Abstract
Three-phase liquid–liquid gas reactions are promising strategies to combine highly active and selective homogeneous-catalysed oxidation reactions with in-situ product isolation. Several approaches like the three-phasic oxidation of biomass to formic acid (OxFA process) or the three-phasic extraction-coupled oxidative desulfurization (ECODS process) of fuels have been developed. Hereby, an aqueous polyoxometalate (POM) catalyst solution in combination with molecular oxygen as oxidant is used. However, contrary effects on the oxidation performance of the POM-catalyst were observed for different carboxylic acids as reaction products or intermediates. By using model calculations employing Density-Functional Theory (DFT) in combination with magnetic and optical spectroscopy, we could explain the experimental observations that oxalic acid activates the POM catalyst and therefore promotes its oxidation performance while acetic and especially formic acid form stable complexes with the active centres and therefore inhibit the oxidation activity. These findings greatly improve the understanding of POM-acid complexes and their effect on the catalytic performance.
Published Version
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