Highly Efficient Oxidation of Biomass Xylose to Formic Acid with CeOx-Promoted MnOx Catalyst in Water

Abstract

Formic acid is a versatile chemical, which is industrially produced from fossil resources. In this work, biomass-derived xylose was used as a potential feedstock to synthesize formic acid with Mn–Ce oxides as the catalyst in water. Among the Mn–Ce oxides with different molar ratios, Mn4Ce0.05Ox showed the best catalytic activity, offering a formic acid yield up to 65.1% at 160 °C with 3 MPa of O2, which was much higher than that using pristine MnOx (40.5%) and CeOx (9.9%). In addition, Mn4Ce0.05Ox was shown to be tolerant to a higher xylose concentration. The introduction of CeOx into MnOx increased the total surface area (55.8 vs 33.7 m2 g–1), gave a higher ratio of (Mn2++Mn3+)/Mn4+ (1.94 vs 1.54), and produced more surface adsorbed oxygen (39.0% vs 26.0%). The DFT calculations revealed that the adsorption energy of xylose on the Ce site (−1.231 eV) was much lower than that on the Mn site (−0.884 eV), thus facilitating the binding of xylose on the catalyst. Mechanism studies of xylose–catalyst–water reaction systems indicated that glyceric acid and glycolic acid were the main intermediates, while CO2 was cogenerated with the formic acid.