Au Clusters Research Articles

Unraveling the Synergy of Au and Polar MgO(111) Surface in Photothermal Catalytic Oxidative Coupling of Methane

AbstractDirect and selective catalytic oxidative coupling of methane (OCM) into high‐carbon products is a great challenge in C1 chemistry. Herein, the successful fabrication of a series of Au clusters loaded on different MgO facets of (111), (110), and (100) is reported. This work demonstrates the Au‐loaded MgO(111) (denoted as Au/MgO(111)) shows the highest C2H6 yield of 12733.4 µmol g−1 h−1 and selectivity of 90.4%, which is 2.46 times higher than that of Au/MgO(110) (5171.4 µmol g−1 h−1) and 25.14 times higher than that of Au/MgO(100) (506.4 µmol g−1 h−1). Moreover, the high activity of Au/MgO(111) can be well maintained over 100 h. Detailed in situ experiments and theoretical calculation reveal such great performance can be attributed to 1) the strong electronic affinity of the surface oxygen species on polar MgO(111) and CH4with the lowest adsorption energy of −0.82 eV; 2) the Au/MgO(111) shows the lowest ΔERDS of 0.53 eV in the rate‐deterime step of OCM that comes in activating the second CH4 molecule; 3) the Au can act as a hole acceptor under light irradiation and adsorb *CH3 with a strong d‐σ hybridization, resulting in an increased C2H6 selectivity.

Enhanced performance of a promising Au/TMDC heterostructure composed of MoTe2 nanosheets decorated with Au5 clusters: A DFT study

Enhanced performance of a promising Au/TMDC heterostructure composed of MoTe2 nanosheets decorated with Au5 clusters: A DFT study

DFT study of the structures and electronic properties of Au cluster– and Pt cluster–functionalized BC3 nanosheets and their effects on sensing and adsorption of volatile organic compounds

DFT study of the structures and electronic properties of Au cluster– and Pt cluster–functionalized BC3 nanosheets and their effects on sensing and adsorption of volatile organic compounds

Resistance of a PdAu12(8e) Core to Growth in Collision-Induced Sequential Reductive Elimination of (C≡CR)2 from [PdAu24(C≡CR)18]2.

Previous studies have reported that [PdAu24(PAF)18]2- (PAF = 3,5-(CF3)2C6H3C≡C) with an icosahedral superatomic PdAu12(8e) core underwent collision-induced sequential reductive elimination (CISRE) of 1,3-diyne (PAF)2 ( J. Phys. Chem. C 2020, 124, 19119). The most likely scenario after the CISRE of (PAF)2 is the growth of the PdAu12(8e) core via the fusion of the Au(0) atoms produced from the Au2(PAF)3 units on the core surface. Contrary to expectation, anion photoelectron spectroscopy and theoretical calculations regarding the CISRE products [PdAu24(PAF)18-2n]2- (n = 1-6) revealed that the electronically closed PdAu12(8e) core does not grow to a single superatom with (8 + 2n)e but assembles with Au2(2e) units. Characterization of the CISRE products of other alkynyl-protected Au clusters suggested that even the non-superatomic Au17(8e) core was resistant to growth due probably to rigidification by PA ligands. We propose that there is a kinetic bottleneck in the growth process of protected Au clusters at the stage where they are electronically closed and/or lose their structural fluxionality by ligation.

C60 Fullerene‐Induced Reduction of Metal Ions: Synthesis of C60‐Metal Cluster Heterostructures with High Electrocatalytic Hydrogen‐Evolution Performance

