Integration of dry-reforming and sorption-enhanced water gas shift reactions for the efficient production of high-purity hydrogen from anthropogenic greenhouse gases

https://doi.org/10.1016/j.jiec.2021.10.016Get rights and content

Highlights

  • The Ru-SYT perovskite catalyst was successfully applied to dry-reforming reactions.

  • 2–4 nm sized of small Ru particles formed on the SYT perovskite surface by exsolution.

  • Exsolution of Ru on the catalyst could further improve the catalytic activity by about 2%.

  • An integrated system combining dry-reforming and sorption-enhanced water gas shift reactions was suggested.

  • As-proposed system could directly produce high-purity H2 (>99.5%) from greenhouse gases (CO2 + CH4).

Abstract

With growing interest in the bulk production of the alternative energy carrier hydrogen, dry-reforming of methane using carbon dioxide has attracted great interest as one of the possible carbon capture and utilization (CCU) technologies and hydrogen production methods. An integrated system combining the dry-reforming and water gas shift reactions is suggested to improve the productivity of hydrogen, and a system has also been developed for high-purity hydrogen production from a single system using the sorption-enhanced reaction concept. To realize the proposed system, we develop the Ru-doped Sr0.92Y0.08TiO3 perovskite catalysts and investigate their characteristics using various analyses. The prepared catalysts exhibit excellent CH4 conversion of 92.2% for the dry-reforming reactions at 800 °C without performance degradation by coke formation. Moreover, high-purity hydrogen (>99.5%) is directly produced by the proposed integrated system using anthropogenic greenhouse gases as reactants, and the efficiency is further enhanced by recycling the captured CO2 to the dry-reforming reactor.

Introduction

With the demand for energy rapidly increasing due to intensive industrial development, conventional power generation processes based on the combustion of fossil fuels create enormous amounts of anthropogenic greenhouse gas emissions and severe environmental issues. Inspired by developing feasible technologies to simultaneously reduce anthropogenic greenhouse gas emission and convert them to valuable products, much research has been focused on a new energy system based on hydrogen (H2), the so-called “hydrogen economy”, where energy production, transport, and storage rely on the alternative energy carrier H2. A dry-reforming (DR) reaction of CH4 using CO2 is one of possible techniques and can achieve producing alternative energy carrier H2 from greenhouse gases (i.e., CO2 and CH4) [1], [2], [3], [4], [5]. Since the DR reaction is endothermic reaction, it generally proceeds at a temperature of 600 °C or higher. The rate determining step of the DR reaction has been reported as the decomposition of CH4 over the catalyst surface [6], [7]. The conventional Ni-based catalysts are facing serious problems with deactivation by sintering and coke formation under the DR reaction conditions [8], [9], [10]. Many studies have been intensively conducted to solve this problem. Li et al. and Bian et al. presented core–shell structured catalysts and they showed enhanced catalytic performance for the DR reaction and coke resistance [11], [12]. Han et al. and Wang et al. also successfully synthesized the Ni@SiO2 and (Ni/CeO2)@SiO2 catalysts via microemulsion method and they showed stable performance under DR reactions at 600–800 °C [13], [14]. Additionally, Gao et al. proposed the Ni-Co bimetallic catalysts and measured their CH4 conversion as 79% for the DR reaction at 700 °C [15]. There have been other efforts to inhibit coke formation by impregnation promoters such as Co, Ce, La, Y, and Sm [16], [17], [18], [19][20]. These promoters facilitate oxygen transfer and attribute to not only increase catalytic performance, but also help in preventing coke formation.

From the viewpoint of materials having great capability of oxygen mobility, perovskites (in general, ABO3, where A is a rare-earth element and B is a transition metal) have attracted great interest as promising support materials for heterogeneous catalyst with excellent resistances to coke formation and stabilities at high temperatures [21], [22]. As an effort to uniformly disperse active metal into the highly ordered mixed oxide structure, Gallego et al. prepared LaNiO3-based catalysts and they were highly resistant to coke deposition in the long-term DR reaction at 700 °C [23]. One of LaNiO3-based catalysts, LaNi0.9Mg0.1O3-δ was measured its CH4 conversion as 56% at 700 °C DR reaction. Oh et al. also prepared noble metal (Co, Rh, and Ir)-doped LaCrO3 perovskite catalysts and applied to the DR reactions [24]. From this work, the catalytic activity for the DR reaction could be enhanced by formation of nano-sized Ir or Rh particles on the perovskite surface via exsolution. The CH4 conversion of the prepared LaCr-.95Ir0.05O3-δ perovskite catalyst was measured as about 80% at 750 °C DR reaction and its performance was well maintained during long-term operation (75 h) without deactivation. However, the CH4 conversion is greatly reduced as the space velocity increase, so there is a limit to the treatment of large-scale operation. In our previous work, we reported the synthesis of Ru-doped SrYTiO3 (SYT) perovskites by using the Pechini method and characterized the catalytic properties for different Ru-loading. The Ru-SYT catalysts having more than 2.4 wt% Ru exhibited excellent CH4 conversion of over 75% at 800 °C [25].

