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Steam Reforming

Steam reforming hydrogen Grey hydrogen Blue hydrogen natural gas CO2 emissions Industry CCS Electrolysis

Steam reforming is an industrial process used to obtain hydrogen from natural gas or other hydrocarbon-containing feedstocks. Methane, the main component of natural gas, is usually used. In principle, biogas, propane, ethanol or gasoline can also be reformed. In English-speaking countries the process is called steam methane reforming (SMR). It is the most important production route for hydrogen. In the USA, according to the US Department of Energy, around 95 percent of hydrogen is produced by natural gas reforming in large central plants.

How the process works

In the reformer, methane reacts with hot steam over a catalyst. Carbon monoxide and hydrogen are formed: CH₄ + H₂O → CO + 3 H₂. This reaction is strongly endothermic, so it requires a constant supply of heat. Typical temperatures are about 700 to 1,000 degrees Celsius and pressures of around 3 to 25 bar. The catalyst is usually nickel on a ceramic support. The reaction takes place in many tubes filled with catalyst. These tubes hang in a furnace and are heated from the outside by burners.

This is followed by the water-gas shift reaction. In it, the carbon monoxide reacts with further steam to form carbon dioxide and additional hydrogen: CO + H₂O → CO₂ + H₂. This reaction releases only a little heat. Finally, the hydrogen is usually purified by pressure swing adsorption. This separates CO₂, residual methane, carbon monoxide and other accompanying substances, leaving almost pure hydrogen. The separated residual gas is still combustible and is usually burned in the reformer furnace.

In simplified terms, the overall reaction is: CH₄ + 2 H₂O → CO₂ + 4 H₂. Part of the hydrogen therefore comes from the water. The equation also shows a physical lower limit: from the carbon in the methane feed alone, around 5.5 kilograms of CO₂ per kilogram of hydrogen arise by calculation. In addition there is the CO₂ from the firing that supplies the process heat. This firing is usually fuelled with natural gas and residual gas.

Distinction from electrolysis

Steam reforming is a thermochemical process and not an electricity-based process. In this respect it differs from electrolysis, which splits water into hydrogen and oxygen using electrical energy. The costs of steam reforming depend mainly on the natural gas price, capital costs, the CO₂ price, the gas supply chain and, where applicable, CO₂ capture. For electrolysis, by contrast, the main factors are the electricity price, utilisation, grid connection, the availability of renewable electricity generation and the rules for qualifying as green hydrogen.

Significance for today's hydrogen supply

According to the International Energy Agency (IEA), global hydrogen demand in 2024 was just under 100 million tonnes. Almost all of this came from fossil sources without CO₂ capture, mainly from steam reforming of natural gas and from coal gasification. Low-emission hydrogen accounted for less than one percent. This hydrogen is so far hardly used as an energy store. It serves mainly as a feedstock in refineries, in the production of ammonia and methanol, and in other chemical processes. In debates, one should therefore distinguish: is existing fossil hydrogen to be replaced, or is it a matter of additional demand for new applications such as steel, transport or electricity storage? Depending on the answer, different quantities, infrastructures and climate impacts result.

Emissions: grey hydrogen

If the resulting CO₂ is not captured, this is usually called grey hydrogen. Emissions arise at three points: from the carbon in the feed gas, from the firing for the process heat, and in the upstream chain, that is, during extraction, processing, transport and storage of the natural gas. There, escaping methane is the main climate-relevant factor. Direct plant emissions are often stated as around 9 kilograms of CO₂ per kilogram of hydrogen. Including the upstream chain, depending on the plant and supply chain, they amount to about 10 to 12 kilograms of CO₂ equivalent. For comparison: the EU sets a reference value for fossil hydrogen of 94 grams of CO₂ equivalent per megajoule. Based on the calorific value, this corresponds to around 11.3 kilograms of CO₂ equivalent per kilogram of hydrogen.

Blue hydrogen and CO₂ capture

Blue hydrogen is hydrogen from fossil raw materials in which a large share of the CO₂ is captured and permanently stored geologically. If, by contrast, the CO₂ is used in products from which it is later released again, the climate benefit is considerably lower. In steam reforming, CO₂ capture is more difficult than the colour term suggests. The CO₂ in the process gas after the shift reaction is under pressure and relatively concentrated, so it can be separated comparatively cheaply. The CO₂ from the firing, however, is heavily diluted in the flue gas and can only be captured with considerably more effort. If 90 percent of a partial stream is captured, this therefore does not yet mean a high reduction for the plant as a whole. For the climate balance, methane losses in the gas chain, the energy demand of capture and the permanence of storage also matter.

