Mechanism of catalytic fast co-pyrolysis of cotton stalks and polypropylene for hydrogen production: An experimental and DFT simulation study

Co-pyrolysis of polypropylene (PP) waste and cotton stalks (CS) addresses the dual environmental challenges of plastic pollution and agricultural residue disposal while leveraging their complementary properties (PP: H-rich; CS: C, O-rich) for enhanced H 2 production. This study investigated the hydrogen production mechanism of lignocellulose via microwave-assisted catalytic fast co-pyrolysis (co-MACFP) experiments and density functional theory (DFT) theoretical calculations for the conversion of CS and PP. Co-MACFP (550 °C) with a SiC absorber was applied to PP-CS blends (1:1 ratio), mesoporous HZSM-5 (tetrapropylammonium hydroxide (TPAOH)-modified, HT-1.0), and Ni-loaded HT-1.0 catalysts. The reaction mechanisms were determined via DFT simulations using β- d -glucopyranose and propylene as molecular models. The concentration of H 2 obtained from the co-pyrolysis of CS and PP (the ratio is 1:1) was 32.7 vol% without catalysts, which exceeds the average concentration of 28.4 vol% ((27.1 + 29.7)/2) at 550 °C, indicating a synergistic effect between CS and PP. In addition, synergistic effects boost the H 2 yield to 38.0 vol% with Ni-HT1.0 (vs. 32.7 vol% without catalysts), exceeding the theoretical averages from the individual feedstocks. PP-derived H· radicals (energy barrier: 454.8 kJ/mol) attack CS intermediates as the dominant low-energy pathway (204.4 kJ/mol), suppressing CO/CO 2 formation via DFT. This integrated strategy enables efficient waste valorization and generation of green hydrogen. Future work should scale up catalyst synthesis and explore hybrid processes to improve economic viability.