Sub-nanometer Clusters Research Articles

Structure sensitivity in adsorbate-induced adatom formation on FCC transition-metal surfaces

Recent surface science discoveries reveal that adsorbates may induce in situ sub-nanometer cluster formation on transition-metal surfaces. To elucidate the structure sensitivity behind this phenomenon, we performed density functional theory calculations to construct an adatom formation energy database for eight fcc metals and 26 adsorbates commonly involved in catalytic reactions. We show that the adatom formation on (100) surfaces is generally easier than that on (111) surfaces. Many adsorbate/metal pairs exist, mostly on Pd, Ni, Rh, Pt, and Ir, for which adsorbates might induce adatom formation under near-ambient conditions on the (100) facet, but not on (111), highlighting the role of more open facets in adatom formation on metals intrinsically harder than Ag, Au, and Cu. Our study offers a new perspective towards understanding structure sensitivity in heterogeneous thermal- and electro-catalytic systems such as methane steam reforming, Fischer-Tropsch synthesis, and ammonia decomposition.

From single Cu atoms to sub-nanometric copper clusters deposited on TiO2: a DFT study

From single Cu atoms to sub-nanometric copper clusters deposited on TiO2: a DFT study

Unveiling platinum's electronic and dispersion impacts for enhanced benzene combustion: From nanoparticles to nanoclusters and single atoms

Catalytic combustion using platinum (Pt) supported on metal oxides emerges as an eco-friendly approach for benzene removal. However, relationships between Pt dispersion, adsorptive properties, and reactivity across overall Pt size regimes remain unclear, as many previous studies have focused on only one or two Pt size ranges. This study systematically examines the oxidation state, electron density, and resulting adsorptive properties of Pt across a range of sizes, including isolated atoms, sub-nanometer clusters, and nanoparticles. The as-synthesized Pt/Fe2O3 catalysts with defined Pt dispersion and electronic states on faceted Fe2O3 supports. Benzene combustion kinetics are measured over Pt entities from single atoms to sub-nanometer clusters and 2 nm particles, elucidating mechanisms and structure–reactivity links. Findings reveal surprising non-monotonic activity trends that deviate from dispersion features, with an order of: Pt sub-nanometer clusters < Pt single atoms < Pt nanoparticles. Despite high dispersion, single Pt atoms and nanoclusters exhibit lower benzene combustion activity than 2 nm Pt particles on Fe2O3. This reduced activity stems from diminished adsorptive affinity of single atoms and nanoclusters for benzene and O2, tracing back to their oxidized Pt valence states. In contrast, 2 nm Pt particles show excellent benzene and oxygen adsorption capacities enabled by metallic Pt ensembles, thus maximizing reactivity. Additional insights indicate single Pt atoms supported on Fe2O3 avoid competitive benzene/O2 adsorption through a non-competitive mechanism, moderately enhancing performance versus nanoclusters with competitive adsorption. However, Pt valence state has a greater impact than adsorption mechanisms, as Pt nanoparticles are considerably more active than single atoms and nanoclusters. In situ analysis proposes plausible benzene decomposition routes over active Pt sites. The novel findings that fine-tuning Pt dispersion and electronic structure—along with kinetic mechanisms—lead to significant variations in benzene combustion reactivity will assist rational design of efficient Pt catalysts for benzene elimination.

State-of-the-art strategies for the synthesis of zeolite-encapsulated subnanometric metal clusters

Novel and conventional strategies for the synthesis of zeolite-encapsulated subnanometric metal clusters are reviewed. Further perspectives for the rational design of zeolite-encapsulated subnanometric metal clusters are analyzed.

What could be the low-temperature limit of atomic layer deposition of platinum using MeCpPtMe3 and oxygen?

We explore the low-temperature limit of atomic layer deposition of Pt using MeCpPtMe3 and O2. We reveal that by supplying a sufficiently high O2 exposure, highly dispersed and thermally stable Pt sub-nanometer clusters can be deposited onto the surface of P25 TiO2 nanoparticles even at room temperature by atmospheric-pressure ALD.

Continuous flow synthesis of atom-precise platinum clusters.

