Influence of morphology of zirconium-doped mesoporous silicas on 5-hydroxymethylfurfural production from mono-, di- and polysaccharides

Abstract

Different zirconium-doped mesoporous silicas (Zr-KIT-6, Zr-SBA-15, Zr-MCM-41 and Zr-HMS) were synthesized and evaluated in the glucose dehydration to 5-hydroxymethylfurfural (HMF). A Si/Zr molar ratio of 5 was chosen for this purpose after the optimization of this parameter for the KIT-6 support. These materials were characterized by using XRD, N2 sorption, TEM, XPS, NH3-TPD and pyridine adsorption coupled to FTIR spectroscopy. All catalysts were active in glucose dehydration, being HMF the main product, and their catalytic performance is enhanced after CaCl2 addition to the reaction medium. However, Zr-doped mesoporous HMS silica showed the highest values of glucose conversion and HMF yield, mainly at short reaction times, due to this catalyst displayed the highest surface zirconium concentration and its 3D morphology favored the access of glucose molecules to active sites. This fact also caused a faster deactivation due to coke deposition on the catalyst surface, although leaching of zirconium was negligible. The Zr-HMS(5) catalyst could be reused for four catalytic runs without any treatment and the initial catalytic activity could be recovered after washing with water and acetone. This catalyst also demonstrated to be active for hydrolysis of disaccharides and polysaccharides, such as sucrose, maltose, cellobiose, inulin and cellulose, and subsequent dehydration of resulting monomers for HMF production.