Abstract
Background: A variety of catalysts have been developed for HMF production from glucose. However, there is less information available concerning the mechanism of HMF dehydration from glucose arisen from heterogeneous catalyst in aqueous medium. It is of great significance to figure out the mechanism of HMF formation from glucose catalyzed by molecular sieve.
Methods: A combined experimental and theoretical research on dehydration of glucose to HMF catalyzed by Sn-KIT-6 in aqueous media has been performed. We conducted Density functional theory (DFT) to investigate the effects of catalyst on the reaction mechanism.
Results: In the first part, Sn-KIT-6 catalyst can greatly reduce the enthalpy of 1, 2-enediol, the key intermediate, from 70.88kcal/mol in non-catalyst system to 46.57kcal/mol. The second part undergoes sequential removal of three water molecules from fructose. The elimination of the second water molecule in the presence of Sn-KIT-6 is the rate-limiting step in the second part with enthalpy of 29.47kcal/mol, which is less than that of non-catalyst condition with enthalpy of 55.69kcal/mol.
Conclusion: The reaction mechanism was developed so that the isomerization of glucose into fructose together with the subsequent dehydration is generally considered as two main parts of the whole reaction. The change of the reaction enthalpy calculated from DFT in the rate-controlling step illustrates that Sn-KIT-6 catalyst greatly promotes HMF yield from dehydration of glucose.
Keywords: Glucose, fructose, dehydration, 5-HMF, reaction mechanism, DFT.
Graphical Abstract
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