Turning farm waste into climate solutions

A new study has shown that turning sugarcane waste into a smart catalyst can efficiently convert carbon dioxide into methane, offering a promising route to recycle greenhouse gases into useful fuel. The research team designed a cobalt and cerium based catalyst supported on biochar made from sugarcane bagasse, achieving high CO2 conversion and methane selectivity under relatively mild conditions.

Sugarcane bagasse, the fibrous residue left after juice extraction, is often treated as low value waste, but it is rich in carbon and naturally porous. In this work, the team converted bagasse into biochar through controlled pyrolysis, then used it as a sustainable support for metal nanoparticles. This approach adds value to agricultural residues while reducing the need for conventional mineral supports such as silica or alumina.​

“Sugarcane bagasse is abundant, inexpensive, and often discarded, so transforming it into a functional catalyst support is attractive for both environmental and economic reasons,” notes lead author Ahmed Gamal. Co author Khouloud Jlassi adds that the combination of biochar and earth abundant metals aligns well with circular economy concepts in the energy sector.​

Engineering a cobalt–cerium biochar catalyst

The researchers prepared a series of catalysts by loading different amounts of cobalt onto sugarcane bagasse biochar and then introducing cerium to create a bimetallic system. Microscopy revealed honeycomb like and “fishing net” pore structures in the biochar, with elongated slit pores that help expose more active sites to the reacting gases. Advanced surface analysis showed that adding cerium improved metal dispersion, reduced particle size from about 18.5 to 11.5 nanometers, and introduced beneficial cerium oxide species on the surface.​

These structural features translated into higher surface area and pore volume for the metal loaded biochars compared with the bare support, enhancing gas–catalyst contact during CO2 methanation. The optimized bimetallic catalyst contained 0.5 mmol cobalt and 0.25 mmol cerium per gram of biochar, balancing metal loading with good dispersion and avoiding excessive aggregation.​

Converting CO2 to methane efficiently

The team tested the catalysts in a continuous flow reactor between 200 and 500 degrees Celsius at atmospheric pressure, using a mixture of hydrogen and carbon dioxide. Pure biochar and cerium only samples showed no measurable activity, confirming that the metals are essential for CO2 hydrogenation. Cobalt only catalysts were active, with performance improving as cobalt loading increased up to an optimal value before aggregation reduced efficiency at the highest loading.​

The bimetallic cobalt–cerium catalyst delivered the best overall performance, achieving about 60 percent CO2 conversion at 500 degrees Celsius and showing especially strong selectivity toward methane at 430 degrees Celsius. At this optimal temperature, the catalyst reached approximately 51 percent CO2 conversion, 80 percent methane selectivity, and 41 percent methane yield, and remained stable for at least 12 hours of continuous operation. By contrast, cobalt only biochar catalysts favored carbon monoxide formation through the reverse water gas shift reaction, highlighting the key role of cerium in steering the reaction toward methane.​

Implications for renewable methane

The results place the cobalt–cerium sugarcane biochar catalyst among the more active biochar supported systems reported for CO2 methanation, while operating at atmospheric pressure and moderate temperature. Compared with previously reported nickel–cerium biochar catalysts, the new material offers competitive methane selectivity under similar or milder conditions, without relying on noble metals. Because the catalyst is based on agricultural waste and abundant metals, it could be scaled up in regions where sugarcane production is significant.​

According to the authors, this work opens a path to tailor biochar based catalysts for CO2 utilization by tuning metal combinations and loadings on renewable carbon supports. They suggest that the cerium promotion strategy could be extended to other transition metals that alone show limited activity or selectivity in CO2 methanation. The study demonstrates how smart materials design can link waste management, greenhouse gas mitigation, and renewable fuel production in a single process.​

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Journal Reference: Gamal, A., Tang, M., Chehimi, M.M. et al. Effect of metal loading and Ce addition on biochar-supported Co catalysts for CO₂ methanation. Biochar 7, 73 (2025). 

https://doi.org/10.1007/s42773-025-00459-x

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About Biochar

Biochar is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field. 

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