Agradecimentos: The author authors thank the financial supported by the "National Council for Scientific and Technological Development—CNPq" (Process 142364/2016-9) and "São Paulo Research Foundation—FAPESP" (Process no. 2018/20532-0). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. This work is financially supported by the "National Council for Scientific and Technological Development—CNPq" (Process 142364/2016-9) and "São Paulo Research Foundation—FAPESP" (Process no. 2018/20532-0). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior—Brasil (CAPES)—Finance Code 001. This work has also been supported by the "National Council for Scientific and Technological Development—CNPq" (Universal Call MCTIC/CNPq 28/2018 process no. 431272/2018-2) and was conducted within the scope of grant #2015/20630-4, São Paulo Research Foundation (FAPESP) Ver menos

Abstract: 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 degrees C using water or a 1:0.8 (v/v) water/isopropanol mixture as solvents. The solids were characterized by XRD, N-2 adsorption, TGA, XPS, TPD-NH3 and FTIR-Pyridine. Results indicated a specific surface area of 144 and 108 m(2)/g and an average pore diameter of 44 and 76 angstrom to NB and NB-AL respectively. The solids presented similar density of acid sites (6.0 for NB and 5.7 mu molNH(3)/m(2) for NB-AL), but different strength distribution of the acid sites. Moreover, the fraction of Bronsted 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 degrees C in water/isopropanol mixture, whilst the highest selectivities to furfural were obtained in reactions with water at 160 degrees 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 Ver menos