Experimental and theoretical atomic-scale insights into the bimetallic catalytic graphitization of biochar

Metal-catalyzed graphitization plays a critical role in the conversion of biochar into sustainable carbon materials. However, the catalytic mechanisms governing the synthesis of graphene-layered structures remain poorly understood. Herein, we investigate the catalytic effect of Fe–Ca bimetallic systems on the graphitization of cellulose-derived biochar (biocarbon) by combining high-energy synchrotron X-ray total scattering with Pair Distribution Function (PDF) analysis. The results show that bimetallic catalysis promotes the transformation of amorphous and turbostratic carbon into medium- and long-range ordered graphitic carbon arrangements, presenting enhanced crystallinity compared to monometallic catalysts. The graphitization mechanism is explained by combination of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and high-resolution X-ray total scattering analysis. Further Density Functional Theory (DFT) calculations identify a stable Fe(110)–graphene interface with strong chemisorption, characterized by high binding energy and short interfacial distance, which facilitates charge transfer and orbital hybridization at the metal–carbon interface. These findings represent a step forward in understanding the catalytic process of enhanced graphitization in bimetallic systems and provide original insights into the role of metal–carbon interactions in catalytic carbon restructuring processes. We believe that these findings make an important contribution to understanding and predicting the thermophysical, thermoelectrical and thermochemical properties of carbonaceous materials derived from renewable resources for energy storage and environmental applications.