Relation between surface acidity and reactivity in fructose conversion into 5-HMF using tungstated zirconia catalysts

Abstract

Catalytic dehydration of fructose and its conversion to 5-hydroxymethylfurfural was studied using tungstated zirconia oxides, with various tungsten oxide loadings (1–20 wt.%). The samples were prepared by incipient wetness impregnation and thoroughly characterized using a combination of different techniques: structural, thermal and calorimetric analyses. Zirconia was predominantly present in the investigated samples in the tetragonal phase when the WO3 loading was above 10 wt.%. The samples exhibited amphoteric characteristics, as they adsorbed both ammonia and sulfur dioxide on their surface. The number of surface acid sites increased with increasing WO3 content. Fructose dehydration tests evidenced the formation of 5-hydroxymethylfurfural and by-products (formic and levulinic acids). The results show that the ratio of basic to acidic sites of the solid catalysts is the key parameter for the selectivity in 5-HMF, while the global fructose conversion was mainly related to the presence of acid sites of a given strength with 150 > Qdiff > 100 kJ·molNH3− 1.