Hi, I found out that most of the catalyst researchers have used mixed gas of hydrogen with inert gas (5% - 20% H2 with balanced inert gas) instead of pure hydrogen gas. Is there a specific reason behind this? Thanks!
Dear Yeonsu Kwak many thanks for asking this interesting and important technical question. I'm not an expert in this field, but personally I always treat hydrogen with great respect. As you certainly know, hydrogen forms highly explosive and dangerous mixtures with oxygen, often called "oxyhydrogen". Such mixtures can violently explode upon ignition. Thus I'm pretty sure that mixing hydrogen with intert gases such as argon or nitrogen greatly reduces the risk of eplosions and enables the safe handling of hydrogen e.g. for reduction ad hydrogenation reactions.
To watch examples of oxyhydrogen explosions, please have a look at our demonstration videos:
Oxyhydrogen explosion
Experiment Findings Oxyhydrogen explosion
and
Oxyhydrogen jumping cracker
Experiment Findings Oxyhydrogen jumping cracker
For some more general information about this problem, please see e.g. the following useful link:
How Not To Do It: Hydrogen Gas Mixtures
https://blogs.sciencemag.org/pipeline/archives/2010/06/30/how_not_to_do_it_hydrogen_gas_mixtures
Try to keep constant pressure in the reaction system and also the inert gas may behave as carrying gas, maybe?
Hello Yeonsu Kwak ,
You mentioned catalyst reduction and the following gas mixtures of H2 + Ar or H2 + N2. I am assuming that atomic hydrogen, H, is the reducting agent. The one way to control (reduce) the speed of this reaction is by recombination of the atomic hydrogen back into diatomic hydrogen, H + H → H2 + heat. This recombination can take place in two different locations: 1) the surface of the reaction vessel, and 2) the gas phase. In the gas phase, the aforementioned recombination reaction is highly exothermic and has very low activation energy because of the high reactivity of H. Because the heat released by the recombination wil contibute to forming more H by disassociation of H2, it is necessary to include a third body (which is not reactive), e.g., Ar or N2, to carry off this energy (heat). The recombination of atomic hydrogen can also occur at the surface of the reaction vessel, where this recombination depends on pressure and the size of the vessel: lower pressure and larger vessel size yields reduced recombination; temperature also plays a part. For various reasons increasing recombination at the surface may not be possible so we are left with increasing recombination in the gas phase by the addition of a nonreactive dilutant. All of this is discussed in reference [1].
[1] Walter J. Moore; Physical Chemistry, 3rd Ed.; Prentice-Hall, Inc; 1962; pp.289-291.
Regards,
Tom Cuff
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