Synthesis of nitrogen-doped ordered mesoporous carbons for catalytic dehydrochlorination of 1,2-dichloroethane

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Available at www.sciencedirect.com

ScienceDirect journal homepage: www.elsevier.com/locate/carbon

Synthesis of nitrogen-doped ordered mesoporous carbons for catalytic dehydrochlorination of 1,2-dichloroethane Jinming Xu, Xiaochen Zhao, Aiqin Wang, Tao Zhang

*

State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Science, Dalian 116023, PR China

A R T I C L E I N F O

A B S T R A C T

Article history:

Nitrogen-doped ordered mesoporous carbons (N-OMCs) were prepared via a two-step

Received 30 April 2014

approach, using resorcinol (R) and formaldehyde (F) as the carbon precursor and dicyandia-

Accepted 2 September 2014

mide (DCD) as the nitrogen precursor. In this approach, dicyandiamide, formaldehyde and

Available online 15 September 2014

resorcinol were pre-polymerized in the first step using a basic catalyst to produce DCD-RF resol. The DCD-RF resol was mixed with a solution of triblock copolymer Pluronic F127 followed by the addition of an acid catalyst to facilitate the self-assembly and condensation in the second step. After calcination, N-OMCs were obtained and further characterized by nitrogen sorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The well-prepared N-OMCs were evaluated for the catalytic dehydrochlorination of 1,2-dichloroethane and exhibited superior catalytic performances and excellent stability over 72 h. Ó 2014 Elsevier Ltd. All rights reserved.

1.

Introduction

Ordered mesoporous carbons (OMCs) have attracted great interest due to their high surface area, large pore volume, uniform pores, and tunable pore sizes [1,2]. Their performances are influenced not only by their structural parameters but also by their chemical compositions and surface functionalities [3,4]. Particularly, the incorporation of nitrogen species into the framework of OMCs could change the properties of carbon, and improve their performance in certain catalytic, capacitive, and adsorptive applications [5]. Nitrogen-doped ordered mesoporous carbons (N-OMCs) have been prepared by different approaches with many efforts. The conventional methods to synthesize N-OMCs involve a nanocasting strategy, which employed nitrogen-

* Corresponding author. E-mail address: [email protected] (T. Zhang). http://dx.doi.org/10.1016/j.carbon.2014.09.004 0008-6223/Ó 2014 Elsevier Ltd. All rights reserved.

containing molecules, such as acetonitrile [6], ethylenediamine [7], polyacrylonitrile [8], aniline [9], polypyrrole [10] and diaminobenzene [11] as the carbon and nitrogen precursors, and ordered mesoporous oxides as the hard templates. Hard material templating is typically time-consuming and expensive to carry out at large scale. Therefore, a soft-template method based on supramolecular assemblies of surfactants and carbon precursors is highly desired as an alternative option. However, the synthesis of N-OMCs by the self-assembly approach is difficult to achieve for two main reasons. Firstly, the nitrogen precursor must be capable to co-polymerize with the chosen polymeric carbon precursor for the formation of ordered mesostructures. Secondly, the involved nitrogen species must be highly thermal stable to retain in carbon framework during pyrolysis. Recently, several

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groups reported the synthesis of N-OMCs via soft-template process by using phenolic resins as carbon sources and m-aminophenol [12], 1,6-diaminohexane [13], urea [14], melamine [15,16], or dicyandiamide [17] as nitrogen sources. Besides, nitrogen can be also introduced into OMCs by treated with nitrogen-containing molecules, which decompose into reactive radicals at high temperature [18,19]. Previously, we demonstrated a reproducible synthesis of ordered mesoporous resorcinol–formaldehyde (RF) polymers and carbons by a two-step method [20]. In this method, resorcinol and formaldehyde is pre-polymerized in the first step using a basic catalyst to produce RF resol. Then, the RF resol is mixed with a triblock copolymer Pluronic F127 solution followed by the addition of an acid catalyst to allow the rapid self-assembly and condensation in the second step. In the present work, we added dicyandiamide (DCD) to the synthetic solution in the first step and fabricated a series of N-OMCs. The structure and nitrogen content of N-OMCs can be controlled by adjusting the dicyandiamide content. Furthermore, the obtained N-OMCs showed excellent activities in the catalytic dehydrochlorination of 1,2-dichloroethane reaction. The conversion of 1,2-dichloroethane increased along with the nitrogen content and the selectivity of vinyl chloride were all above 99.5%.

