Methanol steam reforming by heat-insulated warm plasma catalysis for efficient hydrogen production

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Methanol steam reforming by heat-insulated warm plasma catalysis for efficient hydrogen production ⁎

Hao-Yu Lian, Xiao-Song Li, Jing-Lin Liu , Ai-Min Zhu

⁎

Laboratory of Plasma Physical Chemistry, School of Physics, Dalian University of Technology, Dalian, 116024, China

A R T I C LE I N FO

A B S T R A C T

Keywords: Plasma catalysis Methanol reforming Hydrogen production Energy efficiency

Efficient hydrogen production from methanol steam reforming is carried out in a heat-insulated warm plasmacatalytic (WPC) reactor. Methanol steam reforming in warm plasma and warm plasma-catalytic cases is investigated. For warm plasma alone, methanol mainly converts via pyrolysis reaction and its conversion linearly increases with specific energy input (SEI). The arc channel temperature and electron density of warm plasma are respectively measured to be around 2500 K and 3 × 1014 cm−3, based on optical emission spectra. To take advantage of energy from plasma, Fe-Cu/γ-Al2O3 catalyst for methanol steam reforming and water gas shift is placed after the warm plasma. Compare with plasma alone, methanol conversion in WPC case is nearly double therefore the energy cost decreases from 1.71 kW h/Nm3 to 0.85 kW h/Nm3. Energy efficiency of 84% and H2 selectivity of 98% with methanol conversion of 94% are achieved in this warm plasma-catalytic reactor.

CO + H2 O → CO2 + H2

1. Introduction In 21st century, the massive consumption of fossil fuels brings a series of problems such as environmental pollution, global warming and the coming energy crisis. One of the most promising alternative energy sources is hydrogen, which is clean, zero (low) carbon emission (depends on the sources) and renewable. As a secondary energy source, hydrogen is generally produced from reforming of hydrocarbons in large scale factories [1]. The centralized production of hydrogen inevitably involves the storage and delivery of compressed or liquefied hydrogen which is expensive and has potential risk [2–4]. One feasible solution is on-site generation of hydrogen at decentralized infrastructures by reforming of liquid fuels which are easy to storage and transport [5–7]. Methanol is a promising hydrogen-rich liquid fuel which has a H/C ratio of 4, so that it can convert to hydrogen with high H2 yield [8,9]. Hydrogen production from methanol can be carried out through steam reforming [10], pyrolysis reforming [11], and partial oxidation reforming [12] reactions. Among those reactions, the highest H2 yield is offered by methanol steam reforming (R1),

CH3 OH + H2 O → CO2 + 3H2

(R1)

which can be considered as pyrolysis reforming (R2)

CH3 OH → CO + 2H2 followed by water gas shift reaction (R3). ⁎

(R2)

(R3)

Conventional catalytic technique for methanol steam reforming has been numerously reported [13–15], features the high methanol conversion and hydrogen selectivity but is more suitable for large scale and continuous production due to the large reformer volume and slow startup. For distributed hydrogen production, the reformer is required to be in small or medium size, fast start-up and high efficient. The nonthermal plasma reforming technique is a very promising candidate due to the compact configuration and fast start-up [16–18], but still has the problems with the high energy cost and low energy efficiency. It has been reported that, warm plasma (WP, produced by microwave [19–21] and gliding arc discharge [22,23]) exhibits much lower energy cost and higher energy efficiency than cold plasma (includes dielectric barrier discharge [24–26], corona discharge [27]) in methanol reforming process due to the higher gas temperature and electron density. However, to date, the energy efficiency of methanol reforming without O2 is still lower than 50%. Our previous work [28] combined partial oxidation reforming with pyrolysis reforming of methanol in a heatinsulated gliding arc plasma reactor, achieved an energy efficiency of 74% with methanol conversion of 88%. However, the hydrogen concentration in gaseous product was lower than 48% due to the oxidative reforming of methanol with air. In the present work, a heat-insulated warm plasma-catalytic (WPC) reactor without any external heating, of which the catalysts are placed after the plasma, is employed to produce hydrogen from methanol

Corresponding authors. E-mail addresses: [email protected] (J.-L. Liu), [email protected] (A.-M. Zhu).

https://doi.org/10.1016/j.cattod.2019.03.068 Received 3 December 2018; Received in revised form 26 February 2019; Accepted 29 March 2019 0920-5861/ © 2019 Elsevier B.V. All rights reserved.

