• • At 850 °C with steam flow 2 mL/min and N2 flow 75 mL/min, all biomass-coal gangue systems achieved peak syngas yields at a 5:5 mass ratio; the high-cellulose pine stick system produced the highest H2 yield (9.06 mmol/g) and H2+CO yield (15.25 mmol/g), with a H2 synergy index (SI) of 1.75, demonstrating efficient volatile reforming and offering a route to maximize hydrogen production from biomass wastes.
• • The high-ash/K+ corn stover system exhibited the strongest CO synergy (SI = 1.22), attributed to catalytic Boudouard reaction, making it an ideal feedstock for CO-rich syngas production; this is critical for industries requiring CO as a chemical building block.
• • The high-nitrogen soybean straw system achieved an optimal H2/CO ratio of 2.00, suitable for Fischer-Tropsch synthesis, but its high nitrogen content led to nitrogenous tars that suppressed overall syngas yield (Ysyngas = 13.00 mmol/g), highlighting a trade-off between syngas quality and quantity.
• • Synergy indices varied significantly across systems: for H2, SI ranged from 1.43 (corn stover) to 1.75 (pine stick); for CO, from 0.97 (pine stick) to 1.22 (corn stover); for CH4, from 0.70 (pine stick) to 1.44 (soybean straw); these quantitative differences guide feedstock selection for targeted syngas composition.