Subnanometer clusters with precise atom numbers hold immense potential for applications in catalysis, as single atoms can significantly impact catalytic properties. Typically, inorganic clusters are produced using batch processes with high dilutions, making the scale-up of these processes time-consuming and its reproducibility challenging. While continuous-flow systems have been employed for organic synthesis and, more recently, nanoparticle preparation, these approaches have only rarely been applied to cluster synthesis. In a flexible, continuous flow synthesis platform, we integrate multiple continuous stirred tank reactors (CSTR) into a cascade to synthesize clusters with a precise number of atoms, demonstrating the potential of this approach for atom precise cluster synthesis and expanding the application of continuous-flow systems beyond organic synthesis.

Small luminescent silver clusters stabilized in porous crystalline solids.

Subnanometric or small metal clusters (SMCs) have been extensively researched due to their unique electronic, optical, catalytic, and magnetic properties, which differ from those of bulk samples. Among the SMCs, silver (Ag) clusters have received significant interest due to their affordability and unique luminescent properties. Currently, two major approaches, gas-phase and liquid-phase synthesis, have been employed to obtain Ag clusters with precise control of size and structure. More recently, attention has been directed toward the utilization of porous crystalline solids such as metal-organic frameworks (MOFs), zeolites, and porous ionic crystals (PICs) to synthesize and stabilize Ag clusters. In this review, we aim to provide a comprehensive overview of the synthesis, structures, and luminescent properties of Ag clusters in porous crystalline solids.

Subnanometric Pt clusters dispersed over Cs-doped TiO2 for CO2 upgrading via low-temperature RWGS: operando mechanistic insights to guide an optimal catalyst design

Cs-doped Pt/TiO2 advanced catalysts for CO2 conversion via low-temperature RWGS: from operando and mechanistic study to real-catalyst design to combat global warming.

Engineering the electronic structure of sub-nanometric Ru clusters via Pt single-atom modification for highly efficient electrocatalytic hydrogen evolution

We report herein an environmentally friendly and pyrolysis-free synthesis strategy to prepare an efficient supported catalyst with Pt single-atom modified sub-nanometric Ru clusters for all-pH HER.

The sub-nanometer In2O clusters on Ag nanoparticles with highly selective electrochemical CO2 reduction to formate

Electrochemical CO2 reduction (ECR) is a potential route for establishing a carbon–neutral economy. Despite notable breakthroughs, designing a catalytic system with desired product selectivity remains a formidable challenge. Herein, we demonstrate a novel nanoarchitecture comprising sub-nanometer In2O3 clusters on Ag nanoparticles (henceforth denoted as Ag2-In8/C) for highly selective formate (HCOOH) production in ECR. As-prepared Ag2-In8/C NC with the Ag/In atomic ratio of 2/8 achieved the formate faradaic efficiency (FEHCOOH) of as high as 95.5 % at −0.9 VRHE with no obvious degradation after 7 h, surpassing the monometallic counterparts (Ag/C and In2O3/C) in selectivity and activity. The in-situ X-ray absorption spectroscopy reveals the formation of sub-nanometer In2O clusters (i.e. Indium changed its phase from In2O3 to In2O) on Ag nanoparticles under potential-driven conditions, where the high activity and selectivity of Ag2-In8/C NC originates from the robust synergistic cooperation between Ag and In2O domains at the Ag-In2O interface, underscoring its role as the active site for highly selective ECR. Moreover, an amalgamation of the physical and electrochemical analysis suggests that In2O clusters assist *OCHO formation on the surface of Ag2-In8/C NC during ECR and thus pronounced formate selectivity is achieved. In light of our findings, this study promises to unravel intricate mechanistic insights, thus paving the way for the rational design of exceptionally selective catalysts for ECR.

Single-Walled Cluster Nanotubes for Single-Atom Catalysts with Precise Structures.