2.

Experimental

2.1.

Chemicals

All chemicals were used as received without further purification. Pluronic F127 (Mav = 12,600, EO106PO70EO106) was purchased from Sigma–Aldrich. Formaldehyde (37 wt.%), Ethanol and Na2CO3 were purchased from Tianjin Kermel Chemical Reagent Corp. Ltd. HCl (37 wt.%) was purchased from Tianjin Windship Chemistry Technological Corp. Resorcinol and dicyandiamide were obtained from Sinopharm Chemical Reagent Corp.

2.2. Synthesis of mesoporous nitrogen-doped polymers and carbons In a typical synthesis, 0.0056 g of Na2CO3 and 0.168 g of dicyandiamide was dissolved in 1.13 g of formaldehyde solution (37 wt.%) in a water bath at about 18 °C, then 1.10 g of resorcinol was added to the solution to produce a DCD-RF resol. After stirring for 4 h, the DCD-RF resol solution was mixed with a solution composed of 0.80 g of F127, 4.00 g of H2O and 5.00 g of ethanol, and then 1.00 mL of 2 M HCl was quickly added to this solution. After vigorously stirring for about 0.5 min, the transparent solution turned turbid, indicating a phase separation and the formation of DCD-RFF127 nano-composite. The mixture was stirred for 1 h and then left standing for 10 h to obtain the polymer rich gel phase. Finally, the polymer rich gel was calcined under N2 atmosphere at 350 and 800 °C for 3 h, respectively, to get the ordered mesoporous polymer 0.2DCD-RF-350 and the ordered mesoporous carbon 0.2DCD-RF-800. The other samples were prepared by varying the molar ratios of the reactants (dicyandiamide and formaldehyde, see Table 1), while

611

maintaining the molar ratio of resorcinol to F127, and the mass ratio of water to ethanol.

2.3.

Characterization

The X-ray diffraction (XRD) measurement was taken on a PANalytical X’Pert PRO powder X-ray diffractometer using Cu Ka radiation. Transmission electron microscopy (TEM) was conducted on a Tecnai G2 Spirit electronic microscope. The acceleration voltage was 100 kV. The samples for TEM observations were ultrasonically dispersed in ethanol and dropped onto a holey carbon film on a Cu grid. Nitrogen sorption analysis was performed on a Micromeritics ASAP 2010 apparatus at 196 °C. Prior to the measurements, the samples were degassed at 200 °C for about 6 h. The Brunauer–Emmett– Teller (BET) method was used to calculate the specific surface areas, SBET. The pore size distributions (PSD) were calculated from the adsorption branches of the isotherms using the Barrett–Joyner–Halenda (BJH) method. The pore size, Dp, was determined by the maxima in the pore size distribution curves. The total pore volume, Vp, was determined from the adsorbed amount at a relative pressure (P/P0) of 0.998. The micropore volume, Vmicro, was estimated according to the tplot method. X-ray photoelectron spectroscopy (XPS) was performed on ESCALAB250 (Thermo VG Corporation) equipped with an Al Ka radiation source (1486.6 eV, 15 kV, 10 mA, 150 W). All binding energies (B.E.) were calibrated with graphitic carbon C1s peak at 284.5 eV as a reference.

2.4.

