I have read that hydrogen can undergo self-heating, through a catalytic process, without the presence of oxygen or air. Is that true?

I understand that this is not "burning" or "ignition", since this occurs without oxygen, and I don't think this is due to decomposition or rearrangement, as happens to $\ce{NI3}$ or 1,2,3-trinitroxypropane (nitroglycerine), since there's just molecular hydrogen, $\ce{H2}$.

Could someone explain if that occurs, and if so, where does the heat (energy) come from?

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    $\begingroup$ In case of hydrogen, it is not possible without oxidant, that may not be oxygen. Unless you mean nuclear reactions, like catalytic CNO cycle in massive stars. $\endgroup$
    – Poutnik
    Commented Nov 15, 2023 at 16:23
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    $\begingroup$ Jack, I've taken some liberties in editing your question to make it more meaningful, i.e., changing "ignition" to "heating". Please let me know if my understanding is correct. $\endgroup$ Commented Nov 15, 2023 at 17:01

1 Answer 1


Perhaps you're thinking of para-ortho conversion of hydrogen, which is certainly not combustion, but does release a bit of heat.

Nuclei (e.e., protons) in a hydrogen molecule can have parallel or anti-parallel spins, called spin isomers. Weitzel at al state, "Freshly liquefied hydrogen... consists of a 3-to-1 ortho-para mixture." When hydrogen is liquified, the para spin isomer is energetically preferred. Slowly, the protons reorient, releasing about 1.5 kJ/mol as heat -- which causes hydrogen to boil off, even though the container is insulated from outside heat sources.

Clearly, it's not desirable for rocket fuel, for example, to be lost due to that energy release. During production of liquid hydrogen, catalysts, such as $\ce{Cr2O3}$, $\ce{Fe2O3}$ and $\ce{Fe3O4}$, can speed up the transition, so that the work of the extra "cooling" is done during production, rather than in storage.


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