Metal Cluster Catalysts Research Articles

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.

Solid-State Surface-Anchoring Strategy to Prepare Anti-Sintering Supported Metal Cluster Catalysts.

Due to the unique geometric and electronic structures, supported metal clusters with sizes below 3 nm have appealed to great interest in heterogeneous catalysis. However, these supported ultrasmall metal clusters would endure severe particle coalescences under high reaction temperatures. Herein, based on the technology of ball-milling processing, we propose a solid-state "surface-anchoring" strategy to synthesize thermally stabilized Al2O3-supported Ni nanoclusters. Interestingly, when the theoretical Ni loading weight was 1 wt %, highly dispersed Ni species were found where no Ni nanoparticles would be seen after 500 °C calcination. Until the Ni loading weight increased to 5 wt % and the calcination temperature increased to 750 °C, the Ni nanoparticles became significant but still with a size of only about 6.8 nm. With the small Ni nanoparticles, the final 5-Ni-Al2O3-OAm-750 sample worked well as methane dry reforming catalysts with excellent anticoking performance during a 500 h stability test.

Top-down fabrication of active interface between TiO2 and Pt nanoclusters. Part 2: Catalytic performance and reaction mechanism in CO oxidation

In this work, following Part 1 that has found a redispersion process from Pt nanoparticles (NPs, about 3.4 nm) to nanoclusters (NCs, about 1 nm) on TiO2 and elucidated its mechanism, we carefully investigated the catalytic performance of the obtained Pt NC catalyst in CO oxidation as well as the corresponding reaction mechanism. The Pt NC catalyst excels than its parent catalyst in terms of both intrinsic and apparent activity. Detailed studies by combining kinetic measurements, isotopic labeling reaction experiments, and low-temperature operando FT-IR unambiguously demonstrated that the Pt NCs deposited on TiO2 can form unique interfacial sites that enable to active O2 at very low temperature, thus the CO adsorbed on TiO2 can diffuses to, and reacts with, the activated oxygen, rendering a high activity at low temperatures. This work is contributory in understanding the origin of the high activity of the supported metal cluster catalysts.

Metal-support interactions in metal oxide-supported atomic, cluster, and nanoparticle catalysis.

Supported metal catalysts are essential to a plethora of processes in the chemical industry. The overall performance of these catalysts depends strongly on the interaction of adsorbates at the atomic level, which can be manipulated and controlled by the different constituents of the active material (i.e., support and active metal). The description of catalyst activity and the relationship between active constituent and the support, or metal-support interactions (MSI), in heterogeneous (thermo)catalysts is a complex phenomenon with multivariate (dependent and independent) contributions that are difficult to disentangle, both experimentally and theoretically. So-called "strong metal-support interactions" have been reported for several decades and summarized in excellent review articles. However, in recent years, there has been a proliferation of new findings related to atomically dispersed metal sites, metal oxide defects, and, for example, the generation and evolution of MSI under reaction conditions, which has led to the designation of (sub)classifications of MSI deserving to be critically and systematically evaluated. These include dynamic restructuring under alternating redox and reaction conditions, adsorbate-induced MSI, and evidence of strong interactions in oxide-supported metal oxide catalysts. Here, we review recent literature on MSI in oxide-supported metal particles to provide an up-to-date understanding of the underlying physicochemical principles that dominate the observed effects in supported metal atomic, cluster, and nanoparticle catalysts. Critical evaluation of different subclassifications of MSI is provided, along with discussions on the formation mechanisms, theoretical and characterization advances, and tuning strategies to manipulate catalytic reaction performance. We also provide a perspective on the future of the field, and we discuss the analysis of different MSI effects on catalysis quantitatively.

