Highly Efficient Oxidation of Biomass Xylose to Formic Acid with CeO<sub><i>x</i></sub>-Promoted MnO<sub><i>x</i></sub> Catalyst in Water
Siyu Xu, Jirui Yang, Jialu Li, Feng Shen
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, Mn 4 Ce 0.05 O x showed the best catalytic activity, offering a formic acid yield up to 65.1% at 160 °C with 3 MPa of O 2, which was much higher than that using pristine MnO x (40.5%) and CeO x (9.9%). In addition, Mn 4 Ce 0.05 O x was shown to be tolerant to a higher xylose concentration. The introduction of CeO x into MnO x increased the total surface area (55.8 vs 33.7 m 2 g –1 ), gave a higher ratio of (Mn 2+ +Mn 3+ )/Mn 4+ (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 CO 2 was cogenerated with the formic acid.