Please cite this article as: Hao-Yu Lian, et al., Catalysis Today, https://doi.org/10.1016/j.cattod.2019.03.068

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Fig. 1. Schematic diagram of the reactor for (a) activity test and (b) optical emission spectroscopy diagnosis.

coupled device (ICCD) detector (Andor iStar DH334) is used for measuring the optical emission spectra. An optical fiber (a fiber bundle composing of 19 fiber cores, each of the fiber cores has a NA value of 0.22) points perpendicularly to the quartz window to collect the light emitted from the plasma.

Table 1 Experimental conditions for methanol reforming with steam in warm plasma.

Constant Fin Constant Pin

S/C

SEI (kJ/mol)

Flow rate (SLM)

Power input (W)

1.5 1.5

43-75 46-80

2.5 3.5-2.0

80-140 120

2.2. Catalyst preparation and characterization steam reforming. This reactor has the advantages of both plasma reforming and catalytic reforming technique, which is compact, fast startup and has excellent hydrogen selectivity. Moreover, by combining the warm plasma with Fe-Cu catalyst, the energy in plasma can be further utilized to convert more methanol over the catalyst, therefore decreases energy cost and increases energy efficiency.

Fe-Cu/γ-Al2O3 catalyst is prepared by incipient wetness co-impregnation method. The γ-Al2O3 pellets (particle size: Φ1 mm) are impregnated overnight with Fe(NO3)3·9H2O and Cu(NO3)2·3H2O aqueous solution at room temperature, followed by drying in air at 110 °C for 6 h and calcination in air at 500 °C for 6 h. The Fe and Cu loadings of the prepared catalyst are both nominally 10 wt.%. The actual loadings are Fe of 8.27 wt.% and Cu of 8.29 wt.%, measured by inductively coupled plasma-atomic emission spectroscopy (ICP-AES, Optima 2000DV, Perkin Elmer). Brunauer-Emmett-Teller (BET) surface area of the asprepared catalyst is measured to be 99 m2/g by N2 adsorption using a surface area analyzer (AUTO SORB-1-MP, Quantachrome). The asprepared catalysts are packed into the reactor without pre-reduction. X-ray diffraction (XRD) patterns are obtained from an X-ray diffractometer (XRD-6000, Shimadzu) using a Cu Kα radiation at 40 kV and 30 mA in the 2θ range from 20° to 80°. Scanning electron microscope (SEM) images and energy dispersive X-ray spectroscopy (EDS) elemental mappings are obtained from a field emission scanning electron microscope (Nova Nano SEM 450).

2. Experimental 2.1. Warm plasma-catalytic reactor The reactor in the present work is upgraded based on the gliding arc plasma reactor used in our previous work [28,29]. As shown in Fig. 1a, the stainless steel reactor is grounded and wrapped with ceramic fiber cotton at outside for heat insulation. The high voltage (HV) electrode, a nickel-alloy rod with a diameter of 3 mm, is partially covered with a ceramic electric insulator. The naked length of the HV electrode inside the reactor is 2 mm. The HV electrode is located at the axis of the cylindrical reactor (with an inner diameter of 20 mm). The ground electrode, with an inner diameter of 12 mm and a length of 29 mm, is made of stainless steel and coaxial with the HV electrode. The gliding arc plasma is powered by a sine-wave AC power source (CTP-2000 K, Nanjing Suman electronics Company, China) with a frequency of 90 kHz. A solution of methanol in de-ionized water flows continuously into a vaporizer through a HPLC (high-performance liquid chromatography) pump and then tangentially feeds into the reactor. In warm plasma case, a thermocouple sheathed with a one-end sealed stainless steel tube is placed at 0.5 cm away from the plasma to measure the gas temperature of plasma. In warm plasma-catalytic case, Fe-Cu/γ-Al2O3 catalysts with bed height of 8 cm are packed into the reactor. The distance between the entrance of the catalyst-bed position and the plasma zone is about 0.5 cm. The temperature variation with axial distance from the catalyst-bed entrance is also measured by the thermocouple. For optical emission spectra (OES) diagnosis, a quartz window is added in front of the plasma zone as shown in Fig. 1b. A high resolution spectrograph (Andor Shamrock SR-750) with an intensified charge-

