Aqueous-Phase Transformation of Glucose into Hydroxymethylfurfural and Levulinic Acid by Combining Homogeneous and Heterogeneous Catalysis.

Homogeneous (HCl) and heterogeneous catalysts (various zeolites) were combined to enhance the upgrading of glucose into two different platform molecules: 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). β-Zeolite was the most active material for the glucose isomerization to fructose, improving also the activity of HCl for the subsequent steps. Reaction time, temperature, and pH were then modified, identifying 140 °C, 200 ppm of HCl, and 5 h as the optimum conditions for HMF formation (41 % selectivity; 0.06 mol L-1 ) and 140 °C, 400 ppm of HCl, and 24 h for LA formation (34 % selectivity; 0.12 mol L-1 ). This new approach is also relevant because of significant changes to the mechanism for humins formation. All results are successfully fitted to a kinetic model simultaneously considering both catalytic mechanisms.