AbstractMetal clusters, due to their small dimensions, contain a high proportion of surface atoms, thus possessing a significantly improved catalytic activity compared with their bulk counterparts and nanoparticles. Defective and modified carbon supports are effective in stabilizing metal clusters, however, the synthesis of isolated metal clusters still requires multiple steps and harsh conditions. Herein, we develop a C60 fullerene‐driven spontaneous metal deposition process, where C60 serves as both a reductant and an anchor, to achieve uniform metal (Rh, Ir, Pt, Pd, Au and Ru) clusters without the need for any defects or functional groups on C60. Density functional theory calculations reveal that C60 possesses multiple strong metal adsorption sites, which favors stable and uniform deposition of metal atoms. In addition, owing to the electron‐withdrawing properties of C60, the electronic structures of metal clusters are effectively regulated, not only optimizing the adsorption behavior of reaction intermediates but also accelerating the kinetics of hydrogen evolution reaction. The synthesized Ru/C60‐300 exhibits remarkable performance for hydrogen evolution in an alkaline condition. This study demonstrates a facile and efficient method for synthesizing effective fullerene‐supported metal cluster catalysts without any pretreatment and additional reducing agent.

Efficient ensemble uncertainty estimation in Gaussian processes regression

Abstract Reliable uncertainty measures are required when using data-based machine learning interatomic potentials (MLIPs) for atomistic simulations. In this work, we propose for sparse Gaussian process regression (GPR) type MLIPs a stochastic uncertainty measure akin to the query-by-committee approach often used in conjunction with neural network based MLIPs. The uncertainty measure is coined ‘label noise’ ensemble uncertainty as it emerges from adding noise to the energy labels in the training data. We find that this method of calculating an ensemble uncertainty is as well calibrated as the one obtained from the closed-form expression for the posterior variance when the sparse GPR is treated as a projected process. Comparing the two methods, our proposed ensemble uncertainty is, however, faster to evaluate than the closed-form expression. Finally, we demonstrate that the proposed uncertainty measure acts better to support a Bayesian search for optimal structure of Au20 clusters.

Unraveling the roles of atomically-dispersed Au in boosting photocatalytic CO2 reduction and aryl alcohol oxidation

Atomically-dispersed metal-based materials represent an emerging class of photocatalysts attributed to their high catalytic activity, abundant surface active sites, and efficient charge separation. Nevertheless, the roles of different forms of atomically-dispersed metals (i.e., single-atoms and atomic clusters) in photocatalytic reactions remain ambiguous. Herein, we developed an ethylenediamine (EDA)-assisted reduction method to controllably synthesize atomically dispersed Au in the forms of Au single atoms (AuSA), Au clusters (AuC), and a mixed-phase of AuSA and AuC (AuSA+C) on CdS. In addition, we elucidate the synergistic effect of AuSA and AuC in enhancing the photocatalytic performance of CdS substrates for simultaneous CO2 reduction and aryl alcohol oxidation. Specifically, AuSA can effectively lower the energy barrier for the CO2→*COOH conversion, while AuC can enhance the adsorption of alcohols and reduce the energy barrier for dehydrogenation. As a result, the AuSA and AuC co-loaded CdS show impressive overall photocatalytic CO2 conversion performance, achieving remarkable CO and BAD production rates of 4.43 and 4.71 mmol g−1 h−1, with the selectivities of 93% and 99%, respectively. More importantly, the solar-to-chemical conversion efficiency of AuSA+C/CdS reaches 0.57%, which is over fivefold higher than the typical solar-to-biomass conversion efficiency found in nature (ca. 0.1%). This study comprehensively describes the roles of different forms of atomically-dispersed metals and their synergistic effects in photocatalytic reactions, which is anticipated to pave a new avenue in energy and environmental applications.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N‐Heterocyclic Carbenes

AbstractCoinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer “artificial atoms” with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N‐heterocyclic carbene (NHC) ligands and an amine‐terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster—a POM cluster sandwiched by two Au clusters protected by NHCs. Single‐crystal X‐ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Enhancing Stability of Surface Au under Oxidizing Conditions through Reduced Bulk Au Content.

