Fe–Ca‐Catalyzed Conversion of Cellulose Into Highly Ordered Graphitic Carbon Revealed by Solid‐State 1 3 C NMR and Mössbauer Spectroscopy

ABSTRACT An earth‐abundant Fe–Ca bimetallic catalyst was developed to drive the structural transformation of renewable cellulose into highly ordered graphitic carbon. Solid‐state 13 C NMR T 1 relaxation measurements monitored the gradual reorganization of carbon as the temperature changed. The results demonstrate a clear correlation between elevated graphitization temperatures and longer relaxation time, with the Fe–Ca‐catalyzed biocarbon at 1800°C achieving a T 1 value of 102.5 s, which closely approaches the 117.5 s threshold for commercial graphite. 57 Fe Mössbauer spectroscopy revealed a highly coordinated sequential reduction mechanism, shifting from nanoscale superparamagnetic oxides at low temperatures (400°C–600°C) to a reactive iron carbide intermediate at 800°C. At high temperatures (1400°C–1800°C), calcium serves as a vital structural modifier that prevents Fe nanoparticle sintering, thereby maintaining high metal dispersion and enabling complete deoxygenation and advanced graphitic crystallization. Although the resulting highly reduced ferromagnetic α‐Fe matrix induces a strong bulk magnetic susceptibility (BMS) effect, which complicates conventional carbon chemical‐shift identification, advanced 13 C T 1 and Raman analyses confirm the formation of a highly ordered graphitic carbon network. This work provides profound atomic‐scale insights into the valorization of bio‐feedstocks into highly crystalline carbon materials suitable for energy storage applications, offering a sustainable alternative to fossil‐derived graphite.