In-Situ Investigations of Polyoxometalate-Catalysed Biomass Oxidation to Formic Acid by Using Multinuclear High Resolution Flow NMR Spectroscopy

Biomass valorisation over polyoxometalate-based (POM) catalysts is a promising strategy for green and sustainable chemistry. In order to further improve such processes e. g. by using different additives, a better understanding of the chemical influence of various additives on the catalyst is paramount. The main objective of this study is to gain a deeper understanding of the effects caused by various additives on the catalytically active vanadium species in the selective aerobic oxidation of carbohydrates to formic acid (esters). After carefully choosing a suitable model system, the oxidation of glycolaldehyde using the heteropolyacid H₅PV₂Mo₁₀O₄₀ (HPA-2) as a catalyst was studied in situ by Flow Nuclear magnetic resonance (FlowNMR) spectroscopy. These measurements allowed to identify the catalytically active isomer of the HPA-2-catalyst and to observe the influence of additives on the reaction kinetics in situ. These findings provide a good basis for further improving POM-based catalytic aerobic oxidation of biomass.