Versatile Hybrid Niobium Pentoxide‐Based Catalyst Applied in Reactions of the Fuels Industry: Oleic Acid Esterification and Quinoline Oxidation

Hybrid niobium‐based catalysts were synthesized and applied in two kinds of reactions: oleic acid esterification to produce biodiesel and oxidation of quinoline, an important contaminant of fossil fuels. Niobium oxides were functionalized with p‐toluenesulfonic acid, which conferred amphiphilic properties on the materials and an increase in Brønsted acidic sites due to the incorporation of sulfo groups on the material surface. The oleic acid esterification reaction with methanol showed very high efficiency of the hybrid material with 90 % conversion, even after three reuse cycles, under very mild conditions. Moreover, the catalyst was capable of promoting quinoline oxidation in a biphasic reaction. Niobium oxides are widely used acid catalysts for various organic reactions. Nb2O5 was functionalized with p‐toluenesulfonic acid to increase its Brønsted acidity and make it amphiphilic. Catalyst tests in fuel industry reactions, i.e., esterification of oleic acid with methanol to give biodiesel and removal of nitrogenous fuel contaminants by oxidative denitrogenation of quinoline, were promising.