Catalyst evaluation

Dehydrochlorination of 1,2-dichloroethane was performed in a tubular quartz micro reactor (4.8 mm) under atmospheric pressure. Under each catalysis condition, 0.10 g of catalyst was supported on a fritted disk. The 1,2-dichloroethane was metered into the reaction system by flowing a sweep gas of He (20 mL/min) through a saturator filled with the liquid 1,2-dichloroethane. A constant 1,2-dichloroethane concentration was ensured by maintaining the saturator at a fixed temperature of 0 °C using an ice-water bath. The reaction was run at 300 °C for 72 h and sampled every 2 h. The catalytic activities were measured with time on stream at a fixed temperature. The outlet gases were analyzed on line with an Agilent Technologies 6890N gas chromatograph equipped with a FID detector using a 30 m Poraplot Q capillary column.

3.

Results and discussion

3.1. Synthesis and characterization of nitrogen-doped mesoporous polymers In the present work, dicyandiamide was introduced to the synthetic solution in the first step of the two-step method [20]. Just like resorcinol, in the presence of a base catalyst, dicyandiamide also reacted with formaldehyde rapidly at low temperatures to produce the hydroxymethyl compounds. Resorcinol and hydroxymethylated resorcinol could be connected with hydroxymethylated dicyandiamide either by methylene or ether bridges to give a dicyandiamide modified

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Table 1 – Synthesis conditions and textual parameters of ordered mesoporous samples. Sample

DCD/R/Fa

tpb (h) tsc (min) N contentd (wt.%) SBET (m2/g) Vp (cm3/g) Vmicro (cm3/g) Dp (nm) a0e (nm)

0.2DCD-RF-350 0.4DCD-RF-350 0.8DCD-RF-350 1.0DCD-RF-350 0.2DCD-RF-800 0.4DCD-RF-800 0.8DCD-RF-800 1.0DCD-RF-800

0.2/1.0/1.4 0.4/1.0/1.7 0.8/1.0/2.5 1.0/1.0/2.8 0.2/1.0/1.4 0.4/1.0/1.7 0.8/1.0/2.5 1.0/1.0/2.8

4 4 2 2 4 4 2 2

a b c d e

0.23 1.00 2.70 4.20 0.14 0.45 1.54 2.30

0.5 0.7 15 50 0.5 0.7 15 50

603 604 521 376 718 703 634 556

0.68 0.78 0.63 0.42 0.65 0.74 0.60 0.47

0.07 0.06 0.06 0.05 0.16 0.15 0.15 0.14

7.5 9.3 9.2 7.5 5.5 6.4 6.4 6.0

14.0 14.6 15.3 – 11.8 12.1 12.9 –

Molar ratio. Pre-polymerization time. Time for occurrence of phase separation. Determined by ICP. p a0 is the unit cell parameter calculated as a0 = 2d100/ 3.

resorcinol–formaldehyde (DD-RF) resol. Subsequently, in the presence of an acid catalyst, DD-RF resol polymerized further and self-assembled with F127 to form a DD-RF-F127 nano-composite gel. After phase separation, the polymer gel was calcined under N2 atmosphere at 350 °C to remove F127 and obtain ordered mesoporous DCD-RF polymer. The content of nitrogen in the ordered mesoporous polymers and carbons can be easily varied by changing the amount of dicyandiamide. As shown in Table 1, the nitrogen mass fraction gradually increases with the increase of dicyandiamide. When the molar ratio of dicyandiamide to resorcinol is 1.0/ 1.0, the actual contents of nitrogen runs up to 4.20% in 1.0DCD-RF-350. The structures of the ordered mesoporous DCD-RF polymers pyrolyzed at 350 °C were examined with XRD. As shown in Fig. 1, in the range of DCD/R molar ratio from 0.2/1.0 to 0.8/

