 250
℃. The product was
analyzed with an Agilent 7890A gas chromatograph equipped
with a DB-1 capillary column and a flame ionization detector.
2 | J. Name., 2012, 00, 1-3
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22
20
18
16
14
12
10
8
CN-DMF
a
6
4
2
0.0
0.2
0.4
0.6
0.8
1.0
P/P0
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
CN-DMF
b
Fig. 3 HRTEM images of CN-DMF (a, b), CN-water (c) and SBA-
15(d)
The carbon nitride samples fabricated have been analyzed by
energy dispersive spectrometer (EDS) several times for
average value. No trail of Si was found in EDS result (Fig.4),
indicating the SBA-15 template we used has been removed
completely. We also noticed the C/N ratio of the mesoporous
carbon nitride sample synthesized by using DMF as solution
was 0.54, which was lower than the theoretical value of 0.75,
indicating the N content was higher than theoretical value.
And a small weight amount of O (about 4% of total weight)
was observed in it. These phenomena may due to the use of
DMF introducing extra O and N into the carbon nitride matrix.
0
10
20
30
40
50
pore size (nm)
Fig. 2 N2-adsorption/desorption isotherms of the CN-DMF (a),
BJH pore-size distribution of CN-DMF (b)
Table 1. Textural parameters of CN samples and SBA-15
Sample SBET(m2g-1)
Vpore(cm3g-1) Dpore(nm)
C/N ratio
EDS
CN-water
CN-DMF
SBA-15
78.08
350.43
479.71
0.16
0.72
0.67
8.5
8.07
5.73
0.69
0.54
-
HRTEM measurement was applied to investigate the
morphology of the carbon nitride samples and the
microstructure images of CN-DMF, CN-water and SBA-15 were
shown in fig. 3. An orderly, regular pattern of bright lines and
honeycomb-like hexagonal structures can be observed in the
images of CN-DMF sample in fig.3a and Fig.3b, respectively.
These phenomena indicated that the CN-DMF sample
possessed a well-developed mesoporous pore system. The CN-
DMF (Fig.3a) and CN-water (Fig.3c) samples both exhibited
similar structure with the SBA-15(Fig. 3d) while the pores sizes
were smaller than the template. These features can be due to
the negative replica of the silica template, meanwhile proving
the microstructure of SBA-15 had been well-retained in the
carbon nitride materials. The pores size of the samples
determined from HRTEM images are consistent with the
calculation from the nitrogen adsorption isotherms.
Fig.4 EDS pattern of CN-DMF
To investigate the chemical bonding state of the carbon nitride
samples we synthesized, FT-IR spectroscopy was employed to
characterize the CN samples. The band at about 785 cm-1
showed in Fig. 5 was characteristic of N=N vibrations of
triazine rings 18. The intense peaks of 1359 cm-1 and 1524 cm-1
were attributed to C=N stretching bonds and aromatic ring
modes, respectively 19. The peaks at 850cm-1 and 914cm-1
indicated the presentation of triazine heterocycles structure20
,
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revealed the formation of tri-s-triazine matrix. Furthermore,
the broad peaks at 3296 cm-1 and 3654 cm-1 were attributed to
the NH stretching of NH2 groups attached to the sp2-hybridized
C atoms and to OH stretching of the water molecules 21. The
result suggested that the input of DMF brought extra N groups
into the CN structure, in the form of NH2 groups attached to
the tri-s-triazine structure.
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DOI: 10.1039/C5RA22214A
conversion
selectivity
100
90
80
70
60
50
40
30
20
10
0
1.6
CN-DMF
CN-water
1.4
1290.648
1.2
1589.083
CN-EtOH
--
CN-water
--
CN-DMF
1524.478
1.0
Fig. 6 Catalytic performances of the carbon nitride prepared by
using various dispersing media. The catalytic results were
average within 6h.Reaction condition: 2mL of catalyst,
1359.591
914.1083
3654.987
0.8
0.6
0.4
3296.768
785.381
500
10mL/min N2, 250
℃
850.4678
Another test was performed to analogize the differences
between CN-water and CN-DMF. The sample prepared with
DMF was applied in the reaction, the catalytic conversion
reached a high point of 20.3% and the selectivity manifested
no less than 99%. No significant reduction was observed
during 6 h of reaction. While the conversion of CN-water only
stabilized around 10% as well as a selectivity of around 92%
(Fig. 7). The better performances of the CN-DMF catalyst may
due to the extra nitrogen content provided by the use of DMF
during the synthesize process and larger surface area offering
more active sites to improve the selective conversion of TCE.
