Indexed on: 15 Aug '18Published on: 15 Aug '18Published in: ChemSusChem
The sustainable conversion of vegetable biomass-derived feeds to useful chemicals requires innovative routes matching environmental and economical criteria. The approach herein pursued is the synthesis of water-tolerant, unconventional solid acid monolithic catalysts based on a mixed niobia-titania skeleton building up a hierarchical open-cell network of meso and macropores, and tailored for use under continuous flow conditions. The materials were characterized by spectroscopic, microscopy and diffraction techniques showing a reproducible, isotropic structure and an increasing Lewis / Brønsted acid sites ratio with increasing Nb content. The catalytic dehydration reaction of xylose to furfural was investigated as representative application. The efficiency of the catalyst showed to be dramatically affected by the niobia content in the titania lattice. The presence of as low as 2% wt niobium resulted in ther highest furfural yield at 140 °C reaction temperature under continuous flow conditions, using H2O / Υ-valerolactone as safe monophasic solvent system. The interception of a transient 2,5-anhydroxylose species suggested the dehydration process to occur via a cyclic intermediates mechanism. The catalytic activity and the formation of the anhydro intermediate were related to the LAS/BAS ratio and indicated a significant contribution of xylose-xylulose isomerization. No significant catalyst deactivation was observed over 4 days usage. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.