Syntheses and catalytic applications of the high-N-content, the cup-stacking and the macroscopic nitrogen doped carbon nanotubes

doi:10.1016/j.jmst.2017.01.011

Abstract

Abstract:

The high-N-content, the cup-stacking and the macroscopic nitrogen doped carbon nanotubes (NCNT) were synthesized via an easily manufactured catalytic chemical vapor deposition (CCVD) method. Nitrogen physisorption, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the as-obtained NCNTs. High reaction temperatures were found to be the key point to the formation of inner-cup-stacking NCNTs. However, the synthesis of the outer-cup-stacking NCNT needs special demands not only to the reaction temperature but also to the catalyst and the carrier gas. The possibility of CO oxidation by NCNT was proved to be very small, and the outer-cup-stacking NCNT showed obvious advantage in the oxidative dehydrogenation (ODH) of butene to butadiene compared to a bamboo-like NCNT with an even higher N content.

Key words: High-N-content NCNT, Cup-stacking NCNT, Macroscopic NCNT, CO oxidation, Oxidative, dehydrogenation

Wang Qi, Wang Haihua, Zhang Yajie, Wen Guodong, Liu Hongyang, Su Dangsheng. Syntheses and catalytic applications of the high-N-content, the cup-stacking and the macroscopic nitrogen doped carbon nanotubes[J]. J. Mater. Sci. Technol., 2017, 33(8): 843-849.

Figures/Tables 12

Fig. 1. Structural models of the inner-cup-stacking NCNT (a) and the outer-cup-stacking NCNT (b).

Fig. 2. Schematic diagram of the experimental setup.

Fig. 3. (a) TEM image of Fe-Mo/Al2O3-1; (b) pore size distribution of NCNT-700-C1-G1, NCNT-800-C1-G1, NCNT-900-C1-G1; (c) TEM image of NCNT-700-C1-G1; (d) TEM image of NCNT-800-C1-G1; (e) TEM image of NCNT-900-C1-G1.

Table 1 BET surface areas and pore structures of the as-obtained NCNTs.

Sample	Pore volume (cm³/g)	Pore diameter (nm)	S_BET (m²/g)
NCNT-700-C1-G1	0.19	9.39	82.40
NCNT-800-C1-G1	0.29	13.71	85.76
NCNT-900-C1-G1	0.25	13.06	72.81

Fig. 4. Deconvolution of the N1s spectra of NCNT-700-C1-G1, NCNT-800-C1-G1 and NCNT-900-C1-G1.

Table 2 XPS analyses of the as-obtained NCNTs.a

Sample	N (at.%)	N1 (at.%)	N2 (at.%)	N3 (at.%)	N4 (at.%)	N5 (at.%)	N6 (at.%)
NCNT-700-C1-G1	16.3	6.34 (38.9)	4.06 (24.9)	4.16 (25.5)	1.08 (6.63)	0.65 (3.99)	-
NCNT-800-C1-G1	6.6	1.75 (26.5)	0.72 (10.9)	2.70 (40.9)	0.55 (8.33)	0.29 (4.39)	0.60 (9.09)
NCNT-900-C1-G1	6.8	1.26 (18.5)	0.74 (10.9)	2.59 (38.1)	0.55 (8.09)	0.74 (10.9)	1.10 (16.2)

Fig. 5. (a) TGA result of NCNT-700-C1-G1; (b) the evolution of CO and CO2 for NCNT-700-C1-G1 in 0.5% O2/He and in CO oxidation; TEM images of (c) NCNT-700-C1-G1; (d) NCNT-700-C1-G1 after treated in 0.5% O2/He; (e) NCNT-700-C1-G1 after CO oxidation.

Table 3 A summary of the morphologies and N contents of the as-obtained NCNTs.

Entry	NCNTs	Bamboo-like	Outer-cup-stacking	Inner-cup-stacking	N content (at.%)
1	NCNT-700-C1-G1	√	-	-	16.3
2	NCNT-800-C1-G1	√	-	-	6.6
3	NCNT-900-C1-G1	-	-	√	6.8
4	NCNT-750-C2-G2	√	-	-	4.7
5	NCNT-800-C2-G2	-	√	-	3.6
6	NCNT-850-C2-G2	√	-	-	1.5
7	NCNT-900-C2-G2	-	-	√	1.9
8	NCNT-750-C2-G1	√	-	-	11.7
9	NCNT-750-C2-Ar	√	-	-	9.6
10	NCNT-800-C1-G2	√	-	-	4.4

Fig. 6. TEM image (a) and XRD pattern (b) of Fe-Mo/Al2O3-2; TEM images of NCNT-750-C2-G2 (c), NCNT-800-C2-G2 (d), NCNT-850-C2-G2 (e), NCNT-900-C2-G2 (f), NCNT-800-C1-G2 (g), NCNT-750-C2-G1 (h), NCNT-750-C2-Ar (i).

Fig. 7. Catalytic performances of outer-cup-stacking NCNT-800-C2-G2 and bamboo-like NCNT-800-C1-G1 in the ODH of butene to butadiene.

Fig. 8. TGA results of the as-obtained NCNT/SiCs.

Table 4 Analyses of N in NCNT/SiCs.

Samples	Loading amount (wt%)	N content (wt%)	N in NCNT (wt%)	N in NCNT^a (at.%)
NCNT/SiC-750-G2	2.7	0.11	4.07	3.51
NCNT/SiC-800-G2	2.9	0.27	9.30	8.08
NCNT/SiC-850-G2	4.7	0.20	4.26	3.67
NCNT/SiC-900-G2	3.8	0.06	1.66	1.43

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