Because of the better diffusion of the DCDC-DMF solution in
SBA-15, the well-developed mesoporous pore system of CN-
DMF enhanced the mass transfer and further promoted the
catalytic performance of CN-DMF.
1000 1500 2000 2500 3000 3500 4000 4500
wavenumber (cm-1)
Fig. 5 FT-IR spectrum of CN samples
As we mentioned above, the catalytic dehydrochlorination of
TCE into DCE requires the existence of basic site to conduct, on
the other hand, the acidic site tend to converse the TCE into
cis-1, 2- dichloroethene22. Since the basic site in carbon nitride
materials was focused on the N content, the CN-DMF sample
with higher N content and extra N group in the heterocycles
structure was the catalyst we desired. Aside of the desirable
DCE, hydrogen chloride is another main product in the
reaction. With the formation of hydrogen chloride, the basic
site would be occupied as the process continued 2, 23. That is
the reason for the fast deactivation of conventional basic
catalysts after only one or two pulses using the pulse
technique 2, 3, 22. On the other hand, 1, 1-DCE selectivity of the
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
c
d
traditional catalysts ranging from 75 to 90% with different
treatment like various loading metal and support
Owning to the inbuilt basic site, the carbon nitride materials
can be engaged into the catalytic dehydrochlorination of TCE
into DCE reaction as a solid base catalyst.
5, 22, 23
.
To compare with the carbon nitride samples prepared by
DCDA dissolved in water, we use another solvent, a mixture of
ethanol and water 24, to disperse DCDA. We tested the carbon
nitride samples synthesized by dissolving DCDA in water, DMF
and mixture of ethanol and water. The conversion of TCE and
the selectivity of 1, 1-DCE are showed in Fig. 6. No significant
difference had been noticed between the CN-water and the
CN-ethanol/water. The conversion of 1, 1, 2-TCE was around
11% while the selectivity of 1, 1-DCE stabilized at 90%. On the
other hand, a much higher conversion of 18.9% and DCE
selectivity of 99% was obtained by the CN-DMF sample.
a
b
1
2
3
4
5
6
time (h)
Fig. 7 Catalytic performances of the obtained CN materials.
Conversion of CN-DMF (a) and CN-water (b), selectivity of CN-
DMF(c) and CN-water (d). Reaction condition: 2mL of catalyst,
10mL/min N2, 250
℃
4 | J. Name., 2012, 00, 1-3
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Notes and references
View Article Online
Milchert E, Pazdzioch W, Myszkowski JD, OInId: 1.0E.1n0g3.9C/Ch5eRmA2.2R2e14sA.,
1995, 34, 2138.
To figure out the stability of the catalyst, the CN-DMF sample
was applied in a catalysis activity test of a total time of 110h,
the result was provided in Fig. 8. The selectivity was above
99% all along the experiment, and the conversion stayed
above 15% within 35 h, and then reduced gradually from 15%
to 5% during 40 h to 85 h, followed by a rapid drop to less than
5% in 90 h to 110 h. The selectivity remained no less than 99%
suggested that the inbuilt nitrogen group of the carbon nitride
material we synthesized preformed as a great catalytic active
site for the selective dehydrochlorination reaction. On the
contrary, the graduate decreasing of the conversion of TCE
was representation of the loss of catalytic activity which can be
due to the graduate occupation of basicity cause by the
hydrogen chloride.
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9
Conclusions
3
In summary, by dissolving dicyandiamide precursor in DMF,
the impregnation process of DCDA-DMF solution into SBA-15
template have been accelerated, fabricated a well-constructed
mesoporous carbon nitride sample with extra N groups. The
material was engaged as basic catalyst in dehydrochlorination
of 1,1,2-trichloroethane into 1,1-dichloroethene reaction and
exhibited high catalytic activity, especially stability. The
enhanced catalytic activity should be due to the input of DMF
brought extra N groups into the CN structure in form of NH2
groups attached to the tri-s-triazine structure. The extra NH2
groups along with the mesoporous structure led to the better
performance of catalytic dehydrochlorination of 1,1,2-
trichloroethane into 1,1-dichloroethene reaction.
Acknowledgements
The financial support by the National Natural Science
Foundation of China (NSFC-21476207), National Basic
Research Program of China (973 Program) (No.
2011CB710800), is gratefully acknowledged.
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DOI: 10.1039/C5RA22214A
We synthesized the carbon nitride material and used it as heterogeneous catalyst in
dehydrochlorination of 1,1,2-trichloroethane into 1,1-dichloroethene reaction.