Metal Single-atom Catalysts Research Articles

Comparative Study of NO and CO Oxidation Reactions on Single-Atom Catalysts Anchored Graphene-like Monolayer.

Noble metal single-atom catalysts (NM-SACs) anchored at novel graphene-like supports has attracted enormous interests. Gas sensitivity, catalytic activity, and d-band centers of single NM (Pt and Pd) atoms at graphenylene (graphenylene-NM) are investigated using first-principle calculations. The adsorption geometries of gas reactants on graphenylene-NM sheets are analyzed. It is found that the adsorption energies of reactant species on graphenylene-Pt are larger than those on graphenylene-Pd, because the d-band center of the Pt atom is closeser to the Fermi level. The NO and CO oxidation reactions on graphenylene-NM are investigated via four catalytic mechanisms, including Langmuir-Hinshelwood (LH), Eley-Rideal (ER), New ER (NER), and termolecular ER (TER). The results show that the NO and CO oxidations via LH and TER mechanisms can occur owing to the relatively small energy barriers. Moreover, the interaction of 2NO+2CO via ER mechanism is the energetically more favorable reaction. Although the NO oxidation via the NER mechanism has rather low energy barriers, the reaction is unlikely to occur due to the low adsorption energy of O2 compared with CO and NO. This research may provide guidance for exploring the catalytic performance of SACs on graphene-like materials to remove toxic gas molecules.

Soluble/MOF-Supported Palladium Single Atoms Catalyze the Ligand-, Additive-, and Solvent-Free Aerobic Oxidation of Benzyl Alcohols to Benzoic Acids.

Metal single-atom catalysts (SACs) promise great rewards in terms of metal atom efficiency. However, the requirement of particular conditions and supports for their synthesis, together with the need of solvents and additives for catalytic implementation, often precludes their use under industrially viable conditions. Here, we show that palladium single atoms are spontaneously formed after dissolving tiny amounts of palladium salts in neat benzyl alcohols, to catalyze their direct aerobic oxidation to benzoic acids without ligands, additives, or solvents. With this result in hand, the gram-scale preparation and stabilization of Pd SACs within the functional channels of a novel methyl-cysteine-based metal-organic framework (MOF) was accomplished, to give a robust and crystalline solid catalyst fully characterized with the help of single-crystal X-ray diffraction (SCXRD). These results illustrate the advantages of metal speciation in ligand-free homogeneous organic reactions and the translation into solid catalysts for potential industrial implementation.

Folic acid self-assembly synthesis of ultrathin N-doped carbon nanosheets with single-atom metal catalysts

The development of single-atom catalysts anchored on two-dimensional (2D) conductive matrix with well exposed active sites has great significance in electrocatalytic energy storage yet remains challenging. Inspired by the power of biomolecular self-assembly in making delicate nanostructures, we report a novel template-free folic acid (FA) self-assembly strategy to achieve the facile preparation of ultrathin N-doped carbon nanosheet confining single-metal-atom catalysts (M-N-C SAC, M = Co, Ni, Zn, Fe). The 2D association of FA is developed for the first time via the ribbon-like H bonding pattern and metal-FA coordination in a mixed solvent. A tunable metal loading content of the catalysts is facilely realized through a pH-tuned FA partial dissociation chemistry. As a proof of demonstration, Co-N-C SAC shows an excellent performance for lean electrolyte lithium-sulfur battery. Our findinging suggest a new and potentially scalable route for facile fabrication of M-N-C SACs for broad energy storage applications.

Engineering Pt and Fe dual-metal single atoms anchored on nitrogen-doped carbon with high activity and durability towards oxygen reduction reaction for zinc-air battery

Fabrication of Pt-based electrocatalysts with high activity and excellent durability is critical for the practical applications into zinc-air battery (ZAB). In this work. A novel strategy for the encapsulation of Pt species into the cavities of Fe-doped zeolite imidazolate framework is proposed to increase the density of active metal atoms and improve the activity effectively, where both isolated Pt and Fe single atoms anchored on nitrogen-doped carbon (PtFeNC) are obtained by a simple pyrolysis. Impressively, PtFeNC delivers a half-wave potential of 0.895 V (vs. RHE), Moreover, PtFeNC exhibits a lower yield of peroxide species than FeNC. Importantly, the ZAB battery shows a specific capacity of as high as 807 mA h/g at a discharge current density of 10 mA/cm2. Our findings show that dual- and multi- metallic single atom catalysts with abundant active sites can be achieved to boost electrocatalytic activity for their practical applications in energy storage though the new tactic.