2.3. Gas analysis The analysis of gaseous product is the same as in our previous work [28]. Two gas chromatographs (GCs) are employed to online analyze the gaseous products using internal standard method. The first GC equips a thermal conductivity detector (TCD), using N2 as standard gas to quantify CO, CH4, CO2. The second GC has two detectors of TCD and FID (Flame Ionization Detector). The TCD is used to quantify H2 with He as standard gas; the FID is used to detect hydrocarbons such as CH4 and C2Hx (C2H6, C2H4 and C2H2). For convenient reading, definitions of methanol conversion ( XCH3 OH ) and water conversion ( X H2 O ), carbon-based selectivity of CO C C C ), CO2 (SCO ), CH4 (SCH ) and hydrogen selectivity (S H2 ), con(SCO 4 2 sumption rate of methanol (rCH3 OH ), dry-basis concentration of total hydrogen (CtDry − H2 ), specific energy input (SEI), energy cost (EC) and energy efficiency (η) are listed in supporting information. 2

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Fig. 3. Experimental and fitted spectra of (a) OH, (b) N2 and (c) Voigt fitting to Hβ line at the conditions of Pin = 120 W, S/C = 1.5, SEI =65.4 kJ/mol.

3. Results and discussion 3.1. Methanol reforming in warm plasma For plasma reforming processes, SEI is one of the most important parameters that strongly affects the reforming performance. Since the SEI (SE13) is equal to power input (Pin) divided by flow rate (Fin), effect of SEI on methanol steam reforming in warm plasma (WP) case (without catalyst) is investigated in two modes: constant flow rate (2.5 SLM) and constant power input (120 W). The detailed experimental conditions are summarized in Table 1. At a fixed flow rate of 2.5 SLM, the SEI increases from 43 to 75 kJ/mol with the power input rises from 80 to 140 W. When the power input is fixed at 120 W, the SEI increases from 46 to 80 kJ/mol with the decrease of flow rate from 3.5 to 2.0 SLM. To prevent carbon deposition, steam to carbon (S/C) ratio is set to 1.5 which is a little higher than its stoichiometric ratio of 1.0 in R1. The effect of SEI on methanol reforming in warm plasma is shown in Fig. 2. In Fig. 2a, whether in constant Fin or constant Pin mode, as the SEI increases from 43 to 80 kJ/mol, the methanol conversion linearly increases from 26% to 51%. This effect of SEI on reactant conversion has been widely reported in literatures [21,22,28,30–32] and can be explained as the expansion of gliding arc plasma volume induced by the increase of SEI [33,34]. Water conversion almost doesn’t change with SEI and stays below 2%. Such a low water conversion indicates that methanol may not convert via methanol steam reforming reaction (R1). The products of H2, CO, CO2, a small amount of CH4 and negligible C2 hydrocarbons (C2H2, C2H4, C2H6) are detected by gas chromatography

Fig. 2. Effect of SEI on (a) methanol and water conversion, (b) H2 and C-based selectivity, (c) methanol consumption rate and (d) gas temperature of plasma in WP cases under the conditions of Table 1.

3

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Fig. 5. Comparison of (a) conversion, selectivity, (b) energy cost and energy efficiency in WP and WPC cases. Condition: S/C = 1.5, SEI =73.3 kJ/mol, GHSV =7500 mL·gcat−1 h−1.

