Observation of halogen-like behavior of gold in fluorinated bimetallic CoAuF1-2- and CuAuF1-2- clusters: Anion photoelectron spectroscopy and density functional theory

Using size-selected anion photoelectron spectroscopy and density functional theory, we investigated the structures and properties of fluorinated bimetallic clusters CoAuF1-2- and CuAuF1-2- and their neutrals. Both experimental and theoretical results show that in these cluster anions, Au behaves like a halogen atom. For example, the measured vertical detachment energies (VDEs) of CoAuF- (2.00 ± 0.08 eV) and CuAuF- (3.8 ± 0.1 eV) are close to those of CoF2- (2.12 ± 0.08 eV) and CuF2- (3.58 ± 0.08 eV), respectively. The theoretical results show that the geometries and electronic structures of CoAuF- and CuAuF- are similar to those of CoF2- and CuF2-. The natural population analysis and natural electron configuration analyses further confirm that the electronic properties of Au in MAuF- (M = Co, Cu) mimic those of MF2-. In addition, the electron localization function analyses show that the M-Au chemical bonds are similar to the corresponding M-F chemical bonds, providing evidence for the ionic nature of the interactions. When a second F atom is attached to the CoAuF- and CuAuF- clusters, the VDEs of the resulting CoAuF2- and CuAuF2- are 4.38 ± 0.08 eV and 3.71 ± 0.08 eV, respectively, indicating their superhalogen character as these values are higher than those of halogen anions. The results may be useful for understanding the properties of gold at the nanoscale that play an important role in catalysis and nanotechnology.

Effect of Gold Nanoparticle Size on Regulated Catalytic Activity of Temperature-Responsive Polymer-Gold Nanoparticle Hybrid Microgels

Gold nanoparticles (AuNPs) possess attractive electronic, optical, and catalytic properties, enabling many potential applications. Poly(N-isopropyl acrylamide) (PNIPAAm) is a temperature-responsive polymer that changes its hydrophilicity upon a slight temperature change, and combining PNIPAAm with AuNPs allows us to modulate the properties of AuNPs by temperature. In a previous study, we proposed a simpler method for designing PNIPAAm-AuNP hybrid microgels, which used an AuNP monomer with polymerizable groups. The size of AuNPs is the most important factor influencing their catalytic performance, and numerous studies have emphasized the importance of controlling the size of AuNPs by adjusting their stabilizer concentration. This paper focuses on the effect of AuNP size on the catalytic activity of PNIPAAm-AuNP hybrid microgels prepared via the copolymerization of N-isopropyl acrylamide and AuNP monomers with different AuNP sizes. To quantitatively evaluate the catalytic activity of the hybrid microgels, we monitored the reduction of 4-nitrophenol to 4-aminophenol using the hybrid microgels with various AuNP sizes. While the hybrid microgels with an AuNP size of 13.0 nm exhibited the highest reaction rate and the apparent reaction rate constant (kapp) of 24.2 × 10-3 s-1, those of 35.9 nm exhibited a small kapp of 1.3 × 10-3 s-1. Thus, the catalytic activity of the PNIPAAm-AuNP hybrid microgel was strongly influenced by the AuNP size. The hybrid microgels with various AuNP sizes enabled the reversibly temperature-responsive on-off regulation of the reduction reaction.

Surface modification strategies and the functional mechanisms of gold nanozyme in biosensing and bioassay

Gold nanozymes (GNZs) have been widely used in biosensing and bioassay due to their interesting catalytic activities that enable the substitution of natural enzyme. This review explains different catalytic activities of GNZs that can be achieved by applying different modifications to their surface. The role of Gold nanoparticles (GNPs) in mimicking oxidoreductase, helicase, phosphatase were introduced. Moreover, the effect of surface properties and modifications on each catalytic activity was thoroughly discussed. The application of GNZs in biosensing and bioassay was classified in five categories based on the combination of the enzyme like activities and enhancing/inhibition of the catalytic activities in presence of the target analyte/s that is realized by proper surface modification engineering. These categories include catalytic activity enhancer, reversible catalytic activity inhibitor, binding selectivity enhancer, agglomeration base, and multienzyme like activity, which are explained and exemplified in this review. It also gives examples of those modifications that enable the application of GNZs for in vivo biosensing and bioassays.

