Palladium Nanoparticles in Glycerol/Ionic Liquid/Carbon Dioxide Medium as Hydrogenation Catalysts

Abstract

In this work, the influence of carbon dioxide on the synthesis of palladium nanoparticles (PdNPs) in glycerol/ionic liquid mixtures and their further applications in catalytic hydrogenations was studied. In the glycerol/choline tosylalaninate/CO2 medium, small and very well-dispersed metal nanoparticles were obtained (1.3 ± 0.3 nm), exhibiting a relative narrow size distribution. Palladium nanoparticles prepared in the presence of supercritical carbon dioxide (scCO2) showed higher catalytic reactivity in comparison with those prepared in its absence. In addition, we observed a beneficial effect of CO2 in the studied hydrogenations. With the aim of rationalizing this trend, measurements of viscosity of the solvent media were carried out by using fluorescent molecular rotors, allowing the determination of diffusion coefficients for the organic substrates and molecular hydrogen. This study evidenced that CO2 causes a decrease of the viscosity of the medium and an increase of the diffusion constants of reagents including H2; consequently, PdNPs in the glycerol/choline tosylalaninate/CO2 solvent showed enhanced catalytic activity. From both process engineering and environmental points of view, it is important to highlight the efficiency of the extraction of organic products from the catalytic glycerol/ionic liquid solution by scCO2.