Comprehensive microstructural evaluation of biochar, biocoke, and anthracite with respect to the CO₂ reactivity

With the growing interest in carbon biomaterials, understanding their properties and reactivity is principal for resilient metallurgical applications. This study systematically evaluates the microstructural features of biochars obtained at 400 °C and 600 °C, biocoke (5 wt % wood pellets), and anthracite (reference) via advanced characterization techniques. Applying X-ray diffraction (XRD), Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) with van Krevelen plots characterizes in-depth the chemical changes in carbon biomaterials after pyrolysis or carbonization, showing the carbon structure–reactivity relationship. XRD analysis reveals an increase in structural ordering across the carbon materials, with interlayer spacing (d₀₀₂) decreasing from 3.70 Å in biochar at 400 °C and 3.51 Å in biochar at 600 °C to 3.46 Å in both anthracite and biocoke, while crystallite height (L_c) increases from 7.5 Å to 19.4 Å. By applying FT-ICR-MS, the van Krevelen plots, and statistical evaluation of the heteroatomic class distributions, it can be confirmed that biochar samples are rich in oxygen-containing and unsaturated nitrogen-containing compounds. Biocoke and anthracite predominantly contain aromatic and unsaturated compounds, showing their high condensation levels. Key findings suggest that these structural changes strongly influence CO₂ gasification reactivity as determined by the Distributed Activation Energy Model (DAEM), where the average activation energy (E₀) rise from 104.30 kJ/mol for biochar at 400 °C to 135.39 kJ/mol for biochar at 600 °C, 137.22 kJ/mol for anthracite, and reaches at 161.65 kJ/mol for biocoke. Microstructural ordering, van Krevelen plots, and molecular-level assessment by FT-ICR-MS were found to be important determinants of the reactivity of carbon materials.