High-throughput screening of transition metal single-atom catalyst anchored on Janus MoSSe basal plane for hydrogen evolution reaction

Considerable efforts have been made to enhance the hydrogen evolution reaction (HER) catalytic performance of Janus MoSSe monolayer, which have been considered to be a promising candidate due to the unique asymmetry structure. However, the activation effect remains non-optimal for the inert Janus MoSSe basal plane at present. Herein, a train of transition metal (TM) atoms were anchored on the S-/Se-/Mo-defective MoSSe basal plane to screen effective TM single-atom catalysts for HER through density functional theory (DFT) computations. Interestingly, the single Co atom anchored on Mo-defective MoSSe and the single Zn or Cd atom anchored on S-defective MoSSe were judged to possess excellent HER performance yielding a near-zero ΔGH (ΔGH = −0.050, −0.095, −0.098 eV, respectively), which is comparable to the optimized Pt-SACs. The enhanced HER activity is attributed to the doping of TM atoms (Co, Zn and Cd) which improves the conductivity of the original MoSSe and offers unoccupied states near the Fermi level decreasing the energy barrier of electrons transfer between H and TMs@MoSSe surface. In addition, the change of unoccupied antibonding states of active atoms leads to appropriate interaction between the active sites and H. The hybridization between H-s orbital and the TMs@MoSSe systems around the Fermi level also suggests the formation of stable bonding-antibonding hydrogen adsorption states. This work reveals an effective way of activating MoSSe basal plane for HER.

Single atom catalysts supported on N-doped graphene toward fast kinetics in Li–S batteries: a theoretical study

We built a novel strategy to systematically screen 3d to 5d transition metal single atom catalysts supported on N-doped defective graphene, M@N3/G and M@N4/G, toward fast kinetics in Li−S batteries. Cr@N4/G and Mn@N4/G are preferentially recommended.

Oxygen Molecule Activation on Single-Atom Catalysts with Cu, Ag, and Au: A Cluster Model Study

(M = Au, Ag, Cu;n= 1, 2, 3) clusters were used as a cluster model to study the activation of oxygen molecules on single-atom catalysts. Structures of clusters were studied by density functional calculations with global optimization. For each n, the most stable structures are quite similar for different metal types, and the oxygen molecule prefers to be adsorbed onto M atoms. It is found that the activation degree of oxygen is higher on clusters with non-noble metal Cu than that of Ag or Au containing clusters, by comparing the changes of O-O bond length and vibrational frequency, natural charge population analysis, Fuzzy bond order analysis, and energy barriers of O2 dissociation. CO oxidation was used as a probe reaction to study the reactivity of Cu-containing clusters, and it is found that the reactivity decreases with the increase of the size of silicon-oxygen clusters. Our results give a new aspect to understand the reaction mechanism of non-precious metal single-atom catalyst for oxygen activation with high efficiency.

FeS2-anchored transition metal single atoms for highly efficient overall water splitting: a DFT computational screening study

FeS2-anchored transition metal single-atom catalysts show excellent catalytic activity towards the hydrogen evolution reaction.

Metal single-atom catalysts for selective hydrogenation of unsaturated bonds

Single atom catalysts (SACs) show excellent catalytic performance in selective hydrogenation. Herein, the applications of SACs in the selective hydrogenation of unsaturated bonds are reviewed.