Localized ultrafine Cu clusters within MOF-derived metal oxides for collective photochemical and photothermal H2 generation

The ability to prepare ultrafine metal cluster (UMC) in supported catalysts, which exhibit extraordinary physical and chemical properties offers exciting opportunities to tailoring catalytic performance. However, the fabrication of singly-dispersed metal cluster catalysts that are both catalytic stable and active remains challenging. In this work, ultrafine Cu clusters has been spatially immobilized within the MOF derived photocatalyst matrix to realize a unitary photocatalyst with high density and stable active sites for charge separation and photothermal co-functions. Furthermore, the embedded Cu is capable of overcoming challenges related to porous structure collapse, disparate material interfaces and incompatibility between light absorption and charge transfer processes. Resultantly, the photocatalyst (m-TiO2/Cu) exhibits a high and stable H2 generation rate of 17.8 mmolg−1h−1 that is ∼69 times higher compared to the control. In essence, this study presents an efficient approach to immobilize ultrafine metal active sites for the development of high-performance heterogeneous catalysts for energy applications.

Efficient degradation of tetracycline residues in pharmaceutical wastewater by Ni/Fe bimetallic atomic cluster composite catalysts with enhanced electron transfer pathway

Metal cluster catalysts have large atomic load, interaction between atomic sites, and wide application of catalysis. In this study, a Ni/Fe bimetallic cluster material was prepared by a simple hydrothermal method and used as an efficient catalyst to activate the degradation system of peroxymonosulfate (PMS), which showed nearly 100% tetracycline (TC) degradation performance over a wide pH range (pH = 3–11). The results of electron paramagnetic resonance test, quenching experiment and density functional theory (DFT) calculation show that the non-free radical pathway electron transfer efficiency of the catalytic system is effectively improved, and a large number of PMS are captured and activated by high density Ni atomic clusters in Ni/Fe bimetallic clusters. The degradation intermediates identified by LC/MS showed that TC was efficiently degraded into small molecules. In addition, the Ni/Fe bimetallic cluster/PMS system has excellent efficiency for degrading various organic pollutants and practical pharmaceutical wastewater. This work opens up a new way for metal atom cluster catalysts to efficiently catalyze the degradation of organic pollutants in PMS systems.

Tailoring of Three-Atom Metal Cluster Catalysts for Ammonia Synthesis

Electrocatalytic nitrogen reduction reaction (NRR) can realize the green production of ammonia while developing electrocatalysts with high selectivity and ability is still an ongoing challenge. Two-dimensional (2D) graphitic carbon nitride (CN) frameworks can provide abundant hollow sites for stably anchoring several transition metal (TM) atoms to facilitate single-cluster catalysis, promising to overcome the problems of low activity and poor selectivity in the process of ammonia synthesis. Herein, extensive density functional theory (DFT) calculations were performed to investigate the feasibility of six bimetallic triatomic clusters FexMoy (x = 1, 2; x + y = 3) supported on C6N6, C2N, and N-doped porous graphene (NG) as NRR electrocatalysts. Through a systematic screening strategy, we found that the Fe2Mo–NG possesses the highest activity with a limiting potential of –0.36 V through the enzymatic mechanism and could be the promising catalyst for NH3 synthesis. The Fe2Mo moiety in Fe2Mo–NG moderately regulates the electron transfer between reaction intermediates and NG, which is ascribed to enhanced performance. This work accelerates the rational design of catalysts in the field of NRR and contributes to broadening the understanding of cluster catalysis.

Single Atom and Metal Cluster Catalysts in Organic Reactions: From the Solvent to the Solid

AbstractThe supporting of pre‐formed soluble metal catalysts on solids is a typical methodology to transform soluble but unrecoverable metal complexes into recoverable and reusable solid catalysts. However, this methodology has been barely implemented for ligand‐less, bare single metal atoms (SMAs) and nanoclusters (NCs) in organic synthesis, despite these ultrasmall species can be formed in‐situ during reaction and be the truly catalytic species. The aim of this review is to explore how to speciate active single metal atoms and clusters during homogeneous catalysis (in solution), without ligands, and to prepare them independently, to be transferred to solid supports and catalyze organic reactions. In many cases, the translation to solids gives single atom catalysts (SACs). Supporting of ultrasmall metal aggregates gives more stable, reusable and, sometimes, chemoselective catalysts for representative organic reactions.

