Catalytic Valorization of Humins by Selective Oxidation Using Transition-Metal-Substituted Keggin-Type Polyoxometalate Catalysts

The main objective of this study was to gain a deeper understanding of oxidative valorization of humins using polyoxometalate (POM) catalysts. Based on experiments using individual monofuran derivatives as a substrate, evident reaction pathways for the conversion to maleic acid were postulated. By analogous routes, difuran derivatives or branched furan rings could also be converted to maleic acid and formic acid, respectively. Hereby, the monovanadium-substituted catalyst was found to be superior compared to other structures in terms of activity and selectivity due to its unique electrochemical properties. In detail, H4[PVMo11O40] showed the lowest peak potential in Square-Wave-Voltammetry measurements, achieving the highest activity and carboxylic acid selectivity. Hereby, a deeper understanding of the selective oxidation of humin model substrates like furan derivatives of varying complexity could be achieved. Therefore, helpful conclusions can be drawn for the transformation of humins representing a decisive step toward efficient processes for their valorization.