Enhancement of engineered biochar functionality through co-pyrolysis of municipal wastes over metal-doped catalysts

The escalating global waste crisis demands innovative valorization strategies. This study investigates the in-situ catalytic pyrolysis of municipal solid and food wastes to transform this stream into engineered biochar with tailored properties. Unlike prior research that primarily focuses on bio-oil upgrading, this work uniquely prioritizes biochar engineering by systematically evaluating three distinct catalyst families—HZSM-5 (Brønsted acid), Na-ZSM-5 (basic/neutral), and Fe 3 O 4 (redox-active)—and their modification with nickel or cobalt (5 wt%). Pyrolysis at 550 °C was selected based on thermogravimetric analysis to optimize the trade-off between biochar yield and carbonization degree. HZSM-5-based catalysts maximized biochar yield (40.9%), while Fe 3 O 4 -based catalysts favored bio-oil and biogas production. Metal coating generally reduced bio-oil yield, promoting non-condensable gas formation. Critically, catalyst selection and coating dictated biochar properties. Base catalysts, particularly Fe 3 O 4 , produced biochar with high specific surface areas (up to 480 m 2 /g). However, metal coating introduced catalyst particles onto the biochar surface, observed via FESEM/EDX, which reduced this area but significantly enhanced thermal stability (as low as ∼15% weight loss by TGA). These findings demonstrate that catalytic pyrolysis can strategically tailor biochar, creating composites with active sites and robust stability. This positions waste-derived biochar as a promising, sustainable material for advanced applications, including catalysis and energy storage, particularly after post-processing to reclaim surface area. • Metal-doped catalytic pyrolysis was studied, and Fe 3 O 4 -based catalysts produced more bio-oil and biogas. • Nickel and cobalt coatings promoted dehydrogenation and decarbonylation, enhancing biogas production. • Uncoated catalysts yielded biochars with relatively high surface areas, reaching up to 480 m 2 /g. • Biochars from metal-doped catalysts exhibited enhanced thermal stability, active sites and low weight loss.