Facile and Eco-Friendly Approach To Produce Confined Metal Cluster Catalysts

Zeolite-supported metal nanocluster catalysts have attracted significant attention due to their broad application in heterogeneously catalyzed reactions. The preparation of highly dispersed metal catalysts commonly involves the use of organic compounds and requires the implementation of complicated procedures, which are neither green nor deployable at the large scale. Herein, we present a novel facile method (vacuum-heating) which employs a specific thermal vacuum processing protocol of catalysts to promote the decomposition of metal precursors. The removal of coordinated H2O via vacuum-heating restricts the formation of intermediates (metal-bound OH species), resulting in catalysts with a uniform, metal nanocluster distribution. The structure of the intermediate was determined by in situ Fourier transform infrared, temperature-programmed decomposition, and X-ray absorption spectroscopy (XAS) measurements. This alternative synthesis method is eco-friendly and cost-effective as the procedure occurs in the absence of organic compounds. It can be widely used for the preparation of catalysts from different metal species (Ni, Fe, Cu, Co, Zn) and precursors and is readily scaled-up.

Electronic and structural engineering of supported single atomic layer, low-nuclearity palladium catalysts for conversion of levulinic acid to 1,4-pentanediol

The size and geometry of supported metal ensembles have a substantial influence on their catalytic efficacy and are pivotal in the design of effective heterogeneous catalysts. Here we developed a straightforward electronic and structural engineering strategy to create supported single atomic-layered, low-nuclearity palladium catalysts. This atomically dispersed Pd catalyst possesses unique synergistic geometric and electronic effects and nearly full metal availability to the reactant, exhibiting excellent catalytic activity (turnover frequency of 12480 h−1) and yield (>99%) in the hydrogenation of levulinic acid to 1,4-pentanediol under mild conditions, a reaction of importance for conversion of biomass to renewable chemicals. Theoretical calculations reveal that the high catalytic activity results from the cooperation of adjacent Pd atoms, high d-band center, and strong electronic metal-support interactions, thus guaranteeing efficient activation of reactant and facilitating the subsequent ring-opening step. The present work sheds light on the elegant design of low-nuclearity metal cluster catalysts with structure sensitivity to maximize the catalytic efficiency at the atomic scale.

Graphene-confined ultrafast radiant heating for high-loading subnanometer metal cluster catalysts.

Thermally activated ultrafast diffusion, collision and combination of metal atoms comprise the fundamental processes of synthesizing burgeoning subnanometer metal clusters for diverse applications. However, so far, no method has allowed the kinetically controllable synthesis of subnanometer metal clusters without compromising metal loading. Herein, we have developed, for the first time, a graphene-confined ultrafast radiant heating (GCURH) method for the synthesis of high-loading metal cluster catalysts in microseconds, where the impermeable and flexible graphene acts as a diffusion-constrained nanoreactor for high-temperature reactions. Originating from graphene-mediated ultrafast and efficient laser-to-thermal conversion, the GCURH method is capable of providing a record-high heating and cooling rate of ∼109°C/s and a peak temperature above 2000°C, and the diffusion of thermally activated atoms is spatially limited within the confinement of the graphene nanoreactor. As a result, due to the kinetics-dominant and diffusion-constrained condition provided by GCURH, subnanometer Co cluster catalysts with high metal loading up to 27.1wt% have been synthesized by pyrolyzing a Co-based metal-organic framework (MOF) in microseconds, representing one of the highest size-loading combinations and the quickest rate for MOF pyrolysis in the reported literature. The obtained Co cluster catalyst not only exhibits an extraordinary activity similar to that of most modern multicomponent noble metal counterparts in the electrocatalytic oxygen evolution reaction, but is also highly convenient for catalyst recycling and refining due to its single metal component. Such a novel GCURH technique paves the way for the kinetically regulated, limited diffusion distance of thermally activated atoms, which in turn provides enormous opportunities for the development of sophisticated and environmentally sustainable metal cluster catalysts.

