Isophotonic reactor for the precise determination of quantum yields in gas, liquid, and multi-phase photoreactions

Photocatalytic processes are an emerging field with a multitude of potential applications ranging from waste and wastewater treatment over fine chemical production to artificial photosynthesis. Knowing the quantum yield in a photoreaction is thereby essential to both, the selection of suitable photocatalysts and the design of optimized photoreactors. Nevertheless, the precise determination of quantum yields as function of the operating conditions is still a challenge without standardized and reliable procedures and apparatuses. Herein a novel approach for the accurate determination of quantum yields based on a tailored, 3D-printable photoreactor and 3D optical modelling is reported. Besides wavelength, temperature, and reactant concentration control, the unique optical design of an isophotonic reactor enables the control of the local volumetric rate of photon absorption to be homogeneous throughout the reaction volume. The validity of the approach is demonstrated by determining the quantum yield of the standard potassium ferrioxalate actinometer. Further, the adaptability to any gas, liquid, or multi-phase photoreaction is outlined by showcasing the ability of the approach with an exemplary aerogel-supported titania-based methanol reforming photocatalyst. The revealed subtlety and complex nature of the quantum yield in the methanol reforming system highlights the need for meticulous analysis and standardization of the determination of quantum yields and thereby underlines the value of the proposed approach. Software tools and print files provided alongside the publication facilitate adaptation and further development of the approach by researchers in the field

Investigation of mass transport processes in a microstructured membrane reactor for the direct synthesis of hydrogen peroxide

Microstructured membrane reactors present a promising approach to master the productivity and safety challenges during the direct synthesis of hydrogen peroxide. However, various mass transport processes occur in this complex system. In order to gain a deeper understanding of these processes, the saturation and desaturation behaviour of the liquid reaction medium with the gaseous reactants is investigated experimentally to examine possible cross-contamination. Moreover, the employed PDMS membrane’s permeances to hydrogen and oxygen are researched at different pressures, by using a variable-pressure/constant-volume setup for the behaviour at ambient pressure and a constant-pressure/variable-volume setup for the behaviour at elevated pressures. A mathematical model in MATLAB is applied to simulate the results. It is shown that a certain desaturation of the gasses through the membrane occurs, and the results are underlined by the modelled ones using a solution-diffusion model in MATLAB. Thus a constant flushing of the gas channels of the reactor is required for safety reasons. Moreover, the measured permeance values indicate that the species transport is mainly limited by the diffusion in the liquid phase and not the membrane resistance