- Email: [email protected]
Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene
Accepted Manuscript Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene Haiyang Xu, Yanan Liu, Guanwu Sun, Shifei Kang, Yangang Wang, Zheng Zheng, Xi Li PII: DOI: Reference:
S0167-577X(19)30282-4 https://doi.org/10.1016/j.matlet.2019.02.058 MLBLUE 25763
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
19 November 2018 19 January 2019 9 February 2019
Please cite this article as: H. Xu, Y. Liu, G. Sun, S. Kang, Y. Wang, Z. Zheng, X. Li, Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.02.058
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene Haiyang Xu a,†, Yanan Liu b,†, Guanwu Sun c, Shifei Kang c, Yangang Wang b,*, Zheng Zheng a,*, Xi Li b a
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China
b
College of Biological Chemical Science and Engineering, Jiaxing University, Jiaxing, Zhejiang 314001, China
c
School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093,
China †
Equally contributed.
Abstract Graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst was prepared by a simple incipient wetness impregnation and calcination method. The catalytic performance of the prepared catalyst was tested by catalytic steam reforming of toluene (a biomass tar model compound). Compared with mesoporous SBA-15 supported catalyst, the GMC supported catalyst has a higher toluene conversion efficiency of 98 % at 700 °C and remained stable during 24 h of continuous reaction. The excellent catalytic performance is mainly attributed to the better dispersion of Ni nanoparticles on GMC support and the reduced carbon deposition because of the Ce-doping. Keywords: Graphitic mesoporous carbon; Porous materials; Nanoparticles; Ce-doping; Nickel catalyst; Steam reforming
*Corresponding
authors.
Tel/Fax:
+86
21
65642789.
E-mail
[email protected] (Y.G. Wang), [email protected] (Z. Zheng). 1. Introduction 1
addresses:
Catalytic steam reforming of tar is considered to be an environmentally friendly and valueadded route to convert biomass tar into hydrogen-rich gas [1, 2]. Nickel-based catalysts are promising candidates due to their excellent catalytic activity and low cost compared to noble metal catalysts [3]. However, they are rapidly deactivated as a result of coke deposition in viscous tar or sintering at high temperatures [4, 5]. To improve the catalytic performance, several kinds of mesoporous silica supports, such as MCM-41 and SBA-15 have been employed as catalyst supports for the better dispersion of metal catalysts [3, 6]. However, they are poor in hydrothermal stability and mechanical strength [7]. Consequently, the structures of the silica-based porous materials gradually collapsed in hydrothermal conditions, leading to a severe pore blockage that decreases the mass transfer efficiency [8]. Graphitic mesoporous carbon (GMC) is an excellent catalyst support with ideal mechanical strength, thermal and chemical stability [9]. In our previous report, GMC was synthesized by a simple solid-liquid templating method and successfully used as a novel support in the photoreduction of CO2 [10]. Herein, we prepared a GMC supported Ce-doped nickel catalyst by simple incipient wetness impregnation and calcination. Ce was introduced as a catalyst promoter to reduce carbon deposition. The catalytic performance of the prepared catalysts were tested by the catalytic steam reforming of toluene. Compared with SBA-15 supported catalyst, a higher toluene conversion efficiency of 98 % at 700 °C with superb stability was achieved owing to the better dispersion of Ni nanoparticles on GMC support and reduced carbon deposition. 2. Experimental Catalyst supports (SBA-15 and GMC) (Fig. S1) were synthesized according to our previous work [10, 11]. To prepare the GMC supported catalyst, the aqueous solution (5 mL) of metal precursors that contains 0.54 g Ni(NO3)2·6H2O and 0.20 g of Ce(NO3)3·6H2O was added to 2 g of 2
