Synthesis of Supported Heterogeneous Catalysts by Laser Ablation of Metallic Palladium in Supercritical Carbon Dioxide Medium.

To obtain a supported heterogeneous catalyst, laser ablation of metallic palladium in supercritical carbon dioxide was performed in the presence of a carrier, microparticles of γ-alumina. The influence of the ablation process conditions-including supercritical fluid density, ablation, mixing time of the mixture, and laser wavelength-on the completeness and efficiency of the deposition of palladium particles on the surface of the carrier was studied. The obtained composites were investigated by scanning and transmission electron microscopy using energy dispersive spectroscopy. We found that palladium particles were nanosized and had a narrow size distribution (2-8 nm). The synthesized composites revealed high activity as catalysts in the liquid-phase hydrogenation of diphenylacetylene.

Two Approaches to the Laser-Induced Formation of Au/Ag Bimetallic Nanoparticles in Supercritical Carbon Dioxide.

Two approaches are proposed for the synthesis of bimetallic Au/Ag nanoparticles, using the pulsed laser ablation of a target consisting of gold and silver plates in a medium of supercritical carbon dioxide. The differences between the two approaches related to the field of "green chemistry" are in the use of different geometric configurations and different laser sources when carrying out the experiments. In the first configuration, the Ag and Au targets are placed side-by-side vertically on the side wall of a high-pressure reactor and the ablation of the target plates occurs alternately with a stationary "wide" horizontal beam with a laser pulse repetition rate of 50 Hz. In the second configuration, the targets are placed horizontally at the bottom of a reactor and the ablation of their parts is carried out by scanning from above with a vertical "narrow" laser beam with a pulse repetition rate of 60 kHz. The possibility of obtaining Ag/Au alloy nanoparticles is demonstrated using the first configuration, while the possibility of obtaining "core-shell" bimetallic Au/Ag nanoparticles with a gold core and a silver shell is demonstrated using the second configuration. A simple model is proposed to explain the obtained results.