Niobium pentachloride in a biphasic catalytic system for valorization of corn cob biomass†

The unbridled exploitation of fossil resources for obtaining energy, chemical inputs, materials and fuels has generated growing environmental concerns, driving the search for more sustainable alternatives. In this context, the use of lignocellulosic biomasses for the production of biorenewable platform molecules, such as furfural (FF) and 5-hydroxymethylfurfural (HMF), has been widely studied. Among the strategies investigated, the use of niobium-based catalysts stands out due to their high catalytic efficiency, versatility, high acidity and stability. Therefore, this work investigated the valorization of corncob biomass through the synthesis of FF and HMF, using for the first time niobium pentachloride as a catalyst in a biphasic system (ethyl acetate and saturated aqueous NaCl solution). Different reaction parameters were investigated and it was found that the best conditions for the conversion of corncob biomass into furans were 12.5% wt niobium pentachloride, 200 °C and 180 min. Under these conditions, FF and HMF were both obtained with yields of 26%, in addition to obtaining levulinic acid (LA) with a yield of 3%. Furthermore, under these conditions, the formation of three more products was also observed: 5-ethoxymethylfurfural (EMF), 5-acetoxymethylfurfural (AMF) and ethyl levulinate (LE), with yields of 12%, 4% and 2%, respectively. In addition, cellulose, inulin and bamboo biomass were also evaluated as substrate.