Spatially confining isolated atomic sites in low-dimensional nanostructures is a promising strategy for preparing high-performance single-atom catalysts (SACs). Herein, fascinating polyoxometalate cluster-based single-walled nanotubes (POM-SWNTs) with atomically precise structures, uniform diameter, and single-cluster wall thickness are constructed by lacunary POM clusters (PW11 and P2W17 clusters). Isolated metal centers are accurately incorporated into the PW11-SWNTs and P2W17-SWNTs supports. The structures of the resulting MPW11-SWNTs and MP2W17-SWNTs are well established (M = Cu, Pt). Molecular dynamics simulations demonstrate the stability of POM-SWNTs. Furthermore, the turnover frequency of PtP2W17-SWNTs is 20 times higher than that of PtP2W17 cluster units and 140 times higher than that of Pt nanoparticles in the alcoholysis of dimethylphenylsilane. Theoretical studies indicate that incorporating a Pt atom into the P2W17 support induces straightforward electron transfer between them, combining the nanoconfined environment to enhance the catalytic activity of PtP2W17-SWNTs. This work shows the feasibility of using subnanometric POM clusters to assemble single-walled cluster nanotubes, highlighting their potential to prepare superior SACs with precise structures.

DFT Studies on Cun/TiO2 (n=1-7) System for Water Splitting

Copper deposited on titania is active in numerous catalytic reactions, incl. water splitting [1]. The activity of the system depends on the size of the copper phase, whether it is present as single atoms, sub-nanometer clusters, or nanoparticles.The aim of the current contribution is to elucidate the relationship between the size of the copper active phase and its electronic and geometric properties by performing Density Functional Theory (DFT) calculations with PBE functional and the def2-TZVP basis set.Theoretical model of the system comprised of a cluster model of anatase phase of titania – (TiO2)34 - with clusters of copper of varying sizes on top of it. The ground-state geometric and electronic structures were elucidated. Next, their redox and photochemical properties were determined: frontier (HOMO, LUMO) orbitals were defined, energy gaps, total and partial density of states were plotted and analysed. The interactions between components of the systems, in particular the influence of the support on the copper electronic structure, were investigated. Next, the reactivity of the metal phase towards typical intermediates observed during water splitting (H2O, OH, O, and H) was studied.The performed calculations demonstrated that the presence of metal determines the energetics and character of the frontier orbitals of the catalyst. The size of copper active phase influences the bond lengths and bond orders with studied reagents.Acknowledgements: This work was supported by the National Science Centre, Poland within Solar-Driven Chemistry project no 2019/01/Y/ST4/00024. This publication is based upon work from COST Action CA 18234 “Computational materials sciences for efficient water splitting with nanocrystals from abundant elements”, supported by COST (European Cooperation in Science and Technology). We gratefully acknowledge Polish high-performance computing infrastructure PLGrid (HPC Centers: ACK Cyfronet AGH) for providing computer facilities and support within computational grant no. PLG/2020/013927.Literature:[1] Cheng Cheng, Wei-Hai Fang, Run Long, and Oleg V. Prezhdo, JACS Au 2021, 1, 5, 550–559

The Structural and Electronic Properties of the Ag5 Atomic Quantum Cluster Interacting with CO2, CH4, and H2O Molecules

Recent advancements in experimental approaches have made it possible to synthesize silver (Ag5) atomic quantum clusters (AQCs), which have shown a great potential in photocatalysis. This study employs the generalized gradient approximation (GGA) density functional theory (DFT) to explore the adsorption of CO2, CH4, and H2O molecules on the Ag5 AQC. Our investigations focus on the structural and electronic properties of the molecules in Ag5 AQC systems. This involves adsorption energy simulations, charge transfer, charge density difference, and the density of states for the modelled systems. Our simulations suggest that CH4 and H2O molecules exhibit higher adsorption energies on the Ag5 AQC compared to CO2 molecules. Remarkably, the presence of CH4 molecule leads to a significant deformation in the Ag5 AQC structure. The structure reforms from a bipyramidal to trapezoidal shape. This study also reveals that the Ag5 AQC donates electrons to CO2 and CH4 molecules, resulting in an oxidation state. In contrast, gaining charges from H2O molecules results in a reduced state. We believe the proposed predictions provide valuable insights for future experimental investigations of the interaction behaviour between carbon dioxide, methane, water molecules, and Ag5 sub-nanometre clusters.

Subnanometric Bismuth Clusters Confined in Pyrochlore‐Bi2Sn2O7 Enable Remarkable CO2 Photoreduction

AbstractThe development of highly efficient photocatalysts for conversion of carbon dioxide (CO2) with water (H2O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore‐Bi2Sn2O7 frameworks, leading to the remarkable improvements of photocatalytic performances for CO2 reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 μmol g−1 h−1 has been achieved, more than 20‐fold improvement compared with the pristine Bi2Sn2O7 (5.7 μmol g−1 h−1). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge‐separation/electron‐enrichment and adsorption/activation of CO2 molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO2 conversion into solar fuels.

