Catalytic oxidation of cellulose to formic acid in V(V)-Fe(III)-H2SO4 aqueous solution with O2

Abstract

Carboxylic acids are considered as an important group of chemicals. Direct conversion of cellulose to formic acid (FA) by vanadium(V(V))-contained catalyst is of significant conceptual and practical interest. A second metal (from Mg(II), Ca(II), Al(III), Cr(III), Mo(VI), Mn(II), Cu(II), or Fe(III)) incorporated into V(V)-contained catalyst system was screened to further improve the oxidation of cellulose by O2 to yield FA. Fe(III) exhibited the best performance and effects of reaction parameters on the conversion of cellulose in NaVO3-FeCl3-H2SO4 aqueous solution were investigated. Cellulose could be rapidly converted, and the yield of FA (66.8%) was higher than that obtained by the single use of FeCl3 (48.4%) or NaVO3 (57.6%). The conversion of cellulose in another V(V)-contained catalyst system (H5PV2Mo10O40) was explored to verify the universal enhancement of FeCl3. Influences of the second metal Fe(III) on the V(V)-contained catalyst system and mechanism of cellulose oxidation in the V(V)-Fe(III)-H2SO4 system were studied. Compared with single use of V(V), the employment of Fe(III) alone is not active enough in the oxidative CC bond cleavage. V(V) other than Fe(III) is the main active species for selective oxidation of substrates. The incorporation of Fe(III) and V(V) shows both synergistic and competitive relationships. Both the synergistic and competitive effects are beneficial to increase FA yield, as they promote the oxidation of V(IV) to V(V), increase oxidative ability, and inhibit the overoxidation to by-product CO2. The catalyst system was reused four times without decline in activity.