We report a novel method for development of magnetically recoverable catalysts prepared by thermal decomposition of palladium acetylacetonate in the presence of iron oxide nanoparticles (NPs). Depending on conditions, the reaction results either in a dispersed mixture of Pd and iron oxide NPs or in their aggregates. It was demonstrated that the Pd loading, reaction temperature, solvent, and iron oxide NP size and composition are crucial to control the reaction product including the degree of aggregation of Pd and iron oxide NPs, and the catalyst properties. The aggregation controlled by polarization and magnetic forces allows faster magnetic separation, yet the aggregate sizes do not exceed a few hundred nanometers, making them suitable for various catalytic applications. These NP mixtures were studied in a selective hydrogenation of 2-methyl-3-butyn-2-ol to 2-methyl-3-buten-2-ol, demonstrating clear differences in catalytic behavior depending on the catalyst structure. In addition, one of the catalysts was also tested in hydrogenation of 3-methyl-1-pentyn-3-ol and 3-methyl-1-nonyn-3-ol, indicating some specificity of the catalyst toward different alkyne alcohols.
The influence of the content of a hydrophilic Pd(II) compound (disodium tetrachloropalladate, Na 2 PdCl 4 ) on its adsorption and nanoparticle (NP) formation in the pores of hydrophobic micro/mesoporous hypercrosslinked polystyrene (HPS) was systematically investigated. The morphology and composition of HPS-Pd nanocomposites were studied using transmission electron microscopy, X-ray fluorescence measurements, and liquid nitrogen physisorption. The size of Pd-containing NP was found to depend on the content of the hydrophilic Pd(II) compound. Catalytic testing of these nanocomposites in the partial hydrogenation of acetylene alcohols was carried out to illustrate the influence of the NP size on the catalytic activity. The highest catalytic activity was achieved for HPS/Pd-0.1 %, forming small NP.
This work is dedicated to studying the thermal degradation of palladium acetate in commercial MN270 hypercrosslinked polystyrene in the temperature range of 200 to 325°C by means of TGA and XPS. It is shown that palladium acetate distributed in hypercrosslinked polystyrene is destroyed with the formation of palladium metal at lower temperatures than the pure salt powder. It is established that the formation and stabilization of Pd 7 -Pd 10 palladium clusters and their partial aggregation with the formation of palladium nanoparticles occur in the course of destruction. Catalytic testing of the resulting systems in selective triple bond hydrogenation in dimethylethynylcarbinol in a toluene solution at 90°C reveals their considerable supe riority in activity and selectivity over commercial Lindlar catalyst: a more than twofold increase in TOF at 97.8% selectivity.
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