Copper-Catalyzed Synthesis of 3-Aryl-9H-imidazo[1,5-a]indol-9-ones Using Oxygen as the Sole Oxidant

A three-component strategy was developed for 3-phenyl-9H-imidazo[1,5-a]indol-9-one preparation from indole-2-carboxaldehydes, aromatic aldehydes, and ammonium acetate under copper catalysis conditions. In this process, a new five-membered ring was formed and the C3 position in the indole substrate was selectively oxidized into a ketone skeleton using oxygen as the sole oxidant and ammonium acetate as the nitrogen source. Furthermore, same products also could be achieved from indole-2-carboxaldehydes and benzyl amines under similar reaction conditions.

Synthesis of a Novel Spherical-Shell-Structure Polymerized Ionic Liquid Microsphere PILM/Au/Al(OH)3 Catalyst for Benzyl Alcohol Oxidation

In order to selectively oxidize benzyl alcohol, a novel noble metal catalyst based on polymer ionic liquids with a core-shell structure was created. First, polymer ionic liquid microspheres (PILMs) were prepared by free radical polymerization. Second, the in situ adsorption of Au nanoparticles on the surface of PILMs was accomplished, thanks to the strong electrostatic interaction between N atoms and metal ions on the diazole ring of PILMs. Additionally, the introduction of Al(OH)₃ prevented the aggregation of Au nanoparticles and promoted the catalytic reaction. Finally, the PILM/Au/Al(OH)₃ catalyst with a core-shell structure was formed. The effectiveness of the PILM/Au/Al(OH)₃ catalyst was assessed by varying the catalyst's type, quantity, amount of Au, amount of H₂O₂, temperature, and reaction time. After five cycles of experiments, the catalyst was effective and reusable. In addition, the potential catalytic mechanism of the catalyst in the oxidation of benzyl alcohol was proposed.

A mechanistic study of gold nanoparticles catalysis of O2 reduction by ascorbate and hydroethidine, investigating reactive oxygen species reactivity

In this work, the mechanism of dioxygen reduction catalysed by gold nanoparticles (AuNPs) by two electron donors was investigated, i.e., by sodium ascorbate and hydroethidine, focusing on potential ROS (reactive oxygen species) formation, such as O₂˙^- and H₂O₂. According to our results, when AuNPs catalyse the reduction of O₂, ROS are formed only as intermediates on the surface of nanoparticles, and they are unavoidably reduced to water, catalysed by the AuNPs. Thus, the statement on ROS production in the presence of AuNPs often reported in the literature is excessive. The AuNPs can catalyze the oxidation of electron donors in the cell, e.g., antioxidants causing oxidative stress. Therefore we propose that when explaining damage in the living cells observed in the presence of AuNP, the catalysis of redox reactions by AuNPs must be considered.

Recent advances utilized in artificial switchable catalysis

Developing "green" catalytic systems with desirable performance such as solubility, recyclability, and switchability is a great challenge. However, inspired by nature, the studies on synthesis and activity of artificial switchable metal catalysts and organocatalysts have become an intense, fervid, and challenging field of research. The peculiarity of these catalysts is that they can be generally triggered in the "on" or "off" states by several external stimuli such as light, heat, solvents, pH change, coordination events or ion influxes, redox processes, mechanical forces, or other changes in reaction conditions. A large number of review articles are available in these areas. However, most efforts are currently focused on the invention of new types of switchable catalysts with different forms of stimuli-response units incorporated within their architectures in order to achieve control over the catalytic activity and regio-, chemo- and stereocontrol of various chemical reactions. Thus, in this review, we begin with a brief introduction to switchable catalysts, followed by discussion of types of stimuli and the influence factors on their activities in the field of biomedical engineering, and catalysis as well as related catalytic mechanisms summarized and discussed. The emphasis is on the recent advances utilized in artificial switchable catalysis.

Research Progress of Highly Efficient Noble Metal Catalysts for the Oxidation of 5-Hydroxymethylfurfural

5-hydroxymethylfurfural (HMF) is considered to be one of the most pivotal multifunctional biomass platform chemicals. This Review discusses recent advances in catalytic oxidation of HMF towards high-value products. The reaction mechanism of different noble metals and the path of HMF oxidation to high-value products have been deeply investigated in the noble metal catalytic system. The reaction mechanisms of different noble metals and HMF conversion paths were compared in detail. Moreover, the factors affecting the performance of different noble metal catalysts were summarized. Finally, effective strategies were put forward to improve the catalytic performance of noble metal catalysts. The purpose is to provide a valuable reference for the academic research on the preparation of oxidation products from biomass-based HMF and the industrial application of noble metal catalysts.

