Pressure-dependent product distribution of citral hydrogenation over micelle-hosted Pd and Ru nanoparticles in supercritical carbon dioxide

In situ synthesis and testing of Ru and Pd nanoparticles as catalysts in the presence of ammonium perfluorohydrocarbo-carboxylate surfactant in supercritical carbon dioxide were carried out in a stainless steel batch reactor at 40 °C over a pressure range of 80–150 bar CO2/H2. Direct visualization of the formation of a supercritical phase at above 80 bar, followed by the formation of homogeneous microemulsions containing dispersed Ru nanoparticles and Pd nanoparticles in scCO2 at above 95–100 bar, were conducted through a sapphire window reactor using a W0W0 (molar water to surfactant ratio) of 30. The synthesised Ru and Pd nanoparticles showed interesting product distributions in the selective hydrogenation of organic molecules, depending critically on the density and polarity of the fluid (which in turn depends on the pressure applied). Thus, selective hydrogenation of the citral molecule, which contains three reducible groups (aldehydes and double bonds at the 2,3 and 6,7 positions), is feasible as a chemical probe.