Reactivity and Recyclability of Ligand-Protected Metal Cluster Catalysts for CO2 Transformation.

It remains a significant challenge to construct an integrated catalyst that combines advantages of homogeneous and heterogeneous catalysis with clarified mechanism and high performance. Here we show atomically precise CuAg cluster catalysts for CO2 capture and utilization, where two functional units are combined into the clusters: metal and ligand. Due to atomic resolution on total and local structures of such catalysts to be achieved, which disentangles heterogeneous imprecise systems and permits tracing the reaction processes via experiments coupled with theory, site-specific catalysis induced by metal-ligand synergy can be accurately elucidated. The CuAg cluster catalysts exhibit excellent reactivity and recyclability to forge the C-N bonding from CO2 formylation with secondary amines that can make the cluster catalysts more unique compared with typically homogeneous complexes.

Reactivity and Recyclability of Ligand‐Protected Metal Cluster Catalysts for CO2 Transformation

AbstractIt remains a significant challenge to construct an integrated catalyst that combines advantages of homogeneous and heterogeneous catalysis with clarified mechanism and high performance. Here we show atomically precise CuAg cluster catalysts for CO2 capture and utilization, where two functional units are combined into the clusters: metal and ligand. Due to atomic resolution on total and local structures of such catalysts to be achieved, which disentangles heterogeneous imprecise systems and permits tracing the reaction processes via experiments coupled with theory, site‐specific catalysis induced by metal‐ligand synergy can be accurately elucidated. The CuAg cluster catalysts exhibit excellent reactivity and recyclability to forge the C−N bonding from CO2 formylation with secondary amines that can make the cluster catalysts more unique compared with typically homogeneous complexes.

Ordered Mesopore Confined Pt Nanoclusters Enable Unusual Self-Enhancing Catalysis.

As an important kind of emerging heterogeneous catalyst for sustainable chemical processes, supported metal cluster (SMC) catalysts have received great attention for their outstanding activity; however, the easy aggregation of metal clusters due to their migration along the substrate's surface usually deteriorates their activity and even causes catalyst failure during cycling. Herein, stable Pt nanoclusters (NCs, ∼1.06 nm) are homogeneously confined in the uniform spherical mesopores of mesoporous titania (mpTiO2) by the interaction between Pt NCs and metal oxide pore walls made of polycrystalline anatase TiO2. The obtained Pt-mpTiO2 exhibits excellent stability with well-retained CO conversion (∼95.0%) and Pt NCs (∼1.20 nm) in the long term water-gas shift (WGS) reaction. More importantly, the Pt-mpTiO2 displays an unusual increasing activity during the cyclic catalyzing WGS reaction, which was found to stem from the in situ generation of interfacial active sites (Ti3+-Ov-Ptδ+) by the reduction effect of spillover hydrogen generated at the stably supported Pt NCs. The Pt-mpTiO2 catalysts also show superior performance toward the selective hydrogenation of furfural to 2-methylfuran. This work discloses an efficient and robust Pt-mpTiO2 catalyst and systematically elucidates the mechanism underlying its unique catalytic activity, which helps to design stable SMC catalysts with self-enhancing interfacial activity in sustainable heterogeneous catalysis.

Three-way metal cluster catalysts confined in zeolites produced by pulsed laser ablation in liquid

Three-way metal cluster catalysts confined in zeolites produced by pulsed laser ablation in liquid

Design of efficient noble metal single-atom and cluster catalysts toward low-temperature preferential oxidation of CO in H2

The preferential oxidation of CO in H2 is attractive for the removal of trace amounts of CO to meet the requirement of proton-exchange membrane fuel cells (PEMFCs) application. The key is to design highly effective catalysts that work well in a wide range of low temperatures. Here, the recent progress in Au and Pt group metal catalysts for the PROX reaction is summarized, covering those with single-atom and cluster dispersed metal species with remarkable performance. Firstly, the progress of some representative catalysts is overviewed, with an emphasis on the strategies for improving low-temperature activity, selectivity, and stability. Then, special attention is focused on the key parameters affecting performance in the PROX reaction. Moreover, the reaction mechanisms in terms of adsorption and activation of reactants are discussed. Finally, the challenges and opportunities are offered for guiding the design of advanced noble metal catalysts toward the PROX process.

