Thermal carbonization of woody biomass under inert atmosphere with temperature-dependent switching of catalytic effects of Cu and Ti

Background Carbonization of woody biomass under inert atmospheres is a practical route to producing functional carbon materials. However, carbon yield and microstructural development are strongly influenced by temperature and by the presence of metal additives. The temperature-dependent roles of such additives remain insufficiently clarified. Methods The catalytic effects of copper and titanium were systematically examined during heat-induced carbonization of Todo fir ( Abies sachalinensis ) wood flour at 500 °C and 800 °C under nitrogen, using controlled heating rates. Carbonization behavior was analyzed by thermogravimetric–differential thermal analysis. The resulting char was characterized by elemental analysis, scanning electron microscopy, and transmission electron microscopy. Results At 500 °C, copper addition promoted the formation of partially layered turbostratic carbon structures with expanded interlayer spacing, suggesting stabilization of carbon frameworks with reduced bond cleavage. In contrast, titanium enhanced devolatilization and fragmentation, leading to lower carbon retention and more heterogeneous microstructures. At 800 °C, thermally stable, carbon-rich residues were obtained largely independent of heating rate, indicating that the final hold temperature governed bulk carbon ordering. Under these conditions, copper suppressed carbon consumption and increased char yield, whereas titanium promoted interfacial reactions and accelerated carbon decomposition. Transmission electron microscopy showed that overall structural ordering was primarily determined by the final temperature rather than by the additive. These findings indicate temperature-dependent catalytic role-switching, with copper favoring solid carbon formation at moderate temperatures and titanium promoting decomposition, particularly at elevated temperatures. Conclusions The results clarify distinct, temperature-dependent functions of copper and titanium during biomass carbonization and provide a basis for controlling carbon yield and microstructure through additive selection and thermal design.