Contrary to the common assumption that a higher bulk content of precious metals facilitates the preservation of more surface noble metal by serving as a reservoir for surface enrichment, we demonstrate that a lower bulk content of Au results in a more stable arrangement of Au atoms at the surface of Cu-Au nanoparticles when exposed to an O2 atmosphere. Using ambient pressure X-ray photoelectron spectroscopy, we investigate the surface segregation and oxidation behavior of Cu-Au nanoparticles across various compositions. Our results reveal that in Au-rich nanoparticles exposed to an H2 atmosphere, surface segregation prompts the formation of a continuous Au-enriched shell, which subsequently oxidizes into a complete CuOx shell upon transitioning to an O2 atmosphere. Conversely, in Au-poor nanoparticles during H2 treatment, segregation results in the emergence of Au clusters embedded within the surface layer, persisting upon exposure to O2. This unexpected phenomenon shows that reducing the bulk content of precious metals can enhance the surface stability of noble atoms under oxidizing conditions, as further demonstrated by comparing the catalytic performance of Cu-Au nanoparticles with varying Au bulk contents in CO oxidation.

Supported Binuclear Gold Phosphine Complexes as CO Oxidation Catalysts: Insights into the Formation of Surface‐Stabilized Au Particles

Atomically precise gold phosphine complexes as precursors for supported Au catalysts tested in CO oxidation are presented. Using a variety of analytical techniques, including in situ and operando X‐ray absorption spectroscopy, it is discovered that minor changes in the ligand of the molecular complexes result in significantly different activation behaviors of supported Au catalysts under reaction conditions. When using [Au2(μ2‐POP)2]OTf2 (POP = tetraphenylphosphoxane) as single‐source precursor, an active supported oxidation catalyst in second light‐off is obtained, outperforming a commercial Au/TiO2 and a P‐free Au/Al2O3 reference catalyst. Conversely, using [Au2(μ2‐dppe)2]OTf2 (dppe = diphenylphosphinoethane) on alumina leads to a significant decrease in CO oxidation activity. This difference is attributed to the formation of P‐containing ligand residues on the support in the case of [Au2(μ2‐POP)2]OTf2/Al2O3, which enhances the thermal stability of the Au particles and affects the particle's electronic properties through charge transfer processes. This work provides insights into the dynamic ligand decomposition of molecular gold complexes under reaction conditions and demonstrates the delicate balance between the stabilization of Au particles, clusters, and complexes using ligands and the blocking of active sites. This knowledge will pave the way for the targeted use of molecular transition metal complexes as precursors in synthesizing surface‐stabilized nanoparticles.

Preparation and Catalytic Properties of Gold Single-Atomand Cluster Catalysts Utilizing Nanoparticulate Mg-Al Layered Double Hydroxides.

Au single atoms and clusters were stabilized on Mg-Al layered double hydroxide nanoparticles (LDH NPs), and the obtained Au@LDH NPs were supported on SiO2 and CeO2. After hydrogen reduction, Au single atoms were found together with Au clusters on LDH/SiO2. In contrast to Au single-atomcatalysts which are deposited in metal vacancies of oxide supports, the LDH NPs stabilize small Au species despite the absence of metal vacancies. The obtained Au(0)@LDH/SiO2 catalyzed aerobic oxidation of alcohols, and Au single atoms maintained after the reaction. Given that only Au NPs were observed on bulk LDH, the abundant surface OH group of LDH NPs would contribute to stabilize Au, resulting in higher activity than Au/LDH-bulk. After calcination to transform LDH to mixed metal oxide (MMO), the obtained Au(0)@MMO/SiO2 also exhibited high catalytic activity. Moreover, Au(0)@LDH/CeO2 exhibited higher activity and excellent selectivity for hydrogenation of 4-nitrostyrene to 4-aminostyrene than conventional Au catalysts such as Au/CeO2 and Au/TiO2 even though onlyAu NPs were present. We demonstrated that Au size can be minimized using LDH NPs, exhibiting in high catalytic performance. The basic surface OH groups of LDH would be also beneficialfor deprotonation of alcohols and heterolytic H2dissociation in the catalytic reactions.

Auranofin loaded silk fibroin nanoparticles for colorectal cancer treatment.

