DOI: 10.25824/redu/75heg6
title: PhD thesis: study of niobium phosphate as an acid catalyst for the conversion of furfuryl alcohol and as a support in bifunctional metal catalysts for the conversion of furfural

description: Biomass conversion allows the production of both chemicals and fuels in biorefineries, and is a viable alternative to the use of fossil resources. Furfural is a platform molecule with more than 80 derivatives, and in the presence of a metallic catalyst, it can be hydrogenated to furfuryl alcohol and tetrahydrofurfuryl alcohol. Moreover, in the presence of an acid catalyst, furfuryl alcohol can be transformed into several value-added products such as difurfuryl ether, isopropyl levulinate, cyclopentanone and levulinic acid. In this context, this work investigates the use of niobium phosphate as an acid catalyst for the conversion of furfuryl alcohol and as a support in bifunctional metal catalysts for the conversion of furfural. The main motivation was to find a suitable bifunctional catalyst and favorable operating conditions which allow the production of acid-site products directly from furfural, in a cascade reaction system, to diversify the reaction pathways in biorefineries. Niobium phosphate (NbOPO4) was chosen due to its high acidity and was obtained by calcination of NbOPO4.nH2O. For furfuryl alcohol conversion, the reaction was performed with NbOPO4 in natura and calcined at 400°C, in two conditions. Ni and Cu catalysts (5 or 10 wt% loading) were synthesized by deposition-precipitation, and activation consisted in calcination, reduction via H2 flow (400 or 600°C), and passivation. For furfural conversion, three parameters were varied: catalyst mass (0.125 to 1 g), reaction temperature (130 to 170°C) and H2 pressure (1 to 5 MPa of H2). The quantification was made in GC and GC-MS, and the materials were subjected to characterization analyses (TGA/DSC, SEM/EDS, N2 physisorption, XRD, TPR, TPD-NH3 and XPS). Furfuryl alcohol conversion with NbOPO4 in natura and calcined at 400°C presented similar outcomes, as calcination at this temperature did not induce significant changes in the material. Water favored the formation of α-angelica lactone, while 2-propanol favored the formation of isopropyl levulinate. Supported catalysts were then applied in furfural conversion. For catalysts activated at 400°C, Ni was more active than Cu, as textural properties were impaired in Cu catalysts, and hydrogenation was the main route in all cases. For Ni catalysts activated at 600°C, higher values of H2 pressure led to the greatest increase in conversion and allowed a more profound hydrogenation level. Conversely, an increase in reaction temperature, catalyst mass or metallic loading favored acid-site activity, with main formation of difurfuryl ether and 5-hydroxy-2-pentanone. Increasing the activation temperature from 400 to 600°C impaired Ni accessibility on the surface, but the higher degree of reduction was proven beneficial to activity and bifunctional selectivity. In summary, the influence of metallic and acid sites was successfully studied in many reaction conditions and catalyst constitutions, and a Ni/NbOPO4 catalyst with adjusting selectivity to different products of interest was obtained for the first time in this reaction system.