and their selectivities are shown in Fig. 2b. SEI shows an independence on product selectivity: selectivities of H2, CO, CO2 and CH4 respectively stay around 97%, 84%, 10% and 4% with increasing SEI. According to the high H2 and CO selectivity, it can be deduced that methanol mainly converts via pyrolysis reaction (R2) in WP case. Unlike methanol conversion, variation in methanol consumption rate with SEI is much different in constant Pin and constant Fin modes. As shown in Fig. 2c, methanol consumption rate linearly increases from 264 to 475 SCCM with SEI in constant Fin mode but stays around 420 SCCM in constant Pin mode. As a commonsense knowledge, reaction rate strongly depends on temperature. Therefore, gas temperature of plasma, which is measured at 0.5 cm downstream the warm plasma, shows the similar variation trend to methanol consumption rate. In Fig. 2d, with the increasing SEI, gas temperature of plasma increases from 400 to 485 °C in constant Fin mode and meanwhile stays around 460 °C in constant Pin mode. If replace SEI with power input as the abscissa, as shown in Fig. S1, it is easier to see the linear dependence of both methanol consumption rate and gas temperature of plasma on power input. This relationship suggests that the increase of methanol consumption rate is attributed to the increase of arc channel temperature (Tarc) with power input. Besides, the expansion of plasma volume with power input is another possible explanation. 3.2. Diagnosis of warm plasma by OES Fig. 4. Effect of SEI on (a) methanol and water conversion, (b) H2 and C-based selectivities, (c) axial distribution of catalyst-bed temperature, (d) energy cost and energy efficiency in WPC case. Condition: S/C = 1.5, GHSV =7500 mL·gcat−1 h−1.

In plasma, the chemical reactions are determined by the plasma parameters. In order to understand how the methanol steam reforming happens in the gliding arc plasma, the key parameters of plasma including arc channel temperature and electron density (ne) are diagnosed by OES. From OES of the plasma with a gas mixture of CH3OH 4

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temporal averaged gas temperature of arc channel is obtained. In Fig. 3a, with the good agreement of experimental and fitted OH spectra using the simulated software (SPECAIR [38]), Trot under the conditions of Pin = 120 W, S/C = 1.5, SEI =65.4 kJ/mol is obtained to be around 4300 K. Introduction of 5 vol.% N2 has no significant effect N2 OH on Trot . Moreover, Trot which could more closely reflect the arc channel temperature is obtained to be 2500 K in Fig. 3b. In terms of thermodynamic equilibrium state at Tarc (2500 K), selectivities of CO, CO2 and H2 are calculated to be 90.5%, 9.5% and 100% (calculated by the HSC Chemistry software(v7.0) using Gibbs free energy minimization method), respectively, close to that of the experimental results in Fig. 2b. The agreement of experimental and equilibrium calculation indicates that pyrolysis of methanol in arc channel is mainly responsible for methanol conversion. The electron density of the warm plasma can be estimated based on the Stark broadening of Hβ line at 486.1 nm (The calculation method is available in [39]). According to the Voigt fitting to Hβ line in Fig. 3c, the ne is calculated to be 3.0 × 1014 cm−3. It is worth noting that the increase of SEI can hardly affect the rotational temperature and electron density of plasma within the range of this experiment as shown in Fig. S2, which explains the insensitivity of the product selectivity towards the change of SEI. On the other hand, the increases of methanol consumption rate and gas temperature with power input shown in Fig. S1 are more likely to result from the expansion of plasma volume rather than the increase of arc channel temperature. 3.3. Steam reforming of methanol in WPC reactor According to Fig. 2d, the gas temperature of more than 400 °C implies that there exists substantial energy remained in the effluent gas from the plasma. To take advantage of the heat and the reactive species from plasma, warm plasma followed by catalyst is employed to further reform the residual reactant. Because the most commonly used Cu/Zn/ Al catalyst would be sintered at temperature higher than 300 °C, an alternative Fe-Cu/γ-Al2O3 catalyst which can operate at mid-temperature is used. In warm plasma-catalytic case, Fe-Cu/γ-Al2O3 catalysts with a weight of 20 g and a bed-height of 8 cm are packed into the reactor. The gas hour space velocity is set as 7500 mL·gcat−1 h−1 with a constant flow rate of 2.5 SLM, where gcat−1 is per gram catalyst. Effect of SEI on methanol steam reforming in WPC case is experimentally investigated and the results are shown in Fig. 4. With increasing SEI, methanol conversion increases from 50% to 94% as shown in Fig. 4a. The methanol conversions are much higher than that in WP case (Fig. 2a), suggesting that the additional methanol reactants are converted on the catalyst. Meanwhile, water conversion also increases from 18% to 44%. As mentioned before, water is barely converted in warm plasma, therefore the water conversion is attributed to the catalytic reaction of steam reforming (R1) or water gas shift (R3). The increase in SEI leads an increase of catalyst bed temperature as shown in Fig. 4c, hence accelerates the R1 and R3, which explains the increase of water conversion. For the same reason, CO selectivity decreases and CO2 selectivity increases with SEI (Fig. 4b). The H2 selectivity as high as 98% maintains unchanged. Energy cost and energy efficiency stay around 0.85 kW h/Nm3 and 84% respectively as shown in Fig. 4d. According to their definition in SE11 and SE12, the constant EC and η indicate the production rate of total hydrogen increases with power input in equal proportion. Methanol steam reforming in WP and WPC case are compared under the same conditions of S/C = 1.5, SEI =73.3 kJ/mol, Fin = 2.5 SLM. As shown in Fig. 5a, compare with WP alone, methanol conversion increases from 48% to 94% while the water conversion increases from 2% to 44% in WPC case. The ratio of additional water consumption to additional methanol consumption in WPC case is calculated to be 1.36, being higher than the stoichiometric ratio in R1. This indicates that not only R1 but also R3 occur over the catalyst. Under the combined action of R1 and R3, the selectivity of CO decreases from 82% to 22% and the