Colorectal cancer (CRC) is the second most common cause of cancer related deaths worldwide and the prevalence in young people especially is increasing annually. In the search for innovative approaches to treat the disease, drug delivery systems (DDS) are promising owing to their unique properties, which allow improved therapeutic results with lower drug concentrations, overcoming drug resistance and at the same time potentially reducing side effects. Silk fibroin is a biopolymer that can be processed to obtain biocompatible and biodegradable nanoparticles that can be efficiently loaded by surface adsorption with small-molecule therapeutics and allow their transport and sustained release by modulating their pharmacokinetics. Auranofin (AF) has recently been repurposed for its strong anticancer activity and is currently in clinical trials. Its mechanism of action is through the inhibition of thioredoxin reductase enzymes, which play an essential role in several intracellular processes and are overexpressed in some tumours. Taking into account that AF has a low solubility in water, we propose silk fibroin nanoparticles (SFN) as AF carrier in order to improve its bioavailability, increasing cellular absorption and preventing its degradation or avoiding some resistance mechanisms. Here we report the preparation and characterization of a new formulation of AF-loaded silk fibroin nanoparticles (SFN-AF), its functionalization with FITC for the analysis of cellular uptake, as well as its cytotoxic activity against cell lines of human colorectal cancer (HT29 and HCT116) in both 2D and 3D cell cultures. 3D spheroid models provide a 3D environment which mimics the 3D aspects of CRC observed in vivo and represents an effective 3D environment to screen therapeutics for the treatment of CRC. The loaded nanoparticles showed a spherical morphology with a hydrodynamic diameter of ~ 160nm and good stability in aqueous solution due to their negative surface charges. FESEM-EDX analysis revealed a homogeneous distribution of Au clusters with high electron density on the surface of the nanoparticles. SFN-AF incubated in phosphate buffer at 37°C released 77% of the loaded AF over 10 days, showing an initial burst and then sustained release. Flow cytometry analysis showed that FITC-SFN-AF was efficiently internalized by both cell lines, which was confirmed by confocal microscopy imaging. SFN enhanced the cytotoxicity of AF in 2D cultures in both CRC lines. Promising results were also obtained in 3D culture paving the way for future application of this strategy as a therapy for CRC.

Unraveling the mechanism of CH3CH2OH dehydrogenation on m-ZrO2(111) surface, Au13 cluster, and Au13 cluster/m-ZrO2(111) surface: A DFT and microkinetic modeling study

The dehydrogenation of CH3CH2OH to produce CH3CHO and H2 is crucial for generating valuable chemicals. This study uses density functional theory (DFT) and microkinetic modeling to elucidate the reaction pathways on the m-ZrO2 (111) surface, Au13 cluster, and Au13 cluster/m-ZrO2(111) surface. Dehydrogenation on both the m-ZrO2(111) surface and Au13 cluster occurs via two key steps. The first step involves the cleavage of the OH bond in CH3CH2OH, forming a CH3CH2O moiety and an OH bond with the lattice oxygen on m-ZrO2 (111) surface or with a low-coordination Au atom in the Au13 cluster, respectively; while the formation of H2 takes place in the second step; however, the results microkinetic modeling render low values for the corresponding rate constants for this reaction path. Although the Au13cluster/m-ZrO2(111) surface introduces an additional step, where the H atom migrates from the m-ZrO2 (111) surface to the Au13 cluster, we shown that the relative energy of the three transition states is similar, the activation barriers are lower, and the rate constants are favorable for the dehydrogenation of CH3CH2OH. These results demonstrate the potential of the Au13 cluster supported on m-ZrO2(111) for efficient and selective CH3CHO and H2 production, providing valuable insights for advanced catalytic system design.

Photothermal Synergistic Effect Induces Bimetallic Cooperation to Modulate Product Selectivity of CO2 Reduction on Different CeO2 Crystal Facets

