• Biochar with abundant oxygen-containing functionalities (600C) exhibits superior catalytic activity for cracking and aromatization of volatiles, increasing gas yield by 40.2%.
• Developed pore structures (800AC) do not directly catalyze reactions but can trap volatiles, promoting their further conversion via aromatization.
• Volatile-char interactions consume oxygen on the 600C catalyst, enhancing its aromaticity and thermal stability.
• Carbonaceous deposition on high-temperature chars (800C, 800AC) leads to net weight gain, micropore blockage, and formation of additional macropores.