flame synthesized TiO2 catalysts for hydrogen production using thermocatalytic decomposition of methane

South African Journal of Chemical Engineering 25 (2018) 91e97

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Comparison study between Ni/TiO2 and Ni/flame synthesized TiO2 catalysts for hydrogen production using thermocatalytic decomposition of methane K. Srilatha a, D. Bhagawan b, D. Srinivasulu a, V. Himabindu a, * a

Centre for Alternative Energy Options, Institute of Science and Technology, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad, 500085, Telangana, India Centre for Environment, Institute of Science and Technology, Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad, 500085, Telangana, India b

a r t i c l e i n f o

a b s t r a c t :

Article history: Received 21 October 2017 Received in revised form 30 December 2017 Accepted 27 February 2018

Hydrogen is considered as a fuel of future due to its environmental cleanness. Thermo Catalytic Decomposition of Methane (TCD) is one of the most advanced process, which will meet the future demand and attractive route for COx free production of hydrogen. In this study, an attempt made using flame synthesized titanium nanorods as a catalyst support for nickel based catalyst to produce hydrogen. The comparison study between Ni/TiO2 and Ni/Flame synthesized TiO2 (Ni/F-TiO2) catalysts for hydrogen production using thermocatalytic decomposition of methane. The effect of nickel weight percentage (10%, 20%, 30% and 40 wt %) and reaction temperature (650, 700, 750 and 800
C) with Ni/TiO2 and Ni/FTiO2 catalysts were performed for hydrogen production studies at 54sccm flowrate of methane. The maximum hydrogen production was observed with 30 wt% of Ni/TiO2 and 30 wt% of Ni/F-TiO2 as 48 and 55 vol% at 700
C in 60min of reaction time. Before and after the reaction, catalysts were characterized by XRD, BET surface area, SEM, TEM and AAS analysis. Apart from hydrogen production, carbon nanorods were observed with a diameter and length of 5e10 nm and 0.25 mm respectively for Ni/TiO2 and for Ni/FTiO2 catalyst, it was found to be 50e100 nm and 0.5 mm respectively. © 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords: Hydrogen Nano carbon Diffusion flame reactor Ni/TiO2 Ni/F-TiO2 Thermo catalytic decomposition

1. Introduction Hydrogen is considered as a fuel of future due to is environmental cleanness. Hydrogen is becoming an important fuel source for the next generation, due to its energy efficiency and environmental friendly properties, which is a promising alternative to fossil fuels. Hydrogen production in a cost-effective manner is the challenging option to the researchers (Pudukudy et al., 2015a,b). The main source of hydrogen in liquid form is H2O, where it requires high energy in the form of thermal and electrical energy to generate pure hydrogen. Various hydrogen production methods such as bio-hydrogen (Brentner et al., 2010), steam reforming, partial oxidation, coal gasification, water splitting, biomass gasification and thermo chemical processes (Abbas and Daud, 2010;

* Corresponding author. E-mail addresses: [email protected] (K. Srilatha), [email protected]. in (V. Himabindu).

Abbas and Wan Daud, 2010; Wang, 2008) were studied. TCD is one of the green synthesis path for hydrogen production (Steinberg, 1999). TCD of methane reaction is moderately endothermic process. The energy requirement per mole of hydrogen produced (37.8 kJ/ mol H2) is some-what less than other conventional processes of hydrogen production, such as steam reforming process (63.3 kJ/mol H2) (Steinberg, 1999; Muradov Nazim, 2002; Venugopal et al., 2007). Combustion is needed to drive the process. In addition to hydrogen, the process produces very important by-product is clean elemental carbon was shown in Eqn. (1). This process eliminates the concurrent production of carbon oxides and therefore, obviates the need for water gas shift and carbon dioxide removal stages, required by conventional processes which significantly simplify the process. A considerable reduction in overall greenhouse gas emissions, compared to conventional processes is the main advantage of thermo catalytic decomposition process. CH4 Cþ2H2 DH0298K ¼ 37.8 kJ/mol of H2

