Mechanisms of simultaneous activation-ammoniation in co-pyrolysis of cellulose and lignin: Synergistic effects on product distribution and characteristics

In this study, a method of simultaneous activation and ammoniation during cellulose and lignin fast pyrolysis was proposed. The influence of the cellulose-to-lignin mass ratio on the properties of the porous N-doped biochar was investigated. Results showed that with the increasing ratio of lignin, both the yield and N content of the porous N-doped biochar increased, reaching a maximum value of 37 % and 10.43 wt%, respectively. However, the specific surface area (S BET ) and total pore volume (V total ) showed a decreasing trend, with the highest values being 1492.31 m²/g and 0.632 cm³ /g. This could be due to the polymer chains of cellulose, which are connected by β-1,4-glycosidic bonds, undergoing hydrogen bond dissociation, glycosidic bond scission, and deoxygenation reactions under the action of KOH and NH₃. This results in the formation of numerous small molecular intermediates that undergo dehydration, condensation, and other reactions, leading to the generation of a large number of volatile products. In contrast, Lignin forms a cross-linked carbon skeleton that retains active sites for efficient ammoniation while suppressing volatile release from cellulose derivatives, thereby inhibiting pore development. Meanwhile, the interaction between cellulose and lignin exhibits a competitive effect on volatile release, where lignin suppresses cellulose-derived volatile formation, thereby reducing bio-oil yield, while promoting dehydrogenation reactions that enhance H₂ generation in the gas phase. What’s more, the yields of quaternary-N and pyridinic-N-oxide showed no significant correlation with the cellulose-to-lignin mass ratio. This confirms that the two components undergo independent reaction mechanisms, providing critical mechanistic insights into the simultaneous pyrolysis-activation-ammoniation of biomass.