A Review of State of the Art in Phosphine Ligated Gold Clusters and Application in Catalysis

Atomically precise gold clusters are highly desirable due to their well-defined structure which allows the study of structure-property relationships. In addition, they have potential in technological applications such as nanoscale catalysis. The structural, chemical, electronic, and optical properties of ligated gold clusters are strongly defined by the metal-ligand interaction and type of ligands. This critical feature renders gold-phosphine clusters unique and distinct from other ligand-protected gold clusters. The use of multidentate phosphines enables preparation of varying core sizes and exotic structures beyond regular polyhedrons. Weak gold-phosphorous (Au-P) bonding is advantageous for ligand exchange and removal for specific applications, such as catalysis, without agglomeration. The aim of this review is to provide a unified view of gold-phosphine clusters and to present an in-depth discussion on recent advances and key developments for these clusters. This review features the unique chemistry, structural, electronic, and optical properties of gold-phosphine clusters. Advanced characterization techniques, including synchrotron-based spectroscopy, have unraveled substantial effects of Au-P interaction on the composition-, structure-, and size-dependent properties. State-of-the-art theoretical calculations that reveal insights into experimental findings are also discussed. Finally, a discussion of the application of gold-phosphine clusters in catalysis is presented.

Comparing Metal-Halide and -Oxygen Adducts in Oxidative C/O-H Activation: AuIII-Cl versus AuIII-OH

High-valent metal–halides have come to prominence as highly effective oxidants. A direct comparison of their efficacy against that of traditional metal–oxygen adducts is needed. [Au^III(Cl)(terpy)](ClO₄)₂ (1; terpy = 2,2′:6′,2-terpyridine) readily oxidized substrates bearing O–H and C–H bonds via a hydrogen atom transfer mechanism. A direct comparison with [Au^III(OH)(terpy)](ClO₄)₂ (2) showed that 1 was a kinetically superior oxidant with respect to 2 for all substrates tested. We ascribe this to the greater thermodynamic driving force imbued by the Cl ligand versus the OH ligand.

We report a direct comparison of the efficacy of metal−halide oxidants to those of traditional metal−oxygen adducts. Au^III−Cl and Au^III−OH oxidants, supported by the same ancillary ligand, readily oxidized substrates via a hydrogen atom transfer mechanism. The Au^III−Cl oxidant was kinetically superior for all substrates. We ascribed this to the greater thermodynamic driving force imbued by the Cl ligand versus the OH ligand.

Identification of active catalysts for the acceptorless dehydrogenation of alcohols to carbonyls

Acceptorless dehydrogenation into carbonyls and molecular hydrogen is an attractive strategy to valorize (biobased) alcohols. Using 2-octanol dehydrogenation as benchmark reaction in a continuous reactor, a library of metal-supported catalysts is tested to validate the predictive level of catalytic activity for combined DFT and micro-kinetic modeling. Based on a series of transition metals, scaling relations are determined as a function of two descriptors, i.e. the surface binding energies of atomic carbon and oxygen. Then, a volcano-shape relation based on both descriptors is derived, paving the way to further optimization of active catalysts. Evaluation of 294 diluted alloys but also a series of carbides and nitrides with the volcano map identified 12 promising candidates with potentially improved activity for alcohol dehydrogenation, which provides useful guidance for experimental catalyst design. Further screening identifies β-Mo2N and γ-Mo2N exposing mostly (001) and (100) facets as potential candidates for alcohol dehydrogenation.

Preparation, Functionalization, Modification, and Applications of Nanostructured Gold: A Critical Review

Gold nanoparticles (Au NPs) play a significant role in science and technology because of their unique size, shape, properties and broad range of potential applications. This review focuses on the various approaches employed for the synthesis, modification and functionalization of nanostructured Au. The potential catalytic applications and their enhancement upon modification of Au nanostructures have also been discussed in detail. The present analysis also offers brief summaries of the major Au nanomaterials synthetic procedures, such as hydrothermal, solvothermal, sol-gel, direct oxidation, chemical vapor deposition, sonochemical deposition, electrochemical deposition, microwave and laser pyrolysis. Among the various strategies used for improving the catalytic performance of nanostructured Au, the modification and functionalization of nanostructured Au produced better results. Therefore, various synthesis, modification and functionalization methods employed for better catalytic outcomes of nanostructured Au have been summarized in this review.