100

1.0, in the low angle region there are one strong peak at around 0.7° and two weak peaks between 1.2° and 2.2°, which can be assigned to (1 0 0), (2 0 0) and (2 1 0) reflections of 2D P6mm hexagonal symmetry, respectively. In particular, with DCD/R = 1.0/1.0, there is only one peak in the low angle region, implying its less ordered structure. Moreover, there is a slight shift towards low angles with increasing the DCD/R ratio. The unit cell parameters (a0) of 0.2DCD-RF-350, 0.4DCD-RF-350, and 0.8DCD-RF-350 are calculated to be 14.0, 14.6, and 15.3 nm, respectively. The increased a0 value of the ordered mesoporous DCD-RF polymers means a decreased contraction degree during the pyrolysis, which can possibly be attributed to the more robust mesoporous structure of the polymers resulting from the DCD. Fig. 2 shows the representative TEM images of ordered mesoporous DCD-RF polymers. As shown in Fig. 2, parallel

A

B

C

D

200

Intensity

210 X10

0.2DCD-RF-350

0.4DCD-RF-350

X10

X10

0.8DCD-RF-350

1.0DD-RF-350

1.0

2.0

3.0

4.0

5.0

2 Theta (degree) Fig. 1 – Low angle XRD patterns of ordered mesoporous DCD-RF polymers.

Fig. 2 – TEM images of ordered mesoporous DCD-RF polymers, (A) 0.2DCD-RF-350, (B) 0.4DCD-RF-350, (C) 0.8DCDRF-350, (D) 1.0DCD-RF-350.

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-1

Volume Adsorbed (cm STP g )

channels are clearly observed on 0.2DCD-RF-350, 0.4DCD-RF350, and 0.8DCD-RF-350, which are in consistent with the XRD results, and confirmed that the highly ordered mesoporous structure was well maintained. In contrast, some wormhole-like disordered structure can be seen on 1.0DCDRF-350 in agreement with its low-angle XRD pattern. A more detailed pore structural characterization was revealed by N2 adsorption–desorption. The N2 sorption isotherms and the corresponding pore size distributions are shown in Fig. 3, and the corresponding textural parameters are listed in Table 1. All samples present type IV isotherms and very narrow pore size distributions, characteristic of highly ordered mesoporous materials. The adsorption and desorption isotherms of all the samples are not closed due to the polymer framework [20,21]. From Table 1, one can see that the BET surface areas decrease from about 603 to 376 m2 with an increase of the DCD/R ratio from 0.2/1.0 to 1.0/1.0. The pore size calculated by BJH method using adsorption branches increases along with the increase of DCD/R ratio at first, but then decreases when its value reached to 1.0/1.0. These results indicate that if the amount of dicyandiamide is too large in the framework, dicyandiamide might disturb the assembly process between the RF resol and the structure-directing agent F127.

800

A

600 0.2DCD-RF-350 0.4DCD-RF-350

400

0.8DCD-RF-350

200

3.2.

Synthesis and characterization of N-OMCs

The DCD-RF polymer was further pyrolyzed at 800 °C to obtain N-OMC, for N-OMCs with different nitrogen content are supposed to be obtained by pyrolyzing their corresponding mesoporous DCD-RF polymers above 600 °C under inert atmosphere [20,21]. The number of peaks doesn’t change in the low angle XRD patterns (Fig. 4), and the uniform, highly ordered stripe-like and hexagonally arranged images in large domains are retained in TEM images (Fig. 5), which indicate that the ordering of mesoporous structure maintains after pyrolyzation at 800 °C. The peaks in the low angle XRD patterns in all samples shift towards to high angles, thus the unit cell parameters (a0) of 0.2DCD-RF-800, 0.4DCD-RF800 and 0.8DCD-RF-800 are calculated to be 11.8, 12.1 and 12.9 nm, respectively, and the lattice shrinkage is calculated to be about 15% compared to their corresponding polymers. Meanwhile, the decrease of the pore diameters along with the increasing pyrolysis temperature also confirms the structural shrinkage was caused by high-temperature (see Table 1 and Fig. 6b). However, the specific surface areas and micropore volumes of N-OMCs are higher than that of polymers. These suggest that new micropores were generated in the walls during the carbonization of the DCD-RF polymer. It is worth to note that, the nitrogen contents in N-OMCs are much lower than that of DCD-RF polymers, only about 50%, because some of the nitrogen species in the carbon framework decomposed during the pyrolysis. The as-prepared N-OMCs, bear not only highly ordered mesoporous structures and large surface areas, but also tunable nitrogen content. Therefore, they are expected to provide much more opportunities than activated carbons and OMCs for tuning the activities and selectivities when they are used as catalysts and supports. The corresponding N1s XPS spectra of N-OMCs with different nitrogen content are shown in Fig. 7. RF1-800 was prepared without dicyandiamide according to our previous paper [20],

