Convert the carbon dioxide and sunlight in liquid fuels It's no longer just an exotic laboratory idea. In recent years, several European and Asian research teams have been taking firm steps to ensure that some of the fuels of the future come from CO₂, which is currently considered a waste product.
In Spain, a project led by the Public University of Navarra It works closely with technology centers and companies to design devices that produce renewable synthetic fuels from water and CO₂Meanwhile, in other countries, artificial photosynthesis systems are being perfected that could be integrated into these production chains, painting a picture in which "making fuel from air" no longer sounds like science fiction.
Panel-to-Fuel: manufacturing fuels with sun, water and CO₂ in Spain
The project Panel-to-Fuel, promoted by the Public University of Navarra (UPNA) through the INAMAT² institute, the Lurederra Technology Center and the company Navarra Mechanical Engineering (INM)It aims to demonstrate that it is possible produce synthetic fuels using only renewable resources: solar radiation, water and CO₂ captured from the air.
The central idea is to replace a part of the liquid fuels derived from petroleum by alternatives compatible with current engines, but generated through processes that do not increase CO₂ in the atmosphere. To this end, a cycle is proposed in which CO₂ is captured from the air, and green hydrogen is obtained using sunlight. and both are combined to create synthetic fuels usable in transportation.
This approach seeks to address one of the major climate challenges: decarbonization of sectors that are difficult to electrify, such as heavy road transport, maritime or aviation, where direct replacement with batteries is not always technically or economically viable.
The project is not limited to chemical development, but also includes economic and environmental analyses to find out if the process can compete, in the medium term, with traditional fossil fuel options and other renewable alternatives that are already on the market.
A photocatalytic panel that mimics plants
At the heart of Panel-to-Fuel lies a photocatalytic panel which works differently from a conventional photovoltaic panel. Instead of generating electricity, this device uses sunlight to separate water molecules and produce hydrogenwithout needing to use energy from the grid.
UPNA designs reactors manufactured using 3D printingwith geometries designed to optimally expose the active materials to solar radiation. The goal is to better distribute light across the surface where the reaction takes place, thereby increasing the amount of hydrogen that can be obtained from water.
For its part, the Lurederra Technology Centre contributes nanomaterials capable of capturing and harnessing sunlight with high efficiencyThese compounds act as photocatalysts, that is, they trigger and accelerate chemical reactions when they receive photons, similar to what pigments in plant leaves do during natural photosynthesis.
The company Ingeniería Navarra Mecánica is in charge of the engineering of the first integrated prototype, a demonstration unit that will bring together in one system the production of hydrogen, the capture of CO₂ and the subsequent synthesis of renewable fuels.
In parallel with the development of this equipment, the consortium is working on adsorbent materials to capture CO₂ from the air, capable of retaining this gas on their surface and then releasing it in a controlled manner to introduce it into the conversion reactions.
From CO₂ and hydrogen to liquid fuels: methanol and Fischer-Tropsch
Once you have green hydrogen and captured CO₂The next stage is to transform them into molecules that can be used as liquid fuel. The team led by Luis Gandía Pascual and Fernando Bimbela Serrano is analyzing two main routes to make it.
The first resorts to methanol as an intermediate stepIn this case, CO₂ reacts with hydrogen to form methanol, a molecule that, in turn, can be transformed into more complex fuels or used directly in certain industrial and energy applications.
The second route is based on an adapted version of the process Fisher-Tropscha well-known technology that allows the conversion of mixtures of carbon monoxide and hydrogen into liquid hydrocarbons similar to conventional fuelsThe key here is to adjust the conditions and catalysts to start with CO₂ and obtain suitable gas mixtures to fuel that process.
The consortium compares both options to determine which path fits best into the complete chainTaking into account energy efficiency, operating costs, technical complexity and integration with the CO₂ capture module and the photocatalytic hydrogen production panel.
According to researcher Fernando Bimbela, head of the QuiProVal group at UPNA, the prototypes developed have already allowed Obtain solar methane from CO₂ and green hydrogenand work is underway to scale up towards hydrocarbons with a higher number of carbon atoms, closer to the liquid fuels used daily.
Curved design, modular system and European support
One of the distinctive elements of Panel-to-Fuel is the development of a reactor with curved design This design concentrates solar radiation precisely in the area where the most important chemical reactions take place. This geometry allows for better use of both sunlight and heat, increasing the system's efficiency.
The ultimate goal is to have a modular assembly capable of continuous and stable operationperforming three tasks simultaneously: producing hydrogen, capturing CO₂ from the air, and transforming it into synthetic fuels. Modularity would facilitate adapting production capacity to different environments, from pilot facilities near research centers to larger-scale plants adjacent to industrial or logistics sectors.
In addition to the technical design, the project includes economic feasibility and environmental impact studiesessential to assess whether these synthetic fuels can compete against conventional diesel, gasoline or kerosene, as well as against alternatives such as electric vehicles or compressed hydrogen.
