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Glossary · Energy industry & energy transition

Autothermal reforming

Autothermal reforming hydrogen Blue hydrogen natural gas CCS Industry CO2 capture

Autothermal reforming (ATR) is a chemical process used to produce synthesis gas from natural gas, biomethane, refinery gases, naphtha or other hydrocarbon-containing feedstocks. Synthesis gas is a mixture of hydrogen, carbon monoxide, carbon dioxide and steam. Two processes are coupled in the reactor: part of the feedstock reacts with supplied oxygen and releases heat. This heat drives the heat-consuming (endothermic) reforming, in which hydrocarbons are converted with steam into hydrogen and carbon monoxide. The synthesis gas can be further processed into pure hydrogen or used for ammonia and methanol synthesis.

"Autothermal" means that the process generates the required reaction heat in the reactor itself. In classical steam reforming, by contrast, the heat is supplied externally via fired reactor tubes. The ATR reactor can be pictured as a refractory-lined pressure vessel: a burner with a combustion chamber sits at the top, with a catalyst bed below it. ATR contains elements of partial oxidation and of steam reforming, but is identical to neither process.

Sequence in the reactor and in the overall plant

The preheated and usually desulfurised feedstock is fed into the burner together with steam and oxygen. In the combustion chamber, part of the gas burns substoichiometrically, that is, with too little oxygen for complete combustion. Very high temperatures are reached in the process. In the downstream catalyst bed, usually nickel-based, steam reforming takes place and cools the gas down again. Typical outlet temperatures of large plants are roughly in the range of 900 to 1100 °C. Because part of the oxygen is bound in the product gas, ATR synthesis gas contains a relatively lower ratio of hydrogen to carbon monoxide than synthesis gas from steam reforming. Unlike non-catalytic partial oxidation, ATR operates with a catalyst and with steam addition.

For hydrogen production, the water-gas shift reaction follows: carbon monoxide reacts with steam to form carbon dioxide and additional hydrogen. CO2 is then separated from the pressurised process gas, often by amine scrubbing. The hydrogen is subsequently purified, for example by pressure swing adsorption. The residual gas from purification still contains methane, carbon monoxide and hydrogen and is often burned in preheating furnaces. This is an important detail for the climate balance: an ATR plant, too, generally has fired auxiliary units. Their flue gas is dilute, unless they are largely fired with hydrogen or are themselves equipped with capture.

Distinction from steam reforming

Steam reforming of natural gas is currently the leading production route for hydrogen. According to the International Energy Agency (IEA), about 30 to 40 percent of the natural gas is burned as fuel to provide the reaction heat. This produces a dilute CO2 stream in the furnace flue gas. The remainder is converted into hydrogen and more concentrated process CO2. If only this process CO2 is captured, emissions fall by only about 60 percent according to the IEA. For substantially higher reductions, the furnace flue gas must also be treated, which is more complex. Without abatement, hydrogen from natural gas causes around 9 tonnes of CO2 per tonne of hydrogen according to the IEA.

In ATR, by contrast, most of the carbon dioxide is generated in the process gas, which is under pressure and has a comparatively high CO2 concentration. The process is therefore well suited to a high rate of CO2 capture. Another practical difference: ATR requires pure oxygen, which in large plants is usually obtained in an air separation unit. Steam reforming, autothermal reforming and partial oxidation thus differ in heat management, oxygen demand, plant configuration, CO2 streams, efficiency and costs. The mere statement "hydrogen from natural gas" is therefore not sufficient for an emissions assessment.

Achievable capture rates and maturity

The IEA gives capture rates of about 93 to 94 percent for ATR with CO2 capture. According to a 2024 report by the industry association Hydrogen Europe, ATR projects with capture aim for at least 94 percent. The same report states that ATR with CO2 capture has so far hardly any commercial operating experience, whereas steam reforming with capture is considered mature. Higher values, up to the vicinity of 97 to 99 percent, are discussed in studies and plant concepts. However, they depend on how the plant is designed and on whether secondary CO2 streams are also captured. Such figures are therefore planning or design values and not demonstrated average operating values.

A capture rate describes only the plant. It indicates what share of the CO2 generated in the plant is captured. It says nothing about the upstream chain: extraction, processing and transport of natural gas, methane losses, electricity for air separation and compression, and transport and storage of the captured CO2. The IEA shows that at very high capture rates, the majority of the remaining emissions originate from the upstream and transport chain of the natural gas.

Relationship to blue hydrogen

Autothermal reforming is a production process and not a hydrogen colour. The term blue hydrogen is usually used when fossil-based hydrogen production is combined with capture and permanent storage of CO2. The colour reveals neither the process nor the capture rate, methane emissions, storage site or residual emissions. Because ATR can be combined well with capture, it is sometimes presented as nearly climate-neutral. However, this assessment holds only under several conditions: the plant actually captures a very high share of the CO2, the CO2 is permanently stored geologically, the natural gas supply chain has low methane emissions, and the additional energy demand is included in the balance.