In this study, the DR reaction using the Ru-SYT perovskite is combined with the water gas shift (WGS) reaction for additional H2 production. Through the WGS reactions, CO obtained from DR reaction can be further reacted with equimolar amounts of steam to produce H2 and by-product CO2. With an integrated system combining DR and WGS reactions (scheme 1a), it is possible to directly produce H2 using greenhouse gases as reactants, and the steam required for the WGS reaction can be produced using the waste heat from the DR reaction unit. However, the produced H2 from the proposed system contains a large amount of impurities such as unreacted CH4 and by-product CO2. Thus, additional separation processes, e.g., pressure swing adsorption (PSA), are required for high-purity H2 production [26]. To minimize such complex separation processes, the sorption-enhanced reaction (SER) concept has been proposed and applied to various catalytic processes [27], [28], [29], [30], [31], [32]. As DR reaction combines with sorption-enhanced WGS (SE-WGS) reaction (Scheme 1b), high-purity of hydrogen could be directly produced from an integrated system. For this system, solid sorbents for selectively capturing CO2 were loaded into the SE-WGS unit along with the catalyst. The suggested system has advantage for not only producing high-purity hydrogen during ‘adsorption mode’ in which WGS reaction by catalyst and by-product CO2 removal are simultaneously performed but also enhancing the forward reaction of WGS by Le Chatelier’s principle. Moreover, the captured CO2 could be regenerated and recycled to DR unit as a reactant during ‘desorption mode’.

For experimentally demonstrating the proposed an integrated system, the Ru doped SYT perovskite catalysts and K2CO3-promoted hydrotalcite CO2 sorbents were chosen as DR catalyst and high-temperature CO2 sorbent based on our previous results. The Ru-doped SYT perovskite catalyst measured its activity under different reaction conditions, and the effect of exsolution on the DR reaction performance was investigated. Then, an integrated system combining the DR and SE-WGS reactions to produce high-purity H2 was also experimentally demonstrated using the prepared catalyst and CO2 sorbent, and suggested experimental approaches to increase the process efficiency. By applying the SER concept to the as-proposed integrated system, it is possible to not only produce high-purity H2 from a single system but also recycle captured CO2 using solid sorbents in the DR unit to further improve the efficiency of the process.

Section snippets

Preparation of Sr0.92Y0.08TiO3 (SYT) perovskite and Ru-doped SYT catalysts

The Sr0.92Y0.08TiO3 (SYT) and Ru-doped SYT perovskites were synthesized through the Pechini method [25], which is a type of sol–gel reaction using suspension and nitrate precursor solutions. A suspension solution was prepared by dissolving 27.5 g of titanium isopropoxide (Ti(OCH(CH3)2)4; 99.999%, Sigma-Aldrich) and 70 g of citric acid (ACS reagent, 99.5%, Sigma-Aldrich) in 100 ml of ethylene glycol (anhydrous, 99.8%, Sigma-Aldrich) and stirred for 10 min. A metal nitrate precursor solution was

Characteristics of prepared samples

The XRD spectra in Fig. 1 indicates that the SYT perovskite and Ru5-SYT catalyst were successfully synthesized with highly ordered crystal structures (JCPDS No. 35–0734). In particular, the XRD spectra of the Ru5-SYT exhibited similar patterns to that of the SYT, which infers that the Ru ions were well-dispersed in the perovskite structure. In addition, the XRD peaks of the Ru5-SYT slightly shifted to lower diffraction angles, indicating an expansion of the crystalline structure (see the

Conclusion

To develop a heterogeneous catalyst with a high activity in the DR reaction, Sr0.92Y0.08TiO3 perovskite and Ru5-SYT catalyst were prepared by the Pechini method. To enhance the catalytic activity by surface treatment, formation of 2–4 nm sized Ru particles on the catalyst surfaces could be realized using exsolution. The prepared Ru5-SYT exhibited excellent catalytic activity for the DR reaction at temperatures above 600 °C to produce CO and H2 from anthropogenic greenhouse gases (CH4 and CO2).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the New & Renewable Energy Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040080). This work was also supported by the Hydrogen Energy Innovation Technology Development Program of the National Research Foundation of Korea (NRF) funded by the Korean government (Ministry of Science and ICT(MSIT))

References (51)

  • W.-J. Jang et al.

    Appl. Energy

    (2016)
  • D. Zubenko et al.

    Appl. Catal. B

    (2017)
  • H. Ay et al.

    Appl. Catal. B

    (2015)
  • S. Lee et al.

    J. Ind. Eng. Chem.

    (2020)
  • D. Liu et al.

    J. Catal.

    (2009)
  • J. Guo et al.

    Appl. Catal. A

    (2004)
  • Y. Khani et al.

    Chem. Eng. J.

    (2016)
  • Z. Bian et al.

    Appl. Catal. B

    (2016)
  • F. Wang et al.

    Appl. Catal. B

    (2018)
  • K. Han et al.

    J. Power Sources

    (2021)
  • X. Gao et al.

    Catal. Today

    (2017)
  • M.B. Bahari et al.

    Chem. Eng. Sci.

    (2020)
  • K. Han et al.

    Fuel

    (2021)
  • K. Han et al.

    Chem. Eng. J.

    (2021)
  • G.S. Gallego et al.

    Appl. Catal. A

    (2008)
  • G.S. Kim et al.

    Int. J. Hydrogen Energy

    (2019)
  • F.V.S. Lopes et al.

    Chem. Eng. Sci.

    (2011)
  • H.M. Jang et al.

    Chem. Eng. Sci.

    (2012)
  • G.-H. Xiu et al.

    Chem. Eng. Sci.

    (2002)
  • L.A. Živković et al.

    Appl. Energy

    (2016)
  • L.A. Živković et al.

    Chem. Eng. Sci.

    (2020)
  • C.H. Lee et al.

    Appl. Energy

    (2017)
  • A. Jia et al.

    Solid State Sci.

    (2010)
  • W. Travis et al.

    Chem. Sci.

    (2016)
  • H. Wang et al.

    Appl. Catal. B

    (2019)
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    1

    These authors contribute equally.

    2

    Current address: Korea Institute of Energy Technology (KENTECH), Naju-si, Jeollanam-do, 58330, Republic of Korea

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