Organic transformations on metal nanoparticles: controlling activity, stability, and recyclability by support and solvent interactions

Design of Glycerol-Based Solvents for the Immobilization of Palladium Nanocatalysts: A Hydrogenation Study

Twenty-one green solvents, including glycerol-derived ethers, and their eutectic mixtures with two renewable ammonium salts, were used for the straightforward synthesis, stabilization, and immobilization of palladium nanoparticles (Pd NPs). The nature of the solvent allows tuning of the characteristics and properties of resulting catalytic systems in terms of particle size and morphology, stability, reactivity, and recoverability. Pd NPs immobilized in glycerol-based solvents were applied in the catalytic hydrogenation of alkenes, alkynes, and carbonyl compounds, as well as in the selective semihydrogenation of alkynes to alkenes. The optimal experimental parameters and the influence on the reactivity of the physicochemical properties of solvent, mainly the viscosity, were studied. Moreover, the most active and recoverable catalytic system, Pd NPs/N00Cl-100, was fully characterized both in the liquid phase and in the solid state, and its deactivation upon recovery was analyzed.

RhNPs supported on N-functionalized mesoporous silica: effect on catalyst stabilization and catalytic activity

Amine and nicotinamide groups grafted on ordered mesoporous silica (OMS) were investigated as stabilizers for RhNPs used as catalysts in the hydrogenation of several substrates, including carbonyl and aryl groups. Supported RhNPs on functionalized OMS were prepared by controlled decomposition of an organometallic precursor of rhodium under dihydrogen pressure. The resulting materials were characterized thoroughly by spectroscopic and physical techniques (FTIR, TGA, BET, SEM, TEM, EDX, XPS) to confirm the formation of spherical rhodium nanoparticles with a narrow size distribution supported on the silica surface. The use of nicotinamide functionalized OMS as a support afforded small RhNPs (2.3 ± 0.3 nm), and their size and shape were maintained after the catalyzed acetophenone hydrogenation. In contrast, amine-functionalized OMS formed RhNP aggregates after the catalytic reaction. The supported RhNPs could selectively reduce alkenyl, carbonyl, aryl and heteroaryl groups and were active in the reductive amination of phenol and morpholine, using a low concentration of the precious metal (0.07-0.18 mol%).

Proximity Effects of Methyl Group on Ligand Steric Interactions and Colloidal Stability of Palladium Nanoparticles

Metal nanoparticle catalysts functionalized with small, well-defined organic ligands are important because such systems can provide a spatial control in the catalyst-substrate interactions. This article describes the synthesis, stability, and catalytic property evaluations of four different Pd nanoparticles capped with constitutional isomers of pentanethiolate ligands that have either a straight chain or an alkyl chain with one methyl group at different locations (α, β, or γ from the surface-bound sulfur). The structure and composition analyses of Pd nanoparticles confirm that they have similar average core sizes and organic ligand contents. The presence of methyl group at α position is found to lower the capping ability of short ligands and thus make Pd nanoparticles to lose their colloidal stability during the catalytic reactions. The overall activity and selectivity for hydrogenation and isomerization of pentene and allylbenzene derivatives are investigated for each combination of ligand and substrate. Catalysis results indicate that steric interactions between the ligands on the metal catalyst surface and the alkene substrates are a factor in controlling the activity of Pd nanoparticles. In particular, Pd nanoparticles capped with pentanethiolate isomer having a methyl group at α position exhibit poor and inconsistent catalytic activity due to its low colloidal stability. The presence of a methyl group at β position mildly interferes the adsorption of alkene group on the nanoparticle surface resulting in lower conversion yields. Interestingly, a methyl group at γ position only has a minimal effect on the catalytic property of Pd nanoparticles exhibiting similar catalysis results with Pd nanoparticles capped with straight chain pentanethiolate ligands. This indicates the proximity of steric group at the reactive site controls the nanoparticle activity for surface oriented reactions, such as hydrogenation and isomerization of alkenes in addition to their colloidal stability.

Electrocatalytic Reduction of Oxygen on Platinum Nanoparticles in the Presence and Absence of Interactions with the Electrode Surface

We report that ultraviolet/ozone (UV/O3) treatment can be used to remove sixth-generation, hydroxyl-terminated poly(amidoamine) (PAMAM) dendrimers from dendrimer-encapsulated Pt nanoparticles (Pt DENs) previously immobilized onto a pyrolyzed photoresist film (PPF) electrode. Results from X-ray photoelectron spectroscopy, scanning transmission electron microscopy, and electrochemical experiments indicate that removal of the dendrimer proceeds without changes to the size, shape, or electrocatalytic properties of the encapsulated nanoparticles. The UV/O3 treatment did not damage the PPF electrode. The electrocatalytic properties of the DENs before and after removal of the dendrimer were nearly identical.

Palladium nanoparticles stabilised by cinchona-based alkaloids in glycerol: efficient catalysts for surface assisted processes

Cinchona-based alkaloids led to well-dispersed palladium nanoparticles in neat glycerol, leading to efficient eco-friendly catalytic phases in hydrogenations and hydrodehalogenations.

Active hydrogenation Rh nanocatalysts protected by new self-assembled supramolecular complexes of cyclodextrins and surfactants in water

New supramolecular assemblies as protective agents of rhodium(0) nanoparticles for hydrogenation of various substrates in water.

Gold nanoparticles supported in zirconia-ceria mesoporous thin films: a highly active reusable heterogeneous nanocatalyst

Gold nanoparticles (NP) trapped in the mesopores of mixed zirconia-ceria thin films are prepared in a straightforward and reproducible way. The films exhibit enhanced stability and excellent catalytic activity in nitro-group reduction by borohydride and electrocatalytic activity in CO and ethanol oxidation and oxygen reduction.

Glycerol as suitable solvent for the synthesis of metallic species and catalysis

This Minireview considers the foremost reported works involving glycerol as a solvent in the synthesis of organometallic complexes and metallic nanoparticles. This analysis highlights their catalytic applications. A special emphasis is devoted to the ability of glycerol to immobilize nanometric species, which, in turn, enables an efficient recycling of the catalytic phase to give metal-free organic products.

Recent NMR developments applied to organic-inorganic materials

In this contribution, the latest developments in solid state NMR are presented in the field of organic-inorganic (O/I) materials (or hybrid materials). Such materials involve mineral and organic (including polymeric and biological) components, and can exhibit complex O/I interfaces. Hybrids are currently a major topic of research in nanoscience, and solid state NMR is obviously a pertinent spectroscopic tool of investigation. Its versatility allows the detailed description of the structure and texture of such complex materials. The article is divided in two main parts: in the first one, recent NMR methodological/instrumental developments are presented in connection with hybrid materials. In the second part, an exhaustive overview of the major classes of O/I materials and their NMR characterization is presented.

Metal−organic framework encapsulated Pd nanoparticles: towards advanced heterogeneous catalysts

Palladium precursors were encapsulated through ligand design prior to the MOF assembly, achieving uniformly distributed Pd NPs inside the cavities of MOFs. The embedded Pd NPs exhibited significantly improved catalytic efficiencies as compared to those synthesized by traditional impregnation method, due to the nano-confinement and electron-donation effects offered by MOFs.