The University of Cambridge Creates a Reactor that Recycles 99% of the Gas to Produce Clean Hydrogen and CO2-Free Carbon Nanotubes
A group of researchers from the University of Cambridge have achieved 446 times greater efficiency by producing hydrogen and CNTs with a multi-pass reactor.
Inside a pyrolysis reactor that reaches 1,300 °C, diluted methane is no longer just a fossil gas but becomes two strategic products: hydrogen and carbon nanotubes. No combustion. No carbon dioxide as a byproduct. Just fine-tuned chemistry and a key idea: reuse the gas over and over again until it is almost completely used.
On this occasion, researchers from the University of Cambridge have shown that it is possible to close the methane cycle within the reactor itself, achieving a conversion much higher than that of current systems and opening an interesting path for both the energy transition and the advanced materials economy.
The key to the breakthrough lies in modifying an already known process, chemical vapor phase deposition with floating catalyst (FCCVD). Traditionally, this method is used to produce high-quality carbon nanotubes, which are in high demand in lithium-ion batteries, electronics, or composite materials. The problem has always been the same: inefficiency.
In conventional systems, methane passes through the reactor only once. What does not react, is lost. In addition, external hydrogen is needed to prevent the formation of soot, which makes the process more expensive and complicated. A lot of gas coming in. Little real use.
The Cambridge team decided to change the logic. Instead of a single-pass system, they designed a multi-pass closed loop. The gas repeatedly circulates through the reactor until the methane is almost completely consumed. The hydrogen generated is reused within the system, eliminating the need for external input.
Production of carbon nanotubes (CNTs) and hydrogen
The methane pyrolysis reaction is not new. It consists of decomposing CH₄ at high temperature to obtain solid carbon and gaseous hydrogen. It has typically been seen as a secondary pathway to producing hydrogen, with modest yields.
Something different is happening here. Carbon is not deposited in any way, but as long, well-structured nanotubes with high industrial value. And hydrogen ceases to be an almost anecdotal by-product to become a continuous and usable flow.
The system works even when the input gas contains methane and carbon dioxide, a mixture similar to that which comes out of a biogas plant. That detail is not minor. He suggests that this technology could be integrated with existing infrastructure, without relying exclusively on pure fossil gas.
Multi-step methane pyrolysis
The operation of the reactor is as simple as it is insistent. After each passage through the hot zone, approximately 1% of the gas is extracted, separating the hydrogen and collecting the nanotubes that are deposited in the form of a mesh. The rest come back in. Over and over again.
That internal recycling drastically reduces waste and completely changes the overall efficiency of the process. Against a single-pass reactor, the team observed an 8.7-fold improvement in carbon yield and a more than 400-fold increase in molar efficiency, a metric that reflects how many gas molecules are actually harnessed.
Efficiency improvements
To test whether this could go beyond the lab, the researchers fed a computational model with real data from industrial plants. The result was consistent: the multistep design could convert about 75% of the gas into useful products, generating nanotubes and hydrogen in an approximate 3-to-1 ratio.
It is not an inflated promise. It is a conservative estimate based on real industrial conditions. Even so, it represents a significant leap compared to current technologies for producing hydrogen from methane, such as steam reforming, which continue to generate carbon monoxide and dioxide.
This type of reactor is not going to solve the climate crisis on its own. But it fits well into a more hybrid and pragmatic energy future, where not everything depends on a single miracle solution.
It can be used to decarbonise part of hydrogen production in the short and medium term, while fully renewable alternatives are deployed. It can strengthen supply chains of key battery materials, reducing external dependency. And it can be integrated with biogas plants, agricultural or industrial waste, closing cycles that are currently wasted.
It is not a technological utopia. It is a concrete, measurable and replicable improvement. One of those that don't make noise, but change the rules little by little. And sometimes, that's just what is most needed.