From single component to real biomass: insights into phenolic formation via N-doped biochar-catalyzed pyrolysis experiment and theoretical calculation

Correlation between biomass composition and catalytic phenolic content was built. • Lignin volatiles formed more phenolics via side-chain cleavage over N -doped biochar. • Phenolic proportion in holocellulose bio-oil nearly doubled under catalysis. • “Heterocyclic isomerization” pathway towards phenolics was newly proposed. • Phenolic formation mechanisms of different components were refined and calculated. Biomass catalytic pyrolysis is a promising approach for high‑value phenolic production. Herein, a N‑doped lignin‑derived biochar catalyst (LBC) was prepared via low‑temperature synchronous pyrolysis-activation-ammoniation using enzymatic hydrolysis lignin as feedstock. LBC featured a high specific surface area (826.115 m 2 /g, 85.35% micropores), abundant O‑C O /–OH group (34.5%), and dominant pyrrolic‑N (46.8%) for enhancing Lewis basicity. Ex‑situ catalytic pyrolysis of three major biomass components reduced bio‑oil yield but increased gas yield (CO yield from xylan increased from 168.71 to 221.69 ml/g, and H 2 yield was enhanced by 65.82%). Lignin pyrolysis achieved high phenolic content (60%), and LBC promoted side‑chain cleavage of intermediate to form simple phenolics. Phenolic content of holocellulose derived bio-oil doubled to nearly 10%, and phenolic selectivity in bamboo sawdust reached up to 54%, which positively correlated with lignin content. Multi‑component synergy further elevated phenolic content than theoretical levels. Transition of catalyst properties was mainly attributed to coke deposition from lignin volatiles and loss of active sites. DFT calculations detailedly evaluated the energetics and feasibility of competing pathways for lignin side‑chain cleavage reaction and demethoxylation into simple phenolics. For holocellulose, the calculations identified levoglucosan as the key phenolic precursor, which tended to form phenolics via a favorable low-energy-barrier “heterocyclic isomerization” pathway. This work revealed the synergistic mechanism between biomass components and catalyst property, providing guidance for high‑value phenolic production from biomass. Download: Download high-res image (119KB) Download: Download full-size image