Metal Single-atom Catalysts Research Articles

Noble Metal Single-Atom Catalysts for the Catalytic Oxidation of Volatile Organic Compounds.

Volatile organic compounds (VOCs) are detrimental to the environment and human health and must be eliminated before discharging. Oxidation by heterogeneous catalysts is one of the most promising approaches for the VOCs abatement. Precious metal catalysts are highly active for the catalytic oxidation of VOCs, but they are rare and their high price limits large-scale application. Supported metal single-atom catalysts (SACs) have a high atom efficiency and provide the possibility to circumvent such limitations. This Review summarizes recent advances in the use of metal SACs for the complete oxidation of VOCs, such as benzene, toluene, formaldehyde, and methanol, as well as aliphatic and Cl- and S-containing hydrocarbons. The structures of the metal SACs used and the reaction mechanisms of the VOC oxidation are discussed. The most widely used SACs are noble metals supported on oxides, especially on reducible oxides, such as Mn2 O3 and TiO2 . The reactivity of most SACs is related to the activity of surface lattice oxygen of the oxides. Furthermore, several metal SACs show better reactivity and improved S and Cl resistance than the corresponding nanocatalysts, indicating that SACs have potential for application in the oxidation of VOCs. The deactivation and regeneration mechanisms of the metal SACs are also summarized. It is concluded that the application of metal SACs in catalytic oxidation of VOCs is still in its infancy. This Review aims to elucidate structure-performance relationships and to guide the design of highly efficient metal SACs for the catalytic oxidation of VOCs.

Unprecedentedly high activity and selectivity for hydrogenation of nitroarenes with single atomic Co1-N3P1 sites

Transition metal single atom catalysts (SACs) with M1-Nx coordination configuration have shown outstanding activity and selectivity for hydrogenation of nitroarenes. Modulating the atomic coordination structure has emerged as a promising strategy to further improve the catalytic performance. Herein, we report an atomic Co1/NPC catalyst with unsymmetrical single Co1-N3P1 sites that displays unprecedentedly high activity and chemoselectivity for hydrogenation of functionalized nitroarenes. Compared to the most popular Co1-N4 coordination, the electron density of Co atom in Co1-N3P1 is increased, which is more favorable for H2 dissociation as verified by kinetic isotope effect and density functional theory calculation results. In nitrobenzene hydrogenation reaction, the as-synthesized Co1-N3P1 SAC exhibits a turnover frequency of 6560 h−1, which is 60-fold higher than that of Co1-N4 SAC and one order of magnitude higher than the state-of-the-art M1-Nx-C SACs in literatures. Furthermore, Co1-N3P1 SAC shows superior selectivity (>99%) toward many substituted nitroarenes with co-existence of other sensitive reducible groups. This work is an excellent example of relationship between catalytic performance and the coordination environment of SACs, and offers a potential practical catalyst for aromatic amine synthesis by hydrogenation of nitroarenes.

Engineering the Local Atomic Environments of Indium Single‐Atom Catalysts for Efficient Electrochemical Production of Hydrogen Peroxide

The in-depth understanding of local atomic environment-property relationships of p-block metal single-atom catalysts toward the 2 e- oxygen reduction reaction (ORR) has rarely been reported. Here, guided by first-principles calculations, we develop a heteroatom-modified In-based metal-organic framework-assisted approach to accurately synthesize an optimal catalyst, in which single In atoms are anchored by combined N,S-dual first coordination and B second coordination supported by the hollow carbon rods (In SAs/NSBC). The In SAs/NSBC catalyst exhibits a high H2 O2 selectivity of above 95 % in a wide range of pH. Furthermore, the In SAs/NSBC-modified natural air diffusion electrode exhibits an unprecedented production rate of 6.49 mol peroxide gcatalyst -1 h-1 in 0.1 M KOH electrolyte and 6.71 mol peroxide gcatalyst -1 h-1 in 0.1 M PBS electrolyte. This strategy enables the design of next-generation high-performance single-atom materials, and provides practical guidance for H2 O2 electrosynthesis.

