Catalyst-Free Thermal CO2 Reduction: A Pathway to Methane and Carbon Nanotubes with Industrial Potential

The growing impacts of climate change, fueled by increasing carbon dioxide (CO₂) emissions, have become a massive challenge for humanity to tackle. Over the past century, CO₂—largely produced through the burning of fossil fuels—has built up in our atmosphere, significantly contributing to the greenhouse effect and global warming. The results of this are undeniable: rising sea levels, unpredictable weather, expanding deserts, and a worrying loss of biodiversity. In response to this urgent issue, scientists and engineers all over the world are racing to find ways to reduce CO₂ emissions. Some are exploring ways to capture and store it, while others aim to convert it into something useful. However, many of these approaches are still far from ideal for large-scale use, mainly because they are too expensive, inefficient, or technically complicated. At present, carbon capture, utilization, and storage (CCUS) technologies are far from perfect. Capturing CO₂ often takes up a lot of energy, and using it afterward typically requires catalysts. These catalysts are not only costly but also fragile—they can degrade or lose effectiveness over time. On top of that, they often need very specific operating conditions to work well. Many existing systems are also hard to run continuously, relying on setups that are intricate and prone to interruptions. Even thermocatalytic methods, which hold promise for converting CO₂ into methane, run into trouble. Catalysts can wear out, performance may drop over time, and extra steps are needed to clean up the reaction products afterward. Faced with these challenges, researchers Wenlong Chen and Yuting Chen, along with their mentors, Professors Runwei Mo and Jiannong Wang, developed a groundbreaking method for reducing CO₂. Their study, published in Chemical Engineering Science, presents a new approach that skips the need for catalysts altogether. Instead, it uses sodium borohydride (NaBH₄) as a reducing agent in a thermal reduction process which helped them avoid relying on expensive and tricky catalysts. This innovative method simplifies how CO₂ is reduced and also delivers impressive results, with high yields and selectivity under moderate conditions. Better still, the system is designed for continuous operation, which make it scalable and suitable for large-scale industrial use.

The researchers designed a setup featuring a vertical furnace with a quartz tube reactor. This configuration allowed for the continuous introduction of reactants, creating stable conditions for the reaction to take place. By adjusting variables like temperature, the concentration of NaBH4, and the flow rates of carbon dioxide, the team was able to figure out what worked best for the process. Their experiments showed that the thermal reduction worked really well within a temperature range of 500 to 700°C and under atmospheric pressure. By atomizing a NaBH₄ solution and introducing it into the high-temperature zone of the reactor, they triggered a reaction with CO₂ that produced methane as the main product. There were also smaller amounts of carbon monoxide (CO) and hydrogen (H₂) formed during the process. Under the best conditions, which included a NaBH4 concentration of 200 mg/mL and a reaction temperature of 600°C, the system achieved an impressive methane selectivity of up to 90%. What stood out even more was the high methane yield, showing this process could be scaled up for industrial use. Plus, the setup was efficient enough to ensure that nearly all the CO₂ entering the reactor was captured and converted. The team demonstrated the importance of getting the NaBH4 concentration just right. If the concentration was too low, methane production dropped off. On the other hand, if it was too high, the solution became too thick, which caused mixing issues and incomplete reactions. Temperature also played a key role: while higher temperatures increased gas yields overall, they also led to more CO being produced, reducing methane selectivity. By carefully balancing these factors, the researchers were able to optimize the system. To highlight the potential of their method, they used the methane and carbon monoxide produced in the reaction to make carbon nanotubes (CNTs). These gases were fed into a horizontal furnace containing a catalyst solution, where they broke down to form high-quality CNTs. The nanotubes self-assembled into hollow cylinders that could be collected as thin films or fibers. Tests showed the CNTs had double-walled and few-walled structures, with diameters between 4 and 8 nanometers. They demonstrated excellent mechanical and thermal properties, making them suitable for advanced applications like energy storage, thermal management, and composite materials.

In conclusion, the new research work by the scientists of East China University of Science and Technology  is a significant advancement because designed a new thermal reduction process that does not rely on expensive or sensitive catalysts, which is a major breakthrough in CCUS technology. We think what makes this approach stand out is how efficient and scalable it is—it achieves high methane selectivity under moderate conditions and could work on a much larger scale without breaking the bank. Moreover, the authors looked at how the new method could be adopted by industries focused on sustainability and resource efficiency. The process continuously transforms CO₂ into methane and carbon monoxide, both of which are incredibly versatile raw materials. Methane is widely used to produce hydrocarbons and fuels, while carbon monoxide is essential for synthesizing a variety of organic compounds. Plus, the hydrogen produced as a byproduct is a clean energy source that is becoming more and more sought after. The study also makes a huge contribution to the production of CNTs, which are known for their outstanding mechanical, electrical, and thermal properties. By repurposing the gases generated during the CO₂ reduction process, the researchers developed a sustainable way to create CNTs on a continuous scale. These nanotubes have an impressive range of uses, from making advanced composite materials to improving energy storage and thermal management systems. This seamless integration of CO₂ reduction with CNT production highlights how smart engineering can turn waste into valuable materials, perfectly fitting into the circular economy model. On an environmental level, this research provides clearly a practical way to reduce greenhouse gas emissions. With the successful conversion of CO₂ into something useful, the method provides a real solution to combating climate change. It also has the potential to pair well with carbon-heavy industries like power generation or steel manufacturing and by this creates closed-loop systems that shrink their environmental footprint. What makes this method so promising is how simple and scalable it is. The low-cost setup and continuous operation solve many of the issues that hold back current CCUS techniques. Businesses aiming for sustainable solutions are likely to find this technology attractive. Additionally, its reliance on sodium borohydride, a regenerable reducing agent, makes it even more appealing for long-term use.