Subnanometric Bismuth Clusters Confined in Pyrochlore-Bi2 Sn2 O7 Enable Remarkable CO2 Photoreduction.

The development of highly efficient photocatalysts for conversion of carbon dioxide (CO2 ) with water (H2 O) into chemical fuels is of great importance for energy sustainability and carbon resource utilization. Herein, we demonstrated a facile hydrothermal method for in situ construction of subnanometric Bi metallic clusters in pyrochlore-Bi2 Sn2 O7 frameworks, leading to the remarkable improvements of photocatalytic performances for CO2 reduction into CO in the absence of sacrificial reagent. More specifically, an outstanding CO evolution activity of 114.1 μmol g-1 h-1 has been achieved, more than 20-fold improvement compared with the pristine Bi2 Sn2 O7 (5.7 μmol g-1 h-1 ). Detailed experiments together with in situ characterizations reveal that the spatially confined Bi clusters could significantly promote charge-separation/electron-enrichment and adsorption/activation of CO2 molecules, which provides highly efficient reaction channels to facilitate the generation of *COOH intermediate as well as the subsequent desorption of *CO towards CO formation. These demonstrations provide an important knowledge for precise design and fabrication of highly efficient photocatalysts for CO2 conversion into solar fuels.

Sub-nanometric Pt clusters supported Co aerogel electrocatalyst with hierarchical micro/nano-porous structure for hydrogen evolution reaction

The construction of interactions and synergies between sub-nanometric clusters and supports provides unexpected opportunity to realize high performance and low-cost composite catalysis. However, hierarchical micro/nano-porous structured catalysts closely related to mass transport have been neglected as support, which may play a leading role in industrial practical applications. Herein, we report sub-nanometric Pt clusters supported Co aerogel (Ptx/Co, X is the wt% of Pt) with hierarchical micro/nano-porous structure, and after optimization of the loading, Pt0.25/Co shows excellent HER performance. Additionally, Pt0.25/Co demonstrates the industrially needed current density of 1.0 A cm−2 at 1.8 V in PEM electrolyser, achieving stability in excess of 200 h. Theoretical calculations show that the advantages of the hierarchical micro/nano-porous structure accelerate the mass transport at the three-phase interface, and the strong interaction between sub-nanometric Pt clusters and Co aerogel not only optimizes the electronic structure of Pt0.25/Co, but also inhibits the dissolution of sub-nanometric Pt clusters.

Synergistic effect of platinum single atoms and nanoclusters for preferential oxidation of carbon monoxide in hydrogen-rich stream

Despite the maximum atom-utilization efficiency and remarkable activity of single-atom catalysts, further improvement of catalytic activity can be obtained by the synergistic effect of single atoms and nanoclusters in some catalytic systems. Herein, CeFeOx-supported Pt single atoms coupling with subnanometric clusters (Pt1-Ptn) structures are developed via a facile strategy. They are applied as the highly efficient catalysts for the preferential oxidation of CO in H2-rich stream (CO-PROX), which achieve complete elimination of CO at low temperature of 50 °C, with a wide operating temperature window and extraordinary stability for over 500 h without noticeable deactivation. The exceptional performance is attributed to the synergistic effect of distinctive Pt1-Ptn structures, which couple the benefits of Pt single atoms and subnanometric clusters in a remarkable way. The disadvantages of single Pt species catalysts, such as sensibility to strong adsorption of CO or reduced lattice oxygen reactivity due to excessive coordination, can be well mitigated. The results of detailed characterizations and density functional theory calculations confirm that the unique structures possess moderate adsorption strength for CO and create abundant active interfacial oxygen species, because of the absence of bulk metallic Pt0 and appropriate coordination to lattice oxygen, which synergistically facilitate the catalytic performance.