Regulating the coordination environment of Ru single-atom catalysts and unravelling the reaction path of acetylene hydrochlorination

In this work, DFT calculations were used firstly to simulate the nitrogen coordinated metal single-atom catalysts (M-Nx SACs, M = Hg, Cu, Au, and Ru) to predict their catalytic activities in acetylene hydrochlorination. The DFT results showed that Ru-Nx SACs had the best catalytic performance among the four catalysts, and Ru-Nx SACs could effectively inhibit the reduction of ruthenium cation. To verify the DFT results, Ru-Nx SACs were fabricated by pyrolyzing MOFs in-situ spatially confined metal precursors. The N coordination environment could be controlled by changing the pyrolysis temperature. Catalytic performance tests indicated that low N coordination number (Ru–N2, Ru–N3) exhibited excellent catalytic activity and stability compared to RuCl3 catalyst. DFT calculations further revealed that Ru–N2 and Ru–N3 had a tendency to activate HCl at the first step of reaction, whereas Ru–N4 tended to activate C2H2. These findings will serve as a reference for the design and control of metal active sites.

Structural rule of N-coordinated single-atom catalysts for electrochemical CO2 reduction

Metal single-atom catalysts (SACs) on N2-coordinated N-doped graphenes exhibit an attractive prospect in electrochemical CO2 reduction.

Machine learning assisted high-throughput screening of transition metal single atom based superb hydrogen evolution electrocatalysts

Carbon-based transition metal (TM) single-atom catalysts (SACs) have shown great potential toward electrochemical water splitting and H2 production.

Metal-organic framework derived single-atom catalysts for electrochemical CO2 reduction.

With maximum atomic utilization, transition metal single atom catalysts (SACs) show great potential in electrochemical reduction of CO2 to CO. Herein, by a facile pyrolysis of zeolitic imidazolate frameworks (ZIFs) assembled with tiny amounts of metal ions, a series of metal-nitrogen-carbon (M-N-C) based SACs (M = Fe, Ni, Mn, Co and Cu), with metal single atoms decorated on a nitrogen-doped carbon support, have been precisely constructed. X-ray photoelectron spectroscopy (XPS) for M-N-C showed that the N 1s spectrum was deconvoluted into five peaks for pyridinic (∼398.3 eV), M-N coordination (∼399.6 eV), pyrrolic (∼400.4 eV), quaternary (∼401.2 eV) and oxidized (∼402.9 eV) N species, demonstrating the existence of M-N bonding. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) indicates homogeneous distribution of metal species throughout the N-doped carbon matrix. Among the catalysts examined, the Fe-N-C catalyst exhibits the best catalytic performance in electrocatalytic CO2 reduction reaction (CO2RR) with nearly 100% faradaic efficiency for CO (FECO) at -0.9 V vs. the reversible hydrogen electrode (RHE). Ni-N-C is the second most active catalyst towards CO2RR performance, then followed by Mn-N-C, Co-N-C and Cu-N-C. Considering the optimum activity of Fe-N-C catalyst for the CO2RR, we then further investigate the effect of pyrolysis temperature on CO2RR of the Fe-N-C catalyst. We find the Fe-N-C catalyst pyrolyzed at 1000 °C exhibits the best catalytic activity in CO2RR with excellent CO selectivity.

Screening of transition metal single-atom catalysts supported by a WS2 monolayer for electrocatalytic nitrogen reduction reaction: insights from activity trend and descriptor.

