Editing Haber process (section)

=== Hydrogen production ===
The major source of [[hydrogen]] is [[methane]]. Steam reforming of natural gas extracts hydrogen from methane in a high-temperature and pressure tube inside a reformer with a nickel catalyst. Other [[fossil fuel]] sources include coal, [[heavy fuel oil]] and [[naphtha]].

[[Green hydrogen]] is produced without [[fossil fuels]] or carbon dioxide emissions from [[biomass]], [[electrolysis of water|water electrolysis]] and [[thermochemical]] (solar or another heat source) water splitting.<ref>{{Cite journal |last1=Wang |first1=Ying |last2=Meyer |first2=Thomas J. |date=14 March 2019 |title=A Route to Renewable Energy Triggered by the Haber–Bosch Process |journal=Chem |volume=5 |issue=3 |pages=496–497 |doi=10.1016/j.chempr.2019.02.021 |s2cid=134713643 |doi-access=free|bibcode=2019Chem....5..496W }}</ref><ref>{{Cite journal |last1=Schneider |first1=Stefan |last2=Bajohr |first2=Siegfried |last3=Graf |first3=Frank |last4=Kolb |first4=Thomas |date=13 January 2020 |title=State of the Art of Hydrogen Production via Pyrolysis of Natural Gas |url=https://onlinelibrary.wiley.com/doi/abs/10.1002/cben.202000014 |journal=ChemBioEng Reviews |volume=7 |issue=5 |pages=150–158 |doi=10.1002/cben.202000014 |s2cid=221708661 |via=Wiley Online Library}}</ref><ref>{{Cite web|url=https://www.researchgate.net/publication/304537323|title=Progress in the Electrochemical Synthesis of Ammonia &#124; Request PDF}}</ref>

Starting with a [[natural gas]] ({{chem|link=methane|CH|4}}) feedstock, the steps are as follows;
* Remove [[sulfur]] compounds from the feedstock, because sulfur deactivates the [[catalyst]]s used in subsequent steps. Sulfur removal requires catalytic [[hydrogenation]] to convert sulfur compounds in the feedstocks to gaseous [[hydrogen sulfide]] ([[hydrodesulfurization]], hydrotreating):
::<chem>H2 + RSH -> RH + H2S</chem>
* Hydrogen sulfide is adsorbed and removed by passing it through beds of [[zinc oxide]] where it is converted to solid [[zinc sulfide]]:

[[File:SMR+WGS-1.png|thumb|upright=1.6|Illustrating inputs and outputs of [[steam reforming]] of natural gas, a process to produce hydrogen]]
::<chem>H2S + ZnO -> ZnS + H2O</chem>
* Catalytic [[steam reforming]] of the sulfur-free feedstock forms hydrogen plus [[carbon monoxide]]:
::<chem>CH4 + H2O -> CO + 3 H2</chem>
* Catalytic [[Water gas shift reaction|shift conversion]] converts the carbon monoxide to [[carbon dioxide]] and more hydrogen:
::<chem>CO + H2O -> CO2 + H2</chem>
* Carbon dioxide is removed either by absorption in aqueous [[ethanolamine]] solutions or by adsorption in [[Pressure swing adsorption|pressure swing adsorbers]] (PSA) using proprietary solid adsorption media.
* The final step in producing hydrogen is to use catalytic [[methanation]] to remove residual carbon monoxide or carbon dioxide:
::<chem> CO + 3 H2 -> CH4 + H2O</chem>
::<chem> CO2 + 4 H2 -> CH4 + 2 H2O</chem>