(569fu) Biochar-Catalyzed Methane Decomposition Towards Green Hydrogen Production: Role of Biochar Properties and Its Environmental Impacts

Catalytic methane decomposition (CMD) is distinguished by its ability to generate ‘green’ hydrogen along with value-added solid carbon co-products, theoretically eliminating the need for CO₂ capture and sequestration. This study explored the catalytic activity of various woody biochar types and temperatures in CMD. Biochar, derived from pine, poplar, and pine bark, were examined at CMD temperatures of 600°C, 800°C, and 1000°C. Results highlighted the superior performance of heat-treated (HT) poplar biochar, exhibiting enhanced acidic site concentration and reduced specific surface area. Specifically, HT poplar biochar showed the lowest specific surface area at 215.1 m²g⁻¹, and the highest concentration of acidic sites among the examined samples based on ammonia temperature-programmed reduction (NH₃-TPD) and Bohem titration analyses. Furthermore, kinetics models developed using genetic algorithms revealed a consistent second-order reaction and an activation energy range of 300-330 kJ/mol for all biochar samples.

In parallel, we investigated the potential environmental benefits of employing biochar as a catalyst in CMD over conventional Ni/Al₂O₃ catalysts. Considering 1 kg H₂ production as the functional unit, the system boundary followed a cradle-to-gate approach, covering raw material extraction, catalyst preparation, methane decomposition, electricity, catalyst regeneration, and gas product separation. An attributional life cycle assessment (LCA) comparing the environmental impact of Ni/Al₂O₃ and biochar catalyst was conducted using 1 kg H₂ production as the functional unit. The LCA demonstrated that catalyst type has a significant environmental impact on methane decomposition, with biochar as a superior catalyst compared to Ni/ Al₂O₃. Specifically, the global warming effect for the overall CMD process showed 260.5 kg CO₂ eq and 42.7 kg CO₂ eq for Ni/Al₂O₃ and biochar catalysts, respectively, for 1 kg hydrogen production. Furthermore, the electricity source played a significant role in all impact categories. Notably, using a mix of electricity sources substantially reduced the global warming effect compared with fossil-based sources.