Magic number Pt13 and misshapen Pt12 clusters: which one is the better catalyst?

Explaining the Size Dependence in Platinum-Nanoparticle-Catalyzed Hydrogenation Reactions

Hydrogenation reactions are industrially important reactions that typically require unfavorably high H₂ pressure and temperature for many functional groups. Herein we reveal surprisingly strong size-dependent activity of Pt nanoparticles (PtNPs) in catalyzing this reaction. Based on unambiguous spectral analyses, the size effect has been rationalized by the size-dependent d-band electron structure of the PtNPs. This understanding enables production of a catalyst with size of 1.2 nm, which shows a sixfold increase in turnover frequency and 28-fold increase in mass activity in the regioselective hydrogenation of quinoline, compared with PtNPs of 5.3 nm, allowing the reaction to proceed under ambient conditions with unprecedentedly high reaction rates. The size effect and the synthesis strategy developed herein may provide a general methodology in the design of metal-nanoparticle-based catalysts for a broad range of organic syntheses.

Partially oxidized iridium clusters within dendrimers: size-controlled synthesis and selective hydrogenation of 2-nitrobenzaldehyde

Iridium clusters nominally composed of 15, 30 or 60 atoms were size-selectively synthesized within OH-terminated poly(amidoamine) dendrimers of generation 6. Spectroscopic characterization revealed that the Ir clusters were partially oxidized. All the Ir clusters efficiently converted 2-nitrobenzaldehyde to anthranil and 2-aminobenzaldehyde under atmospheric hydrogen at room temperature in toluene via selective hydrogenation of the NO2 group. The selectivity toward 2-aminobenzaldehyde over anthranil was improved with the reduction of the cluster size. The improved selectivity is ascribed to more efficient reduction than intramolecular heterocyclization of a hydroxylamine intermediate on smaller clusters that have a higher Ir(0)-phase population on the surface.

Tailoring the structure and electronic properties of platinum and gold–platinum nanocatalysts towards enhanced O2 activation

The structural designing of a precious metal molecular catalyst by doping is proved to significantly enhance its activity.

Catalytic activity of Pt38 in the oxygen reduction reaction from first-principles simulations

Mechanism of OH_ads/Pt₃₈ diffusion via transient hydronium species in first-principles molecular dynamics simulations.

Formation of fluorescent platinum nanoclusters using hyper-branched polyethylenimine and their conjugation to antibodies for bio-imaging

Fluorescent Pt NCs@PEI were formed in the cavities coiled by PEI ligands and bio-imaged HeLa cells via conjugation with antibodies.

Grouping and aggregation of ligand protected Au9 clusters on TiO2 nanosheets

Au₉ clusters forming groups of clusters on titania nanosheets at least partially consist of individual clusters both before and after annealing. Au₉ clusters also can attach as individual clusters.

Reactivity of diatomics and of ethylene on zeolite-supported 13-atom platinum nanoclusters

CO and NO react on hydrogen-covered 13-atom Pt clusters, O₂ does not, and the hydrogenation of ethene shows structure sensitivity.

Effect of graphene support on large Pt nanoparticles

Large scale DFT calculations of Pt nanoparticles supported on graphene explore the non-trivial interplay of size and support effects.

A self-assembling dendritic reactor: versatile formation of characteristic patterns with nanoscale dimension

Spherical dendrimers with phenylazomethine backbones are modified onto atomically flat mica or graphite substrates with a simple solvent based spin-coating method, and the resulting surfaces are observed by atomic force microscopy. Especially on the mica substrate, dendrimers form very fine and highly regular patterns with aligned nano-dot arrays and lines. An important observation is that the interval of each dot or line is ≈400 nm whereas previously reported self-assembling patterns exhibit longer intervals than 5 μm. It is revealed that spherical dendrimers with relatively low intermolecular interactions without any terminal modifications are suitable for the fine self-assembling pattern formation. This fact suggests that the regular pattern arises from a physical dissipative structure formation due to a fingering instability induced by Marangoni convection but not by anisotropic intermolecular interactions.

Evolution of self-assembled ZnTe magic-sized nanoclusters

Three families of ZnTe magic-sized nanoclusters (MSNCs) were obtained exclusively using polytellurides as a tellurium precursor in a one-pot reaction by simply varying the reaction temperature and time only. Different ZnTe MSNCs exhibit different self-assembling or aggregation behavior, owing to their different structure, cluster size, and dipole-dipole interactions. The smallest family of ZnTe MSNCs (F323) does not reveal a crystalline structure and as a result assembles into lamellar triangle plates. Continuous heating of as synthesized ZnTe F323 assemblies resulted in the formation of ZnTe F398 MSNCs with wurzite structure and concomitant transformation into lamellar rectangle assemblies with the organization of nanoclusters along the ⟨002⟩ direction. Further annealing of ZnTe F398 assembled lamellar rectangles leads to full organization of MSNCs in all directions and formation of larger ZnTe F444 NCs that spontaneously form ultrathin nanowires following an oriented attachment mechanism. The key step in control over the size distribution of ZnTe ultrathin nanowires is, in fact, the growth mechanism of ZnTe F398 MSNCs; namely, the step growth mechanism enables formation of more uniform nanowires compared to those obtained by continuous growth mechanism. High yield of ZnTe nanowires is achieved as a result of the wurzite structure of F398 precursor. Transient absorption (TA) measurements show that all three families possess ultrafast dynamics of photogenerated electrons, despite their different crystalline structures.

