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The possibility of immobilizing ex situ‐synthesized colloidal bimetallic nanoparticles (NPs) of well‐defined characteristics inside hollow core photonic crystal fiber (HC‐PCF) microreactors is demonstrated. With the developed method, PtNi clusters remain strongly attached to the fiber core and can be used as active catalysts for the hydrogenation of an azobenzene dye. The study revealed that optical transmission exhibits a size‐dependent behavior, i.e., smaller NPs bring in less optical signal loss. Sufficient light transmission was achieved for all particle sizes. Furthermore, with these catalytic PCF microreactors, kinetic data can be obtained with a much lower amount of precious metals compared to a conventional batch reactor, opening a new pathway for in situ catalyst screening.

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.

A liquid core waveguide membrane microreactor combining intense light matter interaction for in situ sensing and/or photo activation and excellent gas‐liquid mass transfer is presented. Basis is a liquid‐filled Teflon AF tube, which provides light transmission within the liquid core and gas permeation through the wall. The study shows that a wide spectral range (UV‐vis) with relatively low optical losses is accessible. A working regime preventing gas bubble formation was deduced for semi‐batch and in flow operation for gas pressures up to 8 bar. Residence time distribution experiments revealed Bodenstein numbers from 21 to 60 in the studied flow range. As example, the methylene blue catalyzed oxidation of D‐glucose by O2 was studied at different pressures, while methylene blue was monitored in situ.

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

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