Fig. 6. Variations in (a) methanol and water conversion, (b) H2 and CO selectivity and dry-basis concentration of t-H2 with TOS.

Fig. 7. XRD patterns for the samples of fresh and two used Fe-Cu catalysts.

and H2O, spectra of OH (A2Σ+ - X2Π), CO (B1Σ+ - A1Π) Hα and Hβ are observed. Amongst those spectra, CO spectra has a poor signal to noise ratio. The rotational temperature of OH can’t be used to evaluate arc channel temperature due to that its population is deviated from Boltzmann distribution induced by the non-thermal feature of plasma [35–37]. However, OH radicals are the important species responsible for the reactions, thus the rotational temperature of OH is also calculated as a reference accounting for the non-thermal equilibrium of N2 plasma. As reported that the rotational temperature of N2(C-B) (Trot ) is close to arc channel temperature [33], 5 vol.% N2 is therefore introduced during OES diagnosis to estimate the arc channel temperature during the reforming reaction. Note that the temperature distribution in the arc channel cannot be measured due to the arc movement and the reactor configuration. In addition, the plasma is powered by an AC power supply with a frequency of 90 kHz. Thus only a spatial and 5

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Fig. 8. SEM images for the samples of (a, b) fresh and two used Fe-Cu catalysts after activity test of (c, d)1 h and (e–g) 8 h.

for 1 h and 8 h, respectively) are characterized by XRD, SEM and EDS method. The XRD patterns of the fresh and two used Fe-Cu catalyst are shown in Fig. 7. For the fresh catalyst, the peaks corresponding to Fe2O3 and Al2O3 can be clearly identified and the peaks of CuO are weak. After 1-hour plasma-catalytic reforming, the Fe2O3 phase disappears and is reduced to Fe3O4 which is responsible for the WGS reaction [40]. Along with the reduction of Fe2O3, diffraction peaks of metallic copper appear, which indicates that CuO is reduced during the reforming. The XRD pattern of the used catalyst for 8-hours activity test has no distinct difference from that for 1-hour activity test, which suggests that the deactivation of catalyst may not be caused by the change of crystal during the reforming. The surface appearance of the fresh and used catalysts are photographed by scanning electron microscope. The complete pictures of the fresh and two used spherical catalysts are shown in Fig. 8a, c, and e, respectively. Their corresponding magnified images on right side are indicated in Fig. 8b, d and f, g. According to Fig. 8b and d, there has little change of the catalyst surface with one-hour activity test. After run for 8 h, some of catalysts at the top of catalyst bed are partially covered by fibers with diameter of ten to a hundred nanometers as shown in Fig. 8g. According to the EDS elemental mapping in Fig. S4, these fibers are made of carbon. Besides, the surface without carbon fibers in Fig. 8f has no difference with the surface of fresh and 1-hour-used catalyst. As a consequence, the deactivation of catalyst may cause by coke formation. The resistance to coke formation of the catalyst should be further improved in our future work.