Research Progress of Carbon-Supported Metal Single Atom Catalysts for Oxygen Reduction Reaction

Research Progress of Carbon-Supported Metal Single Atom Catalysts for Oxygen Reduction Reaction

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

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

Multilayer stabilization for fabricating high-loading single-atom catalysts

Metal single-atom catalysts (M-SACs) have emerged as an attractive concept for promoting heterogeneous reactions, but the synthesis of high-loading M-SACs remains a challenge. Here, we report a multilayer stabilization strategy for constructing M-SACs in nitrogen-, sulfur- and fluorine-co-doped graphitized carbons (M = Fe, Co, Ru, Ir and Pt). Metal precursors are embedded into perfluorotetradecanoic acid multilayers and are further coated with polypyrrole prior to pyrolysis. Aggregation of the metals is thus efficiently inhibited to achieve M-SACs with a high metal loading (~16 wt%). Fe-SAC serves as an efficient oxygen reduction catalyst with half-wave potentials of 0.91 and 0.82 V (versus reversible hydrogen electrode) in alkaline and acid solutions, respectively. Moreover, as an air electrode in zinc–air batteries, Fe-SAC demonstrates a large peak power density of 247.7 mW cm−2 and superior long-term stability. Our versatile method paves an effective way to develop high-loading M-SACs for various applications.

Regulating kinetics and thermodynamics of electrochemical nitrogen reduction with metal single-atom catalysts in a pressurized electrolyser.

Using renewable electricity to synthesize ammonia from nitrogen paves a sustainable route to making value-added chemicals but yet requires further advances in electrocatalyst development and device integration. By engineering both electrocatalyst and electrolyzer to simultaneously regulate chemical kinetics and thermodynamic driving forces of the electrocatalytic nitrogen reduction reaction (ENRR), we report herein stereoconfinement-induced densely populated metal single atoms (Rh, Ru, Co) on graphdiyne (GDY) matrix (formulated as M SA/GDY) and realized a boosted ENRR activity in a pressurized reaction system. Remarkably, under the pressurized environment, the hydrogen evolution reaction of M SA/GDY was effectively suppressed and the desired ENRR activity was strongly amplificated. As a result, the pressurized ENRR activity of Rh SA/GDY at 55 atm exhibited a record-high NH3 formation rate of 74.15 μg h-1⋅cm-2, a Faraday efficiency of 20.36%, and a NH3 partial current of 0.35 mA cm-2 at -0.20 V versus reversible hydrogen electrode, which, respectively, displayed 7.3-, 4.9-, and 9.2-fold enhancements compared with those obtained under ambient conditions. Furthermore, a time-independent ammonia yield rate using purified 15N2 confirmed the concrete ammonia electroproduction. Theoretical calculations reveal that the driving force for the formation of end-on N2* on Rh SA/GDY increased by 9.62 kJ/mol under the pressurized conditions, facilitating the ENRR process. We envisage that the cooperative regulations of catalysts and electrochemical devices open up the possibilities for industrially viable electrochemical ammonia production.

Heterogeneous Atomic Catalysts Overcoming the Limitations of Single-Atom Catalysts

Recent advances in heterogeneous single-atom catalysts (SACs), which have isolated metal atoms dispersed on a support, have enabled a more precise control of their surface metal atomic structure. SACs could reduce the amount of metals used for the surface reaction and have often shown distinct selectivity, which the corresponding nanoparticles would not have. However, SACs typically have the limitations of low-metal content, poor stability, oxidic electronic states, and an absence of ensemble sites. In this review, various efforts to overcome these limitations have been discussed: The metal content in the SACs could increase up to over 10 wt %; highly durable SACs could be prepared by anchoring the metal atoms strongly on the defective support; metallic SACs are reported; and the ensemble catalysts, in which all the metal atoms are exposed at the surface like the SACs but the surface metal atoms are located nearby, are also reported. Metal atomic multimers with distinct catalytic properties have been also reported. Surface metal single-atoms could be decorated with organic ligands with interesting catalytic behavior. Heterogeneous atomic catalysts, whose structure is elaborately controlled and the surface reaction is better understood, can be a paradigm with higher catalytic activity, selectivity, and durability and used in industrial applications.

Theoretical Understandings of Graphene-based Metal Single-Atom Catalysts: Stability and Catalytic Performance.

Research on heterogeneous single-atom catalysts (SACs) has become an emerging frontier in catalysis science because of their advantages in high utilization of noble metals, precisely identified active sites, high selectivity, and tunable activity. Graphene, as a one-atom-thick two-dimensional carbon material with unique structural and electronic properties, has been reported to be a superb support for SACs. Herein, we provide an overview of recent progress in investigations of graphene-based SACs. Among the large number of publications, we will selectively focus on the stability of metal single-atoms (SAs) anchored on different sites of graphene support and the catalytic performances of graphene-based SACs for different chemical reactions, including thermocatalysis and electrocatalysis. We will summarize the fundamental understandings on the electronic structures and their intrinsic connection with catalytic properties of graphene-based SACs, and also provide a brief perspective on the future design of efficient SACs with graphene and graphene-like materials.

