Deciphering the microscopic mechanism of cross-coupling interactions between cellulose and lignin during biomass pyrolysis

The cross-coupling interaction mechanisms among biomass components pose a critical challenge in pyrolysis mechanism research. In this study, β -d-glucose and 2-phenoxy-1-phenylethanol ( α -OH-PPE) were employed as model compounds for cellulose and lignin, respectively. By integrating density functional theory (DFT) calculations with experiments from synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), a unified and hierarchical mechanistic framework was established to elucidate the progressively evolving hydrogen transfer-mediated interactions during biomass pyrolysis. Specifically, the identified interaction pathways were categorized into three modes: (i) mutual reactant–reactant cooperative hydrogen transfer, (ii) reactant-assisted hydrogen transfer, and (iii) product/intermediate-assisted hydrogen transfer. The results demonstrated that β - d -glucose and α -OH-PPE exhibited coupled bond cleavage through a cooperative hydrogen transfer mechanism, with energy barrier lying between those of the individual component reactions. Intermediates from β - d -glucose ring-opening (e.g., hydroxyacetaldehyde) could serve as hydrogen transfer mediators to promote bond cleavage reactions like Maccoll elimination in α -OH-PPE. Conversely, phenolic products and tautomers (e.g., 2,4-cyclohexadienone) derived from α -OH-PPE pyrolysis were found to lower the energy barriers for ring-opening, dehydration and secondary reactions of β - d -glucose. Product evolution from SVUV-PIMS showed that α -OH-PPE lowered the formation temperature of 1,4:3,6-dianhydro- α - d -glucopyranose and furan derivatives from β - d -glucose, while β - d -glucose broadened the temperature range over which α -OH-PPE maintained its maximum decomposition rate. This study provides a mechanistic framework for understanding component interactions in biomass pyrolysis. Novelty and significance statement This work addresses a critical challenge in understanding biomass pyrolysis mechanisms by clarifying the microscopic cross-coupling interactions between cellulose and lignin via intermolecular hydrogen transfer reactions. The main novelty lies in the development of a unified and hierarchical mechanistic framework that organizes multiple hydrogen transfer-mediated interaction modes into a progressively evolving representation of biomass pyrolysis, categorizing them into three modes: (i) mutual reactant–reactant cooperative hydrogen transfer, (ii) reactant-assisted hydrogen transfer, and (iii) product/intermediate-assisted hydrogen transfer. This framework enables a systematic interpretation of cross-coupling evolution across the pyrolysis process, elucidating the initial reaction steps in biomass combustion. These findings provide critical insights into establishing a mechanistic foundation for understanding the combustion of complex biomass components, thereby advancing sustainable energy utilization.