Photodriven Catalytic Hydrogenation of CO2 to CH4 with Nearly 100% Selectivity over Ag25 Clusters.

The conversion of chemically inert carbon dioxide and its photoreduction to value-added products have attracted enormous attention as an intriguing prospect for utilizing the principal greenhouse gas CO2. Herein, we explore the use of Ag25 clusters with well-defined atomic structures for high-selectivity photocatalytic hydrogenation of CO2 to methane. Ag25 clusters, with molecular-like properties and surface plasmon resonance, exhibit competitive catalytic activity for light-driven CO2 reduction that yield an almost 100% product selectivity of methane at a relatively mild temperature (100 °C). DFT calculations reveal that the absorption of CO2 on Ag25 clusters is energetically favorable. The methanation of the Ag25 cluster catalyst has been investigated by operando infrared spectroscopy, verifying that methane was produced through a -H-assisted multielectron reaction pathway via the transformation of formyl and formaldehyde species to form surface CHx. This work presents a highly efficient strategy for high-performance CO2 methanation via well-defined metal cluster catalysts.

Exploring Metal Cluster Catalysts Using Swarm Intelligence: Start with Hydrogen Adsorption

Exploring Metal Cluster Catalysts Using Swarm Intelligence: Start with Hydrogen Adsorption

Surface reconstruction induced highly efficient N-doped carbon nanosheet supported copper cluster catalysts for dimethyl carbonate synthesis

N-doped hierarchical porous carbon nanosheets-supported copper catalysts (Cu/NCNS-x) were fabricated to solve the problem of deactivation caused by the leaching, agglomeration and oxidation of Cu nanoparticles (NPs) in the dimethyl carbonate (DMC) synthesis. The optimal Cu/NCNS-12 exhibited superb activity and stability without obvious deactivation after 10 cycles. The nanosheet structure produced new defects resulting in Cu reconstruction during the reaction process, while the strong interaction between Cu0 and N atoms greatly inhibited the oxidation of Cu0. The reconstruction of Cu was stimulated at above 100 °C, regardless of atmosphere, solvent types, pressure and rotation speed. The mechanism was elaborated that the initial Cu NPs (11 nm) migrated and then was trapped into newly created defects, finally formed into clusters (0.91 nm) as well as single-atom sites. This work provides profound potential in understanding metal reconstruction and developing a promising synthetic strategy of metal cluster catalysts.

Theoretical studies about C2H2 semi-hydrogenation on the carbon material supported metal cluster catalysts: Influences of support type and cluster size on the catalytic performance

The support type and cluster size of the supported catalysts strongly affect their catalytic performance toward the targeted reaction. This study is designed to investigate the influences of support type and cluster size on C2H4 selectivity and activity of C2H2 semi-hydrogenation; density functional theory calculations were utilized to illustrate C2H2 semi-hydrogenation mechanism on the catalysts with the different carbon material supported different sizes of metal clusters. The results show that for the different carbon material supported single-atom Cu or Pd catalysts, the support types greatly affect C2H4 selectivity and activity, among them, GDY support shows excellent catalytic performance. On the other side, as to the Mn/GDY (M=Cu, Pd) catalysts with different cluster sizes, the activity of Pdn/GDY is generally better than that of Cun/GDY; while the selectivity of Cun/GDY is better than that of Pdn/GDY. Interestingly, Pd1/GDY presents excellent C2H4 selectivity and activity for C2H2 semi-hydrogenation, attributing to its moderate Mulliken charge of metal atoms. This study could provide valuable structure clue for the obtaining of highly-efficient supported catalysts with suitable carbon material support and cluster size.