1.0DCD-RF-350

0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0 ) 0.20

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100

B 200 210 X10

0.12 0.2DCD-RF-350 0.4DCD-RF-350 0.8DCD-RF-350 1.0DCD-RF-350

0.08 0.04

0.2DCD-RF-800

Intensity

3 -1

-1

dV/dD (cm g nm )

0.16

X10

0.4DCD-RF-800

0.00 10

20

30

40

50 X10

Pore Diameter (nm)

Fig. 3 – N2 sorption isotherms (A) and pore size distributions (B) of ordered mesoporous DCD-RF polymers. The isotherms for 0.2DCD-RF-350, 0.4DCD-RF-350 and 0.8DCD-RF-350 were offset vertically by 300, 200 and 100 cm3/g, respectively.

0.8DCD-RF-800

1.0DCD-RF-800

1.0

2.0

3.0

4.0

5.0

Fig. 4 – Low angle XRD patterns of N-OMCs.

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A

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B 1.0DCD-RF-800

0.8DCD-RF-800

D

C

RF1-800

410.0

Fig. 5 – TEM images of N-OMCs, (A) 0.2DCD-RF-800, (B) 0.4DCD-RF-800, (C) 0.8DCD-RF-800, (D) 1.0DCD-RF-800.

100

-1

A 600

Conversion (%)

3

0.2DCD-RF-800 0.4DCD-RF-800

400 0.8DCD-RF-800 1.0DCD-RF-800

200

1.0DCD-RF1-800

60

0.8DCD-RF1-800

40

0.4DCD-RF1-800

20

0.2

0.4

0.6

0.8

1.0

RF1-800

0 0

B

10

20

30 40 Time (h)

50

60

70

100

B

0.16 80

-1

0.12

Selectivity (%)

3 -1

A

N-AC 0.0

0.20

390.0

80

Relative Pressure (P/P0)

dV/dD (cm g nm )

400.0 395.0 Binding Energy(eV)

Fig. 7 – XPS spectrum of nitrogen-containing ordered mesoporous carbons. (A color version of this figure can be viewed online.)

800 Volume Adsorbed (cm STP g )

405.0

0.2DCD-RF-800 0.4DCD-RF-800 0.8DCD-RF-800 1.0DCD-RF-800

0.08 0.04

RF1-800 0.4DCD-RF-800 0.8DCD-RF-800 1.0DCD-RF-800 N-AC

60 40 20

0.00 5

10

15

20

25

Pore Diameter (nm)

0 0

10

20

30

40

50

60

70

Time (h)

Fig. 6 – N2 sorption isotherms (A) and pore size distributions (B) of N-OMCs. The isotherms for 0.2DCD-RF-800, 0.4DCDRF-800 and 0.8DCD-RF-800 were offset vertically by 300, 200 and 100 cm3/g, respectively.

