Synergistic effects of iron with alkali and alkaline earth metals on catalytic pyrolysis of biomass for highly graphitized carbon

To prepare highly graphitized carbon from biomass and understand the synergistic effects of iron with alkali and alkaline earth metals (AAEMs), K and Ca were introduced to iron-catalyzed graphitization of biomass. Results showed that both K and Ca accelerated the thermal decomposition rate of biomass, and the activation energy of the devolatilization stage with K and Ca reduced to 60.882 kJ/mol and 45.342 kJ/mol respectively, compared to 73.657 kJ/mol without K/Ca. The porous graphitic carbon obtained at 850 °C with the existence of K and Fe exhibited the highest graphitization degree parameter (g = 0.5193) with a big surface area (170.504 m²/g). The carbon with Ca and Fe showed a developed mesoporous structure (198.979 m²/g) and high graphitization parameter (g = 0.1783), compared to g = 0.0934 without K and Ca. Finally, the tailor-catalyzed mechanism of iron-catalyzed graphitization of biomass in the presence of K/Ca was proposed. K reduced the sp³ amorphous carbon structures and intercalated carbon framework while Ca produced the in-situ CaO template and extra gasification gas of CO₂, resulting in an acceleration of the graphitization of biomass.