Heterogeneous zirconium and titanium catalysts for the selective synthesisof 5-hydroxymethyl-2-furaldehyde from carbohydrates

Layered zirconium- and titanium- hydrogenphosphates in the alpha and gamma structural arrangements, their corresponding alpha- and gamma-layered pyrop hosphates as well as cubic pyrophosphates were used as acid catalysts in th e dehydration of fructose and inulin to 5-hydroxymethyl-2-furaldehyde. The experiments were carried out either in batch or in subsequent cycles charac terized by extraction of the reaction products, recovery and re-use of both the catalyst and the substrate solution. Good results, in terms of activit y and selectivity, have been achieved. In particular, when cubic zirconium pyrophosphate was employed in batch aq. fructose dehydration a turnover num ber (TN) of about 9 mmol of HMF/g of catalyst x h was obtained with almost complete selectivity towards the target product. Under analogous conditions , gamma-titanium phosphate revealed also promising performances (TN > 6 and selectivity to HMF similar to 98%). When the reaction products were extrac ted and the above catalysts recycled, the cited performances were retained up to very high conversion for both fructose and inulin substrates. The cat alytic performances were discussed and related to the nature of the differe nt acid sites present on the catalyst samples. (C) 2000 Elsevier Science B. V. All rights reserved.