(1)

https://doi.org/10.1016/j.sajce.2018.02.003 1026-9185/© 2018 Published by Elsevier B.V. on behalf of Institution of Chemical Engineers. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

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In TCD process, catalysts were required to decrease the operation temperature. Many transition metals like Ni, Co and Fe were known to be active in methane decomposition reaction. The studies related to methane decomposition reaction began in 1970s and investigations were carried out with a focus on carbon deposition mechanism and carbon formation. Ni-based catalysts were extensively studied for methane decomposition due to their higher activities compared with other transition metals (Lazaro et al., 2008; Takenaka et al., 2001; Takenaka et al., 2003a,b; Li et al., 2011; Abbas and Daud, 2010; Abbas and Wan Daud, 2010; Chesnokov and Chichkan, 2009; Saraswat and Pant, 2013; Bayat et al., 2016a,b; Pudukudy et al., 2015a,b; Ashok et al., 2008; Ogihara et al., 2006; Avdeeva et al., 2002; Buyanov and Chesnov, 2006; Takenaka et al., 2004; Pinilla et al., 2010; Shen et al., 2008; Figueiredo et al., 2010; Awadallah et al., 2014; Saraswat and Pant, 2011; Lazaro et al., 2007; Suelves et al., 2006; Chai et al., 2006; Chen et al., 2004). Recent studies were performed using TiO2 as a support material and it was found to be an effective support for the thermocatalytic decomposition of methane into hydrogen and carbon, giving high catalytic activity and attractive carbon nanotube as well as the longest catalyst lifetime (Sharif Zein and Mohamed, 2004). A series of mesoporous Ni/TiO2 catalyst with different nickel loading from 10 to 50 wt% was successfully prepared by facile one-pot sol-gel method and obtained maximum hydrogen yield of 56% and carbon yield of 1544% were observed for 50% Ni/TiO2 catalyst at 700ºCwith an undiluted methane feed of 150 ml/min for 360min of reaction time (Pudukudy et al., 2017). Very few studies were reported with Ni/TiO2 catalyst for hydrogen production. Till now to our best knowledge, no one was reported on Ni/FTiO2 catalyst, synthesized by diffusion flame reactor using Liquefied Petroleum Gas (LPG) as fuel and oxygen as oxidant. In this study, an attempt made using flame synthesized titanium nanorods as a catalyst support for nickel based catalyst for the hydrogen production. The comparison study between Ni/TiO2 and Ni/Flame synthesized TiO2 (Ni/F-TiO2) catalysts for hydrogen production using thermocatalytic decomposition of methane. The process parameters like different nickel weight percentage (10%, 20%, 30% and 40 wt %) and reaction temperature (650, 700, 750 and 800
C) were performed for hydrogen production studies at 54sccm flowrate of methane.

2. Materials and methods 2.1. Materials Nickel (II) nitrate hexahydrate, acetone, titanium dioxide, titanium tetra iso-propoxide (TTIP) were purchased from Merck-India, LPG (domestic, Bharat Gas), oxygen, methane and nitrogen gases were purchased from Industrial gas Agency of Pvt. Ltd. India. 2.2. Catalyst preparation 2.2.1. Preparation of flame synthesized titanium dioxide nanorods Titanium dioxide nanorods were synthesized in a flame reactor (Fig. 2) by using titanium tetra iso-propoxide as a precursor, LPG as a fuel and oxygen as an oxidant and reaction was kept for 30min. TiO2 formed on glass fiber filter paper was shown in Fig. 1. Later, it was calcined at 350
C in the presence of air for 60min to remove any traces of amorphous carbon (Mahender et al., 2012). Thus, formed product was flame synthesized titanium dioxide nanorods. 2.2.2. Preparation of Ni/TiO2 catalyst and preparation of Ni/F-TiO2 catalyst Nickel supported titanium dioxide catalyst was prepared by wet impregnation. The 0.1M nickel (II) nitrate hexahydrate was dissolved in acetone and required weight of titanium dioxide/flame synthesized titanium dioxide catalyst was added and kept on magnetic stirrer for 24hr. Then the obtained samples were dried and calcined at 350
C under nitrogen flow for 2hr. Thus, formed catalyst was nickel supported titanium dioxide and nickel supported flame synthesized titanium dioxide catalyst. The synthesis of Ni/TiO2 catalyst and Ni/F-TiO2 catalyst were shown in Figs. 2 and 3. 2.3. Experimental set up Thermo catalytic decomposition of methane studies were carried out in an indigenously fabricated conventional gas flow fixed bed reactor system comprising a reactor of internal diameter 16 mm and heating zone length of 250 mm. The detail of the experimental set up was given in previous published paper (Srilatha et al., 2015).