Methane is particularly important here because over short periods it has a substantially stronger greenhouse effect than CO2. Even small percentage losses during extraction, pipeline transport or in LNG chains can significantly worsen the balance of hydrogen from natural gas. A balance at the plant gate does not reflect this upstream chain. Only a life cycle assessment with clearly defined system boundaries is meaningful.

Legal framework in the EU

In the EU, Commission Delegated Regulation (EU) 2025/2359 governs when hydrogen from non-renewable sources qualifies as "low-carbon". The Commission adopted it on 8 July 2025 on the basis of the Directive on the internal markets for renewable and natural gases and for hydrogen (EU) 2024/1788. It was published in the Official Journal on 21 November 2025 and has been in force since 11 December 2025. The Regulation prescribes a life cycle approach. This includes, among other things, upstream methane emissions, the CO2 capture actually achieved and indirect emissions. The fossil comparator is the same value as for renewable fuels of non-biological origin, namely 94 g CO2 equivalent per megajoule.

To qualify as low-carbon, hydrogen must achieve greenhouse gas savings of at least 70 percent relative to this comparator. This corresponds to a maximum of 28.2 g CO2 equivalent per megajoule. Based on the lower heating value of around 120 MJ per kilogram, this amounts to roughly 3.4 kg CO2 equivalent per kilogram of hydrogen as a rough estimate. Whether a specific ATR plant reaches this threshold therefore does not depend on the process, but on the demonstrated emissions along the chain. The Regulation creates a uniform accounting and certification basis, but neither its own demand nor funding. Outside the EU, partly different thresholds and system boundaries apply.

Oxygen, energy demand and infrastructure

Oxygen demand is a major cost factor. The air separation unit consumes a great deal of electricity and increases capital costs. In addition there is electricity for compression, CO2 separation and CO2 transport. Per kilogram of hydrogen, this electricity demand is significantly lower than with electrolysis, but it is not zero. If it is covered by grid electricity with a fossil-heavy mix, the emissions balance worsens. If it is covered by renewable electricity, it competes with other uses.

CO2 infrastructure also becomes a prerequisite. An ATR plant with capture needs a connection to CO2 pipelines, liquefaction and port facilities or storage sites. According to the IEA, many existing hydrogen plants are located in coastal industrial clusters, where transport and storage infrastructure could be shared. Without this infrastructure, the plant's capture capability remains unused. In climate strategies, the term therefore does not stand for a single reactor. It stands for a bundle of natural gas supply, oxygen provision, hydrogen offtake, CO2 transport, storage regulation and emissions monitoring.

Economic assessment

Whether ATR is economically viable depends on gas and CO2 prices, capital costs, capture rate, utilisation, the costs of CO2 transport and storage, and regulatory requirements. High utilisation lowers capital costs per kilogram, but requires reliable offtakers. Typical offtakers are refineries, ammonia and methanol production and, prospectively, direct reduction in the steel industry. According to the IEA, hydrogen from gas with CO2 capture is currently cheaper than electrolysis hydrogen in many regions, provided that cheap natural gas and CO2 storage are available. However, this cost advantage depends strongly on the gas price and can shift.

In energy policy terms, this results in a trade-off. ATR can continuously supply large quantities of lower-emission hydrogen and connect to existing gas and industrial sites. At the same time, it ties investments to natural gas, CO2 storage and the associated infrastructure for decades. These dependencies are part of the practical impact of the technology and are not a side issue.

Typical misinterpretations

  • "Clean natural gas use": The only correct part is that ATR technically facilitates high CO2 capture if the plant is designed for it and storage infrastructure is available. It does not eliminate upstream emissions.

  • High capture rate equals climate neutrality: Even 93 to 95 percent capture leaves residual emissions in the plant. In addition there are methane and energy emissions outside the plant.

  • Process equals certificate: Whether hydrogen qualifies as low-carbon in the EU is decided by the life cycle balance under Delegated Regulation (EU) 2025/2359 and not by the choice of reactor type.

  • ATR and electrolysis as interchangeable variants: Electrolysis converts electricity into hydrogen, whereas ATR uses the chemically bound energy of fossil or biogenic hydrocarbons. A comparison must go beyond cost per kilogram and include emissions, infrastructure, import dependencies and temporal availability.

The term autothermal reforming is precise when it designates a process, and misleading when it is used as proof of a particular climate impact. The strength of ATR lies in the fact that hydrogen production and concentrated CO2 capture fit together well in process engineering terms. Its limit: with fossil feedstock, it remains dependent on natural gas, effective methane control and permanent CO2 storage.

Sources

Related glossary entries

Edited by eCMS on 11.11.2026 14:53

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