For the EU, there has recently been a binding benchmark for this. Delegated Regulation (EU) 2025/2359 lays down the methodology for calculating the greenhouse gas emission savings of low-carbon fuels. It supplements the Gas Market Directive (EU) 2024/1788, was published in the Official Journal on 21 November 2025 and, according to EUR-Lex, has been in force since 11 December 2025. Hydrogen from non-renewable sources is considered low-carbon if it causes at least 70 percent fewer greenhouse gases over its life cycle than the fossil comparator of 94 g CO₂eq/MJ. The maximum permissible is therefore about 28.2 g CO₂eq/MJ, or around 3.4 kg CO₂eq per kilogram of hydrogen. A steam reforming plant with CO₂ capture reaches this threshold only if it captures a very large share of CO₂, keeps methane slip low and has a low-emission upstream gas chain. The rules apply to production in the EU and to imports.

Classifying colour terms correctly

The hydrogen colours grey, blue, green or turquoise say nothing about the chemical nature, because the molecule is always H₂. They describe production routes and emission balances and are not uniformly defined in law. This often leads to misunderstandings. Blue hydrogen is not automatically climate-neutral just because a plant captures CO₂. Green hydrogen, in turn, does not replace fossil hydrogen without side effects, because it creates additional electricity demand that is tied to the expansion and temporal availability of renewable electricity generation.

Significance for the electricity system

For the electricity system, steam reforming is above all a benchmark. If electrolysis replaces grey hydrogen, fossil process emissions fall, but electricity demand rises. An example: for one kilogram of hydrogen, electrolysis today needs roughly 50 to 55 kilowatt-hours of electricity. But the annual quantity is not the only decisive factor. The additional demand has a temporal profile and requires grid connections. If an electrolyser is operated flexibly, it can help integrate wind and solar power. If it runs almost continuously, however, it also needs energy in hours with little renewable electricity. It must then be backed up through storage, supply contracts and guarantees of origin.

Economic position and regulation

That steam reforming is so widespread despite high emissions has economic reasons. The technology is proven on an industrial scale, the plants deliver reliably around the clock, and at low gas prices the hydrogen is comparatively cheap. As long as fossil hydrogen is cheaper and its emissions are not fully priced, it remains the benchmark against which alternatives must be measured. Policy instruments target precisely this cost gap. They include emissions trading, quotas for renewable fuels, certification systems and carbon contracts for difference.

Several areas of law are relevant to a steam reforming plant. The plant itself falls under industrial and emission control law. Depending on its size and classification, its CO₂ emissions may fall under the EU emissions trading system. Gas supply concerns the gas market, import infrastructure and methane regulation. For blue hydrogen, CO₂ transport and storage are added, including permitting, monitoring and long-term liability.

Related processes

  • Autothermal reforming: It combines partial oxidation and steam reforming in one reactor. The heat is generated in the reactor itself, so the CO₂ arises predominantly in concentrated form in the process gas. This makes the process attractive for CCS concepts.

  • Partial oxidation: Hydrocarbons react with too little oxygen to burn completely. The process releases heat, proceeds faster and needs smaller reactors. Per unit of fuel, however, it initially yields less hydrogen than steam reforming.

  • Methane pyrolysis: Methane is split into hydrogen and solid carbon. A climate benefit arises only if the carbon remains permanently bound and the upstream chain is low in emissions. The process is not yet established on an industrial scale.

  • Coal gasification: It also produces synthesis gas and hydrogen, but uses coal as a raw material and usually causes considerably higher CO₂ emissions per kilogram of hydrogen.

Assessment

Steam reforming is one specific fossil production route and does not stand for hydrogen as a whole. Today it forms the basis of industrial hydrogen supply and is thus the benchmark for electrolysis, blue hydrogen and new hydrogen markets. Anyone who looks only at the price at the plant outlet overlooks CO₂ costs and methane emissions. Anyone who looks only at emissions overlooks security of supply, integration into existing industrial processes and the question of how quickly alternatives can be scaled up. The term becomes precise only when feedstock, process heat, CO₂ capture, upstream emissions and intended use are considered together.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 18:26

© 2026 Erik Schmidt. All rights reserved. Quotations with a link to the source are welcome.