Fig. 1. Diffusion Flame reactor setup and Sample collector.

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structure. The presence of amorphous, crystalline phases and orientation of atoms was assessed using PCPDF-2 ICDD data base. The average crystal size was calculated by Scherer's equation (Eqn. (2)) by peak selection D ¼ k l / b cos q

(2)

Where D ¼ Size of the crystal, K ¼ 0.9, l ¼ wavelength of X-ray, b ¼ Full Width at Half maximum (FWHM) of the peak selected, q ¼ Bragg's angle of the peak diffraction. The catalysts (before and after hydrogen production studies) surface studies were analyzed using BET (Brunauer, Emmett, and Teller) measurement Micromeritics 2010 model. The surface morphology of catalysts (before and after hydrogen production studies) were analyzed using Scanning electron micrograph (SEM) with Hitachi Se3700 Super (SEM) operating at an accelerating voltage of 15 kV. The surface morphology of catalysts (before and after hydrogen production studies) were analyzed using JEOL JEM2100 Transmission electron microscopy (TEM). The composition of nickel in both Ni/TiO2 and Ni/F-TiO2 catalysts were experimentally determined by AAS. Atomic Absorption Spectrometer (Senss AA, GBC Scientific equipments), equipped with air-acetylene flame atomizer and hallow cathode lamp is used for the analysis.

Fig. 2. Synthesis of Ni/TiO2 catalyst.

3. Results and discussion 3.1. Hydrogen production studies with Ni/TiO2 catalyst and Ni/FTiO2 catalyst The hydrogen production studies of Ni/TiO2 and Ni/F-TiO2 catalysts were carried out by varying nickel weight percentage, reaction temperature and reaction time. Fig. 3. Synthesis of Ni/F-TiO2 catalyst.

2.4. Experimental procedure 2.5 g of Ni/TiO2 and Ni/F-TiO2 catalysts were used. Experiments were carried out in atmospheric pressure. Weight percentage of nickel at 10, 20, 30 and 40 wt% were evaluated for both supporting materials (TiO2 and F-TiO2) at different reaction temperatures 650800
C. The gas samples were collected in TeddlarTM bags. Hydrogen collected in TeddlarTM bags were analyzed using Agilent 4890 gas chromatograph (TCD detector, nitrogen as carrier gas and Porapak Q column, Oven temperature: 120
C). AIMIL's Gas Chromatograph data station (DASTA-710) was used in the analysis of gas chromatograph data. 2.5. Characterization studies The catalysts were characterized by X-Ray Diffraction (Bruker D8 advanced X-ray diffractometer) functioned at a voltage of 40 kV and a current of 30 mA with CuKa radiation (l ¼ 0.154 nm) between 2q diffraction angles (20
e80
) for analyzing peak data and crystal

3.1.1. Effect of nickel weight percentage and reaction temperature The effect of nickel weight percentage and reaction temperature in Ni/TiO2 and Ni/F-TiO2 catalysts for hydrogen production studies at a constant flowrate of methane as 54sccm. The obtained hydrogen production from Ni/TiO2 and Ni/F-TiO2 catalysts were shown in Table 1. The Ni wt% loading on TiO2 and F-TiO2 was in the range of 10%, 20%, 30% and 40 wt% and hydrogen production volume % was observed to be 5.4%, 15.3%, 48% and 9.3% for TiO2 and 10.20%, 28.24%, 55.00% and 10.54% for F-TiO2 respectively. It was observed that 30 wt% of Ni/TiO2 and Ni/F-TiO2 were shown the maximum hydrogen production of 48 vol% and 55 vol% at 60min of reaction time and at temperature of 700
C. At the different reaction temperatures 650, 700, 750 and 800
C, hydrogen production volume % was observed to be 16.5%, 48%, 15.1% and 7.4% Ni/TiO2 and 28.6%, 55%, 24.5% and 10% for Ni/F-TiO2 respectively. This is due to blockage of the active sites by the carbon deposits produced during the reaction (Srilatha et al., 2015). Therefore, catalysts with 30 wt%Ni for both TiO2 &F-TiO2 and 700
C reaction temperature was investigated in the following experiment.

