Direct Conversion of Methane to Hydrogen using Gas-phase Metal Halides: DFT and Microkinetic Modeling

Sajal Kanti Dutta^a, Vishal Agarwal^a^,^b, Horia Metiu^c

^aDepartment of Chemical Engineering, Indian Institute of Technology Kanpur, Kanpur 208 016, India

^bDepartment of Sustainable Energy Engineering, Indian Institute of Technology Kanpur, Kanpur 208016, India

^cDepartment of Chemistry and Biochemistry, University of California-Santa Barbara, Santa Barbara, California 93106-9510, United States

Proceedings of SUNRISE IV - Transition to Net Zero (SUNRISEIV)

Online, Spain, 2022 February 10th - 11th

Organizers: Georgia Bevan, Ashish Garg, Raju Gupta, Ian Mabbett, Hari Upadhyaya, Adrian Walters and Sara Walters

Poster, Sajal Kanti Dutta, 003
Publication date: 7th February 2022

ePoster:

In recent years, global warming has driven us to find clean fuels without CO₂ generation. Among the various alternatives, hydrogen is a promising alternative for zero CO₂emissions to the atmosphere. The most acceptable industrial process for hydrogen production is steam reforming of methane (SRM).[1]Unfortunately, SRM generates a large quantity of CO₂.[2]On the other hand, methane pyrolysis produces hydrogen without cogeneration of CO₂.[3]Here, we present a combined DFT (ccsd(t)/aug-cc-pvqz//ccsd/6-311++g(d,p))[4],[5],[6]and microkinetic modeling study of hydrogen production from methane (most abundant natural gas) catalyzed by gaseous ZnCl₂ in a batch reactor at 1000⁰C. We also explore the catalyzing effects of AlCl₃, CoCl₂, CuCl₂, FeCl₂ and NiCl₂ for methane decomposition. High vapor pressure of these metal halides provides significant quantity in the gas-phase at the pyrolysis temperature, suggesting catalysis in the gas-phase.

We propose reaction networks of hydrogen production catalyzed by ZnCl₂in the gas-phase. ZnCl₂ catalyst reduces the apparent activation energy by 182 kJ/mol than that in without catalyst (423 kJ/mol[7]), suggesting ZnCl₂to be catalytically active in the gas-phase at 1000⁰C. Our Bader charge analysis shows that the methane decomposition follows a coupled mechanisms of proton and hydride transfers. Microkinetic simulations show that the molecular state of ZnCl₂ is lost at the beginning of the reactions, and the catalyst is recovered for the rest of the pyrolysis. Furthermore, the sensitivity analysis based on degree of rate control (DRC) suggests that four elementary reactions are rate-determining, and the most dominant rate-determining step shifts from one elementary reaction (formation of CH₃^* and H^* radicals from CH₄) to another (formation of CH₃^*and HZnCl from reaction between CH₄ and ZnCl^* radical) as the reaction progresses. Further DFT calculations demonstrate that gas-phase CuCl₂ and NiCl₂are also effective catalysts for methane decomposition in comparison to AlCl₃, CoCl₂ and FeCl₂ catalysts.

Keywords: Methane decomposition; Gas-phase metal halides; DFT; Microkinetic model; DRC-based sensitivity analysis

References:

[1] Weger, L.; Abánades, A.; Butler, T. Methane cracking as a bridge technology to the hydrogen economy. Int. J. Hydrog. Energ., 2017, 42, 720–731.

[2] Abánades, A. In Production of Hydrogen from Renewable Resources; Fang, Z., Smith, R. L., Jr., Qi, X., Eds.; Springer Netherlands: Dordrecht, 2015; pp 149–177

[3] Upham, D. C.; Agarwal, V.; Khechfe, A.; Snodgrass, Z. R.; Gordon, M. J.; Metiu, H.; McFarland, E. W. Catalytic molten metals for the direct conversion of methane to hydrogen and separable carbon. Science 2017, 358, 917–921.

[4] Purvis, G. D.; Bartlett, R. J. A full coupled-cluster singles and doubles model: The inclusion of disconnected triples. J. Chem. Phys., 1982, 76, 1910–1918

[5] Wiberg, K. B. Basis set effects on calculated geometries: 6-311++G** vs. aug-cc-pVDZ. J. Comput. Chem., 2004, 25, 1342–1346.

[6] Weaver, M. N.; Jr, K. M. M. Assessment of the CCSD and CCSD(T) coupled-cluster methods in calculating heats of formation for Cu complexes. Mol. Phys., 2009, 107, 1251–1259.

[7] Skinner, G. B.; Ruehrwein, R. A. Shock tube studies on the pyrolysis and oxidation of methane. J. Phys. Chem., 1959, 63, 1736–1742.

Acknowledgements:

S.K.D. is thankful to IIT Kanpur for financial support under the Institute Post-doctoral Fellowship. V.A. acknowledges the financial support from the Science and Engineering Board (SERB), Department of Science and Technology (DST), Govt. of India. The authors also acknowledge the support of DST, Govt. of India, for the High-Performance Computing (HPC) facility at IIT Kanpur.

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