Asymmetric Total Synthesis of (-)-Spirochensilide A, Part 1: Diastereoselective Synthesis of the ABCD Ring and Stereoselective Total Synthesis of 13(R)-Demethyl Spirochensilide A

A concise and diastereoselective construction of the ABCD ring system of spirochensilide A is described. The key steps of this synthesis are a semipinacol rearrangement reaction to stereoselectively construct the AB ring system bearing two vicinal quaternary chiral centers and a Co-mediated Pauson-Khand reaction to form the spiro-based bicyclic CD ring system. This chemistry leads to the stereoselective synthesis of 13(R)-demethyl spirochensilide A, paving the way for the first asymmetric total synthesis of (-)-spirochensilide A.

Catalysis with Silver: From Complexes and Nanoparticles to MORALs and Single-Atom Catalysts

Silver catalysis has a rich and versatile chemistry now expanding from processes mediated by silver complexes and silver nanoparticles to transformations catalyzed by silver metal organic alloys and single-atom catalysts. Focusing on selected recent advances, we identify the key advantages offered by these highly selective heterogeneous catalysts. We conclude by offering seven research and educational guidelines aimed at further progressing the field of new generation silver-based catalytic materials.

Oxidation of Dichloromethane over Au, Pt, and Pt-Au Containing Catalysts Supported on γ-Al2O3 and CeO2-Al2O3

Au, Pt, and Pt-Au catalysts supported on Al₂O₃ and CeO₂-Al₂O₃ were studied in the oxidation of dichloromethane (DCM, CH₂Cl₂). High DCM oxidation activities and HCl selectivities were seen with all the catalysts. With the addition of Au, remarkably lower light-off temperatures were observed as they were reduced by 70 and 85 degrees with the Al₂O₃-supported and by 35 and 40 degrees with the CeO₂-Al₂O₃-supported catalysts. Excellent HCl selectivities close to 100% were achieved with the Au/Al₂O₃ and Pt-Au/Al₂O₃ catalysts. The addition of ceria on alumina decreased the total acidity of these catalysts, resulting in lower performance. The 100-h stability test showed that the Pt-Au/Al₂O₃ catalyst was active and durable, but the selectivity towards the total oxidation products needs improvement. The results suggest that, with the Au-containing Al₂O₃-supported catalysts, DCM decomposition mainly occurs via direct DCM hydrolysis into formaldehyde and HCl followed by the oxidation of formaldehyde into CO and CO₂.

Catalytic performance of the Ce-doped LaCoO3 perovskite nanoparticles

A series of La1-xCexCoO3 perovskite nanoparticles with rhombohedral phases was synthesized via sol-gel chemical process. X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Electron Diffraction Spectroscopy (EDS), Thermogravimetric Analysis (TGA), UV-Vis spectroscopy, Fourier Transform Infrared spectra (FTIR), Nitrogen Adsorption/desorption Isotherm, Temperature Program Reduction/Oxidation (TPR/TPO), X-ray Photoelectron Spectroscopy (XPS) techniques were utilized to examine the phase purity and chemical composition of the materials. An appropriate doping quantity of Ce ion in the LaCoO3 matrix have reduced the bond angle, thus distorting the geometrical structure and creating oxygen vacancies, which thus provides fast electron transportation. The reducibility character and surface adsorbed oxygen vacancies of the perovskites were further improved, as revealed by H2-TPR, O2-TPD and XPS studies. Furthermore, the oxidation of benzyl alcohol was investigated using the prepared perovskites to examine the effect of ceria doping on the catalytic performance of the material. The reaction was carried out with ultra-pure molecular oxygen as oxidant at atmospheric pressure in liquid medium and the kinetics of the reaction was investigated, with a focus on the conversion and selectivity towards benzaldehyde. Under optimum reaction conditions, the 5% Ce doped LaCoO3 catalyst exhibited enhanced catalytic activity (i.e., > 35%) and selectivity of > 99%, as compared to the other prepared catalysts. Remarkably, the activity of catalyst has been found to be stable after four recycles.