Confined platinum nanoparticle in carbon nanotube: structure and oxidation

Confined metal particles show unexpected structural versatility, leading to higher stability and better catalytic performance, as predicted from first-principles-based global optimization methods.

Being two is better than one—catalytic reductions with dendrimer encapsulated copper- and copper–cobalt-subnanoparticles

Copper and copper–cobalt subnanoparticles have been synthesized using 4-carbomethoxypyrrolidone terminated PAMAM-dendrimers as templates.

Reactivities of platinum subnanocluster catalysts for the oxidation reaction of alcohols

The size-dependent catalytic activity for alcohol oxidation was investigated using the platinum subnanoclusters synthesized by the dendrimer template method.

The effect of the morphology of supported subnanometer Pt clusters on the first and key step of CO2 photoreduction

Other than the chemistry of the Pt cluster, the cluster morphology also determines CO₂ binding, attributed to structural fluxionality and bonding competitions among Pt atoms and CO₂.

Enhancement of platinum mass activity on the surface of polymer-wrapped carbon nanotube-based fuel cell electrocatalysts

Cost reduction and improved durability are the two major targets for accelerating the commercialization of polymer electrolyte membrane fuel cells (PEFCs). To achieve these goals, the development of a novel method to fabricate platinum (Pt)-based electrocatalysts with a high mass activity, deposited on durable conductive support materials, is necessary. In this study, we describe a facile approach to grow homogeneously dispersed Pt nanoparticles (Pt) with a narrow diameter distribution in a highly controllable fashion on polymer-wrapped carbon nanotubes (CNTs). A PEFC cell employing a composite with the smallest Pt nanoparticle size (2.3 nm diameter) exhibited a ~8 times higher mass activity compared to a cell containing Pt with a 3.7 nm diameter. This is the first example of the diamter control of Pt on polymer-wrapped carbon supporting materials, and the study opens the door for the development of a future-generation of PEFCs using a minimal amount of Pt.

Precision synthesis of subnanoparticles using dendrimers as a superatom synthesizer

Classical metal-based nanomaterials come in two prominent types: a mononuclear or multinuclear complex chemically stabilized by organic ligands or a nanoparticle (also called a nanorod, nanosheet, or nanocrystal) physically stabilized by inorganic or polymer supports. Over the last decade, a class of superatoms that lies between these categories of materials has attracted attention because their properties are dramatically different from those typically ascribed to their component elements. Typically the superatoms include a specific, low number of metallic atoms. Because a one-atom difference can alter the properties of these superatoms, their synthesis must be ultraprecise, requiring one-atom resolution. To date, researchers have only been able to prepare monodisperse superatoms using gas-phase synthesis followed by purification through a flight tube. Though this technique provides monodisperse superatoms, it does not allow researchers to produce them in large quantites. Other researchers have proposed ligand-assisted liquid-phase synthesis as an alternative, but this technique is only useful for a few stable "magic number" clusters. Recently researchers have developed a new approach for the synthesis of superatoms that employs a novel class of molecular templates, which can define the number of metal ions or salts precisely. As a result, researchers can now synthesize nanoparticles or even subnanoparticles successfully. A dendrimer-type template has proven to be especially useful for ultraprecise control of the atomicity of the product, but it works with a full range of metal elements. In this Account, we highlight recent advances in the precise preparation of metal-assembling complexes using the dendrimer as a template. Next we discuss the selective assembly of subnanoparticles that utilize the dendrimer as a superatom synthesizer. The resulting subnanoparticles are almost monodisperse, and as a result, some of them exhibited distinctive characteristics based on their atomicity. For example, because of the quantum-size effect, the reduction in particle size of TiO2 and other metal-oxide subnanoparticles led to a significant shift in the band-gap energy. In addition, a miniaturized platinum particle less than 1 nm in diameter showed unexpectedly high catalytic activity for the oxygen reduction reaction (ORR) and other related reactions. Of particular note, in all these examples, this substantial change in their properties arose out of a single-atom difference in the atomicity. These results suggest that next-generation subnanoparticle design could play an important role in new materials and offer an additional palette of physical and chemical properties for new applications.

Photoactive Dendrimer for Water Photoreduction: A Scaffold to Combine Sensitizers and Catalysts

We report on the synthesis and characterization of platinum nanoparticles (PtNps) inside the cavities of a PAMAM dendrimer decorated with [Ru(bpy)3](2+) units at the periphery. The phosphorescent ruthenium complexes are used as signaling units of the Pt(2+) complexation in the dendritic architecture and as photosensitizer units in the photocatalytic production of H2 from water. This is the first example of water photoreduction in which the catalyst and the sensitizer are anchored on a dendritic molecular scaffold. This study provides a new outlook in the design of new supramolecular systems and materials for developing artificial photosynthesis.

Stepwise radial complexation from the outer layer to the inner layer of a dendritic ligand: a phenylazomethine dendrimer with an inverted coordination sequence

A meta-substituted phenylazomethine dendrimer was discovered as a dendritic ligand that sequentially coordinates to Lewis acids from the outer layer to the inner layer in a stepwise radial fashion.

Atomic under-coordination fascinated catalytic and magnetic behavior of Pt and Rh nanoclusters

Atomic under-coordination fascinated catalytic and magnetic properties of Pt and Rh nanoclusters have been studied by DFT calculations, and consistency with the calculation and experimental results confirmed predications based on BOLS correlation.