How to turn exhaust gases into resources

Carbon dioxide is considered a climate problem. But it can also be a resource. Graz-based chemist Johann Hlina is investigating how carbon oxides can be converted back into hydrocarbons and, thus, into raw materials for fuels, plastics, and medications. Rare earth metals are expected to play a key role in this process.

Nature and Technology

by Anna Stockhammer

July 27, 2026

About a thousand shot glasses of carbon dioxide. That’s the amount of CO₂ you would get if you could filter this invisible, odorless substance out of the air in an average-sized room and collect it as a gas. “That’s quite a lot – you wouldn’t think so,” says Johann Hlina, “but if you convert it, you end up with one shot glass of fuel.” This chemist from the University of Graz sees carbon dioxide not only as a climate problem but also as a raw material that in most cases remains in the air unused.

CO₂ is best known for warming the Earth. But it also contains carbon, which is one of the most important building blocks of our world. It’s found in fuels and plastics, medications, paints, solvents, and countless products of the chemical industry. At present, carbon is mostly derived from fossil sources such as crude oil, natural gas, or coal. It is extracted from the ground, processed, burned, and ultimately ends up in the atmosphere as carbon dioxide.

Here is the question: can this carbon be recovered in an efficient way? Can an exhaust gas be turned back into a raw material? “The big goal is to close the industrial carbon cycle,” says Hlina.

Closing the Carbon Cycle

The project is researching energy-efficient ways to convert carbon oxides such as CO2 into valuable hydrocarbons, thereby replacing fossil raw materials. The focus is on the formation of carbon-carbon bonds and the replacement of oxygen with hydrogen using rare-earth metals, with the aim of laying the groundwork for more sustainable industrial processes.

Two metals, one molecule

In an FWF-funded project called “Rare-earth metal-catalyzed carbon monoxide reduction,” Hlina and his team are exploring how carbon oxides can be converted into hydrocarbons. It is a challenging task, because CO₂ is very stable. One can think of it like ashes after a fire: the energy has already been extracted, and the molecule has reached the end of a process.

If it is to be turned back into useful substances, one has to put in energy and rebuild the molecule step by step. One possible route involves carbon monoxide, or CO for short. CO also consists of carbon and oxygen, but it contains less oxygen than CO₂. Thus, it can serve as an important intermediate step for a chemical process: not yet a finished raw material, but a molecule that can be used as a starting point for further processing. This is exactly the approach Hlina’s project takes. He is interested in how carbon monoxide can be modified so that it forms larger molecules. In order to do this, carbon atoms must be bonded together. Such carbon-carbon bonds are the basis of many substances needed by the chemical industry.

Chemical tools for difficult molecules

This said, carbon monoxide is not a loose building block that can be simply attached to other molecules. It first needs to be activated, meaning the molecule must be contained, oriented, or modified in such a way that a new reaction becomes possible. This chemical process requires catalysts, i.e. substances that facilitate reactions.

Catalysts initiate reactions or facilitate them without being used up in the process. You can think of them like tools on a workbench: they hold a molecule in place, position it correctly, and enable specific transformations. Catalysts are indispensable in industry. Although these processes work, they require a great deal of energy. In the best case, new catalysts could make such processes more energy-efficient.

A young researcher in a white lab coat in the lab—his hands are inside a hermetically sealed reactor. — It’s complicated, but chemist Johann Hlina has a plan in mind. He intends to use carbon monoxide to convert carbon oxides resource-efficient into hydrocarbons. © Julia Stöllinger/University of Graz

In order to achieve this goal, Hlina works with metal complexes – i.e. molecules in which metal atoms are bound. He is particularly intrigued by so-called multinuclear metal complexes. These complexes have not just one metal center, but several. The chemist uses an analogy to explain how that works: it’s like having two experts focusing on a problem together. Each has a different skill set; together, they can achieve more than by going it alone.

In chemistry, this is called cooperative reactivity. Multiple metal centers act together on a molecule. They hold it in place, position it correctly, weaken certain bonds, and enable new connections.