GMC dropwise with continuous stirring to form a uniform slurry. After impregnation and drying overnight at 80 °C, the GMC impregnated with metal precursors was calcined at 900 °C for 2 h in a tube furnace under 5% H2/N2 gas mixture. Finally, the obtained GMC was loaded with 5 wt% Ni and 3 wt% Ce. For comparison, SBA-15 supported Ce-doped and undoped Ni catalysts were also prepared as above. The three prepared catalysts were respectively labeled as CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. The structural properties of the prepared catalysts were characterized by X-ray powder diffraction (Bruker, D8 ADVANCE), surface area and pore size analyzer (BeiShiDe, 3H-2000PS4) and transmission electron microscopy (JEOL, JEM-2010). The deposited carbon was analyzed by a thermogravimetric analyzer (PerkinElmer STA-8000). Catalytic performance was tested in a fixed bed quartz reactor (22 mm I.D) at temperatures ranging from 500 °C-800 °C under atmospheric pressure (Fig. S2). 0.5 g catalyst was held by quartz wool and placed in the middle of the reactor. Prior to the catalytic reaction, the catalysts were in situ reduced with 10% H2/Ar gas mixture (30 ml/min) for 4 h at 500 °C, and then purged with N2. Toluene (20 μmol/min) and steam (420 μmol/min) were mixed and then carried by N2 (80 ml/min) into the reactor, thus the contact time is about 0.75 s. In the catalytic stability test at 700 °C, the reaction was allowed to proceed for at least 24 hours. The main reaction products (CO and H2) were passed through a cold trap, and the non-condensable gas products were analyzed using an online gas chromatograph (GC2060 system). Results and discussion Fig. 1 shows the wide-angle XRD patterns, N2 adsorption-desorption isotherms and pore size distribution curves of the synthesized nickel-based catalysts. From Fig. 1a, characteristic peaks of amorphous SiO2 and graphitic carbon are observed at 2θ = 23° and 25°, respectively. 2θ located at 3
44.5° and 51.8° are recognized as the characteristic peaks of Ni0. However, no characteristic peaks of Ce or CeO2 can be detected because of its low amount. Ni0 supported on GMC presents the most remarkable decline in its peak intensity, suggesting a smaller size of Ce-Ni nanoparticles on GMC than on SBA-15. Fig. 1b shows that the isotherm curve of the CeNi/GMC has a strong uptake of N2 at the relative pressure (P/P0) range of 0.4-0.8 and > 0.9 due to sharp capillary condensation, indicating multiform pore size distributions. Hierarchical pores of the CeNi/GMC are respectively centered at about 3 nm, 6 nm and 26 nm (Fig. 1b, inset), which are beneficial to metal nanoparticle dispersion and mass transfer. Nevertheless, the SBA-15 has a unique pore size distribution concentrated at 8 nm. 1600
Vads (cm3 g-1)
1200
(200)
(111)
Intensity (a.u.)
(002)
GMC CeNi/GMC CeNi/SBA-15 Ni/SBA-15
CeNi/GMC
CeNi/SBA-15
800
10
20
30
40
50
Pore size (nm)
400
Ni/SBA-15
(a) 10
(b) 20
30
40
50
60
70
0 0.0
80
0.2
0.4
0.6
0.8
1.0
P/P0
2-Theta(degree)
Fig. 1. XRD patterns (a) and N2 sorption isotherms (b) of CeNi/GMC, CeNi/SBA-15, Ni/SBA-15 and GMC, the inset in (b) is their pore size distribution curves. The textural properties of all samples are listed in Table 1. After loading Ni-based catalyst, the specific surface area of GMC was declined less than 37 % with negligible decrease in pore size and pore volume, indicating a good dispersion of Ce-Ni nanoparticles on GMC. While the specific surface area, pore volume and pore size of SBA-15 were significantly reduced after catalyst loading. Table 1 Textural properties of all prepared samples. Sample
SBET (m2/g )
Pore size (nm) 4
Pore volume (cm3/g)
GMC