The electrocatalytic nitrogen reduction reaction (NRR), as an alternative green technology to the Haber-Bosch process, can efficiently synthesize ammonia under ambient conditions and has a reduced carbon footprint. Here we systematically investigate the NRR activity and selectivity of transition metal (TM) single-atom catalyst (SAC) anchored WS2 monolayers (TM@WS2) by means of first-principles calculations and microkinetic modeling. The construction of the reaction activity trend and the identification of an activity descriptor, namely *N2H adsorption energy, facilitate the efficient screening and rational design of SACs with high activity. Manipulating the adsorption strength of the pivotal *N2H intermediate is a potential strategy for enhancing NRR activity. Utilizing the limiting potential difference of NRR and the hydrogen evolution reaction (HER) as a selectivity descriptor, we screen three SACs with excellent activity and selectivity toward NRR, i.e., Re@WS2, Os@WS2 and Ir@WS2 with favorable limiting potentials of -0.44 V, -0.38 V and -0.69 V. By using the explicit H9O4+ model, the kinetic barriers of the rate-determining steps (0.47 eV-1.15 eV) of the solvated proton transfer on the screened SACs are found to be moderate, indicative of a kinetically feasible process. Microkinetic modeling shows that the turnover frequencies of N2 reduction to NH3 on Re@WS2, Os@WS2 and Ir@WS2 are 1.52 × 105, 8.21 × 102 and 4.17 × 10-4 per s per site at 400 K, achieving fast reaction rates. The coexistence of empty and occupied 5d orbitals of candidate SACs is beneficial for σ donation and π* backdonation, endowing them with extraordinary N2 adsorption and activation. Moreover, the screened SACs possess good dispersity and thermodynamic stability. Our work provides a promising solution for the efficient screening and rational design of high-performance electrocatalysts toward the NRR.

First Principles Screening of Transition Metal Single-Atom Catalysts for Nitrogen Reduction Reaction

First Principles Screening of Transition Metal Single-Atom Catalysts for Nitrogen Reduction Reaction

Single Ni active sites with a nitrogen and phosphorus dual coordination for an efficient CO2 reduction.

Transition metal single-atom catalysts (SACs) have emerged as a research hotspot in CO2RRs. However, tuning the electronic configuration of a metal single-atom by employing new heteroatoms still remains a challenge. Herein, a carbon matrix loaded with a N and P co-coordinated Ni single-atom (denoted as Ni-NPC) was prepared for an efficient CO2RR. XANES and EXAFS were conducted to explore the coordination environment and charge distribution of the Ni-NPC catalyst. DFT calculations indicated that the Ni atom gained electrons from the P atom, and the Ni-NPC sample had a decreased energy barrier of +0.97 eV after doping with P atoms, which was favorable to overcome the limiting-step bottleneck for promoting CO2RR. Due to the rich Ni atomic active sites and superior P-doping effect, Ni-NPC exhibited a maximum FECO of 92% with a high current density of 22.6 mA cm-2 at -0.8V vs. RHE, which was far superior to those of NC, NPC and Ni-NC catalysts. Moreover, both the FECO and current density of the Ni-NPC catalyst remained stable for more than 16 h at -0.8 V vs. RHE, indicating a high stability for long-term CO2RR experiments.

Understanding trends in the mercury oxidation activity of single-atom catalysts

Transition metal single-atom catalysts with nitrogen-doped carbon substrates were designed and analyzed as the catalysts to oxidize Hg0 with O2, using density functional theory calculations, scaling relation analysis, and microkinetic modeling.

Non-precious transition metal single-atom catalysts for the oxygen reduction reaction: progress and prospects.

The massive exploitation and use of fossil resources have created many negative issues, such as energy shortage and environmental pollution. It prompts us to turn our attention to the development of new energy technologies. This review summarizes the recent research progress of non-precious transition metal single-atom catalysts (NPT-SACs) for the oxygen reduction reaction (ORR) in Zn-air batteries and fuel cells. Some commonly used preparation methods and their advantages/disadvantages have been summarized. The factors affecting the ORR performances of NPT-SACs have been focused upon, such as the substrate type, coordination environment and nanocluster effects. The loading mass of a metal atom has a direct effect on the ORR performances. Some general strategies for stabilizing metal atoms are included. This review points out some existing challenges of NPT-SACs, and also provides ideas for designing and synthesizing NPT-SACs with excellent ORR performances. The large-scale preparation and commercialization of NPT-SACs with excellent ORR properties are prospected.