AbstractProduct selectivity of solar‐driven CO2 reduction and H2O oxidation reactions has been successfully controlled by tuning the spatial distance between Pt/Au bimetallic active sites on different crystal facets of CeO2 catalysts. The replacement depth of Ce atoms by monatomic Pt determines the distance between bimetallic sites, while Au clusters are deposited on the surface. This space configuration creates a favourable microenvironment for the migration of active hydrogen species (*H). The *H is generated via the activation of H2O on monatomic Pt sites and migrate towards Au clusters with a strong capacity for CO2 adsorption. Under concentrated solar irradiation, selectivity of the (100) facet towards CO is 100 %, and the selectivity of the (110) and (111) facets towards CH4 is 33.5 % and 97.6 %, respectively. Notably, the CH4 yield on the (111) facet is as high as 369.4 μmol/g/h, and the solar‐to‐chemical energy efficiency of 0.23 % is 33.8 times higher than that under non‐concentrated solar irradiation. The impacts of high‐density flux photon and thermal effects on carriers and *H migration at the microscale are comprehensively discussed. This study provides a new avenue for tuning the spatial distance between active sites to achieve optimal product selectivity.

Structural and Electronic Properties of U5M+ and T5M+ (U = Uracil, T = Thymine, M = Ag and Au) Cluster Cations

The geometric and electronic structures and the bonding of U5M+ and T5M+ (U = uracil, T = thymine, M = Ag, Au) cluster cations have been investigated with density functional theory methods. They have a perfectly planar structure with C5h symmetry and significant stability, containing self-complementary N-H···O hydrogen bonds and five Au-O or Ag-O contacts. The energy gap between the LUMO and HOMO in the U5Ag+ cluster is 4.2 eV, which is twice as large as the HOMO-LUMO gap observed in the U5Au+ cluster. This notable difference clearly indicates that the U5Ag+ cluster possesses substantially greater stability compared to the U5Au+ cluster. This finding is consistent with the results from the energy decomposition analyses, which show that the total interaction energy of U5Ag+ is significantly higher than that of U5Au+. The same trend is observed in T5M+ as well. The interaction between the metal atoms, whether gold (Au) or silver (Ag), and the nucleobase is not predominantly controlled by electrostatic forces, as initially believed. Instead, it is primarily characterized by pronounced covalent bonding effects.

CO Oxidation at Low Temperatures over the Au Cluster Supported on Crystalline Silicotitanate.

Crystalline silicotitanate (CST) with a sitinakite structure has attracted considerable attention as an ion exchanger because of its anionic surface owing to SiO4 tetrahedral and TiO6 octahedral linked structures. In particular, the anionic surface of CST is advantageous in immobilizing single Au atoms derived from a cationic precursor such as Au(en)2Cl3 (en = ethylenediamine). In this study, a Au/CST catalyst was prepared and evaluated for CO oxidation. The transmission electron microscopy and X-ray photoelectron spectroscopy results suggest that Au single atoms and clusters (Auδ+, 0 < δ < 1) were supported on Na+-CST particles. The 1.0 wt % Au/CST catalyst yielded high catalytic activity for CO oxidation, where 50% CO oxidation was achieved at a low temperature of -13 °C. In the low-temperature region (from -84 to 20 °C), CO oxidation over Au/CST may progress through the well-known Langmuir-Hinshelwood mechanism. Conversely, the experimental results of CO oxidation without O2 confirmed that the reaction proceeded according to the Au-assisted Mars-van Krevelen mechanism using the lattice oxygens of the CST particles at temperatures above 20 °C. Therefore, this work contributes to the design of highly dispersed single-atom or cluster catalysts using the anionic surface of the microporous CST.

Atomic Artificial Enzyme for Acute and Chronic Pneumonia.

Pneumonia involves complex immunological and pathological processes leading to pulmonary dysfunction, which can be life-threatening yet lacks effective specialized medications. Natural enzymes can be used as biological agents for the treatment of oxidative stress-related diseases, but limiting to catalytic and environmental stability as well as high cost. Herein, an artificial enzyme, gold nanoclusters (Au NCs) with excellent stability, bioactivity, and renal clearance can be used as the next-generation biological agents for acute lung injury (ALI) and allergic lung disease (ALD). The Au25 clusters can mimic catalase (CAT) and glutathione peroxidase (GPx), and the Km of Au24Er1 with H2O2 reaches 1.28mM, about 22 times higher than natural CAT (≈28.8mM). The clusters inhibit the oxidative stress in the mitochondria and promote the synthesis of adenosine triphosphate (ATP). The molecular mechanism shows that the TLR4/MyD88/NF-κB pathway and M1 macrophage-mediated inflammatory response are suppressed in ALI and the Th1/Th2 imbalance in ovalbumin (OVA)-induced ALD is rescued. Further, the clusters can notably improve lung function in both ALI and ALD models which paves the way for immunomodulation and intervention for lung injury and can be used as a substitute for natural enzymes and potential biopharmaceuticals in the treatment of various types of pneumonia.