Fig. 8 – (A) Conversion of 1,2-dichloroethane over nitrogencontaining ordered mesoporous carbons and (B) the selectivity of vinyl chloride.

and no peaks in N1s XPS spectrum were observed as expected. The XPS spectra of 0.8DCD-RF-800 and 1.0DCD-RF-800 in N1s region of were fitted by five peaks. The peaks at 398.6 and

400.3 eV suggest the presence of pyridine-like and pyrrole-like N atoms, respectively. Pyridine and pyrrole are Lewis bases, and such structures will affect the acid-base properties of car-

Volume Adsorbed (cm3 STP g-1)

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400

A 0.4DCD-RF-800 u 0.8DCD-RF-800 u 1.0DCD-RF-800 u

300

200

100 0.0

0.2

0.4

0.6

0.8

1.0

Relative Pressure (P/P0) 0.20

B dV/dD (cm3g-1nm-1)

0.16 0.12 0.4DCD-RF-800 u 0.8DCD-RF-800 u 1.0DCD-RF-800 u

0.08 0.04 0.00 5

10

15

20

25

Pore Diameter (nm) Fig. 9 – N2 sorption isotherms (A) and pore size distributions (B) of N-OMCs after reaction.

bons. In addition, the peaks observed at binding energies of 399.6, 401.3 and 403.2 eV have been assigned to amide, quaternary nitrogen (N substituting a C atom in the graphitic structure) and pyridine oxide, respectively [22].

3.3.

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Dehydrochlorination of 1,2-dichloroethane

The pyrolysis of 1,2-dichloroethane (1,2-DCE) has been commercialized as one way to produce vinyl chloride. Generally, the dehydrochlorination reactions are assumed to conducted according to base-catalyzed mechanism (e.g. with pyridinelike sites) [24]. It has been reported that PAN-ACF showed a good catalytic activity for the dehydrochlorination of 1,2dichloroethane [25,26]. However, the industrial application of this catalytic decomposition is hindered by a rapid decrease in catalytic activity. Besides, the coke deposition on the reactor wall, transfer lines and heat-exchangers is a big problem [23]. Therefore, if the catalytic dehydrochlorina-

tion reaction can be carried out at lower temperatures, the problem of coke deposition might be suppressed, allowing a continuous long time operation. In this work, the obtained N-OMCs were employed in the catalytic dehydrochlorination of 1,2-dichloroethane reaction. In addition, nitrogen-free mesoporous carbon RF1-800 and N-modified commercial activated carbon (N-AC, N content, 2.6 wt.%) were evaluated as counterpoints. As shown in Fig. 8, over N-OMCs, the conversions of 1,2-dichloroethane increased along with the nitrogen content and the selectivities of vinyl chloride were all above 99.5%. Because there was almost no basic surface functional group on RF1-800, the conversion of 1,2-DCE was very low, less than 1%, and the selectivity of vinyl chloride was about 90%. The nitrogen contents of N-AC and 1.0DCD-RF-800 were nearly the same, but over N-AC the conversion of 1,2-DCE was only about 5%, and the selectivity of vinyl chloride was about 96%. Clearly, N-OMCs exhibited excellent performances in the catalytic dehydrochlorination of 1,2-dichloroethane reactions. This is due to the fact that most of the pores of N-AC are narrow and deep micropores. Such micropores tended to trap the product of vinyl chloride for a long time due to the slow diffusion, and accelerated the formation of polyvinyl chloride and coke. On the contrary, the enrichment of mesopores in NOMCs facilitated the mass transportation, liberated product rapidly into gas phase without its consecutive reaction, and thus greatly improved the performance of 1,2-dichloroethane dehydrochlorination. After reaction we examined the textual parameters of NOMCs with N2 sorption. The N2 sorption isotherms and pore size distributions of N-OMCs after reaction are shown in Fig. 9, and the BET specific surface areas and pore volumes are listed in Table 2. It can be seen that after reaction all NOMCs show typical type IV isotherms with a sharp capillary condensation step at P/P0 = 0.4–0.8 and a well-defined H1-type hysteresis loop, indicating the mesoporous structures of materials with cylindrical channels. The adsorption and desorption isotherms of all the samples are not closed, suggesting that there are polymers in N-OMCs [27]. This might be caused by the formation of polyvinyl chloride or cokes. The pore size distributions of N-OMCs in the mesoporous range are almost the same before and after reaction (Figs. 6B vs. 9B). This indicates that the polyvinyl chloride and coke almost have no effect on the mesopores of N-OMCs. However, the specific surface areas and pore volumes after reaction are smaller than that of the fresh ones. Take 0.8DCD-RF-800 for example, before and after reaction, the difference of the BET specific surface area is 174 m2/g, and the difference of the micropore specific surface area is 155 m2/g. They are very close to each other. This implies that the polyvinyl chloride and