Recent progress in electrochemical reduction of carbon dioxide on metal single‐atom catalysts

AbstractElectrochemical reduction reaction of CO2 (CO2RR) is a promising technology for alleviating the global warming caused by the emission of CO2. This technology, however, is still in the stage of finding efficient catalysts. The catalysts must be able to convert CO2 to other carbon‐based products with high activity and selectivity to valuable chemicals. In this review, previous development of heteroatom‐doped metal‐free carbon materials (H‐CMs) is briefly summarized. Recent progress of CO2RR promoted by metal single‐atom catalysts (M‐SACs) is then discussed with emphasis on the synthesis of M‐SACs, the catalytic performance, and reaction mechanisms. The high temperature pyrolysis method and electrodeposition are attracting attentions recently to prepare M‐SACs with high metal loading on N‐doped carbon materials, a very active M‐SACs system for the CO2RR. Theoretical calculations of free energy change on active sites, the Operando X‐ray absorption near edge structure (XANES), and Bader charge analysis reveal a significant role of metal oxidation state and charge transfer between metal atoms and absorbed CO. The challenges and perspectives for the extensive applications of M‐SACs in CO2RR are also discussed in this review.

Frontispiece: Photocatalytic Activity of Supported Metal Nanoparticles and Single Atoms

Metal nanoparticles (MNPs) and single atom catalysts (SACs) demonstrate photocatalytic behavior because of their unique coordination environment and electronic structure. The metallic photocatalysts can be implanted in porous materials such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and graphitic carbon nitride (g-C3N4) to enhance the photocatalytic activity by exploiting the merits of both the metal species and the porous catalyst supports. For more information, see the review by Najafi and Ghaedi et al. on Page 17999. Adapted with permission from Ref. [74–77]. Copyright 2021, Elsevier; Copyright 2019, Wiley-VCH; Copyright 2016, American Chemical Society; Copyright 2019, Open access, Frontiers Media SA, Creative Commons CC BY.

Screening of transition metal single atom catalysts supported on B36 cluster for nitrogen fixation

Developing efficient catalysis for dinitrogen (N2) fixation is a very important and challenging issue in chemistry. A large number of recent studies have shown that boron containing materials have good catalytic activity for nitrogen reduction reaction (NRR). Meanwhile, many theoretical and experimental studies also focus on the pure boron cluster system. The small size and extremely lack of electrons of the pure boron cluster system make its catalytic performance after being anchored with transition metals (TM) become very promising. Herein, we reported that the potential of a series of TM atoms (including Sc–Zn, Nb, Mo, Ru, Rh, Pd, Ta, W, Re, Os, Ir, Pt) anchored on B36 cluster for NRR. It is found that the Re-anchored B36 is the most promising candidate with a limiting potential of −0.48 V via distal mechanism, and it also has good stability, catalytic activity and selectivity for NRR. It is worth noting that there are relatively rare researches on Re-based catalysts for N2 fixation, our findings suggest that the Re-doped materials should receive attention for NRR.

Vapor-phase self-assembly for generating thermally stable single-atom catalysts

<h2>Summary</h2> Preparation of thermally stable metal single-atom catalysts (SACs) is a challenge in heterogeneous catalysis, especially on conventional supports that provide a weak metal-support interaction. In this work, we report that a modified support MgAl₂O₄ can stabilize Pt single atoms by a mechanism of vapor-phase self-assembly in a high-temperature treatment (800°C, air). The experimental results on the formation mechanism and the structure are validated by DFT and <i>ab initio</i> molecular dynamics simulations. We infer that stable triangular K₃O₃ structures help stabilize Pt single atoms at high temperatures in oxidizing conditions, exhibiting excellent reactivity for methane oxidation. The obtained Pt/K/MgAl₂O₄ SAC presents excellent stability in methane oxidation after steam treatment at elevated temperatures, whereas the Pt/MgAl₂O₄ nanocatalyst suffers from rapid deactivation due to Pt nanoparticle growth. This work paves the way for preparing thermally stable and highly active SACs using conventional high-surface-area supports, despite the weak metal-support interaction.

Photocatalytic Activity of Supported Metal Nanoparticles and Single Atoms.

