Mechanistic insights into slow pyrolysis of hydrothermal carbon

Slow pyrolysis of fructose-derived hydrothermal carbon spheres at temperatures between 200 °C to 600 °C has been investigated using X-ray Raman spectroscopy and pyrolysis gas chromatography-mass spectrometry in combination with infrared spectroscopy, elemental analysis and thermogravimetry. This study demonstrates the application of temperature resolved X-ray Raman spectroscopy to map the evolution of carbon functionality in complex organic materials. The results show that thermolysis of the polyfuranic linking units within hydrothermal carbon occurs between 300 °C to 350 °C. At pyrolysis temperatures above 350 °C, a stable C O species is observed. The combination of X-ray Raman and pyrolysis GCMS is used in a synergistic approach to monitor both evolving pyrolysate chemistry and bulk carbon composition. The evolution of key furanic and aromatic analytes during pyrolysis is reported. This work contributes to our understanding of the thermal stability and reactivity of these materials, which is essential for optimising their applications as catalyst supports. • Polyfuranic linking units in hydrothermal carbon decompose at 300–350 °C, initiating aromatic condensation. • Stable aromatic C O intermediates (quinone/pyran-like species) form above 350 °C during stepwise deoxygenation. • Complete thermal transformation pathway from polyfuranic to turbostratic aromatic carbon structure resolved. • Bulk-sensitive XRS coupled with pyGCMS simultaneously characterises solid carbon evolution and volatile product release. • Integrated analytical framework enables future in situ real-time studies of thermal transformations in carbon materials for catalyst supports.