Computational insights into selective glucose to 5-hydroxymethylfurfural (HMF) conversion by reducing humins formation in aqueous media under Brønsted acid-catalyzed conditions

5-Hydroxymethylfurfural (HMF) is known for its potential in biofuel production and as a platform chemical for many commercially important molecules. The cost-effective large-scale production of HMF from glucose is hampered by its poor yield in aqueous media due to the formation of polymeric side products known as humins. Thus, reducing humins formation is a strategy for the efficient conversion of glucose to HMF. However, the origin of humins formation and their structures are elusive. In this regard, we investigated the polymerization mechanism and the structure of humins formed during the Brønsted-acid-catalyzed dehydration of glucose to HMF in an aqueous medium by employing density functional theory-based calculations and microkinetic analyses. Notably, the results of this work indicate that humins formation occurs only after the formation of HMF in the reaction mixture and the major part of the humins structure (about 60%) is composed of furanic rings. Furthermore, based on the knowledge gained from in-depth mechanistic and microkinetic studies, potential strategies to reduce humins formation and thereby enhance HMF selectivity are proposed here.