C60 Fullerene-Induced Reduction of Metal Ions: Synthesis of C60-Metal Cluster Heterostructures with High Electrocatalytic Hydrogen-Evolution Performance.

Metal clusters, due to their small dimensions, contain a high proportion of surface atoms, thus possessing a significantly improved catalytic activity compared with their bulk counterparts and nanoparticles. Defective and modified carbon supports are effective in stabilizing metal clusters, however, the synthesis of isolated metal clusters still requires multiple steps and harsh conditions. Herein, we develop a C60 fullerene-driven spontaneous metal deposition process, where C60 serves as both a reductant and an anchor, to achieve uniform metal (Rh, Ir, Pt, Pd, Au and Ru) clusters without the need for any defects or functional groups on C60. Density functional theory calculations reveal that C60 possesses multiple strong metal adsorption sites, which favors stable and uniform deposition of metal atoms. In addition, owing to the electron-withdrawing properties of C60, the electronic structures of metal clusters are effectively regulated, not only optimizing the adsorption behavior of reaction intermediates but also accelerating the kinetics of hydrogen evolution reaction. The synthesized Ru/C60-300 exhibits remarkable performance for hydrogen evolution in an alkaline condition. This study demonstrates a facile and efficient method for synthesizing effective fullerene-supported metal cluster catalysts without any pretreatment and additional reducing agent.

Atomically Precise Ternary Cluster: Polyoxometalate Cluster Sandwiched by Gold Clusters Protected by N-Heterocyclic Carbenes.

Coinage metal (Au, Ag, Cu) cluster and polyoxometalate (POM) cluster represent two types of subnanometer "artificial atoms" with significant potential in catalysis, sensing, and nanomedicine. While composite clusters combining Ag/Cu clusters with POM have achieved considerable success, the assembly of gold clusters with POM is still lagging. Herein, we first designedly synthesized two cluster structural units: an Au3O cluster stabilized by diverse N-heterocyclic carbene (NHC) ligands and an amine-terminated POM linker. The subsequent reaction involved amine substitution in the POM linker for the central O atom in the Au3O cluster, resulting in the first ternary composite cluster - a POM cluster sandwiched by two Au clusters protected by NHCs. Single-crystal X-ray diffraction and other characteristic methods characterized their atomically precise structures. Furthermore, altering the NHC ligands decreased the number of gold atoms in the sandwich structures, accompanying the different protonated degrees of amine ligand in the terminal end of the POM linker. These composite clusters showed excellent performances in catalytic H2O2 conversion through the synergistic effect between gold clusters and POM clusters. This work opens a new avenue to functional composite metal clusters and would promote their enhanced catalysis applications through intercluster synergistic interactions within composite systems.

Theoretical investigation of CO oxidation over polyoxometalate-supported Au cluster catalyst

A polyoxometalate-supported Au cluster catalyst (Au/POM) exhibited high catalytic activity for CO oxidation at room temperature; however, its activity decreased at the reaction temperature above 60 ℃. Density functional theory calculations were performed to elucidate the unique catalytic activities. Our calculations show that the interactions between water molecules accommodated within the defect site of the support and the O2 adsorbed on the Au cluster generate active OOH− species. This OOH− species reacts readily with CO, resulting in high CO oxidation catalytic activity between −40 and 40 degrees Celsius. The activation barrier of CO oxidation over Au/POM in the presence of H2O is much lower than that in the absence of H2O. This is in good agreement with the experimental results, indicating that surface-adsorbed water allows for high CO oxidation catalytic activity around room temperature, whereas the activity decreases at higher temperatures owing to the desorption of surface-adsorbed water molecules.