selectivity of CO2 increases from 12% to 74%. Fig. 5b shows the energy cost and energy efficiency in WP and WPC cases. With the nearly double methanol conversion and the unchanged H2 selectivity, the energy cost of WPC declines to 0.85 kW h/Nm3, which is cut down in half compared with that in WP case. The energy efficiency of total hydrogen production increases from 67% of plasma alone to 84% in WPC case. Estimation of energy balance of the WP and WPC cases is made: the energy input includes the electric energy into plasma and the chemical energy of methanol converted; the energy output includes the chemical energy of products and the heat energy of the effluent gas (see SE14). Based on SE15, the energy balance (BE) for WP and WPC cases is calculated to be 82.5% and 91.6%, respectively, which indicates less energy loss in the WPC reactor.

3.4. Stability test and characterization of catalyst The stability test of WPC reforming of methanol with Fe-Cu catalysts is investigated under the conditions of S/C = 1.5, SEI =64.5 kJ/mol, GHSV =7500 mL·gcat−1 h−1 and illustrated in Fig. 6. The top-bed temperature of catalyst increases rapidly to over 400 °C in a few minutes (Fig. S3), thus the WPC reforming system fast start. Methanol and water conversions reach the maximum values of 88% and 44% at TOS of 1 h, then decrease slowly to 72% and 25% at TOS of 8 h, respectively. H2 selectivity and t-H2 dry-basis concentration remain stable at about 98% and 74%, respectively. CO selectivity shows the contrary variation trend to water conversion with TOS, implies the deactivation of catalyst towards R1 and R3. In order to disclose the reason of catalyst deactivation, the samples of fresh and two used catalysts (after activity test 6

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4. Conclusion [14]

Methanol steam reforming for efficient hydrogen production in a heat-insulated warm plasma-catalytic reactor is reported. For plasma alone, methanol conversion linearly increases from 26% to 50% with increasing SEI from 43 to 80 kJ/mol. The major product is CO and H2, which indicates that methanol mainly converts via pyrolysis in warm plasma. Based on optical emission spectra, the arc channel temperature and electron density of warm plasma are measured to be around 2500 K and 3 × 1014 cm−3, respectively, and they do not change with SEI within the range of this experiment. To take advantage of the energy from plasma, the warm plasma followed by Fe-Cu/γ-Al2O3 catalyst is employed. Under the combined action of steam reforming and WGS catalyzed by Fe-Cu catalyst, the methanol conversion is nearly double and the water conversion increases significantly from 2% to 44% compared with WP case. As more methanol converted to hydrogen, energy cost of 0.85 kW h/Nm3 and energy efficiency of 84% with methanol conversion of 94% are achieved. The Fe-Cu catalyst used in WPC reactor could be auto-reduction during the reforming process, but the resistance to coke formation need to be further improved.

[15] [16]

[17] [18] [19]

[20]

[21] [22]

[23]

Acknowledgments

[24]

This work is supported by National Natural Science Foundation of China (11705019).

[25] [26]

Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.cattod.2019.03.068.

[27] [28]

