Hydrolysis-oxidation of starch to formic acid in the presence of vanadium-containing molybdophosphoric heteropoly acid (H3+xPMo12-xVxO40): Effect of acidity and vanadium content on the yield of formic acid

Abstract

Formic acid (FA) is an important chemical commodity as well as a promising medium for hydrogen storage and hydrogen production. Herein, a one-pot hydrolysis-oxidation of starch to formic acid (FA) catalyzed by molybdovanadophosphoric heteropoly acids (H3+xPMo12-xVxO40, x = 1, 2, 4, and 5) (PMo12-xVx) as bifunctional catalysts was demonstrated. The reaction was investigated at 120–150 °C. 2–5 MPa of gas mixture (O2/N2 - 20/80 vol/vol) was used as the oxidant. The rate of starch hydrolysis to glucose was found to decrease with decreasing the strength of PMo12-xVx. The yield of FA was demonstrated to depend on the number of V atoms in the framework of heteropoly anion. The initial rate of FA formation rose with an increasing number of V atoms. However, multi-substituted HPA favors overoxidation of the reaction mixture. Maximum yield of formic acid reached 67 % in 7 h under optimal conditions.