643
3.6
1.43
SBA-15
702
6.6
0.96
CeNi/GMC
407
3.6
1.11
CeNi/SBA-15
350
4.8
0.59
Ni/SBA-15
321
4.6
0.53
The morphologies of the prepared samples were characterized by TEM (Fig. 2). As shown in Fig. 2a, the SBA-15 has ordered one-dimensional parallel channels along the axial direction. However, the mesopores of CeNi/SBA-15 were seriously blocked by aggregated and stripe-like Ce-Ni particles due to the poor structural stability of SBA-15 (Fig. 2b). Interestingly, highly dispersed Ce-Ni nanoparticles with an average size of 5-10 nm was achieved on the CeNi/GMC (Fig. 2c and 2d), which was in accordance with the result of N2-sorption analysis. (a)
(b)
50 nm
50 nm
(c)
(d)
200 nm
50 nm
Fig. 2. TEM images of (a) SBA-15, (b) CeNi/SBA-15 and (c, d) CeNi/GMC The catalytic performance for the steam reforming of toluene was conducted in a continuous fixed-bed reactor. Fig. 3a shows the toluene conversion as a function of temperature over the prepared catalysts. In the temperature range of 500-800 °C, the CeNi/GMC displayed the highest toluene conversion among all catalysts because of a good dispersion of Ce-Ni catalyst on GMC. The catalytic stability of all catalysts was investigated at 700 °C. It is observed that the toluene
5
conversion of the CeNi/GMC is stable at 98 % even after 24 h of continuous reaction, which is better than many other catalysts as previously reported [12, 13], especially metal oxide loaded Ni catalysts. However, as a consequence of the metal particle aggregation or the carbon deposition, the toluene conversion over the CeNi/SBA-15 and Ni/SBA-15 respectively decreased to 89.3% and 85.5%. The better stability of CeNi/SBA-15 than Ni/SBA-15 can be attributed to the doped Ce element that could reduce the carbon deposition [14], which was further confirmed by the TG result in Fig. S5.
100
100
95 90 85 80 75 CeNi/GMC CeNi/SBA-15 Ni/SBA-15
70 65
Toluene conversion (%)
(b)
Toluene conversion (%)
(a)
60
95 90 85 80
CeNi/GMC CeNi/SBA-15 Ni/SBA-15
75 70
500
550
600
650
700
750
0
800
5
10
15
20
25
Time (h)
Temperature (°C)
Fig. 3. Effect of reaction temperature on the toluene conversion (a) and catalytic stability at 700 °C (b) of CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. Moreover, the structure and morphology of the CeNi/GMC after 24 h catalytic test were investigated by XRD and TEM. The similar XRD peaks of the used and fresh CeNi/GMC catalyst in Fig. S3 indicate that the CeNi/GMC catalyst has a favorable stability and can be used for longterm steam reforming of toluene. The TEM image (Fig. S4) reveals that the Ce-Ni nanoparticles are still uniformly distributed on GMC. Based on the above results, it can be concluded that the GMC is a good catalyst support to stabilize the metal nanoparticles even in the high temperature reaction. 3. Conclusions 6
In this work, we have successfully prepared graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst by a simple incipient wetness impregnation and calcination method. The characterization results revealed that the hierarchical structure of GMC with high specific area and porosity is beneficial to the high dispersion of the Ce-Ni metal catalyst. Ce doping reduced carbon deposition and further stabilized the catalyst. Because of these characterizations, the Ce-Ni nanoparticles supported on GMC presented much higher catalytic activity and stability than the one on SBA-15 in the catalytic steam reforming of toluene.
We declare that we have no conflicts of interest to this work.
We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Acknowledgments This work was carried out with financial supports from National Natural Science Foundation of China (Grant No. 21103024), Natural Science Foundation of Zhejiang Province (LY19B060006) and Technology Development Project of Jiaxing University.
