Use of amorphous Nb2O5 and Nb2O5/Al2O3 as acid catalysts for the dehydration of xylose to furfural

This work compared the catalytic performance of the amorphous Nb2O5 (NB) and 12 wt% Nb2O5/Al2O3 (NB-AL) catalysts for the xylose dehydration to furfural carried out for 6 h at 140 and 160 °C using water or a 1:0.8 (v/v) water/isopropanol mixture as solvents. The solids were characterized by XRD, N2 adsorption, TGA, XPS, TPD-NH3 and FTIR-Pyridine. Results indicated a specific surface area of 144 and 108 m2/g and an average pore diameter of 44 and 76 Å to NB and NB-AL respectively. The solids presented similar density of acid sites (6.0 for NB and 5.7 μmolNH3/m2 for NB-AL), but different strength distribution of the acid sites. Moreover, the fraction of Brønsted acid sites on NB was 27%, whereas on NB-AL it was only 2%. Concerning the catalytic tests, the highest conversion of xylose for NB and NB-AL (99.0 and 91.1%, respectively) was achieved for the reactions at 160 °C in water/isopropanol mixture, whilst the highest selectivities to furfural were obtained in reactions with water at 160 °C (60.1% to NB and 35.1% to NB-AL). Finally, using water as solvent, the selectivity to furfural increased with both catalysts at the highest temperature, though the carbon balance decreased.