Comparing the Polyoxometalate-Catalyzed Oxidation of C5-Containing Biomass to Formic Acid in a Taylor-Flow Microreactor and a Stirred-Tank Reactor.

Biomass valorization using polyoxometalate-based (POM) catalysts is a promising strategy for green and sustainable chemistry. In the modified OxFA process, various biogenic substrates can be selectively oxidized to the sustainable hydrogen carrier formic acid using the HPVMoO (HPA-5) POM catalyst in an aqueous-methanolic solution with molecular oxygen or compressed air as an oxidant. A current challenge of the mainly used stirred-tank reactors is the mass transfer limitation with respect to the effective dissolution of oxygen in the reaction media. In order to improve gas-liquid mass transfer, alternative reactor concepts are needed. Herein, we demonstrate the selective catalytic oxidation of the C5 model sugar xylose as well as the commercial C5-hydrolysate Renmatix from the Plantrose process to formic acid in a continuous Taylor-flow microreactor, allowing for effective mixing in combination with intrinsic safety and drastically reduced reaction times. This paves the way for a more efficient biomass valorization strategy with respect to industrial implementation.