Hydrogen Production from Dry-Reforming of Biogas over Pt ... - Core

Available online at www.sciencedirect.com

ScienceDirect Energy Procedia 79 (2015) 18 – 25

2015 International Conference on Alternative Energy in Developing Countries and Emerging Economies

Hydrogen Production from Dry-Reforming of Biogas over Pt/Mg1-xNixO Catalysts FarisJasimAl-Doghachia,b, Zulkarnain Zainala,b, Mohd Izham Saimana,b, Zaidi Embongc Yun Hin Taufiq-Yapa,b* a

Catalysis Science and Technology Research Centre, Faculty of Science, University Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. b Department of Chemistry, Faculty of Science, University Putra Malaysia, 43400 UPM, Serdang, Selangor, Malaysia. c Department of Science, Faculty of Science, Technology and Human Development, University Tun Hussien Onn Malaysia (UTHM), 86400, Parit Raja, Batu Pahat Johor, Malaysia

Abstract Dry reforming of biogas carried out over Pt/Mg1-xNixO catalysts, where x= 0, 0.03, 0.07, and 0.15 with 1 wt% Pt for each, prepared by the co-precipitation method from aqueous solution of Ni(NO3)2.6H2O and Mg(NO3)2.6H2O using K2CO3, then the platinum(II)acetylacetonate impregnated on MgO–NiO. The synthesized catalysts analyzed by XRD, FT-IR, XRF, XPS, BET and TEM. at 700 oC, the catalysts reduced by H2 prior to each reaction. The order of conversions of CO2 and CH4 at 900 oC of the reduced catalysts after being on the stream for 200 h was as follows: Pt/Mg0.85Ni0.15O > Pt/Mg0.93Ni0.07O > Pt/Mg0.97Ni0.03O > Pt/MgO with a CH4:CO2 mole ratio of 2:1 that displayed the best resistance to deactivation by carbon formation and formed high selectivity of H2 and CO. The dry reforming reaction was also carried out with the presence of low concentrations of oxygen (1.25%) flow and showed an enhancement in the conversion of CH4 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

© 2015 The Authors. Published by Elsevier Ltd. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility the Organizing Committee of 2015 AEDCEE. Peer-review under responsibility of theofOrganizing Committee of 2015 AEDCEE Keywords: Synthesis gas, H2 production, Dry-Reforming of biogas, MgO-NiO catalyst

1. Introduction Palm oil biomass is the most abundant and bio-renewable resource in Malaysia and Indonesia with great potential for sustainable production of chemicals and fuels. Effluents from palm oil mills also known as palm oil mill effluent (POME) is always regarded as a highly polluting wastewater. Anaerobic digestion

* Corresponding author. Tel.: +603-89466809, Fax: +603-89466758 E-mail address: [email protected]

1876-6102 © 2015 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the Organizing Committee of 2015 AEDCEE doi:10.1016/j.egypro.2015.11.460

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FarisJasimAl-Doghachi et al. / Energy Procedia 79 (2015) 18 – 25

is widely adopted in the oil palm industry as a primary treatment for POME. At many palm-oil mills, this process is already in place to meet water quality standards for industrial effluent. The biogas, however, is flared off. Biogas contains two greenhouse gases (GHG) i.e. about 60-70 % methane (CH4) and 30-40 % carbon dioxide (CO2) and also trace amount of hydrogen sulphide, (H2S) [1,2]. Dry reforming of methane (DRM) has received great attention due to its environmental benefits from utilizing these two greenhouse gases and producing highly valuable synthesis gas (syngas, H2 and CO) as a feedstock. Dry reforming of methane produces synthesis gas (DRM) (Eq. 1) that attracted much attention due to the conversion of greenhouse gases (namely CH4 and CO2) into highly useful resource gases. Such attention has accelerated researches on catalysts and system development for dry reforming [3-7].

ʹͶ͹ǤͲ Ȁሺͳሻ The critical problem in (DRM) is the formation of particulate (solid) carbon deposits on the catalyst surface arising from two reactions, the decomposition of methane (Eq. 2)and CO disproportionation reaction (Boudouard reaction) (Eq. 3) according to the reactions as follows [8].

