Beneficial effects of calcium chloride on glucose dehydration to 5-hydroxymethylfurfural in the presence of alumina as catalyst

Abstract Aluminas with different acid-base properties (acid, neutral and basic) have been characterized by using XRD, N 2 sorption at −196 °C, XPS and NH 3 -TPD, and tested for the dehydration of glucose to 5-hydroxymethylfurfural (HMF). Under the operating conditions used, the acid alumina showed the highest total acidity and the best catalytic performance, but the HMF yield hardly exceeded 20% since γ-Al 2 O 3 apparently favored the secondary reactions. The presence of CaCl 2 in the reaction medium notably improved the catalytic performance, even at very short reaction times, due to the interaction between Ca 2+ ions and glucose molecules, which favors the α- d -glucopyranose formation, thus enhancing glucose conversion and HMF yield up to 96% and 52%, respectively, at 175 °C after 15 min in presence of 0.65 g CaCl 2 ·g aq.sol. −1 and acid γ-Al 2 O 3 as catalyst. The isomerization of glucose to fructose and subsequent dehydration to HMF does not seem to take place when CaCl 2 is present in the reaction medium, as inferred from 1 H NMR spectroscopy. Moreover, the catalyst was reused at least for three runs maintaining the catalytic activity, without an intermediate regeneration step.