High-throughput identification of high activity and selectivity transition metal single-atom catalysts for nitrogen reduction

Developing efficient catalysts to achieve electrochemical nitrogen reduction reaction (NRR) under mild conditions remains a great challenge. Herein, 24 different transition metal (TM) single atom centers anchored on the C 9 N 4 substrate were employed to form TM@C 9 N 4 candidates catalyzing N 2 reduction. By means of high-throughput density functional theory (DFT) calculations, we conduct a comprehensive screening of catalytic activity, selectivity, and electronic origins of TM@C 9 N 4 candidates. Particularly, we reported a new descriptor φ based on the intrinsic characteristics of TM active centers, realizing a fast-scan/estimation among various candidates. Most importantly, we found that the established W@C 9 N 4 catalyst simultaneously realizes both excellent selectivity and activity toward NRR with an extremely low limiting potential of −0.24 V. These results offer useful insights into designing high-performance TM@C 9 N 4 NRR catalysts for advancing sustainable NH 3 production. • TM@C 9 N 4 candidates are screened toward NRR via high-throughput DFT calculations. • The descriptor φ realizes a fast-scan/estimation among various candidates. • The W@C 9 N 4 catalyst exhibits an extremely low limiting potential of −0.24 V.

Engineering the Low Coordinated Pt Single Atom to Achieve the Superior Electrocatalytic Performance toward Oxygen Reduction.

Configuring metal single-atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost-competitive catalyst for fuel cells' applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal-organic framework (MOF)-derived N-doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size-controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF-NC support. X-ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt-N coordination in the as-prepared Pt SACs. Benefiting from the low-coordination environment and anchoring interaction between Pt atoms and nitrogen-doping sites from MOF-NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N-doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate-determining step and enhances the activity of Pt SACs toward the ORR.

Heterogeneous catalysis under flow for the 21st century fine chemical industry

Due to metal leaching and poor catalyst stability, the chemical industry's fine chemical and pharmaceutical sectors have been historically reluctant to use supported transition metal catalysts to manufacture fine chemicals and active pharmaceutical ingredients. With the advent of new generation supported metal catalysts and flow chemistry, we argue in this study, this situation is poised to quickly change. Alongside heterogenized metal nanoparticles, both single-site molecular and single-atom catalyst will become ubiquitous. This study offers a critical outlook taking into account both technical and economic aspects.

Regulating Electronic Status of Platinum Nanoparticles by Metal–Organic Frameworks for Selective Catalysis

Selective hydrogenation of alkynes to alkenes remains challenging in the field of catalysis due to the ease of over-hydrogenated of alkynes to alkanes. Favorably, the incorporation of metal nanopar...

Non-noble metal single-atom catalyst of Co1/MXene (Mo2CS2) for CO oxidation

MXene is a variety of new two-dimensional (2D) materials with early transition metal carbides, nitrides, and carbonitrides. Quantum chemical studies have been carried out on the geometries, electronic structures, stability and catalytic properties of a non-noble metal single-atom catalyst (SAC) with single Co atom anchored on MXene materials of Mo2CS2. The Co adatom anchored on top of the Mo atom of this MXene is found to be rather stable, and this SAC is appropriate for CO oxidation. The charge transfers from the surface to the adsorbed CO and O2 play a significant role in the activation of these molecules on Co1/Mo2CS2. With this catalyst, the Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and Termolecular Eley-Rideal (TER) mechanisms are explored for CO oxidation. We find that, while all the three mechanisms are feasible at low temperature, Co1/Mo2CS2 possesses higher catalytic activity for CO oxidation through the TER mechanism that features an intriguing OC(OO)CO intermediate (IM) adsorbed on Co single atom. The calculated activation energy barriers of the rate-limiting step are 0.67 eV (TER), 0.78 eV (LH) and 0.88 eV (ER), respectively. The present study illustrates that it is promising to develop and design low-cost, non-noble metal SACs using MXene types of 2D materials.