Tuning the activities of cuprous oxide nanostructures via the oxide-metal interaction

Despite tremendous importance in catalysis, the design of oxide-metal interface has been hampered by the limited understanding of the nature of interfacial sites and the oxide-metal interaction (OMI). Through construction of well-defined Cu₂O/Pt, Cu₂O/Ag and Cu₂O/Au interfaces, we find that Cu₂O nanostructures (NSs) on Pt exhibit much lower thermal stability than on Ag and Au, although they show the same structure. The activities of these interfaces are compared for CO oxidation and follow the order of Cu₂O/Pt > Cu₂O/Au > Cu₂O/Ag. OMI is found to determine the activity and stability of supported Cu₂O NSs, which could be described by the formation energy of interfacial oxygen vacancy. Further, electronic interaction between Cu⁺ and metal substrates is found center to OMI, where the d band center could be used as a key descriptor. Our study provides insight for OMI and for the development of Cu-based catalysts for low temperature oxidation reactions.

The design of oxide-metal interface for heterogeneous catalysis has been hampered by the limited fundamental understanding. Here, the authors demonstrate that the activities of cuprous oxide nanostructures for CO oxidation can be tuned via the oxide-metal (Cu2O/M, M = Pt, Ag, Au) interaction.

Enzyme-Like Properties of Gold Clusters for Biomedical Application

In recent years, the rapid development of nanoscience and technology has provided a new opportunity for the development and preparation of new inorganic enzymes. Nanozyme is a new generation of artificial mimetic enzyme, which like natural enzymes, can efficiently catalyze the substrate of enzyme under mild conditions, exhibiting catalytic efficiency, and enzymatic reaction kinetics similar to natural enzymes. However, nanozymes exist better stability than native enzymes, it can still maintain 85 % catalytic activity in strong acid and alkali (pH 2~10) or large temperature range (4~90°C). This provides conditions for designing complex catalytic systems. In this review, we discussed the enzymatic attributes and biomedical applications of gold nanoclusters, including peroxidase-like, catalase-like, detection of heavy metal ions, and therapy of brain and cancer etc. This review can help us understand the current research status nanozymes.

Hydrogen Atom Transfer Oxidation by a Gold-Hydroxide Complex

Au^III-oxygen adducts have been implicated as intermediates in homogeneous and heterogeneous Au oxidation catalysis, but their reactivity is under-explored. Complex 1, ([Au^III(OH)(terpy)](ClO₄)₂, (terpy = 2,2':6',2-terpyridine), readily oxidized substrates bearing C-H and O-H bonds. Kinetic analysis revealed that the oxidation occurred through a hydrogen atom transfer (HAT) mechanism. Stable radicals were detected and quantified as products of almost quantitative HAT oxidation of alcohols by 1. Our findings highlight the possible role of Au^III-oxygen adducts in oxidation catalysis and the capability of late transition metal-oxygen adducts to perform proton coupled electron transfer.

Metal-Support Synergy of Supported Gold Nanoclusters in Selective Oxidation of Alcohols

Gold catalysts have been reported to exhibit good performance in aerobic oxidation of alcohols, but the intrinsic origin of the catalytic reactivity is still illusive. The catalyst preparation method, the morphology of the gold particles, and even the support might be key factors that determine the activity. Here, we prepared a series of gold catalysts with different supports, i.e., the hydrotalcite (HT), ZnO, MgO, Al2O3, and SiO2, by using the atomically controlled Au25 nanoclusters (NCs) as the gold precursor. The characterization results of the X-ray diffraction (XRD), UV-vis and transmission electron microscopy (TEM) show that the gold particles were mostly uniformly distributed on the supports, with a mean particle size within 3 nm. In aerobic oxidation of benzyl alcohol, the MgAl-HT- and Al2O3-supported Au25 NCs display good performances, with turnover frequency (TOF) values of ~2927 and 2892 h−1, respectively, whereas the SiO2-, MgO-, and ZnO-supported analogues show much inferior activity. The high resolution TEM and X-ray photoelectron spectra (XPS) results suggest that the interactions between gold and the supports in different samples are differing, which influences the morphology and the nature of gold. Our results further point to the importance of acid-base property of the support and the metal-support synergy rather than the gold particle size alone in achieving high-performance in selective alcohol oxidation. Moreover, this work provided a good way to design gold catalysts with controllable sizes that is crucial for understanding the reaction process in aerobic oxidation of alcohol.