Table 1 Effect of nickel weight percentage and reaction temperature on hydrogen production with Ni/TiO2 and Ni/F-TiO2 catalysts. Temperature (
C)

650 700 750 800

Hydrogen Production (Volume %) 10wt%Ni/TiO2

10wt%Ni/F-TiO2

20wt%Ni/TiO2

20wt%Ni/F-TiO2

30wt%Ni/TiO2

30wt%Ni/F-TiO2

40wt%Ni/TiO2

40wt%Ni/F-TiO2

4.12 5.45 3.61 3.00

5.32 10.20 5.10 3.51

9.50 15.35 8.45 5.25

11.43 28.24 10.56 5.25

16.52 48.05 15.14 7.42

28.63 55.00 24.51 10.00

4.32 9.34 3.24 2.63

6.12 10.54 5.45 4.10

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Fig. 4. Effect of reaction time on hydrogen production (Volume %) with Ni/TiO2 and Ni/ F-TiO2 catalysts.

Fig. 6. XRD plot of Ni/TiO2 catalyst after hydrogen production reaction.

3.1.2. Effect of reaction time The effect of reaction time in Ni/TiO2 and Ni/F-TiO2 catalysts were studied for hydrogen production at 700
C by maintaining constant flow rate of methane as 54sccm. The obtained hydrogen production of Ni/TiO2 and Ni/F-TiO2 catalysts were shown in Fig. 4. From Fig. 4, it was observed that hydrogen production increased up to 48 vol% within 60min of reaction time and then further it was decreased to 12 vol% in 300min of reaction time and then catalyst deactivated in 360min due to the carbon deposition on the active sites of nickel. There were only few studies reported in which TiO2 was used as the Ni support or textural promoter in the methane decomposition reaction. Takenaka et al (2003a,b) used very low Ni loadings (2.5%), while Ermakova et al. (1999) used very high loadings (90%). However, both studies were primarily focused on the production of filamentous carbon. From Fig. 4, it was observed that the hydrogen production increased up to 55 vol% within 60min of reaction time and then further it was decreased to 15.3 vol% in 300min of reaction time and then catalyst was deactivated in 360min due to the carbon deposition on the active sites of nickel. As per literature, no studies were found on Ni/Flame synthesized TiO2 catalyst for the hydrogen production. Hence, we made an attempt and optimum results were obtained. The same kind of work was done by Hong Yan Wang using Ni-Cu alloy catalyst with 62.6% Ni achieved 82% at a reaction temperature of 750
C (Yan

3.2.1. X-ray diffraction (XRD) analysis The XRD patterns of the Ni/TiO2 catalyst (Fig. 5) before hydrogen production reaction showed intense peaks at the 2q angles of TiO2 (101) and Ni3C(010) at 25
, Ni (111) at 32
, TiO2 (103) at 35
, TiO2 (004), Ni3C (112) and Ni (111) at 37.5
, TiO2 (200) and Ni3C (011) at 48
, Ni (200) and TiO2 (211) at 56
, Ni (220) and Ni3C (012) at 62
, Ni (311) at 68
and Ni (222) and Ni3C (110) at 76
, the average crystallite size was 35e40 nm and The XRD pattern of the Ni/F-TiO2 catalyst (Fig. 7) before hydrogen production reaction showed intense peaks at the 2q angles of Ni3C (112) at 26
, NiO (111) and TiO2 (103) at 35
, TiO2 (004) at 37.5
, TiO2 (200) and Ni3C (011) at 48
, Ni (200), Ni3C (012) and TiO2 (211) at 56
, NiO (220) at 62
, Ni (311) at 68
and Ni (220) at 78
, the average crystallite size was 30e40 nm.The TiO2 present in the sample before hydrogen

Fig. 5. XRD plot of Ni/TiO2 catalyst before hydrogen production reaction.

