In-situ catalytic cracking of biomass tar using biochar in a micro dual-bed reactor

To enhance biomass gasification efficiency, this study investigated the in-situ catalytic cracking of biomass tar using biochar within a specialized micro dual-bed reactor. The experimental design decoupled primary biomass pyrolysis from secondary tar cracking, enabling a systematic evaluation of cracking temperatures (700-900 °C), biochar types, demineralization, in-situ versus ex-situ preparation, and catalyst recyclability. The results demonstrated that increasing the temperature from 700 to 900 °C markedly improved tar conversion. Specifically, biochar-RHN achieved a peak conversion rate of 96.26% at 900 °C, significantly outperforming inert sand (66.01%) and other biochars. Mechanistically, the superior performance of biochar-RHN is attributed to its synergistic combination of a rich microporous structure and high levels of endogenous Ca and Fe species. Demineralization via acid washing reduced tar conversion from 95.91% to 59.18%, confirming that metallic constituents drive tar fragmentation by weakening aromatic C-C and C-H bonds. In-situ generated biochar outperformed ex-situ biochar, which is attributed to the preservation of pore structure and oxygen-containing functional groups in the in-situ biochar. Coke produced during tar cracking gradually accumulated on the char surface, altering the pore structure and covering active sites; consequently, the biochar's catalytic efficiency declined with continued reuse. These findings provide insight into the fundamental mechanisms of tar cracking and offer a scientific basis for enhancing the efficiency and product quality of biomass gasification.