75.0 kJ/mol

(2)

-172.0 kJ/mol

(3)

The most important point in constructing a dry reforming system is developing a catalyst that has a high tolerance against carbon deposition and is able to efficiently supply reaction energy to the reactive zone since dry reforming is a relatively high endothermic reaction. Nickel and noble metals are widely used as active metals in reforming catalysts. Noble-metal-supported catalysts (Rh, Ru, Pd, Pt and Ir) have shown promising catalytic performance in terms of conversion and selectivity in dry reforming [9]. An alternative metal, nickel, is more commonly used as the active metal in reforming processes due to its relative abundance and low cost. However, the major drawback is that nickel easily induces carbon formation and leads to catalytic deactivation [10]. Therefore, numerous studies have been carried out to enhance the catalytic activity and stability of nickel-based catalysts in reforming processes [11,12].

2. Materials and methods Pt/Mg1-xNixO catalysts, where x= 0, 0.03, 0.07, and 0.15 with 1 wt% Pt for each, were prepared by the coprecipitation method from aqueous solution of Ni (NO 3)2.6H2O and Mg (NO3)2.6H2O using K2CO3. After being filtered and washed with hot water, the precipitate was dried at 120oC for 12 h, and then precalcined in air at 500oC for 5 h. Following that, they were pressed into disks at 600 kg/m2, and calcinated in air at 1150oC for 20h. Pt/NixMg1-xO and Pt/MgO catalysts were prepared by impregnating support with a dichloromethane solution of Pt(C5H7O2)2.H2O. The catalysts were dried at 120oC after impregnation in air for 12h. The synthesized catalysts were analyzed by XRD, BET surface area and TEM. Crystalline structures of the samples were investigated using X-ray diffraction (XRD) with a Shimadzu XRD-6000 diffractometer.The surface area, pore volume and pore size diameter of the samples were determined using N2 adsorption–desorption technique with a Thermo Finnigan Sorptomatic Instrument, model 1900. The coke formation of the used catalysts was examined by temperature programmed oxidation (TPO) using a Thermo Finnigan TPD/R/O 1100 Instrument. The catalytic evaluation for dry reforming of biogas was performed in a continuous flow system using a fixed bed stainless steel micro-reactor. The reactor

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was connected to a mass flow gas controller and an online gas chromatograph (GC) (Agilent 6890N; G 1540N). Prior to reaction, approximately 0.02 g catalyst was reduced by flowing 5% H2/Ar (30 ml/min) from 100 to 700 °C and holding for 3 h. The reforming reaction was performed by flowing a gas mixture consisting of CH4:CO2 = 2:1 and 1:1 at a rate of 30 ml/min from 700 to 900 °C , then holding for 200h.The surface analysis was performed using an X-ray Photoelectron Spectroscopy (XPS) model Kratos Ultra Axis that operated at ultra high vaccum of 10 -11 Torr. A monochromatic Al Kα sources were used as a photon to irradiate the sample surface. The carbon charging correction of the spectrum was corrected using the adventitious carbon binding energy value at 284.6 eV. 3. Results and discussion The XRD patterns of the catalysts are shown in (Figure 1). Reflections of MgO were detected in NiOMgO supported by Platinum catalysts in their wide-angle XRD patterns The smart diffraction peaks at around 2θ = 39.7, 42.9, 62.5,75 and 79° are due to the cubic form of the promoter NiO in the catalyst. Whereas the diffraction lines at about 2θ = 37, 43.1, 62.3, 74.8 and 78.7 o are ascribed to the cubic phase of magnesia. The XRD patterns of the catalysts showed the crystal system for the catalysts are in cubic phase and was confirmed by TEM image (Figure 2).

Intensity (a.u.)

Pt / Mg0.85Ni0.15O

Pt / Mg0.93Ni0.07O

Pt / Mg0.97Ni0.03O

Pt/MgO 30

50

70

2T ( Degree )

Fig. 1.XRD results of catalysts (a) Pt/MgO (b) Pt/Mg0.97Ni0.0 (c) Pt/Mg0.93Ni0.07O (d) Pt/Mg0.85Ni0.15O


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FarisJasimAl-Doghachi et.al/ Energy Procedia 00 (2015) 000–000