References [1] A.S. Al-Rahbi, P.T. Williams, Hydrogen-rich syngas production and tar removal from biomass gasification using sacrificial tyre pyrolysis char, Appl. Energ. 190 (2017) 501-509. [2] N.B. Gao, Y. Han, C. Quan, C.F. Wu, Promoting hydrogen-rich syngas production from catalytic reforming of biomass pyrolysis oil on nanosized nickel-ceramic catalysts, Appl. Therm. Eng. 125 (2017) 297-305. [3] M.J. Ye, Y.W. Tao, F.Z. Jin, H.J. Ling, C.F. Wu, P.T. Williams, J. Huang, Enhancing hydrogen 7
production from the pyrolysis-gasification of biomass by size-confined Ni catalysts on acidic MCM-41 supports, Catal. Today 307 (2018) 154-161. [4] G. Guan, M. Kaewpanha, X. Hao, A. Abudula, Catalytic steam reforming of biomass tar: Prospects and challenges, Renew. Sust. Energ. Rev. 58 (2016) 450-461. [5] E.G. Baker, L.K. Mudge, M.D. Brown, Steam gasification of biomass with nickel secondary catalysts, Ind. Eng. Chem. Res. 26 (1987) 1335-1339. [6] J. Tao, L.Q. Zhao, C.Q. Dong, Q. Lu, X.Z. Du, E. Dahlquist, Catalytic steam reforming of toluene as a model compound of biomass gasification tar using Ni-CeO2/SBA-15 catalysts, Energies 6 (2013) 3284-3296. [7] F.Q. Zhang, Y. Yan, H.F. Yang, Y. Meng, C.Z. Yu, B. Tu, D.Y. Zhao, Understanding effect of wall structure on the hydrothermal stability of mesostructured silica SBA-15, J. Phys. Chem. B 109 (2005) 8723-8732. [8] X. Liu, D. Chen, L. Chen, R. Jin, S. Xing, H. Xing, Y. Xing, Z. Su, Facile Fabrication of welldispersed Pt nanoparticles in mesoporous silica with large open spaces and their catalytic applications, Chem.-Eur. J. 22 (2016) 9293-9298. [9] W.H. Antink, Y. Choi, K.D. Seong, J.M. Kim, Y. Piao, Recent progress in porous graphene and reduced graphene oxide-based nanomaterials for electrochemical energy storage devices, Adv. Mater. Interfaces 5 (2018) 1-19. [10] Y.G. Wang, C.L. Zhang, S.F. Kang, B. Li, Y.Q. Wang, L.Q. Wang, X. Li, Simple synthesis of graphitic ordered mesoporous carbon supports using natural seed fat, J. Mater. Chem. 21 (2011) 14420-14423. [11] Y. Wang, F. Zhang, Y. Wang, J. Ren, C. Li, X. Liu, Y. Guo, Y. Guo, G. Lu, Synthesis of length controllable mesoporous SBA-15 rods, Mater. Chem. Phys. 115 (2009) 649-655. [12] D. Li, M. Tamura, Y. Nakagawa, K. Tomishige, Metal catalysts for steam reforming of tar derived from the gasification of lignocellulosic biomass, Bioresource Technol. 178 (2015) 53-64. [13] F.Q. Guo, X.L. Li, Y. Liu, K.Y. Peng, C.L. Guo, Z.H. Rao, Catalytic cracking of biomass pyrolysis tar over char-supported catalysts, Energ. Convers. Manage. 167 (2018) 81-90. [14] C.X. Zhang, S.R. Li, G.W. Wu, J.L. Gong, Synthesis of stable Ni-CeO2 catalysts via ballmilling for ethanol steam reforming, Catal. Today 233 (2014) 53-60. Figure Captions 8
Fig. 1. XRD patterns (a) and N2 sorption isotherms (b) of CeNi/GMC, CeNi/SBA-15, Ni/SBA-15 and GMC, the inset in (b) is their pore size distribution curves. Fig. 2. TEM images of (a) SBA-15, (b) CeNi/SBA-15 and (c, d) CeNi/GMC. Fig. 3. Effect of reaction temperature on the toluene conversion (a) and catalytic stability at 700 °C (b) of CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. Table 1 Textural properties of all prepared samples.
9
> A graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst was prepared. > The GMC support is beneficial to a high dispersion of Ce-Ni nanoparticles. > Ce doping is effective for the mitigation of carbon deposition on Ni nanoparticles. > The CeNi/GMC exhibited improved catalytic performances in steam reforming of toluene.
10
S0167-577X(19)30282-4 https://doi.org/10.1016/j.matlet.2019.02.058 MLBLUE 25763
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
19 November 2018 19 January 2019 9 February 2019
Please cite this article as: H. Xu, Y. Liu, G. Sun, S. Kang, Y. Wang, Z. Zheng, X. Li, Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.02.058
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Synthesis of graphitic mesoporous carbon supported Ce-doped nickel catalyst for steam reforming of toluene Haiyang Xu a,†, Yanan Liu b,†, Guanwu Sun c, Shifei Kang c, Yangang Wang b,*, Zheng Zheng a,*, Xi Li b a
Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China
b
College of Biological Chemical Science and Engineering, Jiaxing University, Jiaxing, Zhejiang 314001, China
c
School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093,
China †
Equally contributed.