Table 2 – Textual parameters of N-OMCs. Sample

SBET (m2/g)

Smicro (m2/g)

Vp (cm3/g)

Vmicro (cm3/g)

Dp (nm)

0.4 DCD-RF 800 u 0.8 DCD-RF 800 u 1.0 DCD-RF 800 u

543 460 332

201 164 102

0.58 0.48 0.31

0.08 0.07 0.04

6.4 6.4 5.5

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coke are in the micropores of N-OMCs. These also give a proof that mesopores in N-OMCs facilitate the mass transportation and inhibit the coke formation in the catalytic dehydrochlorination of 1,2-dichloroethane reaction.

[10]

4.

[11]

Conclusions

We successfully synthesized a series of N-OMCs with different nitrogen contents using a two-step method. The content of nitrogen in N-OMCs can be easily varied by changing the amount of dicyandiamide. The unit cell parameter increased with increasing the DCD/R ratio. However, if the amount of dicyandiamide was too large in the framework, dicyandiamide might disturb the assembly process of RF resol and the structure-directing agent F127. In the catalytic dehydrochlorination of 1,2-dichloroethane reaction, N-OMCs showed excellent activities, the conversions of 1,2-dichloroethane increased along with the nitrogen content, and the selectivities of vinyl chloride were above 99.5%. The mesopores in N-OMCs facilitated the mass transportation, thus greatly improved the performance of 1,2-dichloroethane dehydrochlorination.

[12]

[13]

[14]

[15]

Acknowledgements [16]

We gratefully acknowledge the financial support of the National Basic Research Program of China (21176235, 51302281 and 21303187).

[17]

R E F E R E N C E S

[18] [1] Wan Y, Shi YF, Zhao DY. Supramolecular aggregates as templates: ordered mesoporous polymers and carbons. Chem Mater 2008;20(3):932–45. [2] Ma TY, Liu L, Yuan ZY. Direct synthesis of ordered mesoporous carbons. Chem Soc Rev 2013;42(9):3977–4003. [3] Liang CD, Li ZJ, Dai S. Mesoporous carbon materials: synthesis and modification. Angew Chem Int Ed 2008;47(20):3696–717. [4] Stein A, Wang ZY, Fierke MA. Functionalization of porous carbon materials with designed pore architecture. Adv Mater 2009;21(3):265–93. [5] Shen WZ, Fan WB. Nitrogen-containing porous carbons: synthesis and application. J Mater Chem A 2013;1(4):999–1013. [6] Xia YD, Mokaya R. Synthesis of ordered mesoporous carbon and nitrogen-doped carbon materials with graphitic pore walls via a simple chemical vapor deposition method. Adv Mater 2004;16(17):1553–8. [7] Datta KKR, Balasubramanian VV, Ariga K, Mori T, Vinu A. Highly crystalline and conductive nitrogen-doped mesoporous carbon with graphitic walls and its electrochemical performance. Chem Eur J 2011;17(12):3390–7. [8] Kruk M, Dufour B, Celer EB, Kowalewski T, Jaroniec M, Matyjaszewski K. Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor. J Phys Chem B 2005;109(19):9216–25. [9] Vinu A, Anandan S, Anand C, Srinivasu P, Ariga K, Mori T. Fabrication of partially graphitic three-dimensional nitrogendoped mesoporous carbon using polyaniline nanocomposite