References [29] [1] J.A. Turner, Sustainable hydrogen production, Science 305 (2004) 972–974. [2] N. Onishi, G. Laurenczy, M. Beller, Y. Himeda, Recent progress for reversible homogeneous catalytic hydrogen storage in formic acid and in methanol, Coord. Chem. Rev. 373 (2018) 317–332. [3] Q. Lai, T. Wang, Y. Sun, K.-F. Aguey-Zinsou, Rational design of nanosized light elements for hydrogen storage: classes, synthesis, characterization, and properties, Int. J. Adv. Mater. Technol. 3 (2018) 1700298. [4] A.M. Abdalla, S. Hossain, O.B. Nisfindy, A.T. Azad, M. Dawood, A.K. Azad, Hydrogen production, storage, transportation and key challenges with applications: a review, Energ. Convers. Manage. 165 (2018) 602–627. [5] L. Bobrova, I. Zolotarsky, V. Sadykov, V. Sobyanin, Hydrogen-rich gas production from gasoline in a short contact time catalytic reactor, Int. J. Hydrog. Energy 32 (2007) 3698–3704. [6] Y. Xin, B. Sun, X. Zhu, Z. Yan, H. Liu, Y. Liu, Effects of plate electrode materials on hydrogen production by pulsed discharge in ethanol solution, Appl. Energy 181 (2016) 75–82. [7] L. Lin, W. Zhou, R. Gao, S. Yao, X. Zhang, W. Xu, S. Zheng, Z. Jiang, Q. Yu, Y.-W. Li, C. Shi, X.-D. Wen, D. Ma, Low-temperature hydrogen production from water and methanol using Pt/α-MoC catalysts, Nature 544 (2017) 80. [8] C. De Bie, J. van Dijk, A. Bogaerts, CO2 hydrogenation in a dielectric barrier discharge plasma revealed, J. Phys. Chem. C 120 (2016) 25210–25224. [9] A. Iulianelli, P. Ribeirinha, A. Mendes, A. Basile, Methanol steam reforming for hydrogen generation via conventional and membrane reactors: a review, Renew. Sust. Energy Rev. 29 (2014) 355–368. [10] D.R. Palo, R.A. Dagle, J.D. Holladay, Methanol steam reforming for hydrogen production, Chem. Rev. 107 (2007) 3992–4021. [11] G. Li, C. Gu, W. Zhu, X. Wang, X. Yuan, Z. Cui, H. Wang, Z. Gao, Hydrogen production from methanol decomposition using Cu-Al spinel catalysts, J. Clean. Prod. 183 (2018) 415–423. [12] J.H. Kim, Y.S. Jang, D.H. Kim, Multiple steady states in the oxidative steam reforming of methanol, Chem. Eng. J. 338 (2018) 752–763. [13] Z.-Q. Huang, B. Long, C.-R. Chang, A theoretical study on the catalytic role of water

[30]

[31]

[32] [33]

[34]

[35]

[36]

[37] [38] [39]

[40]