Abstract Graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst was prepared by a simple incipient wetness impregnation and calcination method. The catalytic performance of the prepared catalyst was tested by catalytic steam reforming of toluene (a biomass tar model compound). Compared with mesoporous SBA-15 supported catalyst, the GMC supported catalyst has a higher toluene conversion efficiency of 98 % at 700 °C and remained stable during 24 h of continuous reaction. The excellent catalytic performance is mainly attributed to the better dispersion of Ni nanoparticles on GMC support and the reduced carbon deposition because of the Ce-doping. Keywords: Graphitic mesoporous carbon; Porous materials; Nanoparticles; Ce-doping; Nickel catalyst; Steam reforming
*Corresponding
authors.
Tel/Fax:
+86
21
65642789.
[email protected] (Y.G. Wang), [email protected] (Z. Zheng). 1. Introduction 1
addresses:
Catalytic steam reforming of tar is considered to be an environmentally friendly and valueadded route to convert biomass tar into hydrogen-rich gas [1, 2]. Nickel-based catalysts are promising candidates due to their excellent catalytic activity and low cost compared to noble metal catalysts [3]. However, they are rapidly deactivated as a result of coke deposition in viscous tar or sintering at high temperatures [4, 5]. To improve the catalytic performance, several kinds of mesoporous silica supports, such as MCM-41 and SBA-15 have been employed as catalyst supports for the better dispersion of metal catalysts [3, 6]. However, they are poor in hydrothermal stability and mechanical strength [7]. Consequently, the structures of the silica-based porous materials gradually collapsed in hydrothermal conditions, leading to a severe pore blockage that decreases the mass transfer efficiency [8]. Graphitic mesoporous carbon (GMC) is an excellent catalyst support with ideal mechanical strength, thermal and chemical stability [9]. In our previous report, GMC was synthesized by a simple solid-liquid templating method and successfully used as a novel support in the photoreduction of CO2 [10]. Herein, we prepared a GMC supported Ce-doped nickel catalyst by simple incipient wetness impregnation and calcination. Ce was introduced as a catalyst promoter to reduce carbon deposition. The catalytic performance of the prepared catalysts were tested by the catalytic steam reforming of toluene. Compared with SBA-15 supported catalyst, a higher toluene conversion efficiency of 98 % at 700 °C with superb stability was achieved owing to the better dispersion of Ni nanoparticles on GMC support and reduced carbon deposition. 2. Experimental Catalyst supports (SBA-15 and GMC) (Fig. S1) were synthesized according to our previous work [10, 11]. To prepare the GMC supported catalyst, the aqueous solution (5 mL) of metal precursors that contains 0.54 g Ni(NO3)2·6H2O and 0.20 g of Ce(NO3)3·6H2O was added to 2 g of 2
GMC dropwise with continuous stirring to form a uniform slurry. After impregnation and drying overnight at 80 °C, the GMC impregnated with metal precursors was calcined at 900 °C for 2 h in a tube furnace under 5% H2/N2 gas mixture. Finally, the obtained GMC was loaded with 5 wt% Ni and 3 wt% Ce. For comparison, SBA-15 supported Ce-doped and undoped Ni catalysts were also prepared as above. The three prepared catalysts were respectively labeled as CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. The structural properties of the prepared catalysts were characterized by X-ray powder diffraction (Bruker, D8 ADVANCE), surface area and pore size analyzer (BeiShiDe, 3H-2000PS4) and transmission electron microscopy (JEOL, JEM-2010). The deposited carbon was analyzed by a thermogravimetric analyzer (PerkinElmer STA-8000). Catalytic performance was tested in a fixed bed quartz reactor (22 mm I.D) at temperatures ranging from 500 °C-800 °C under atmospheric pressure (Fig. S2). 