"Weakly Ligated, Labile Ligand" Nanoparticles: The Case of Ir(0) n ·(H+Cl-) m

It is of considerable interest to prepare weakly ligated, labile ligand (WLLL) nanoparticles for applications in areas such as chemical catalysis. WLLL nanoparticles can be defined as nanoparticles with sufficient, albeit minimal, surface ligands of moderate binding strength to meta-stabilize nanoparticles, initial stabilizer ligands that can be readily replaced by other, desired, more strongly coordinating ligands and removed completely when desired. Herein, we describe WLLL nanoparticles prepared from [Ir(1,5-COD)Cl]₂ reduction under H₂, in acetone. The results suggest that H⁺Cl^--stabilized Ir(0) _n nanoparticles, herein Ir(0) _n ·(H⁺Cl^-) _a , serve as a WLLL nanoparticle for the preparation of, as illustrative examples, five specific nanoparticle products: Ir(0) _n ·(Cl^-Bu₃NH⁺) _a , Ir(0) _n ·(Cl^-Dodec₃NH⁺) _a , Ir(0) _n ·(POct₃)_0.2n (Cl^-H⁺) _b , Ir(0) _n ·(POct₃)_0.2n , and the γ-Al₂O₃-supported heterogeneous catalyst, Ir(0) _n ·(γ-Al₂O₃) _a (Cl^-H⁺) _b . (where a and b vary for the differently ligated nanoparticles; in addition, solvent can be present as a nanoparticle surface ligand). With added POct₃ as a key, prototype example, an important feature is that a minimum, desired, experimentally determinable amount of ligand (e.g., just 0.2 equiv POct₃ per mole of Ir) can be added, which is shown to provide sufficient stabilization that the resultant Ir(0) _n ·(POct₃)_0.2n (Cl^-H⁺) _b is isolable. Additionally, the initial labile ligand stabilizer HCl can be removed to yield Ir(0) _n ·(POct₃)_0.2n that is >99% free of Cl^- by a AgCl precipitation test. The results provide strong support for the weakly ligated, labile ligand nanoparticle concept and specific support for Ir(0) _n ·(H⁺Cl^-) _a as a WLLL nanoparticle.

Manganese-phosphomolybdate molecular catalysts for the electron transfer reaction of ferricyanide to ferrocyanide

Highly reduced phosphomolybdates are catalytically active for the electron transfer reaction of ferricyanide to ferrocyanide.

A mild route to solid-supported rhodium nanoparticle catalysts and their application to the selective hydrogenation reaction of substituted arenes

A clean route is described for the preparation of 1.3% (w/w) supported rhodium nanoparticle (3.0 ± 0.7 nm) catalysts onto commercial ion-exchange resins.

Anisotropic gold nanoparticle doped mesoporous boehmite films and their use as reusable catalysts in electron transfer reactions

Anisotropic Au nanoparticle (NP) doped mesoporous and oriented boehmite films of about 2 microm in thickness were prepared and used as reusable catalysts. The films were characterized by grazing incidence X-ray diffraction (GIXRD), field emission scanning electron and transmission electron microscopies, optical absorptions and surface area and pore size measurements. GIXRD of the doped films showed a preferential growth of boehmite crystallites in the (020) plane. The electron microscopy studies revealed existence of dispersed anisotropic Au NPs of approximately 15-40 nm size range and irregular Au aggregates of approximately 200-300 nm inside the mesoporous boehmite films. The optical absorption of the films showed Au-plasmon bands at 605 nm and broad absorption covering the near-infrared (NIR) region due to the anisotropic Au nanostructures. These films showed excellent catalytic activities in both the organic (p-nitrophenol to p-aminophenol by sodium borohydride) and inorganic (ferricyanide to ferrocyanide by thiosulphate) electron transfer (redox) reactions in aqueous solutions with high rate constant values. The films can be easily separated after the reaction and reused several times without any significant degradation of their original catalytic activity.

Synthesis of thick mesoporous gamma-alumina films, loading of Pt nanoparticles, and use of the composite film as a reusable catalyst

Nanocrystalline mesoporous gamma-Al2O3 film of high thickness has been developed and characterized. The films were prepared on ordinary glass substrates by a single dip-coating method using boehmite (AlOOH) sols derived from aluminum tri-sec-butoxide in presence of cetyltrimethylammonium bromide (CTAB) as structure-directing agent. The dried films were heat-treated at 500 degrees C in air to remove the organics and strengthen the network. The GIXRD of the heat-treated (500 degrees C) film shows a broad peak in the low-angle region supporting the formation of worm-hole-like disordered mesostructures. The high-angle GIXRD, FTIR, and TEM of the films confirm the formation of gamma-Al2O3. N2 adsorption-desorption analyses showed that the heat-treated (500 degrees C) film has a BET surface area of 171 m(2) g(-1) with a pore volume of 0.188 cm(3) g(-1) and mean pore diameter 4.3 nm. Pt nanoparticles (NPs) (approximately 2.7 mol % with respect to the equivalent AlO(1.5)) were generated inside the mesopores of the heat-treated films simply by soaking H2PtCl6 solutions into it, and followed by thermal decomposition at 500 degrees C. The surface area and pore volume of the Pt-incorporated film have been reduced to 101 m(2) g(-1) and 0.119 cm(3) g(-1) respectively, confirming the inclusion of Pt NPs inside the pores. FESEM and TEM studies revealed uniform distribution of Pt NPs (2-8.5 nm; average diameter 4.9 nm) in the films. Catalytic properties of the Pt-incorporated films were investigated in two model (one inorganic and other organic) systems: reduction of hexacyanoferrate(III) ions by thiosulfate to ferrocyanide, and p-nitrophenol to p-aminophenol. In both the cases, the catalyst showed excellent activities, and the reduction reactions followed smoothly, showing isosbestic points in the UV-visible spectra. The catalyst films can be separated easily after the reactions and reused several times.