Photocatalysis has been known as one of the promising technologies due to its eco-friendly nature. However, the potential application of many photocatalysts is limited owing to their large bandgaps and inefficient use of the solar spectrum. One strategy to overcome this problem is to combine the advantages of heteroatom-containing supports with active metal centers to accurately adjust the structural parameters. Metal nanoparticles (MNPs) and single atom catalysts (SACs) are excellent candidates due to their distinctive coordination environment which enhances photocatalytic activity. Metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and carbon nitride (g-C3 N4 ) have shown great potential as catalyst support for SACs and MNPs. The numerous combinations of organic linkers with various heteroatoms and metal ions provide unique structural characteristics to achieve advanced materials. This review describes the recent advancement of the modified MOFs, COFs and g-C3 N4 with SACs and NPs for enhanced photocatalytic applications with emphasis on environmental remediation.

Boosting Activity and Stability of Metal Single-Atom Catalysts via Regulation of Coordination Number and Local Composition.

Controlling the chemical environments of the active metal atom including both coordination number (CN) and local composition (LC) is vital to achieve active and stable single-atom catalysts (SACs), but remains challenging. Here we synthesized a series of supported Pt1 SACs by depositing Pt atoms onto the pretuned anchoring sites on nitrogen-doped carbon using atomic layer deposition. In hydrogenation of para-chloronitrobenzene, the Pt1 SAC with a higher CN about four but less pyridinic nitrogen (Npyri) content exhibits a remarkably high activity along with superior recyclability compared to those with lower CNs and more Npyri. Theoretical calculations reveal that the four-coordinated Pt1 atoms with about 1 eV lower formation energy are more resistant to agglomerations than the three-coordinated ones. Composition-wise decrease of the Pt-Npyri bond upshifts gradually the Pt-5d center, and minimal one Pt-Npyri bond features a high-lying Pt-5d state that largely facilitates H2 dissociation, boosting hydrogenation activity remarkably.

Engineering d‐p Orbital Hybridization in Single‐Atom Metal‐Embedded Three‐Dimensional Electrodes for Li–S Batteries (Adv. Mater. 44/2021)

Lithium–Sulfur Batteries A descriptor, the d–p hybridization state between singleatom metal catalysts (SACs) and sulfur species, to guide the design of SACs for Li–S batteries, is proposed by Shiyong Zhao, Qianfan Zhang, Guangmin Zhou, Hui-Ming Cheng, and co-workers in article number 2105947. The large-sized and flexible 3D electrodes with optimized SACs achieve high specific energy with low catalyst loading and high sulfur loading. The good mechanical stability for bending also shows potential for fabricating bendable/foldable Li–S batteries.

Novel Design Strategy of High Activity Electrocatalysts toward Nitrogen Reduction Reaction via Boron-Transition-Metal Hybrid Double-Atom Catalysts.

Electrocatalytic nitrogen reduction reaction (NRR) is a promising method for sustainable production of NH3, which provides an alternative to the traditional Haber-Bosch process. However, the poor Faraday efficiency caused by N≡N triple bond activation and competitive hydrogen evolution reaction (HER) have seriously hindered the application of NRR. In this work, a novel strategy to promote NRR through boron-transition-metal (TM) hybrid double-atom catalysts (HDACs) has been proposed. The excellent catalytic activity of HDACs is attributed to a significant difference of valence electron distribution between boron and TMs, which could better activate N≡N bonds and promote the conversion of NH2 to NH3 compared with boron or metal single-atom catalysts and traditional double-atom catalysts (DACs). Hence, by means of DFT computations, the stability, activity, and selectivity of 29 HDACs are systematically investigated to evaluate their catalytic performance. B-Ti@g-CN and B-Ta@g-CN are screened as excellent nitrogen-fixing catalysts with particularly low limiting potentials of 0.13 and 0.11 V for NRR and rather high potentials of 0.54 and 0.82 V for HER, respectively. This work provides a new idea for the rational design of efficient nitrogen-fixing catalysts and could also be widely used in other catalytic reactions.