Fig.2.TEM image of Pt/Mg0.85Ni0.15O

100 99 98

P t/M g 0 .8 5 N i0 .1 5 O A b s o rb a n c e

19 07 0 99 98

P t/M g 0 .9 3 N i0 .0 7 O 19 07 0 99 98

P t/M g 0 .9 7 N i0 .0 3 O

19 07 0 99 98

P t/M g O 97 4000

3500

3000

2500

2000

1500

1000

500

W a v e n o .C m -1

Fig. 3.FT-IR for different catalysts (a) Pt/MgO (b) Pt/Mg0.85Ni0.15O(c) Pt/Mg0.97Ni0.03O (d) Pt/Mg 0.93Ni0.07O. FTIR measurement shows (Figure 3) that the bonds for Pt-O, Ni-O, and MgO exists in the far IR region and all the peaks in the spectra are attributed to acetylacetonate. Surface study of the catalyst at a few nanometer layer of its uppermost using XPS indicate that there are a photoelectron signal from C1s, O1s, Mg2p, Ni2p and Pt4f, as illustrated in Figure 4(a-e). A deconvolution of a C1s narrow scan indicated that there are three type of carbon species which is C-C (or C-H), C-O and C=O. The O1s photoelectron

21

22


signal shows that it is contribute by five type of oxygen species which is contributed by O 2- (from the bulk), MgO, NiO, PtO and hydroxyl (OH-) component. This is also a significant splitting of this O1s spectrum, whereby NiO exhibit as the highest intensity of photoelectron signal at the lower binding energy region compared to the others. However, the O2-, NiO, PtO and OH- are detected under a similar photoelectron envelope. However, the contribution of OH- component is considered very low at the binding energy of 533.0 eV. On the other hand, the narrow scan of Mg2p, Ni2p and Pt4f revealed that the oxide species of these metal are a mixture of MgO and Mg(OH)2, NiO and Ni(OH)2 and PtO respectively. The existence of two component of hydroxyl species by Ni and Mg indicate that, these metal is easily to react with water vapour compound (H2O). (a)

(b) C-H C-C

C1s

2000 1800 1600

Intensity

1400 1200 1000 800 600

C=O

C-O

400 200 292

290

288

286

284

282

Binding Energy (eV)

(c)

(d)

700

Ni2p3/2

3600

Mg Mg2p

NiO NiO (sattelite)

3400

600

Intensity

400

Ni(OH)2 (sattelite)

3000 2800

300

MgO 200

2600

100

2400

(e)

0 52

51

50

49

48

47

PtO

Ptmetal

Ptmetal

250

PtO 200

150

100

50 80

78

76

74

868

866

864

862

860

858

856

Binding Energy (eV)

Pt 4f7/2

Pt 4f5/2

300

870

46

Binding Energy (eV)

Y Axis Title

Intensity

Ni(OH)2

3200

500

72

70

854

852

850

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Fig. 4.XPS narrow scan of the Pt/Mg0.85Ni0.15O catalyst. (a) C1s (b) O1s (c) Mg2p (d) Ni2p (e) Pt4f The BET specific surface area (SBET) value and pore properties of catalyst supports and freshly prepared catalysts are shown in Table 1. After impregnation, the SBET value and pore volume decreased in all three of the catalysts. This phenomenon might be caused by pore blocking during the impregnation process. The SBET, pore volume, and average Pt-loading of freshly prepared catalysts are also presented in Table 1.

Specific Surface Area m2/g

Pore Volume Cm3/g

Pore volume to SBET ratio 10-9m

Pore radius o A

Pt b Loading Wt %

Average c Crystal size nm

Pt / Mg0.97Ni0.03O

11.64

0.17

17.6

18.25

0.98

44.7

Pt / Mg0.93Ni0.07O

6.72

0.06

15.7

18.26

0.94

42.4

5.44

0.04

10.6

18.24

0.93

40.4

10.46

0.41

48.4

18.26

0.95

38.7

Sample name

Pt / Mg0.85Ni0.15O Pt / MgO

a

Table 1: The main textural properties of fresh catalysts. a. Specific surface area calculated by BET method. b. Determined by the XRF method. c. Determined by the Debye-Scherrer equation of the Mg (200) plane of XRD. The largest pore volume was found in Pt / MgO, while Pt / Mg0.97Ni0.03O had the largest SBET value. There was no obvious connection between the SBET value and pore volume of catalysts, but the pore volume/SBET ratio increased in the order Pt / MgO > Pt / Mg0.97Ni0.03O > Pt / Mg0.93Ni0.07O > Pt / Mg0.85Ni0.15O which was in accordance with the Pt-dispersion order, and Bappy Saha [14] also proved that a high pore volume/SBET ratio contributes to high catalytic performance. The XRF results in Table 1

