Alcoholic solvents, especially methanol, show an activating affect for heteropolyacids in homogenously catalysed glucose transformation reactions. In detail, they manipulate the polyoxometalate‐based catalyst in a way that thermodynamically favoured total oxidation to CO2 can be completely supressed. This allows a nearly 100 % carbon efficiency in the transformation reaction of glucose to methyl formate in methanolic solution at mild reaction conditions of 90 °C and 20 bar oxygen pressure. By using powerful spectroscopic tools like 51V‐NMR and continuous wave EPR we could unambiguously prove that the vanadate‐methanol‐complex[VO(OMe)3]n is responsible for the selectivity shift in methanolic solution compared to the aqueous reference system.

In this work we combined kinetic studies for aqueous-phase glucose oxidation in a high-pressure autoclave setup with catalyst reoxidation studies in a liquid-core waveguide membrane reactor. Hereby, we investigated the influence of Nb-and Ta-doping on Mo-based Keggin-polyoxometalates for both reaction steps independently. Most importantly, we could demonstrate a significant increase of glucose oxidation kinetics by Ta-and especially Nb-doping by factors of 1.1 and 1.5 compared to the classical HPA-Mo. Moreover, activation energies for the substrate oxidation step could be significantly reduced from around 80 kJ mol À1 for the classical HPA-Mo to 61 kJ mol À1 for the Ta-and 55 kJ mol À1 for the Nb-doped species, respectively. Regarding catalyst reoxidation kinetics, the doping did not show significant differences between the different catalysts.

The recently developed polyoxometalate (POM)− ionosolv concept offers an interesting strategy to generate two valuable product streams from lignocellulosic biomass, a solid cellulose-rich pulp and short-chain carboxylic acids like formic acid and acetic acid in a simple and cost-efficient manner. This study aimed to find optimum parameters for the two steps of the transformation by performing a sensitivity analysis on the initial ionosolv fractionation step as well as kinetic investigations of the following POM-catalyzed oxidation step. The results were transferred to the POM−ionosolv concept to find the overall process optimum. Beech wood was used as an industrially relevant substrate for ionosolv fractionation with the low-cost ionic liquid triethylammonium sulfate, [TEA][HSO 4 ], and the HPA-5 [H 8 PV 5 Mo 7 O 40 ] POM catalyst for the oxidation of the dissolved components in an oxygen atmosphere. As the most seminal finding, we defined optimum conditions of 125 °C, 1200 rpm, 30 bar oxygen, and 24 h reaction time in ionic liquid containing 70% water, achieving 72% xylose extraction from beech wood, which resulted in a 39% formic acid yield. We suggest that the fractionation and catalytic conversion are carried out at different water contents for maximum conversion efficiency for each step.

The selective oxidative conversion of seven representative fully characterized biomasses recovered as secondary feedstocks from the agroindustry is reported. The reaction system, known as the “OxFA process,” involves a homogeneous polyoxometalate catalyst (H8PV5Mo7O40), gaseous oxygen, p-toluene sulfonic acid, and water as solvent. It took place at 20 bar and 90 °C and transformed agro-industrial wastes, such as coffee husks, cocoa husks, palm rachis, fiber and nuts, sugarcane bagasse, and rice husks into biogenic formic acid, acetic acid, and CO2 as sole products. Even though all samples were transformed; remarkably, the reaction obtains up to 64, and 55% combined yield of formic and acetic acid for coffee and cocoa husks as raw material within 24 h, respectively. In addition to the role of the catalysts and additive for promoting the reaction, the influence of biomass components (hemicellulose, cellulose and lignin) into biogenic formic acid formation has been also demonstrated. Thus, these results are of major interest for the application of novel oxidation techniques under real recovered biomass for producing value-added products. Graphical abstract