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Biomass fast pyrolysis has emerged as a highly promising technology for producing renewable fuels and chemicals. However, the inherent multi-scale and multiphase nature of the process and the heterogeneous nature of biomass feedstocks typically lead to low selectivity toward each bio-oil molecule, posing significant commercialization challenges. Molecular-level understanding of the biomass pyrolysis reaction kinetics considering the interactions between the main constituents (i.e., cellulose, hemicellulose, and lignin) is essential to advance the macroscopic design, scale-up, and optimization of the process. In this work, microreactor experiments were conducted to determine the effects of lignin structures on the yields of cellulose-derived products during pyrolysis. We show that levoglucosan formation is inhibited by the β-O-4 lignin linkages or catalyzed by the 5-5 linkages, glycolaldehyde formation is catalyzed by the β-O-4 linkages or inhibited by the 5-5 linkages, and 5-hydroxymethylfurfural formation is inhibited by either linkage. Density functional theory calculations reveal that these catalytic and inhibitory effects on cellulose fast pyrolysis are induced by noncovalent interactions between cellulose and lignin. The molecular-level picture of cellulose–lignin interactions uncovered in this work paves the way for further use of genetic engineering to grow new genotypes of biomass for selective production of value-added chemicals and machine learning approaches to obtain correlations between biomass structures and product yields for biomass fast pyrolysis. 

Fast pyrolysis of lignocellulosic biomass is a promising approach for producing biofuels and renewable chemicals, but the resultant bio-oil quality and diverse product distributions limit its widespread adaptation. Concurrently, the accumulation of waste plastics in the environment, particularly polyolefin thermoplastics, is becoming a growing threat. Co-pyrolysis of biomass with hydrogen-rich thermoplastics has shown promise for producing high-quality bio-oils, presenting an attractive solution to waste management. However, a molecular-level understanding of the synergy of the two components in the molten phase during co-pyrolysis is still lacking. In this work, we report the discovery of catalytic and inhibitory effects on cellulose fast pyrolysis caused by noncovalent interactions (NCIs) induced by molten plastics. Our microreactor experiments demonstrated that selectivity toward cellulose-derived anhydrosugars, small oxygenates, or furans increased due to the presence of polyketone, polyethylene glycol, or polystyrene, respectively, which are three thermoplastics with distinct functional groups. Density functional theory calculations reveal that key cellulose pyrolysis pathways leading to major products are catalyzed or inhibited due to perturbations of transition state geometries and partial charges caused by the NCIs induced by plastic functional groups. This discovery offers insights and opportunities for tuning cellulose fast pyrolysis via NCIs using a new family of unconventional molten plastic catalysts or inhibitors