Fig. 7. XRD plot of Ni/F-TiO2 catalyst before hydrogen production reaction.

Wang Hong and Chong Lua Aik al 2015), Pudukudy and Yaakob (2015) using Ni, Co and Fe based monometallic catalysts supported on sol gel derived SiO2 micro flakes. Ni based catalyst achieved 74% hydrogen yield, a slight deactivation was observed with time on stream. The Co and Fe based monometallic catalysts were found to be less active but more stable than the Ni catalyst. 3.2. Characterization of catalysts

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production reaction were found to be in anatase phase. The XRD pattern of the Ni/TiO2 catalyst (Fig. 6) after hydrogen production reaction showed intense peaks at the 2q angles of C (002) at 25
, TiO2 (110) and Ni3C (112) at 27
, Ni3C (010) at 36
, Ni (111) at 38
, C (101) at 48
, C (004) at 52
, TiO2 (211) at 55
, TiO2 (002) and Ni (220) at 62
, Ni (311) at 68
, TiO2(301) at 70
and C (110) and Ni3C (110) at 75
, the average crystallite size was 40 nm. The XRD pattern of the Ni/F-TiO2 catalyst (Fig. 8) after hydrogen production reaction showed intense peaks at the 2q angles of C (002) and Ni3C (112) at 25
, TiO2 (110) at 27
, Ni (111) and Ni3C(114) at 35
, TiO2 (111), Ni (200), Ni3C(010) and C (100) at 42
, Ni (111) at 47
, TiO2 (211) and C (004) at 55
, Ni (220) and TiO2 (002) at 62
, Ni (311) and TiO2 (301) at 70
and C (110) at 75
, the average crystallite size was 30e40 nm. The TiO2 present in the sample after hydrogen production reaction were found to be in rutile phase. These XRD results were matched with PCPDF-2 ICDD data base (Pudukudy et al., 2017). Fig. 8. XRD plot of Ni/F-TiO2 catalyst after hydrogen production reaction.

3.2.2. BET surface area analysis The surface area, pore volume and average particle size of Ni/

Table 2 BET Surface analysis of Ni/TiO2 and Ni/F-TiO2 catalysts. Catalyst BET surface area before reaction (m2/g)

BET surface area after reaction (m2/g)

Total Pore volume, before reaction (cm3/g)

Total Pore volume, after reaction (cm3/g)

Average Particle size, before Average Particle size, after reaction (nm) reaction (nm)

Ni/TiO2 77.10 Ni/F83.5 TiO2

18.0 21.5

0.45 0.50

0.24 0.25

5.2 7.5

Fig. 9. SEM image of Ni/TiO2 catalyst before and after hydrogen production reaction.

46.5 54.3

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Fig. 10. TEM images of Ni/TiO2 and Ni/F-TiO2 catalysts.