0.5 g catalyst was held by quartz wool and placed in the middle of the reactor. Prior to the catalytic reaction, the catalysts were in situ reduced with 10% H2/Ar gas mixture (30 ml/min) for 4 h at 500 °C, and then purged with N2. Toluene (20 μmol/min) and steam (420 μmol/min) were mixed and then carried by N2 (80 ml/min) into the reactor, thus the contact time is about 0.75 s. In the catalytic stability test at 700 °C, the reaction was allowed to proceed for at least 24 hours. The main reaction products (CO and H2) were passed through a cold trap, and the non-condensable gas products were analyzed using an online gas chromatograph (GC2060 system). Results and discussion Fig. 1 shows the wide-angle XRD patterns, N2 adsorption-desorption isotherms and pore size distribution curves of the synthesized nickel-based catalysts. From Fig. 1a, characteristic peaks of amorphous SiO2 and graphitic carbon are observed at 2θ = 23° and 25°, respectively. 2θ located at 3
44.5° and 51.8° are recognized as the characteristic peaks of Ni0. However, no characteristic peaks of Ce or CeO2 can be detected because of its low amount. Ni0 supported on GMC presents the most remarkable decline in its peak intensity, suggesting a smaller size of Ce-Ni nanoparticles on GMC than on SBA-15. Fig. 1b shows that the isotherm curve of the CeNi/GMC has a strong uptake of N2 at the relative pressure (P/P0) range of 0.4-0.8 and > 0.9 due to sharp capillary condensation, indicating multiform pore size distributions. Hierarchical pores of the CeNi/GMC are respectively centered at about 3 nm, 6 nm and 26 nm (Fig. 1b, inset), which are beneficial to metal nanoparticle dispersion and mass transfer. Nevertheless, the SBA-15 has a unique pore size distribution concentrated at 8 nm. 1600
Vads (cm3 g-1)
1200
(200)
(111)
Intensity (a.u.)
(002)
GMC CeNi/GMC CeNi/SBA-15 Ni/SBA-15
CeNi/GMC
CeNi/SBA-15
800
10
20
30
40
50
Pore size (nm)
400
Ni/SBA-15
(a) 10
(b) 20
30
40
50
60
70
0 0.0
80
0.2
0.4
0.6
0.8
1.0
P/P0
2-Theta(degree)
Fig. 1. XRD patterns (a) and N2 sorption isotherms (b) of CeNi/GMC, CeNi/SBA-15, Ni/SBA-15 and GMC, the inset in (b) is their pore size distribution curves. The textural properties of all samples are listed in Table 1. After loading Ni-based catalyst, the specific surface area of GMC was declined less than 37 % with negligible decrease in pore size and pore volume, indicating a good dispersion of Ce-Ni nanoparticles on GMC. While the specific surface area, pore volume and pore size of SBA-15 were significantly reduced after catalyst loading. Table 1 Textural properties of all prepared samples. Sample
SBET (m2/g )
Pore size (nm) 4
Pore volume (cm3/g)
GMC
643
3.6
1.43
SBA-15
702
6.6
0.96
CeNi/GMC
407
3.6
1.11
CeNi/SBA-15
350
4.8
0.59
Ni/SBA-15
321
4.6
0.53
The morphologies of the prepared samples were characterized by TEM (Fig. 2). As shown in Fig. 2a, the SBA-15 has ordered one-dimensional parallel channels along the axial direction. However, the mesopores of CeNi/SBA-15 were seriously blocked by aggregated and stripe-like Ce-Ni particles due to the poor structural stability of SBA-15 (Fig. 2b). Interestingly, highly dispersed Ce-Ni nanoparticles with an average size of 5-10 nm was achieved on the CeNi/GMC (Fig. 2c and 2d), which was in accordance with the result of N2-sorption analysis. (a)
(b)
50 nm
50 nm
(c)
(d)
200 nm
50 nm
Fig. 2. TEM images of (a) SBA-15, (b) CeNi/SBA-15 and (c, d) CeNi/GMC The catalytic performance for the steam reforming of toluene was conducted in a continuous fixed-bed reactor. Fig. 3a shows the toluene conversion as a function of temperature over the prepared catalysts. In the temperature range of 500-800 °C, the CeNi/GMC displayed the highest toluene conversion among all catalysts because of a good dispersion of Ce-Ni catalyst on GMC. The catalytic stability of all catalysts was investigated at 700 °C. It is observed that the toluene
5
conversion of the CeNi/GMC is stable at 98 % even after 24 h of continuous reaction, which is better than many other catalysts as previously reported [12, 13], especially metal oxide loaded Ni catalysts. However, as a consequence of the metal particle aggregation or the carbon deposition, the toluene conversion over the CeNi/SBA-15 and Ni/SBA-15 respectively decreased to 89.3% and 85.5%. The better stability of CeNi/SBA-15 than Ni/SBA-15 can be attributed to the doped Ce element that could reduce the carbon deposition [14], which was further confirmed by the TG result in Fig. S5.
