Dehydration of fructose to 5‐HMF catalyzed by commercial faujasite zeolites: kinetic study and influence of the properties of the catalyst

We carried out a mechanistic investigation of the dehydration of fructose catalyzed by a series of proton‐exchanged faujasite zeolites. Using a combination of analytical tools (HPLC, GC, NMR), we could solve and quantify most of the variety of products formed, including (i) cyclic intermediates (ii) transient species (monomeric and dimeric) (iii) byproducts (oligomeric species and humins). The results prove that the reaction goes through a cyclic mechanism, and we could propose a kinetic model matching most of our experimental results and describing the interplay between the different categories of products. By comparing the performances of different catalysts with varying properties, we surprisingly find that increasing the concentration of Brønsted acid sites induces lower catalytic activity. Contrary to general expectations, the mesoporous volume seems to be the most determining parameter for the activity of the catalysts over the set of catalysts evaluated here, which may be explained by the importance of allowing the reactant a significant accessibility to the active sites.