TiO2 and Ni/F-TiO2 catalysts were given in Table 2. The surface area and Pore volume of Ni/TiO2 catalyst was decreased from 77.10 to 18.00 m2/g and 0.45 to 0.24 cm3/g and for Ni/F-TiO2 catalyst, it was found to be 83.5 to 21.5 m2/g and 0.50 to 0.25cm3/g respectively over a period of 360min of reaction time. This might be due to the formation of carbon particles deposition on the clear surface of the catalyst. Average particle size of Ni/TiO2 catalyst was observed to be 5.2e46.5 nm and 7.5e54.3 nm for Ni/F-TiO2 catalyst from BET surface area analysis which states that the surface area decreases with increase in particle size. The loss in surface area leads to decrease in hydrogen production. It confirms that based on progressive pore blocking by carbon deposition (Pinilla et al., 2007). 3.2.3. Scanning electron microscope (SEM) analysis of Ni30/TiO2 catalyst The SEM images of Ni/TiO2 and Ni/F-TiO2 catalysts before and after hydrogen production studies were shown in Fig. 9. Before hydrogen production reaction, we observed that Ni/TiO2 sample in porous nature and Ni/Flame synthesized TiO2 sample in amorphous nature. After hydrogen production reaction, Ni/TiO2 sample in combinations of carbon nanorods and particles and Ni/Flame synthesized TiO2 sample, we observed carbon nanorods formation. 3.2.4. Transmission electron microscopy (TEM) analysis The TEM images of Ni/TiO2 and Ni/F-TiO2 catalysts were shown carbon nanorods formation. Carbon nanorods were observed with a diameter and length of 5e10 nm and 0.25 mm respectively for Ni/ TiO2 and for Ni/F-TiO2 catalyst it was found to be 50e100 nm and 0.5 mm respectively, which were shown in Fig. 10. 3.2.5. Atomic Absorption Spectrometer analysis The composition of Ni in both Ni/TiO2 and Ni/F-TiO2 catalysts were theoretically determined using AAS. The comparison of theoretically calculated and experimentally determined Ni wt% in both Ni/TiO2 and Ni/F-TiO2 catalysts (before and after experiment) were given in Table 3. Compared to Ni/TiO2 catalyst, Ni/F-TiO2 catalyst shown Table 3 Composition of Ni in Ni/ TiO2 and Ni/ F-TiO2 catalysts. Sample Code

Ni/TiO2 Ni/ F-TiO2

Wt % of Ni (Theoretical)

30 30

Wt% of Ni (AAS) Before Reaction

After reaction

27.5 28.5

10.85 8.59

optimum hydrogen production due to its high surface area and structural properties. 4. Conclusions  From this study, it can be concluded that Ni/F-TiO2 catalyst showed optimum hydrogen production as 55 vol % and 48 vol % for Ni/TiO2 catalyst.  Flame synthesized titanium nanorods as catalyst support which was prepared by flame reactor enhanced the hydrogen production.  Both Ni/TiO2 and Ni/F-TiO2 catalysts were active for 300min of reaction time and were deactivated at 360min of reaction time which was due to carbon deposition on the active sites of nickel.  Apart from hydrogen production, carbon nanorods were observed with a diameter and length of 5e10 nm and 0.25 mm respectively for Ni/TiO2 and for Ni/F-TiO2 catalyst, it was found to be 50e100 nm and 0.5 mm respectively. Acknowledgements One of the author Dr. K. Srilatha would like to acknowledge Ministry of New and Renewable Energy India, New Delhi for providing financial support (Grant No.: NREF/TU/2011/02). Appendix A. Supplementary data Supplementary data related to this article can be found at https://doi.org/10.1016/j.sajce.2018.02.003. References Abbas, H.F., Daud, W.M.A.W., 2010. Influence of reactor material and activated carbon on the thermo catalytic decomposition of methane for hydrogen production. Appl. Catal. Gen. 388, 232e239. https://doi.org/10.1016/ j.apcata.2010.08.057. Abbas, H.F., Wan Daud, W.M.A., 2010. Hydrogen production by methane decomposition: a review. Int. J. Hydrogen Energy 35, 1160e1190. Ashok, J., Subrahmanyam, M., Venugopal, A., 2008. Hydrotalcite structure derived Ni-Cu-Al catalysts for the production of H2 by CH4 decomposition. Int. J. Hydrogen Energy 33, 2704e2713. Avdeeva, L.B., Reshetenko, T.V., Ismagilov, Z.R., Likholobov, V.A., 2002. Iron-containing catalysts of methane decomposition: accumulation of filamentous carbon. Appl. Catal., A 228, 53e63. Awadallah, A., Aboul-Enein, A., El-Desouki, D., Aboul-Gheit, A., 2014. Catalytic thermal decomposition of methane to COx-free hydrogen and carbon nanotubes over MgO supported bimetallic group VIII catalysts. Appl. Surf. Sci. 296, 100e107. Bayat, N., Rezaei, M., Meshkani, F., 2016a. COx-free hydrogen and carbon nanofibers production by methane decomposition over nickel-alumina catalysts. Kor. J.

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