Selective Synthesis of Renewable Diesel Fuel Precursors via C–C Condensation of Biomass-Derived Furans Using a Niobium Oxide Nanocatalyst

The carbon–carbon (C–C) condensation of biomass-derived molecules represents a promising approach for the production of renewable fuel precursors. We developed a highly selective catalytic route for the C–C condensation of biomass-derived furans (furfural and 2-methylfuran) for the synthesis of a C-15 diesel precursor using a recyclable heterogeneous Nb2O5 nanocatalyst at solvent-free conditions. The shape-engineering of Nb2O5 particles (nanorods) and thermal treatment at 300 °C for 2 h (Nb2O5 NR3) provided a higher concentration of acid sites with optimum Brønsted acid sites, which are the vital active sites for the condensation of furfural with 2-methylfuran. The X-ray photoelectron spectroscopy (XPS) studies showed the presence of more oxygen vacancy defects and electron-deficient Nb5+ sites in the Nb2O5 NR3 catalyst. By optimizing the reaction conditions, a 94% yield of C-15 diesel precursor with 99% conversion of furfural was achieved using the Nb2O5 NR3 catalyst under mild reaction conditions. The versatile efficiency of the Nb2O5 NR3 catalyst is showcased for the synthesis of diverse renewable diesel fuel precursors by using various substituted furans and benzaldehydes. The structure and morphological stability of the Nb2O5 NR3 catalyst were elucidated by powder X-ray diffraction, XPS, and transmission electron microscopy studies. The good reusability of Nb2O5 nanocatalyst for up to 5 cycles and sustainable green chemistry metrics show the practical feasibility of this catalytic approach for the C–C condensation of biomass-based furans.