Methanol oxidation reaction on core-shell structured Ruthenium-Palladium nanoparticles: Relationship between structure and electrochemical behavior

In this work the relationship between structural composition and electrochemical characteristics of Palladium(Pd)-Ruthenium(Ru) nanoparticles during alkaline methanol oxidation reaction is investigated. The comparative study of a standard alloyed and a precisely Ru-core-Pd-shell structured catalyst allows for a distinct investigation of the electronic effect and the bifunctional mechanism. Core-shell catalysts benefit from a strong electronic effect and an efficient Pd utilization. It is found that core-shell nanoparticles are highly active towards methanol oxidation reaction for potentials â¥0.6 V, whereas alloyed catalysts show higher current outputs in the lower potential range. However, differential electrochemical mass spectrometry (DEMS) experiments reveal that the methanol oxidation reaction on core-shell structured catalysts proceeds via the incomplete oxidation pathway yielding formaldehyde, formic acid or methyl formate. Contrary, the alloyed catalyst benefits from the Ru atoms at its surface. Those are found to be responsible for high methanol oxidation activity at lower potentials as well as for complete oxidation of CH3OH to CO2 via the bifunctional mechanism. Based on these findings a new Ru-core-Pd-shell-Ru-terrace catalyst was synthesized, which combines the advantages of the core-shell structure and the alloy. This novel catalyst shows high methanol electrooxidation activity as well as excellent selectivity for the complete oxidation pathway

Kinetic analysis of the partial synthesis of artemisinin: Photooxygenation to the intermediate hydroperoxide

The price of the currently best available antimalarial treatment is driven in large part by the limited availability of its base drug compound artemisinin. One approach to reduce the artemisinin cost is to efficiently integrate the partial synthesis of artemisinin starting from its biological precursor dihydroartemisinic acid (DHAA) into the production process. The optimal design of such an integrated process is a complex task that is easier to solve through simulations studies and process modelling. In this article, we present a quantitative kinetic model for the photooxygenation of DHAA to an hydroperoxide, the essential initial step of the partial synthesis to artemisinin. The photooxygenation reactions were studied in a two-phase photo-flow reactor utilizing Taylor flow for enhanced mixing and fast gas-liquid mass transfer. A good agreement of the model and the experimental data was achieved for all combinations of photosensitizer concentration, photon flux, fluid velocity and both liquid and gas phase compositions. Deviations between simulated predictions and measurements for the amount of hydroperoxide formed are 7.1 % on average. Consequently, the identified and parameterized kinetic model is exploited to investigate different behaviors of the reactor under study. In a final step, the kinetic model is utilized to suggest attractive operating windows for future applications of the photooxygenation of DHAA exploiting reaction rates that are not affected by mass transfer limitations

Use of 'smart interfaces' to improve the liquid-sided mass transport in a falling film microreactor

It has been shown in the past, that the use of a falling film microreactor is advantageous for operation conditions, during which conventional processing equipment reaches its limits. The reactor design facilitates the development of well controlled, stable menisci. The very large specific gas/liquid interface (up to 20 000 m2/m3) provides excellent mass transfer capabilities between the phases. Nevertheless, despite the excellent gas/liquid mass transfer that occurs the chemical reactions are limited by the mass transfer within the phases. Commonly, the rate limiting step is the diffusive mass transport within the liquid side. This study investigates the potential of falling film microreactors equipped with structured channels to enhance the mass transfer within the liquid phase. To do this, four different reaction plates have been fabricated and are experimentally examined. Besides two reaction plates with straight, unstructured channels (channel width: 600 or ), one plate with fins and one plate with additional grooves in straight wide channels forming a so-called staggered herringbone mixer are used. Taking carbon dioxide absorption as benchmark reaction it is shown that structured channel walls can significantly enhance the mass transfer within the liquid phase. This leads to an increase of the overall performance of the benchmark reaction. Properly chosen channel geometry can increase the conversion by up to 42%. Hence, by using an optimal reaction plate it is possible to more than double the flow rate, without any loss in conversion