Biochar powered two stage catalytic process boosts clean hydrogen production from corn straw while cutting catalyst coking

Biochar can help turn agricultural waste into clean hydrogen fuel while cutting carbon pollution, according to a new study in the journal Biochar. Researchers report that a simple two stage catalytic system using corn straw, biochar, and nickel based catalysts more than doubled the hydrogen content of the gas produced during biomass pyrolysis and sharply reduced the carbon deposits that normally deactivate catalysts.

Cleaner hydrogen from corn straw

In the study, scientists at the Chinese Academy of Agricultural Sciences converted corn straw into hydrogen rich gas using a high temperature pyrolysis reactor coupled with a tailor made catalyst bed. By carefully tuning temperature, catalyst loading, and catalyst composition, they achieved gas yields of over 70 percent by weight with hydrogen reaching up to 45.24 percent by volume in a single catalytic stage. When they added a biochar layer as a pre catalyst, the hydrogen content increased further to as high as 48.87 percent by volume.​

Lead author Xinyi Zhang explains that the goal was to solve two persistent problems in catalytic biomass conversion: low hydrogen selectivity and heavy carbon deposition. Nickel catalysts are very effective at breaking carbon hydrogen and carbon carbon bonds, but they tend to coke and lose activity over time, especially when exposed to heavy tars from raw biomass vapors. The team designed the process to guide biomass vapors through a protective biochar layer before they encounter the nickel based catalyst, reshaping the reaction environment and product distribution.​

Biochar as a protective pre catalyst

The innovation lies in using biochar, itself a product of biomass pyrolysis, as a first stage “filter” and reaction medium. The biochar layer, rich in pores and oxygen containing functional groups, selectively adsorbs large tar molecules and highly reactive radicals that would otherwise form coke directly on the metal catalyst surface. These macromolecular tars are cracked and reformed on the char into smaller gases, which then pass to the downstream catalyst as a cleaner, more reactive feed.​

“Biochar is not just a byproduct in this system, it becomes an active partner in steering the chemistry toward hydrogen and away from problematic carbon buildup,” says corresponding author Lili Huo. “By placing biochar ahead of the nickel catalyst, we extend catalyst life, upgrade the gas quality, and create a more sustainable closed loop for biomass utilization.” The authors report that with biochar pre catalysis, gas yields increased by up to nearly 9 percentage points while tar yields fell across all tested catalyst formulations.​

Smarter nickel based catalysts

Downstream of the biochar bed, the team used a family of nickel based catalysts supported on porous alumina and modified with different metals including cobalt, iron, molybdenum, and cerium. The cerium containing catalyst NiCeAl2O3 delivered the highest hydrogen content in one stage operation thanks to a redox cycle between Ce3 plus and Ce4 plus that supplies active oxygen and helps crack aromatic tars while suppressing condensed carbon deposits. Other bimetallic combinations such as NiFe and NiMo showed strong gas yields but favored methane and more disordered carbon deposition, illustrating how subtle changes in metal composition shift reaction pathways.​

Advanced characterization techniques including X ray diffraction, Raman spectroscopy, electron microscopy, and temperature programmed oxidation revealed how the two stage system alters carbon structure and catalyst surfaces. With biochar pre catalysis, the spent catalysts showed less amorphous carbon, more graphitic and ordered deposits, and less pore blockage, all signatures of improved resistance to deactivation. The char itself became more graphitized and lamellar, indicating that the staged reactions favor more stable carbon structures rather than sticky tar like residues.​

Economic and climate implications

To test whether the concept could make sense beyond the lab, the researchers performed a techno economic assessment for processing one metric ton of corn straw. When the pre catalytic biochar layer was included, the system generated an additional net benefit of 0.31 US dollars per kilogram of biomass compared with conventional non catalytic pyrolysis, driven by higher yields of hydrogen rich gas and savings in tar treatment and carbon tax costs. In a scenario without the biochar stage and with faster catalyst deactivation, the process turned into a loss of 2.72 US dollars per kilogram because of higher catalyst costs and lower valuable gas output.​

The authors emphasize that nickel catalysts remain a major cost and that their experimental catalyst loading is higher than what would likely be used in industry, but they argue that the two stage design points to a practical way forward. Recycling biochar produced in the process back into the reactor as a pre catalyst could cut fresh catalyst consumption, extend metal catalyst lifetimes, and close material loops in rural biorefineries. The team suggests that supportive carbon policies and further optimization of low cost biochars and robust nickel alternatives could help scale this strategy into real world renewable hydrogen systems.​

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Journal Reference: Zhang, X., Zhao, L., Yao, Z. et al. Enhanced hydrogen production and carbon suppression via a two-stage catalytic system of biochar pre-catalysis and Ni-based catalysts during biomass pyrolysis. Biochar 7, 120 (2025).   

https://doi.org/10.1007/s42773-025-00533-4  

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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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