Panel-to-Fuel features funding from the State Research Agency, from the Recovery, Transformation and Resilience Plan and from European funds NextGenerationEUas well as aid such as RENOCogenThis reinforces the role of this type of project in the decarbonization and green reindustrialization strategy of Spain and the European Union.
The team includes researchers from UPNA such as Luis Gandía, Fernando Bimbela and Ismael Pellejero; from Lurederra, as Cristina Salazar and Carmen Garijo; and from the company Ingeniería Navarra Mecánica, among them Uxue LlorenteThis demonstrates a close collaboration between the university, the technology center, and the business sector.
Artificial photosynthesis: international advances pointing towards solar fuels
While in Navarre they are working to integrate the entire process into a single modular system, other international groups are making progress on the complementary component: high-performance photonic catalysts capable of transforming CO₂ using only sunlight and water as main inputs.
A recent example comes from a team in the Chinese Academy of Sciences and from the Hong Kong University of Science and Technology, which has presented a system of artificial photosynthesis published in the journal Nature Communications. Their approach involves using a material called Ag/WO₃, a silver-modified tungsten trioxide, which acts as a kind of temporary electron storage within the catalyst.
When this material is illuminated, it can store and release electrons in a controlled manner, which is key to reducing CO₂ more efficiently. When combined with a cobalt-based molecular catalyst, the cobalt phthalocyanineThe system manages to convert CO₂ and water into carbon monoxide with a speed far superior to that of previous configurations.
Under laboratory conditions, production levels on the order of 1,5 millimoles of carbon monoxide per gram of catalyst per hourapproximately one hundred times more than the same cobalt catalyst without the “charge reservoir” provided by Ag/WO₃. Although still on small scales, the performance improvement is scientifically significant.
That carbon monoxide is not a fuel ready for use in a tank, but it does constitute one of the basic chemical building blocks for the manufacture of synthetic fuels, through industrial routes already known such as gas synthesis (syngas) followed by Fischer-Tropsch type processes, precisely the same logic that is explored in projects such as Panel-to-Fuel.
A cleaner design: water as a source of electrons
One of the common problems with many artificial photosynthesis schemes is the need to employ expendable agentsAdditional substances facilitate the reaction but are consumed and generate waste. The Chinese design attempts to overcome this limitation by using water as a source of electrons, an approach closer to the functioning of a real leaf.
In nature, molecules like plastoquinone briefly store electrons to coordinate several photochemical reactions at onceInspired by this behavior, the Ag/WO₃ system allows tungsten to change its oxidation state by receiving and giving up electrons, so that the catalyst that reduces CO₂ has more charge available for a longer time.
This mechanism of intermittent charge storage It reduces losses and improves the overall efficiency of the process, which is essential if these systems are to move from the laboratory to practical applications where the cost per kilogram of product is crucial.
An interesting point is that the device not only works under controlled artificial lighting, but has also been tested with natural sunlightwhile maintaining its ability to transform CO₂ into carbon monoxide. This detail suggests that the technology could be integrated into reactors powered directly by renewables, without necessarily using the electrical grid.
From a materials design perspective, the Ag/WO₃ strategy presents itself as a relatively versatile approach, since the same support could be combined with different specific catalysts depending on the desired end product, opening the door to a wider range of fuels and chemical compounds of solar origin.
Climate impact, challenges and alignment with European policies
The possibility of convert CO₂ into synthetic fuels with the help of sunlight It fits perfectly into European decarbonization strategies, but its real contribution will depend on the entire life cycle. For these fuels to be climate-neutral, the CO₂ used must come from captured sourceswhether industrial emissions or directly from the air, and the entire process must be fed with renewable energy.
Even when those conditions are met, experts point out that the Overall efficiency is still far from ideal.Each stage —CO₂ capture, hydrogen production, conversion to liquid fuels, storage and distribution— involves energy losses that translate into economic costs and the need for more installed renewable capacity.
Even so, these solar fuels could play a relevant role in those sectors where It's not easy to electrify directly or replace existing engines and infrastructure in the short term. Aviation, maritime transport, and certain heavy industries appear repeatedly on this list of “difficult to reduce.”
From an energy policy perspective, very practical questions also arise: How much will a liter of this type of fuel cost? Compared to traditional diesel or gasoline, how will it be integrated into existing refineries and networks, and what level of support will these technologies receive compared to other options such as electric vehicles or hydrogen for fuel cells?
In Europe, the combination of projects like Panel-to-Fuel with international advances en artificial photosynthesis and new catalysts It points to a scenario in which CO₂ is no longer seen solely as a problem and is considered partially as a resource. As the climate warms and fuel prices fluctuate, the development of renewable synthetic fuels based on sunlight and CO₂ It is emerging as a complementary way for industry and the environment to start moving in the same direction.