Hydrolytic oxidation of cellulose to formic acid in the presence of Mo-V-P heteropoly acid catalysts

Abstract

The reduction of oxygen-containing compounds, which is employed to produce biofuels from plant feedstock, requires a great amount of reductant that is commonly represented by molecular hydrogen obtained from non-renewable fossils. Formic acid can also serve as the reductant or hydrogen source in the production of such fuels. It is shown that formic acid can be obtained from mechanically activated microcrystalline cellulose with high yields (66%) by the one-pot catalytic process of hydrolytic oxidation in the presence of Mo-V-P heteropoly acids (HPA) possessing bifunctional (acidic and oxidizing) catalytic properties. Mechanical activation has a crucial influence on the cellulose reactivity and formic acid yields. The highest yield of formic acid was obtained by using the cellulose activated in a planetary mill, when its crystal structure was mainly crushed. The temperature of 150–160°C and the oxidizing atmosphere (20% O2 and 80% N2) are found to be the optimal reaction conditions. Pressure was shown to exert no effect on the observable kinetics of the process. A search for the optimal HPA composition demonstrates that a maximum reaction rate is observed in the presence of HPA that provides the most acidic reaction medium. A linear dependence of the reaction rate on the concentration of H+ ions and a more complicated dependence on vanadium content were revealed.