100
100
95 90 85 80 75 CeNi/GMC CeNi/SBA-15 Ni/SBA-15
70 65
Toluene conversion (%)
(b)
Toluene conversion (%)
(a)
60
95 90 85 80
CeNi/GMC CeNi/SBA-15 Ni/SBA-15
75 70
500
550
600
650
700
750
0
800
5
10
15
20
25
Time (h)
Temperature (°C)
Fig. 3. Effect of reaction temperature on the toluene conversion (a) and catalytic stability at 700 °C (b) of CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. Moreover, the structure and morphology of the CeNi/GMC after 24 h catalytic test were investigated by XRD and TEM. The similar XRD peaks of the used and fresh CeNi/GMC catalyst in Fig. S3 indicate that the CeNi/GMC catalyst has a favorable stability and can be used for longterm steam reforming of toluene. The TEM image (Fig. S4) reveals that the Ce-Ni nanoparticles are still uniformly distributed on GMC. Based on the above results, it can be concluded that the GMC is a good catalyst support to stabilize the metal nanoparticles even in the high temperature reaction. 3. Conclusions 6
In this work, we have successfully prepared graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst by a simple incipient wetness impregnation and calcination method. The characterization results revealed that the hierarchical structure of GMC with high specific area and porosity is beneficial to the high dispersion of the Ce-Ni metal catalyst. Ce doping reduced carbon deposition and further stabilized the catalyst. Because of these characterizations, the Ce-Ni nanoparticles supported on GMC presented much higher catalytic activity and stability than the one on SBA-15 in the catalytic steam reforming of toluene.
We declare that we have no conflicts of interest to this work.
We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.
Acknowledgments This work was carried out with financial supports from National Natural Science Foundation of China (Grant No. 21103024), Natural Science Foundation of Zhejiang Province (LY19B060006) and Technology Development Project of Jiaxing University.
References [1] A.S. Al-Rahbi, P.T. Williams, Hydrogen-rich syngas production and tar removal from biomass gasification using sacrificial tyre pyrolysis char, Appl. Energ. 190 (2017) 501-509. [2] N.B. Gao, Y. Han, C. Quan, C.F. Wu, Promoting hydrogen-rich syngas production from catalytic reforming of biomass pyrolysis oil on nanosized nickel-ceramic catalysts, Appl. Therm. Eng. 125 (2017) 297-305. [3] M.J. Ye, Y.W. Tao, F.Z. Jin, H.J. Ling, C.F. Wu, P.T. Williams, J. Huang, Enhancing hydrogen 7
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Fig. 1. XRD patterns (a) and N2 sorption isotherms (b) of CeNi/GMC, CeNi/SBA-15, Ni/SBA-15 and GMC, the inset in (b) is their pore size distribution curves. Fig. 2. TEM images of (a) SBA-15, (b) CeNi/SBA-15 and (c, d) CeNi/GMC. Fig. 3. Effect of reaction temperature on the toluene conversion (a) and catalytic stability at 700 °C (b) of CeNi/GMC, CeNi/SBA-15 and Ni/SBA-15. Table 1 Textural properties of all prepared samples.
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> A graphitic mesoporous carbon (GMC) supported Ce-doped nickel catalyst was prepared. > The GMC support is beneficial to a high dispersion of Ce-Ni nanoparticles. > Ce doping is effective for the mitigation of carbon deposition on Ni nanoparticles. > The CeNi/GMC exhibited improved catalytic performances in steam reforming of toluene.
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