Insight into the α-MnO2 boosts concentrated furfural or xylose conversion to furoic acid over 1,4-dioxane-H2O mixed solvent

Conversion of furfural or carbohydrates at concentrated feeds is highly desirable on an industrial scale of biobased fuels and chemicals but challenging. In this contribution, α-MnO2 was presented as an effective catalyst for the oxidation of concentrated furfural (10 wt%) to FA in 1,4-dioxane-H2O cosolvent media, offering satisfactory FA yields of 90%. Especially, an outstanding space-time yield (STY) of 23.2 kg m−3·h was achieved, which is the highest value achieved so far among the reported catalytic system. Importantly, 1,4-dioxane served not only functioned to improve the dispersity of furfural to strengthen the interaction of furfural with α-MnO2 but also contributed to lessening their tendency to polymerize via the solvation effect and significantly cuts down the solubility of base additive, improving the stability of furfural in 1,4-dioxane-H2O cosolvent media. Additionally, α-MnO2 with superior characteristics, including high lattice oxygen ratio as well as oxygen coordination capacity, boosting the excellent activity for furfural oxidation via the redox of Mn4+-Mn3+. Eventually, efficient synthesis of FA from concentrated xylose (20 wt%) by a two-step process without furfural separation was realized with an overall yield of 58%.