High-quality biochar from the catalytic pyrolysis of Brachychiton seeds: Optimization and characterization

This study aims to describe the effect of pyrolysis conditions (temperature, particle size, and type of catalyst) on the production of biochar from Brachychiton seeds. Pyrolysis experiments were conducted at between 300 °C–550 °C with particle sizes from <315 μm to 800–1600 μm and catalysts including Al₂O₃, CaO, H 3 BO 3 , ZrO(NO 3 ) 2 , V₂O₅, ZnO, Fe₂O₃, and TiO₂. The results showed that the temperature range from maximum biochar yield was 400 °C and smaller particle (smaller than <315 μm) showed higher biochar yield.Char yield was significantly improved by Al 2 O 3 even at low temperatures while higher catalyst concentration led to an increased yield till 2% catalyst. Biochar had alkaline pH values, varying from 7.81 to 9.80, making them suitable as soil ameliorants. Electrical conductivity ranged from 308 μS.cm −1 to 1650 μS.cm −1 with the effect of temp and catalyst type measured, demonstrating ranges of ion concentrations available for agricultural application. ATR-IR analysis also revealed a decrease in the concentration of functional groups such as OH, C H and C O, signifying a conversion of the original biomass to more aromatic species with increasing temperature. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and elemental analyses indicate a remarkable change in the surface morphology as well as the composition of biochars, such as increased pore volume, the formation of numerous mineral phases and the successful incorporation of catalysts. Notably, TiO₂, H₃BO₃ and Fe₂O₃ are effective in enhancing their calorific value, which reaches 49.464 MJ.kg- 1 . The results highlight the importance of biochar pyrolysis conditions for improving their properties for energy, environmental and agricultural use. • Catalytic pyrolysis effectively upgraded Brachychiton seed biochar into a high-energy solid fuel. • Metal oxide catalysts strongly governed carbonization pathways and fuel quality. • TiO₂, Fe₂O₃, and H₃BO₃ produced biochars with calorific values up to 49.46 MJ·kg −1 . • Al₂O₃ accelerated cellulose decomposition and aromatic carbon formation at low temperatures. • Temperature, particle size, and catalyst loading controlled carbon retention and mineral phases.