Enhancing Biogenic Formic Acid Production in the Modified OxFA Process by Acetonitrile Addition

Developing homogeneously catalyzed, selective biomass transformation techniques toward an industrially viable biomass valorization process is one of the major tasks of a more sustainable chemical industry. Specifically, the production of short-chain carboxylic acids like formic acid (FA) in the OxFA process is a promising strategy. In this study, we show the beneficial effect of using acetonitrile as a co-solvent in the modified OxFA process outperforming methanol, demonstrating improved reaction kinetics combined with high selectivity for the HPA-2 (H₅PV₂Mo₁₀O₄₀) catalyzed oxidation of xylose to FA. Ex situ spectroscopic ⁵¹V-NMR as well as optical UV-vis and electrochemical SWV investigations in combination with advanced pulse EPR measurements and DFT calculations clearly reveal the direct interactions of the co-solvents methanol and acetonitrile with the HPA-2 catalyst. This leads to improved selectivity for methanol addition whereby acetonitrile addition leads to both enhanced kinetics and improved selectivity on the kinetics of xylose oxidation to FA compared to the classical OxFA process in pure aqueous solution. This study shows interesting new correlations allowing us to further push the limits of the OxFA technology toward higher productivity.