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show that the Pt-loading was slightly lower than the set value of 1%.This might be caused by weight loss during the pre-calcination of the supports, resulting in a higher Ni content in the catalyst. The dry reforming of methane reaction’s activity was indicated by the conversion of CH 4 and CO2, and the selectivity was expressed in terms of the H 2/CO ratio. Figure 5 shows the most active catalyst in the dry reforming of biogas. The reaction was carried out for 200h at 900oC and revealed that the catalyst gave > 95% conversion for both CO2 and CH4. The order of conversions of CO2 and CH4 are as follows: Pt/Mg0.85Ni0.15O > Pt/Mg0.93Ni0.07O > Pt/Mg0.97Ni0.03O > Pt/MgO with a CH4:CO2 mole ratio of 2:1. Pt/Mg0.85Ni0.15O displayed the best resistance to deactivation by carbon formation and formed high selectivity of H2 and CO. Both pore of supporter and doping metal played a vital role in the conversion process as indicated by BET results. Dry reforming of biogas reaction was also carried out with the presence of low concentration of oxygen flow (1.25%) and Figure 6 showed an enhancement in the conversion of CH4.This oxygen reacted with CH4 to produce CO and H2O Eq. (4), and finally the steam reacts with deposited carbon to gives syngas Eq. (5). CH4 + 1.5O2 ė CO + 2H2O

(4)

C(s) + H2O ė CO + H2

(5)

4. Conclusions Incorporation of NiO onto MgO exhibited a notable conversion when a compared to MgO alone, while addition of Pt to MgO-NiO as promoter has augmented conversion of CO2 up to 99%.CH4 to CO2 gases at 2:1 ratio had produced highest conversion as compared to that obtained by 1:1 ratio. Hence, as result of this process, the carbon deposition is reduced and consequently the life time of the catalyst has improved. Acknowledgment I would like to express special thanks and my appreciation to my supervisor Professor Dr. Yun Hin Taufiq Yap, who have been a great mentor for me. I would like to thank you for supporting my research and for guiding me to grow as a research scientist. Your advices have been priceless I would also


especially like to thank the maintenance group and my colleagues in the department of Chemistry, Faculty of Science, University Putra Malaysia. I appreciate your help and being there to support me when I needed advices regarding the functioning of the different instruments such as, BET, TPR,TEM, and XRD.A special thanks to the University of Basrah, Iraq for providing me a scholarship and sponsoring me.. References [1] Chin, M. J., Poh, P. E., Tey, B. T., Chan E. S. and Chin, K. L. Renewable and Sustainable Energy Reviews 2013; 26: 717-726. [2] Poh, P. and Chong, M.. Bioresource Technology 2009;100(1): 1-9. [3] Chen P, Zhang H-B, Lin G-D, Tsai K-R.. Appl Catal 1998;166:343-50. [4] Wang S, Lu GQM, Appl Catal 1998;16:269-77. [5] Ruckenstein E, Hu YH. Catal Lett. 1998;51:18:3-5. [6] Fujimoto K, Tomsighe K, Yamazaki O, Chen Y, Li X-H. Res Chem Intermed 1998;24:259-71. [7] Choudhary VR, Uphade BS, Mamman AS. Appl Catal: Gen 1998;168:34-46. [8] Hu, YH, Ruckenstein, E. catalysts. Langmuir, 13(7), 2055-2058. Langmuir 1997;13(7): 2055–58. [9] S. Zeng, L. Zhang, X. Zhang, Y. Wang, H. Pan, H. Su, Int. J. Hydrog. Energy 2012; 37:9994–10001. [10] J. Ashok, S. Kawi, , Int. J. Hydrog. Energy 2013;38:13938–13949. [11] B. Li, S. Zhang, Int. J. Hydrog. Energy 2013;38:14250–14260. [12] Y. Liu, Z. He, L. Zhou, Z. Hou, W. Eli, Catal. Commun 2013;42: 40–44. [13] Matsuo, Y. and Tomishige, K., Catalysis Today 2000;63: 439-445. [14] Saha, B., Khan, A., Ibrahim, H., Idem, R.. Fuel 2014;120: 202-217.

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