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

through nanotemplating method. Microporous Mesoporous Mater 2008;109(1–3):398–404. Fulvio PF, Jaroniec M, Liang CD, Dai S. Polypyrrole-based nitrogen-doped carbon replicas of SBA-15 and SBA-16 containing magnetic nanoparticles. J Phys Chem C 2008;112(34):13126–33. Liu NN, Yin LW, Wang CX, Zhang LY, Lun N, Xiang D, et al. Adjusting the texture and nitrogen content of ordered mesoporous nitrogen-doped carbon materials prepared using SBA-15 silica as a template. Carbon 2010;48(12):3579–91. Feng CM, Li HX, Wan Y. Fabrication of N-doped highly ordered mesoporous polymers and carbons. J Nanosci Nanotechnol 2009;9:1558–63. Hao GP, Li WC, Qian D, Wang GH, Zhang WP, Zhang T, et al. Structurally designed synthesis of mechanically stable poly(benzoxazine-co-resol)-based porous carbon monoliths and their application as high-performance CO2 capture sorbents. J Am Chem Soc 2011;133(29):11378–88. Yang JP, Zhai YP, Deng YH, Gu D, Li Q, Wu QL, et al. Direct triblock-copolymer-templating synthesis of ordered nitrogen-containing mesoporous polymers. J Colloid Interface Sci 2010;342(2):579–85. Yu J, Guo MY, Muhammad F, Wang AF, Yu GL, Ma HP, et al. Simple fabrication of an ordered nitrogen-doped mesoporous carbon with resorcinol–melamine–formaldehyde resin. Microporous Mesoporous Mater 2014;190:117–27. Kailasam K, Jun YS, Katekomol P, Epping JD, Hong WH, Thomas A. Mesoporous melamine resins by soft templating of block-co-polymer mesophases. Chem Mater 2010;22(2):428–34. Wei J, Zhou DD, Sun ZK, Deng YH, Xia YY, Zhao DY. A controllable synthesis of rich nitrogen-doped ordered mesoporous carbon for CO2 capture and supercapacitors. Adv Funct Mater 2013;23(18):2322–8. Wu ZX, Webley PA, Zhao DY. Post-enrichment of nitrogen in soft-templated ordered mesoporous carbon materials for highly efficient phenol removal and CO2 capture. J Mater Chem 2012;22(22):11379–89. Wang XQ, Liu CG, Neff D, Fulvio PF, Mayes RT, Zhamu A, et al. Nitrogen-enriched ordered mesoporous carbons through direct pyrolysis in ammonia with enhanced capacitive performance. J Mater Chem A 2013;1(27):7920–6. Xu JM, Wang AQ, Zhang T. A two-step synthesis of ordered mesoporous resorcinol–formaldehyde polymer and carbon. Carbon 2012;50(5):1807–16. Meng Y, Gu D, Zhang FQ, Shi YF, Yang HF, Li Z, et al. Ordered mesoporous polymers and homologous carbon frameworks: amphiphilic surfactant templating and direct transformation. Angew Chem Int Ed 2005;44(43):7053–9. Arrio R, Havercker M, Wrabetz S, Blume R, Lerch M, McGregor J, et al. Tuning the acid/base properties of nanocarbons by functionalization via amination. J Am Chem Soc 2010;132(28):9616–30. Mochida I, Tsunawaki T, Sotowa C, Korai Y, Higuchi K. Coke produced in the commercial pyrolysis of ethylene dichloride into vinyl chloride. Ind Eng Chem Res 1996;35(10):3803–7. Sotowaa C, Kawabuchi Y, Mochida I. Catalytic dehydrochlorination of 1,2-dichloroethane over pyridine deposited pitch-based active carbon fiber. Chem Lett 1996;1996(11):967–8. Mochida I, Yasumoto Y, Watanabea Y, Fujitsu H, Kojima Y, Morita M. Catalytic dehydrochlorination of 1,2dichloroethane over pyridine deposited pitch-based active carbon fiber. Chem Lett 1994;1994(2):197–200. Sotowaa C, Watanabea Y, Yatsunamia S, Koraib Y, Mochida I. Catalytic dehydrochlorination of 1,2-dichloroethane into