Why rare earth metals might help

Hlina uses rare earth metals for these metal complexes. The name sounds like something precious and exotic, but: “That’s a bit misleading – these metals aren’t really all that rare,” notes the chemist. Rare earth metals are best known for their technical applications: they’re found in powerful magnets, in wind turbine generators, in displays, and in storage media. Hlina, however, is interested in another aspect of these elements: their chemistry.

Rare earth metals can bind to and influence molecules in a very special way, thereby helping to convert carbon monoxide in a targeted manner. But several things must occur in order for that to succeed: oxygen must be removed or replaced with hydrogen. At the same time, carbon atoms must be linked together. Rare earth metals could facilitate controlling these difficult steps.

This said, there is still much to be learned about rare earth metals. While the catalysis of transition metals such as iron, nickel, or palladium has been well researched, the so-called f-block of the periodic table – which also includes rare earth metals – is less familiar. Hlina notes that this field is also often neglected in scientist training, which is precisely what makes it so appealing to him. He is doing research in a niche that could open up new possibilities.

Besides the conversion of carbon oxides, there are other questions raised by these compounds. In collaboration with partners in Austria and abroad, aspects Hlina and his team are investigating include optical and magnetic properties – properties that could be of interest for future applications.

Thermodynamics is an important factor

But before these possibilities can be turned into practical applications, the chemists must solve a fundamental problem: they must reverse a process that, by nature, runs in the opposite direction. Energy is the key issue in this context. When hydrocarbons burn, they release energy. In order to reverse the process, one must input energy. Or, as Hlina puts it: “Thermodynamics is breathing down your neck.” That’s why his project isn’t about outsmarting the laws of nature, but about using the required energy as smartly as possible. If chemists can understand all intermediate steps and learn which metal centers perform which tasks in the process, more efficient methods can be developed in the long term.

According to Hlina, one particularly interesting target would be the raw material ethylene. It is used to produce polyethylene, one of the world’s most widely used plastics. Producing ethylene from carbon oxides would be “a very exciting endeavor,” says Hlina.

Some things already work in the laboratory

Hlina and his team in Graz have already made progress in developing multicore systems –that is, molecules in which multiple metal centers are set to work together in a coordinated manner. Currently, one focus issue relates to metal hydride compounds – compounds in which hydrogen is directly bonded to a metal. These compounds are central to Hlina’s research, because oxygen is to be gradually replaced by hydrogen during the conversion of carbon oxides. It is precisely these intermediate steps that must be understood if one eventually wants to control larger reactions in a focused manner.

Hlina describes his profession as a “creative job.” You design molecules, build them in the lab, test them, discard ideas, and pursue new avenues. Not everything works out. Sometimes things work out in a different way than expected. That’s exactly why he considers his work exciting. “You have your own ideas and visions, and of course, they’re constantly being challenged.”

A small contribution to a big problem

Hlina’s research could deliver a small building block toward closing the carbon cycle and thus contribute to combatting the climate crisis. He is convinced that the chemical industry will continue to need carbon in the future. For some areas alternatives exist – for others, there are none. All the more important to control where this carbon comes from: from fossil deposits? From biomass? From captured carbon dioxide? From carbon monoxide as an intermediate product? Hlina believes there probably won’t be a single solution, but rather several approaches coexisting side by side.

The important thing is to keep working on the issue: “It’s better to develop the technologies while we don’t need them yet,” says Hlina. Ultimately, his project is a story of turning things around. Combustion should be turned into assembly; exhaust gas should become a raw material; carbon monoxide should become a building block for larger molecules. There is one thing Hlina is convinced of: carbon dioxide isn’t just a problem floating in the air. It’s also an indication of just how many resources there are that we are making no use of.

About the researcher

Johann Hlina is a chemist at the University of Graz. In his project “Rare-Earth Metal-Catalyzed Carbon Monoxide Reduction” (2023–2027), which has been awarded approx. EUR 405,000 in funding by Austrian Science Fund FWF, he is exploring how carbon oxides can be converted into hydrocarbons with the help of rare earth metals. The project focuses on multinuclear metal complexes, cooperative reactivity, and a better understanding of key steps toward more energy-efficient and resource-conserving industrial processes.