Vanadium-Substituted Phosphomolybdic Acid: Efficient Catalyst to Produce Bioadditives from Biomass Derived Furfural

In this work, the activity of vanadium-doped and undoped phosphomolybdic acids, H3+n PMo12-nVnO40 (n = 0, 1, 2 and 3), was evaluated in the acetalization reaction of furfural with alkyl alcohols. The main focus was to verify how vanadium charge impact catalytic activity of phosphomolybdic acid, and to try to link these effects to changes in their structural properties. The main reaction parameters such as catalyst charge, catalyst concentration, temperature, time, type of alcohol, type of aldehyde, vanadium charge, and H+ ion charge were studied. Various Brønsted acids (sulfuric, p-toluenesulfonic, undoped and doped phosphomolybdic acids) were evaluated in condensation reactions of furfural with methyl alcohol. Notably, H4PMo11V1O40 was the most active and selective catalyst toward the formation of methyl acetal furfural. The water has a leveling effect over the strength of these acids. Nonetheless, under reaction conditions, the presence vanadium impacted the strength of phosphomolybdic acids, allowing distinguish what is the strongest; vanadium monosubstituted phosphomolybdic acid. The superior performance of H4PMo11V1O40 was attributed to its additional acidity, resulting from the presence of very strong (H+) and Lewis and Brønsted acid sites, due to the substitution of Mo6+ by V5+ in its structure.