Palladium(0) Nanoparticle Formation, Stabilization, and Mechanistic Studies: Pd(acac)(2) as a Preferred Precursor, [Bu4N](2)HPO4 Stabilizer, plus the Stoichiometry, Kinetics, and Minimal, Four-Step Mechanism of the Palladium Nanoparticle Formation and Subsequent Agglomeration Reactions

Palladium(0) nanoparticles continue to be important in the field of catalysis. However, and despite the many prior reports of Pd(0)(n) nanoparticles,, missing is a study that reports the kinetically controlled formation of Pd(0)(n) nanoparticles with the simple stabilizer [Bu4N](2)HPO4 in an established, balanced formation reaction where the kinetics and mechanism of the nanoparticle-formation reaction are also provided. It is just such studies that are the focus of the present work. Specifically, the present studies reveal that Pd(acac)(2), in the presence of 1 equiv of [Bu4N](2)HPO4 as stabilizer in propylene carbonate, serves as a preferred precatalyst for the kinetically controlled nucleation following reduction under 40 +/- 1 psig initial H-2 pressure at 22.0 +/- 0.1 degrees C to yield 7 +/- 2 nm palladium(0) nanoparticles. Studies of the balanced stoichiometry of the Pd(0)(n) nanoparticle-formation reaction shows that 1.0 Pd(acac)(2) consumes 1.0 equiv of H-2 and produces 1.0 equiv of Pd(0)(n) while also releasing 2.0 +/- 0.2 equiv of acetylacetone. The inexpensive, readily available HPO42- also proved, to be as effective a Pd(0)(n) nanoparticle stabilizer as the more anionic, sterically larger, "Gold Standard" stabilizer P2W15Nb3O629-. The kinetics and associated minimal mechanism of formation of the [Bu4N](2)HPO4-stabilized Pd(0)(n) nanoparticles are also provided, arguably the most novel part of the present studies, specifically the four-step mechanism of nucleation (A -> B, rate constant k(1)), autocatalytic surface growth (A + B -> 2B, rate constant k(2)), bimolecular agglomeration (B + B -> C, rate constant k(3)), and secondary autocatalytic surface growth (A + C -> 1.5C, rate constant k(4)), where A is Pd(acac)(2), B represents the growing, smaller Pd(0)(n) nanopartieles, and C represents the larger, most catalytically active Pd(0)(n) nanoparticles. Additional details on the mechanism and catalytic properties of the resultant Pd(0)(n)center dot HPO42- nanoparticles are provided in this work.


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The synthesis of highly stable ultrasmall monodisperse populations of palladium nanoparticles in the range of 1-3 nm in size was achieved via polyol reduction within 1,2-dioleoyl-sn-glycero-3-phosphor-rac(1-glycerol) liposomal nanoreactors exploiting glycerol as both reducing and stabilizing agent. The liposome-based green method was compared with synthesis in solution, and the reducing agent concentration and the lipidic composition of the liposomal nanoreactors were demonstrated to have a strong effect on...
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Active Janus Particles at Interfaces of Liquid Crystals
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We report an investigation of the active motion of silica palladium Janus particles (JPs) adsorbed at interfaces formed between nematic liquid crystals (LCs) and aqueous phases containing hydrogen peroxide (H2O2). In comparison to isotropic oil aqueous interfaces, we observe the elasticity and anisotropic viscosity of the nematic phase to change qualitatively the active motion of the JPs at the LC interfaces. Although contact line pinning on the surface of the JPs is observed. to restrict out-of-plane rotat...
Citation Formats
S. Özkar, “Palladium(0) Nanoparticle Formation, Stabilization, and Mechanistic Studies: Pd(acac)(2) as a Preferred Precursor, [Bu4N](2)HPO4 Stabilizer, plus the Stoichiometry, Kinetics, and Minimal, Four-Step Mechanism of the Palladium Nanoparticle Formation and Subsequent Agglomeration Reactions,” LANGMUIR, pp. 3699–3716, 2016, Accessed: 00, 2020. [Online]. Available: