Direct atomic imaging and density functional theory study of the Au24Pd1 cluster catalyst

Atomically precise Au and Ag nanoclusters doped with a single atom as model alloy catalysts

Gold and silver nanoclusters (NCs) composed of <200 atoms are novel catalysts because their catalytic properties differ significantly from those of the corresponding bulk surface and can be dramatically tuned by the size (number of atoms). Doping with other metals is a promising approach for improving the catalytic performance of Au and Ag NCs. However, elucidation of the origin of the doping effects and optimization of the catalytic performance are hampered by the technical challenge of controlling the number and location of the dopants. In this regard, atomically precise Au or Ag (Au/Ag) NCs protected by ligands or polymers have recently emerged as an ideal platform because they allow regioselective substitution of single Au/Ag constituent atoms while retaining the size and morphology of the NC. Heterogeneous Au/Ag NC catalysts doped with a single atom can also be prepared by controlled calcination of ligand-protected NCs on solid supports. Comparison of thermal catalysis, electrocatalysis, and photocatalysis between the single-atom-doped and undoped Au/Ag NCs has revealed that the single-atom doping effect can be attributed to an electronic or geometric origin, depending on the dopant element and position. This minireview summarizes the recent progress of the synthesis and catalytic application of single-atom-doped, atomically precise Au/Ag NC catalysts and provides future prospects for the rational development of active and selective metal NC catalysts.

Dynamic behaviour of platinum and copper dopants in gold nanoclusters supported on ceria catalysts

Understanding the behaviour of active catalyst sites at the atomic level is crucial for optimizing catalytic performance. Here, the evolution of Pt and Cu dopants in Au25 clusters on CeO2 supports is investigated in the water-gas shift (WGS) reaction, using operando XAFS and DRIFTS. Different behaviour is observed for the Cu and Pt dopants during the pretreatment and reaction. The Cu migrates and builds clusters on the support, whereas the Pt creates single-atom active sites on the surface of the cluster, leading to better performance. Doping with both metals induces strong interactions and pretreatment and reaction conditions lead to the growth of the Au clusters, thereby affecting their catalytic behaviour. This highlights importance of understanding the behaviour of atoms at different stages of catalyst evolution. These insights into the atomic dynamics at the different stages are crucial for the precise optimisation of catalysts, which ultimately enables improved catalytic performance.

Synergistically Activated Pd Atom in Polymer-Stabilized Au23Pd1 Cluster

Single Pd atom doped Au₂₃Pd₁ clusters stabilized by polyvinylpyrrolidone (Au₂₃Pd₁:PVP) were selectively synthesized by kinetically controlled coreduction of the Au and Pd precursor ions. The geometric structure of Au₂₃Pd₁:PVP was investigated by density functional theory calculation, aberration-corrected transmission electron microscopy, extended X-ray absorption fine structure analysis, Fourier transform infrared spectroscopy of adsorbed CO, and hydrogenation catalysis. These results showed that Au₂₃Pd₁:PVP takes polydisperse but the same atomic arrangements as undoped Au₂₄:PVP while exposing all the atoms including the Pd atom on the surface. Au₂₃Pd₁:PVP exhibited a significantly higher catalytic activity than Au₂₄:PVP for the aerobic oxidation of p-substituted benzyl alcohols. The kinetic studies showed that the rate-determining step was the hydride abstraction from the α-carbon of the alkoxides for both systems. The activation energy for hydride abstraction by Au₂₃Pd₁:PVP was lower than that by Au₂₄:PVP, indicating that the doped Pd atom acts as the active center.

Exploring the materials space in the smallest particle size range: From heterogeneous catalysis to electrocatalysis and photocatalysis

Ultrasmall clusters of subnanometer size can possess unique and even unexpected physical and chemical propensities which make them interesting in various fields of basic science and for potential applications, such...

Account of chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation: a DFT investigation

The chemical bonding and enhanced reactivity of vanadium-doped rhodium clusters toward C–H activation were investigated using DFT.

Optical absorption spectra of palladium doped gold cluster cations

Photoabsorption spectra of gas phase Au(n)(+) and Au(n-1)Pd(+) (13 ≤ n ≤ 20) clusters were measured using mass spectrometric recording of wavelength dependent Xe messenger atom photodetachment in the 1.9-3.4 eV photon energy range. Pure cationic gold clusters consisting of 15, 17, and 20 atoms have a higher integrated optical absorption cross section than the neighboring sizes. It is shown that the total optical absorption cross section increases with size and that palladium doping strongly reduces this cross section for all investigated sizes and in particular for n = 14-17 and 20. The largest reduction of optical absorption upon Pd doping is observed for n = 15.

Doped golden fullerene cages

A first-principles investigation of the effect of the doping of golden cages of 32 atoms is proposed.

Coordination-resolved bonding and electronic dynamics of Na atomic clusters and solid skins

Atomic undercoordination shortens the interatomic bond, deepens the energy level, raises the local energy density and lowers the atomic cohesive energy of Na solid skins and clusters.

Optical properties of nanoalloys

Optical absorption spectra of bare (left) and monolayer-protected (right) metal nanoalloys.

Structural and electronic properties of uranium-encapsulated Au₁₄ cage

The structural properties of the uranium-encapsulated nano-cage U@Au₁₄ are predicted using density functional theory. The presence of the uranium atom makes the Au₁₄ structure more stable than the empty Au₁₄-cage, with a triplet ground electronic state for U@Au₁₄. Analysis of the electronic structure shows that the two frontier single-occupied molecular orbital electrons of U@Au₁₄ mainly originate from the 5f shell of the U atom after charge transfer. Meanwhile, the bonding orbitals and charge population indicate that the designed U@Au₁₄ nano-cage structure is stabilized by ionocovalent interactions. The current findings provide theoretical basis for future syntheses and further study of actinide doped gold nanoclusters, which might subsequently facilitate applications of such structure in radio-labeling, nanodrug carrier and other biomedical applications.

Crystal structure and electronic properties of a thiolate-protected Au24 nanocluster

Solving the total structures of gold nanoclusters is of critical importance for understanding their electronic, optical and catalytic properties. Herein, we report the X-ray structure of a charge-neutral Au24(SCH2Ph-(t)Bu)20 nanocluster. This structure features a bi-tetrahedral Au8 kernel protected by four tetrameric staple-like motifs. Electronic structure analysis is further carried out and the optical absorption spectrum is interpreted. The Au24(SCH2Ph-(t)Bu)20, Au23(S-c-C6H11)16 and Au25(SCH2CH2Ph)18 nanoclusters constitute the first crystallographically characterized "trio".

Nonscalable oxidation catalysis of gold clusters

Small, negatively charged gold clusters isolated in vacuum can oxidize CO via electron-transfer-mediated activation of O2. This suggests that Au clusters can act as aerobic oxidation catalysts in the real world when their structure parameters satisfy given required conditions. However, there is a technical challenge for the development of Au cluster oxidation catalysts; the structural parameters of the Au clusters, such as size and composition, must be precisely controlled because the intrinsic chemical properties of the clusters are strongly dependent on these parameters. This Account describes our efforts to achieve precision synthesis of small (diameter <2 nm) Au clusters, stabilized by polymers and immobilized on supports, for a variety of catalytic applications. Since we aim to develop Au cluster catalysts by taking full advantage of their intrinsic, size-specific chemical nature, we chose chemically inert materials for the stabilizers and supports. We began by preparing small Au clusters weakly stabilized by polyvinylpyrrolidone (PVP) to test the hypothesis that small Au clusters in the real world will also show size-specific oxidation catalysis. The size of Au:PVP was controlled using a microfluidic device and monitored by mass spectrometry. We found that only Au clusters smaller than a certain critical size show a variety of aerobic oxidation reactions and proposed that the reactions proceed via catalytic activation of O2 by negatively charged Au clusters. We also developed a method to precisely control the size and composition of supported Au clusters using ligand-protected Au and Au-based bimetallic clusters as precursors. These small Au clusters immobilized on mesoporous silica, hydroxyapatite, and carbon nanotubes acted as oxidation catalysts. We have demonstrated for the first time an optimal Au cluster size for the oxidation of cyclohexane and a remarkable improvement in the oxidation catalysis of Au25 clusters by single-atom Pd doping. The non-scalable catalysis of Au clusters that we reported here points to the possibility that novel catalysis beyond that expected from bulk counterparts can be developed simply by reducing the catalyst size to the sub-2 nm regime.