The pore structure and active functional groups of biochar play a critical role in determining its catalytic performance. In this study, coconut shell-derived biochar underwent modification with nitric acid to serve as a catalyst in the pyrolysis of a corn stover/high-density polyethylene composite (CHC) in a fixed bed reactor. The effects of nitric acid concentration, treatment time, and temperature on the catalytic performance of biochar were investigated, specifically targeting the production of aromatics during the CHC pyrolysis process. The results revealed that a higher modification temperature, a longer treatment time, and a lower concentration of nitric acid effectively enhanced the catalytic performance of biochar in producing aromatics, while simultaneously reducing the formation of aliphatics and oxygenates. The highest yield of aromatic hydrocarbons (56.1 %) was obtained under the conditions of a modification temperature of 90 degrees C, a modification time of 10 h, and a nitric acid concentration of 1.0 mol/L. Furthermore, the nitric acid-modified biochar catalyst promoted the production of CO and CH4 during the CHC pyrolysis process, indicating that the decarbonylation and end-chain breaking reactions were enhanced due to the presence of abundant oxygen-containing functional groups introduced by nitric acid oxidation.