Carbon dot-based composites for catalytic applications

We summarize the construction methods and influencing factors of CDs-based composites and discuss their catalytic applications, including photocatalysis, chemical catalysis, peroxidase-like catalysis, Fenton-like catalysis and electrocatalysis.

Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes

Supporting gold nanoparticles have shown to be extremely active for many industrially important reactions, including oxidations. Two representative examples are the oxidation of alcohols and alkanes, that are substrates of industrial interest, but whose oxidation is still challenging. This review deals with these reactions, giving an insight of the first studies performed by gold based catalysts in these reactions and the most recent developments in the field.

Gold nanomaterials as key suppliers in biological and chemical sensing, catalysis, and medicine

BACKGROUND

Gold nanoparticles (AuNPs) with unique physicochemical properties have received a great deal of interest in the field of biological, chemical and biomedical implementations. Despite the widespread use of AuNPs in chemical and biological sensing, catalysis, imaging and diagnosis, and more recently in therapy, no comprehensive summary has been provided to explain how AuNPs could aid in developing improved sensing and catalysts systems as well as medical settings.

SCOPE OF REVIEW

The chemistry of Au-based nanosystems was followed by reviewing different applications of Au nanomaterials in biological and chemical sensing, catalysis, imaging and diagnosis by a number of approaches, and finally synergistic combination therapy of different cancers. Afterwards, the clinical impacts of AuNPs, future application of AuNPs, and opportunities and challenges of AuNPs application were also discussed.

MAJOR CONCLUSIONS

AuNPs show exclusive colloidal stability and are considered as ideal candidates for colorimetric detection, catalysis, imaging, and photothermal transducers, because their physicochemical properties can be tuned by adjusting their structural dimensions achieved by the different manufacturing methods.

GENERAL SIGNIFICANCE

This review provides some details about using AuNPs in sensing and catalysis applications as well as promising theranostic nanoplatforms for cancer imaging and diagnosis, and sensitive, non-invasive, and synergistic methods for cancer treatment in an almost comprehensive manner.

Crystal phase effect upon O2 activation on gold surfaces through intrinsic strain

Crystal phase engineering is a promising strategy to tune the catalytic performance of metal nanomaterials. Generally, the crystal phase effect on catalysis is ascribed to distinct surface atomic arrangements of catalysts with different crystal phases. Here we show that even for similar surfaces, such as the close-packed surfaces, different crystal phases have considerably different surface reactivities due to their distinct intrinsic surface strains. Using first-principles calculations, we find that the close-packed surfaces of hexagonal close-packed (HCP) and double HCP (4H) gold have significantly smaller intrinsic strains (∼1.3%) than those of face-centered cubic (FCC) gold (∼2.3%). These distinct intrinsic surface strains result in various oxygen adsorption energies and O2 dissociation barriers on these close-packed gold surfaces, and the dissociation of O2 on different crystal phases and surfaces follows the Brønsted-Evans-Polanyi principle.

Heterogeneous Cross-Coupling over Gold Nanoclusters

Au clusters with the precise numbers of gold atoms, a novel nanogold material, have recently attracted increasing interest in the nanoscience because of very unique and unexpected properties. The unique interaction and electron transfer between gold clusters and reactants make the clusters promising catalysts during organic transformations. The AunLm nanoclusters (where L represents organic ligands and n and m mean the number of gold atoms and ligands, respectively) have been well investigated and developed for selective oxidation, hydrogenation, photo-catalysis, and so on. These gold clusters possess unique frameworks, providing insights into the catalytic processes and an excellent arena to correlate the atomic frameworks with their intrinsic catalytic properties and to further investigate the tentative reaction mechanisms. This review comprehensively summarizes the very latest advances in the catalytic applications of the Au nanoclusters for the C-C cross-coupling reactions, e.g., Ullmann, Sonogashira, Suzuki cross-couplings, and A3-coupling reactions. It is found that the proposed catalytically active sites are associated with the exposure of gold atoms on the surface of the metal core when partial capping organic ligands are selectively detached under the reaction conditions. Finally, the tentative catalytic mechanisms over the ligand-capped Au nanoclusters and the relationship of structure and catalytic performances at the atomic level using computational methods are explored in detail.