Metal sulfide sub-nanometer clusters formed within calix(8)arene Langmuir-Blodgett films

This work describes the construction of layered Langmuir-Blodgett (LB) films of a calixarene and the use of these as matrices for the synthesis of a range of metal sulfide nanoparticles. CuS, CdS, HgS, and PbS nano-clusters were formed within LB films of an octa-tertbutyl-calix(8)arene substituted with carboxylic acid groups deposited on different substrates (glass, quartz, and silicon) from either: (i) aqueous sub-phases containing 0.5 mM of the respective metal chloride salt (e.g. CuCl2, CdCl2, HgCl2, PbCl2), or (ii) by soaking the LB films in 10 mM solutions of the above salts for 1 h. The formation of metal-sulfide (MeS) nanoparticles was then achieved by exposing samples to H2S gas for 10–12 h.Deposition from salt containing subphases was more reliable and resulted in stoichiometric metal sulfides (CdS, HgS, PbS) being formed within LB films of the calix(8)arene carboxylic acid whereas Cu tended to form polysulfides. UV–vis absorption spectroscopy showed the presence of multiple absorption bands corresponding to electron transitions between energy levels in nanoclusters formed as result of quantum confinement of electrons and holes. The MeS clusters obtained by this process are amongst the smallest reported for LB films, being of the range 0.6–1.2 nm.

Light-assistance in nitrogen fixation to ammonia by highly dispersed Cs-promoted Ru clusters supported on ZrO2

Light-assisted N2 fixation to NH3 under mild conditions is attracting massive attention to circumvent energy crisis and global warming. Herein, highly dispersed Cs-decorated Ru sub-nanometric clusters supported on ZrO2 NPs have been prepared by means of MOF-templated transformation method. The obtained catalyst exhibited N2 hydrogenation activity of 1.6 mmolNH3 gcat−1 h−1 in the dark (350 °C, 0.1 MPa). Remarkably this value increased by over 300 %, reaching 5.1 mmolNH3 gcat−1 h−1 (204 mmolNH3 gRu−1 h−1) under 1 Sun power illumination (1080 W/m2) The influence of the incident light wavelength has been evaluated, revealing 81 % and 213 % enhancement in the NIR and visible region, respectively. DFT calculations were carried out to understand the static adsorption states of Ru sub-nanoclusters. Mechanistic studies have confirmed the co-existence of a photothermal and a nonthermal-hot electron mechanism. XPS, PXRD and FTIR analysis have determined that the Cs species block surface Zr4+ acidity, increasing the basicity of the ZrO2 support. Moreover, partially reduced Csδ+ (0 <δ < 1) species surrounding the Ru active sites are donating electron density to the adjacent Ru sites, favoring N2 adsorption and subsequent activation. Finally, this photocatalyst has shown an extended stability for 100 h irradiation under continuous flow.

Ethanol Dehydrogenation over Copper-Silica Catalysts: From Sub-Nanometer Clusters to 15 nm Large Particles.

Non-oxidative ethanol dehydrogenation is a renewable source of acetaldehyde and hydrogen. The reaction is often catalyzed by supported copper catalysts with high selectivity. The activity and long-term stability depend on many factors, including particle size, choice of support, doping, etc. Herein, we present four different synthetic pathways to prepare Cu/SiO2 catalysts (∼2.5 wt % Cu) with varying copper distribution: hydrolytic sol-gel (sub-nanometer clusters), dry impregnation (A̅ = 3.4 nm; σ = 0.9 nm and particles up to 32 nm), strong electrostatic adsorption (A̅ = 3.1 nm; σ = 0.6 nm), and solvothermal hot injection followed by Cu particle deposition (A̅ = 4.0 nm; σ = 0.8 nm). All materials were characterized by ICP-OES, XPS, N2 physisorption, STEM-EDS, XRD, RFC N2O, and H2-TPR and tested in ethanol dehydrogenation from 185 to 325 °C. The sample prepared by hydrolytic sol-gel exhibited high Cu dispersion and, accordingly, the highest catalytic activity. Its acetaldehyde productivity (2.79 g g-1 h-1 at 255 °C) outperforms most of the Cu-based catalysts reported in the literature, but it lacks stability and tends to deactivate over time. On the other hand, the sample prepared by simple and cost-effective dry impregnation, despite having Cu particles of various sizes, was still highly active (2.42 g g-1 h-1 acetaldehyde at 255 °C). Importantly, it was the most stable sample out of the studied materials. The characterization of the spent catalyst confirmed its exceptional properties: it showed the lowest extent of both coking and particle sintering.