Substrate–Solvent Crosstalk—Effects on Reaction Kinetics and Product Selectivity in Olefin Oxidation Catalysis

In this work, we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study demonstrated that polar and apolar aprotic solvents modulated the reactions in different ways. Experimental data showed that acetonitrile (aprotic polar) could largely hinder the reaction rate, whereas toluene (aprotic apolar) did not. In both cases, product selectivity at isoconversion was not affected. Further insights were obtained by means of neutron diffraction experiments, which confirmed the kinetic data and allowed for the proposal of a model based on substrate–solvent crosstalk by means of hydrogen bonding. In addition, the model was also validated in the ring-opening reaction (overoxidation) of styrene oxide to benzaldehyde, which progressed when toluene was the solvent (reaching 31% styrene oxide conversion) but was strongly hindered when acetonitrile was used instead (reaching only 7% conversion) due to the establishment of H-bonds in the latter. Although this model was confirmed and validated for olefin oxidation reactions, it can be envisaged that it may also be applied to other catalytic reaction systems where reaction control is critical, thereby widening its use.

Substrate-Solvent Crosstalk – Effects on Reaction Kinetics and Product Selectivity in Olefin Oxidation Catalysis

In this work we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study evidenced that polar and apolar aprotic solvents modulated the reactions in different ways. Experimental data showed that acetonitrile (aprotic polar) could hinder largely the reaction rate whereas toluene (aprotic apolar) did not. In both cases product selectivity at isoconversion was not affected. Further insights were obtained by means of neutron diffraction experiments, which confirmed the kinetic data allowing to propose a model based on substrate-solvent crosstalk by means of hydrogen bonding. In addition, the model was also validated in the ring-opening reaction (overoxidation) of styrene oxide towards benzaldehyde, which progressed when toluene was the solvent (reaching 31% styrene oxide conversion) but was strongly hindered when acetonitrile was used instead (reaching only 7% conversion), due to the establishment of H-bonds in the latter. Although this model was confirmed and validated for olefin oxidation reactions, it can be envisaged that it may also be applied to other catalytic reaction systems where reaction control is critical, while widening its use.

Electrochemical investigations of the anticorrosive behaviour of the phosphated electrogalvanized steel additionally coated with conversion layer of cerium oxide

The anticorrosive behaviour of the electrogalvanized carbon steel with PZn, PZnCa and PZnNi phosphate layers additionally coated with the conversion layers of cerium oxide in chloride-contaminated media has been studied. The composition and structure of investigated samples were characterized by scanning electron microscope SEM, while the corrosion behaviour was investigated applying voltammetric and electrochemical impedance spectroscopy EIS measurements. The data obtained have shown that all investigated samples additionally coated with cerium oxide conversion coatings exhibited better protective abilities. To summarize the results of electrochemical and SEM measurements it was stated that the most porous (F = ~1–2%) PZnNi/Ce coating exhibited the best protective abilities in a chloride-contaminated solution. Therefore, cerium ions are able to penetrate into the substrate, which is zinc coated steel, through the open pores of the PZnNi layer.