Researchers from Nanjing Forestry University and Tsinghua University have developed a two-stage chemical process that converts polystyrene plastic waste directly into high-quality jet fuel using a single-atom ruthenium catalyst operating at lower temperatures and pressures, and at significantly lower cost than any comparable method developed so far. The study, published in the journal Nature Energy, reports that the process converts polystyrene into jet-fuel-range cycloalkanes with a yield of 94.8 per cent under low-pressure conditions, outperforming previous approaches that required high-pressure batch reactors and reaction times of up to 144 hours. A preliminary techno-economic analysis puts the minimum competitive selling price of the fuel produced at between $1.0 and $1.8 per kilogram, figures that, the researchers say, make this route genuinely viable alongside conventional fossil-based jet fuel on cost. Coming at a time when UNEP reports that humanity generates around 400 million tonnes of plastic waste annually, with plastic packaging alone accounting for half of all plastic waste, the breakthrough's timing is difficult to ignore.
Why Converting Plastic Waste to Jet Fuel Is So Difficult and Why This Catalyst Changes the Equation
The fundamental problem with recycling plastic through chemical breakdown has always been selectivity. When plastic is melted or heated, the result is a disorganised mix of gases, wax, tar, char, and light hydrocarbons, with any usable fuel fraction making up only a small fraction of the total output. Steering the breakdown towards specific, useful molecules rather than a chaotic mixture has been the central challenge in plastic-to-fuel chemistry for decades. Previous attempts at plastic hydrogenolysis, the process of breaking plastic polymer chains using hydrogen, have relied on high pressures of around 3 megapascals and extended reaction times. A peer-reviewed study in Research on site-selective polyolefin hydrogenolysis using single-atom ruthenium demonstrated that the design of the catalyst at the atomic scale is critical to controlling which bonds break and how, noting that Ru single-atom catalysts can suppress the formation of unwanted methane while achieving liquid fuel yields above 94 per cent, pointing in the same direction as the new Nature Energy work. The Nanjing and Tsinghua team, led by Professors Yadong Li and Dingsheng Wang, approached the problem from the catalyst design side. Their core question was whether building the active catalytic centre at the atomic scale, one ruthenium atom at a time, deposited on a cobalt-aluminium oxide support, could finally provide the precise control over product distribution that conventional approaches had failed to deliver.
How the Two-Stage Plastic-to-Fuel Process Works
The process unfolds in two sequential steps inside a tandem fixed-bed reactor that runs continuously rather than in batches, a practical advantage for any future industrial application. The first stage is pyrolysis, in which polystyrene is heated to around 460°C in the presence of hydrogen. At this temperature, the long polymer chains that give polystyrene its solid structure crack apart into smaller hydrocarbon fragments, primarily styrene monomers and short oligomers. Polystyrene is a particularly useful starting material for this process because it breaks down relatively cleanly when heated, releasing consistent intermediate products rather than the highly variable mix that other plastics produce. The second stage is where the chemistry becomes precise. The vapour-phase fragments from pyrolysis are passed over the single-atom ruthenium catalyst at just 160°C, well below the temperatures most industrial chemical processes require. At this stage, the catalyst's isolated ruthenium sites hydrogenate the styrene intermediates into ethylcyclohexane and related cycloalkanes: dense, energy-rich molecules that sit squarely in the jet fuel molecular range. The catalyst achieved a turnover frequency of 144 per second for benzene hydrogenation at atmospheric pressure, more than 100 times that of commercial ruthenium catalysts.
Why Polystyrene and Why Cycloalkanes?
Polystyrene is one of the most common plastic waste streams in the world, produced in enormous volumes for food packaging, disposable cups, protective foam, and insulation. It is notoriously difficult to recycle due to its low density, which makes collection uneconomical, and most of it ends up in landfill or incineration. Cycloalkanes, ring-shaped hydrocarbon molecules, are the preferred fuel molecules for aviation because of their high energy density and compatibility with existing jet engines and fuel infrastructure. Current sustainable aviation fuel (SAF) pathways produce cycloalkane-rich blends to meet these requirements. A plastic-derived cycloalkane product that falls within established jet fuel specifications is therefore not merely a laboratory curiosity: it is a molecule the aviation industry already uses and needs. The study reports a cycloalkane yield of 94.8 per cent at 0.15 megapascals pressure, a fraction of the pressure required by previous high-pressure batch processes and 59 per cent yield at fully atmospheric pressure. The difference between the two figures reflects the trade-off between system complexity and output, with even the atmospheric-pressure result representing a substantial improvement on what came before.
Catalyst Stability and Scale-Up: What the Results Show
One of the persistent challenges with single-atom catalysts is that they are often difficult and expensive to produce consistently at scale, and their performance can degrade as batch sizes increase. The Nanjing-Tsinghua team addressed this directly by preparing and testing the catalyst at the gram scale beyond the milligram quantities typical of laboratory catalyst studies and found that both catalyst preparation and the hydrogenation step scaled up reliably. The continuous fixed-bed reactor format also distinguishes this approach from earlier batch-reactor methods. Running continuously rather than in intermittent cycles is a basic requirement for industrial-scale chemical production, and the demonstration that the process functions this way is a meaningful step towards real-world application. The team has identified a continuous solid-feeding system as the next engineering challenge to improve the overall workflow further.
The Aviation Industry's Plastic Problem and Its Fuel Problem
The convergence of two large, unsolved industrial problems gives this research its broader significance. Global plastic waste is on a trajectory that UNEP projects could see volumes nearly triple to around 1.2 billion tonnes by 2060 under a business-as-usual scenario. At the same time, aviation remains one of the hardest sectors to decarbonise jet engines require energy-dense liquid hydrocarbon fuels, and no battery or hydrogen system currently comes close to matching that for long-haul flight. Sustainable aviation fuel made from biological feedstocks like waste cooking oil or agricultural residue is already in commercial use, but feedstock availability is a genuine constraint on how much SAF can realistically be produced. Plastic waste, which exists in effectively unlimited supply and currently costs money to dispose of, represents a feedstock that could complement biological routes without the same land-use or competition-with-food concerns. The research remains at the pre-commercial scale and will require further validation in larger reactor systems before it can be considered ready for industrial deployment. But the cost figure of $1.0 to $1.8 per kilogram lands in a range that makes further investment in scale-up commercially rational. The next steps, according to Li and Wang, involve optimising the catalyst further, scaling preparation to the kilogram level and beyond, and refining the solid-feeding system to make continuous operation more efficient. Whether it reaches aircraft fuel tanks depends on how that engineering work proceeds.
