Roles of Ball Milling Pretreatment and Titanyl Sulfate in the Synthesis of 5-Hydroxymethylfurfural from Cellulose

Production of 5-hydroxymethylfurfural (HMF) from cellulose has been expected for a long time, but most catalytic systems generally give low yield and selectivity due to the difficulty of balancing cellulose deconstruction with the uncontrollable degradation of the target product under harsh conditions. Here we show that the ball milling pretreatment could markedly facilitate the conversion of microcrystalline cellulose to HMF by titanyl sulfate (TiOSO4). The ball milling pretreatment remarkably decreases the degree of crystallinity of microcrystalline cellulose with a reduction of molecular weight via disrupting the hydrogen bond and partially breaking the β-1,4-glycosidic bond. TiOSO4 functions as both Lewis and Brønsted acid to catalyze the efficient conversion of cellulose with high HMF yield (45.4%), far exceeding that (14.1%) from untreated cellulose. The reaction pathway was revealed by liquid chromatograph–mass spectra analysis. In addition, phosphorylated titanium dioxide also afforded a notable HMF yield (21.8%), showcasing the great potential of Ti-based heterogeneous catalyst.