7

in methanol steam reforming on PdZn(111), Catal. Sci. Technol. 5 (2015) 2935–2944. Y.-H. Huang, S.-F. Wang, A.-P. Tsai, S. Kameoka, Catalysts prepared from copper–nickel ferrites for the steam reforming of methanol, J. Power Sources 281 (2015) 138–145. L. De Rogatis, T. Montini, B. Lorenzut, P. Fornasiero, NixCuy/Al2O3 based catalysts for hydrogen production, Energy Environ. Sci. 1 (2008) 501–509. G. Petitpas, J.D. Rollier, A. Darmon, J. Gonzalez-Aguilar, R. Metkemeijer, L. Fulcheri, A comparative study of non-thermal plasma assisted reforming technologies, Int. J. Hydrog. Energy 32 (2007) 2848–2867. A. Bogaerts, E.C. Neyts, Plasma technology: an emerging technology for energy storage, ACS Energy Lett. 3 (2018) 1013–1027. X. Zhang, M.S. Cha, Partial oxidation of methane in a temperature-controlled dielectric barrier discharge reactor, Proc. Combust. Inst. 35 (2015) 3447–3454. E. Tatarova, N. Bundaleska, F.M. Dias, D. Tsyganov, R. Saavedra, C.M. Ferreira, Hydrogen production from alcohol reforming in a microwave ‘tornado’-type plasma, Plasma Sources Sci. Technol. 22 (2013) 065001. N. Bundaleska, D. Tsyganov, R. Saavedra, E. Tatarova, F.M. Dias, C.M. Ferreira, Hydrogen production from methanol reforming in microwave “tornado”-type plasma, Int. J. Hydrog. Energy 38 (2013) 9145–9157. Y.-F. Wang, Y.-S. You, C.-H. Tsai, L.-C. Wang, Production of hydrogen by plasmareforming of methanol, Int. J. Hydrog. Energy 35 (2010) 9637–9640. H. Zhang, X. Li, F. Zhu, Z. Bo, K. Cen, X. Tu, Non-oxidative decomposition of methanol into hydrogen in a rotating gliding arc plasma reactor, Int. J. Hydrog. Energy 40 (2015) 15901–15912. R. Burlica, K.-Y. Shih, B. Hnatiuc, B.R. Locke, Hydrogen generation by pulsed gliding arc discharge plasma with sprays of alcohol solutions, Ind. Eng. Chem. Res. 50 (2011) 9466–9470. S. Futamura, H. Kabashima, Effects of reactor type and voltage properties in methanol reforming with nonthermal plasma, IEEE Trans. Ind. Appl. 40 (2004) 1459–1466. D.H. Lee, T. Kim, Plasma-catalyst hybrid methanol-steam reforming for hydrogen production, Int. J. Hydrog. Energy 38 (2013) 6039–6043. V.J. Rico, J.L. Hueso, J. Cotrino, V. Gallardo, B. Sarmiento, J.J. Brey, A.R. GonzálezElipe, Hybrid catalytic-DBD plasma reactor for the production of hydrogen and preferential CO oxidation (CO-PROX) at reduced temperatures, Chem. Commun. (2009) 6192–6194. X.Z. Liu, C.J. Liu, B. Eliasson, Hydrogen production from methanol using corona discharges, Chin. Chem. Lett. 14 (2003) 631–633. H.-Y. Lian, X.-S. Li, J.-L. Liu, X. Zhu, A.-M. Zhu, Oxidative pyrolysis reforming of methanol in warm plasma for an on-board hydrogen production, Int. J. Hydrog. Energy 42 (2017) 13617–13624. K. Li, J.-L. Liu, X.-S. Li, X. Zhu, A.-M. Zhu, Warm plasma catalytic reforming of biogas in a heat-insulated reactor: dramatic energy efficiency and catalyst autoreduction, Chem. Eng. J. 288 (2016) 671–679. J.-L. Liu, X.-S. Li, X. Zhu, K. Li, C. Shi, A.-M. Zhu, Renewable and high-concentration syngas production from oxidative reforming of simulated biogas with low energy cost in a plasma shade, Chem. Eng. J. 234 (2013) 240–246. B. Zhu, X.-S. Li, C. Shi, J.-L. Liu, T.-L. Zhao, A.-M. Zhu, Pressurization effect on dry reforming of biogas in kilohertz spark-discharge plasma, Int. J. Hydrog. Energy 37 (2012) 4945–4954. J.-L. Liu, Z. Li, J.-H. Liu, K. Li, H.-Y. Lian, X.-S. Li, X. Zhu, A.-M. Zhu, Warm-plasma catalytic reduction of CO2 with CH4, Catal. Today (2018). T.-L. Zhao, Y. Xu, Y.-H. Song, X.-S. Li, J.-L. Liu, J.-B. Liu, A.-M. Zhu, Determination of vibrational and rotational temperatures in a gliding arc discharge by using overlapped molecular emission spectra, J. Phys. D Appl. Phys. 46 (2013) 345201. T.-L. Zhao, J.-L. Liu, X.-S. Li, J.-B. Liu, Y.-H. Song, Y. Xu, A.-M. Zhu, Temporal evolution characteristics of an annular-mode gliding arc discharge in a vortex flow, Phys. Plasma 21 (2014) 053507. P.J. Bruggeman, N. Sadeghi, D.C. Schram, V. Linss, Gas temperature determination from rotational lines in non-equilibrium plasmas: a review, Plasma Sources Sci. Technol. 23 (2014) 023001. D. Yanjun, N. Gaurav, O. Gaku, D. Yanjun, P. Zhimin, J.B. Peter, Emission considering self-absorption of OH to simultaneously obtain the OH density and gas temperature: validation, non-equilibrium effects and limitations, Plasma Sources Sci. Technol. 26 (2017) 095007. B. Peter, D. Joris, V. Jan, L. Christophe, DC-excited discharges in vapour bubbles in capillaries, Plasma Sources Sci. Technol. 17 (2008) 025008. C.O. Laux, T.G. Spence, C.H. Kruger, R.N. Zare, Optical diagnostics of atmospheric pressure air plasmas, Plasma Sources Sci. Technol. 12 (2003) 125. J.M. Luque, M.D. Calzada, M. Sáez, Experimental research into the influence of ion dynamics when measuring the electron density from the Stark broadening of the H α and H β lines, J. Phys. B At. Mol. Opt. 36 (2003) 1573. M. Zhu, I.E. Wachs, Iron-based catalysts for the high-temperature water–gas shift (HT-WGS) reaction: a review, ACS Catal. 6 (2016) 722–732.