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Theoretically, single‐atom catalysts (SACs) offer 100 % atom utilization, making them strong candidates to replace expensive nanoparticles for catalysis. However, the structural supports used to anchor the SACs dramatically reduce the utilization efficiency of atoms (i. e., the percent of atoms actually accessible by reactants) by either encapsulating the SACs completely or creating severe diffusion limitation. Either of which leads to an overall low atom utilization and thus poor electrocatalytic activity similar to that of nanoparticles. In addressing this issue, we systematically investigated how the porous structure of carbon nanospheres affects the activity of Ir‐SACs toward formic acid oxidation (FAO). Specifically, we utilized a kinetically‐controlled growth strategy to produce uniform carbon nanospheres featuring yolk‐shell, mesoporous, and hollow structures with Ir‐SACs loaded throughout the structure. At a high specific surface area of 441 m2 g−1 and exposed metal content of 1.82 wt %, the Ir‐SACs based on mesoporous carbon nanospheres showed a remarkable FAO peak current density of 30.6 mA cm−2, which was 283 and 46 times greater when benchmarked against the catalysts based on solid carbon nanospheres and 20 wt % Ir/C, respectively. [ABSTRACT FROM AUTHOR]

Palladium is one of the most utilized metals in catalysis, particularly for hydrogenation and oxidation, cross C–C coupling, hydrogen formation, photocatalytic and electrocatalytic energy conversion reactions. Heterogeneous catalysis is undergoing a considerable move involving molecular aspects, which allows a better control and understanding of the structure–reactivity relationship toward optimization of the catalyst performances and selectivities. Inspired by organometallic catalysis, nanocatalytic materials that provide heterogeneization, nanocatalyst stabilization and optimized synergies include iron oxides, polymers, dendrimers, magnetic iron oxides, metal–organic and covalent-organic frameworks, carbons, atomically precise nanoclusters and other subnanoclusters such as single atoms, dual atoms and their combination and synergies with nanoparticles. In these nanocomposites, the number of catalytically utilized expansive Pd atoms is minimized. This mini-review addresses new trends of Pd nanocatalysis including these aspects with selected examples and examines perspectives. Progress of Pd nanocatalysis are reviewed including dramatic recent decrease of Pd sub-nanoparticle size utilizing modern organic or inorganic framework matrices. [ABSTRACT FROM AUTHOR]

Developing highly efficient single-atom catalysts (SACs) for electrocatalytic carbon dioxide reduction reaction (CO2RR) is a promising approach to promoting carbon neutrality. However, challenges such as low activity, selectivity and high costs hinder industrial scaling, attributed to the lack of innate activity or insufficient transition metal (TM) active site density in current catalysts. Therefore, the focus of CO2RR research remains on developing SACs with intrinsic catalytic activity, high TM coverage and cost-effectiveness. This study presents the design of carbon-based materials with ultra-high TM coverage (TM2C12) (TM = Mo, Ru, Rh, W, Re, Os and Ir) as electrocatalyst SACs for CO2RR using density functional theory calculations. Among these materials, W2C12 (W represents tungsten) demonstrates superior selectivity and catalytic activity for CO2RR to carbon monoxide (CO) products with overpotentials of 0.45 V and a W coverage of up to 71.84 wt%. To further enhance its catalytic activity, non-metallic (NM) coordination modification (NM = B, N, O, P doping and C vacancy) was explored on W2C12. The results indicate that N-doped W2C12 (N-W2C12) can significantly improve selectivity and catalytic activity, achieving an extremely low overpotential of 0.34 V. This research offers valuable insights into designing SACs with high activity, selectivity and stability for CO2RR and other catalytic reactions.

The ubiquity of refractory organic matter in aquatic environments necessitates innovative removal strategies. Sulfate radical-based advanced oxidation has emerged as an attractive solution, offering high selectivity, enduring efficacy, and anti-interference ability. Among many technologies, sulfite activation, leveraging its cost-effectiveness and lower toxicity compared to conventional persulfates, stands out. Yet, the activation process often relies on transition metals, suffering from low atom utilization. Here we introduce a series of single-atom catalysts (SACs) employing transition metals on g-C3N4 substrates, effectively activating sulfite for acetaminophen degradation. We highlight the superior performance of Fe/CN, which demonstrates a degradation rate constant significantly surpassing those of Ni/CN and Cu/CN. Our investigation into the electronic and spin polarization characteristics of these catalysts reveals their critical role in catalytic efficiency, with oxysulfur radical-mediated reactions predominating. Notably, under visible light, the catalytic activity is enhanced, attributed to an increased generation of oxysulfur radicals and a strengthened electron donation-back donation dynamic. The proximity of Fe/CN's d-band center to the Fermi level, alongside its high spin polarization, is shown to improve sulfite adsorption and reduce the HOMO-LUMO gap, thereby accelerating photo-assisted sulfite activation. This work advances the understanding of SACs in environmental applications and lays the groundwork for future water treatment technologies.

The need to tackle CO2 emissions arising from the continuously rising combustion of fossil fuels has sparked considerable interest in investigating the reverse water gas shift (RWGS) reaction. This reaction holds great promise as an alternative technique for the conversion and utilization of CO2. In this study, a scalable method was employed to synthesize a single-atom Pt catalyst, uniformly dispersed on SiC, where up to 6.4 wt% Pt1 was loaded onto a support based on ligand modification and UV photoreduction. This Pt1/SiC catalyst exhibited a high selectivity (100%) towards the RWGS reaction; 54% CO2 conversion was observed at 900 °C with a H2/CO2 feed-in ratio of 1:1, significantly higher than the conventional Pt nanoparticle counterparts. Moreover, Pt1/SiC displayed a robust stability during the long-term test. The activation energy with as-synthesized Pt1/SiC was further calculated to be 61.6 ± 6.4 kJ/mol, which is much lower than the 91.6 ± 15.9 kJ/mol of the Pt nanoparticle counterpart and other Pt-based catalysts reported so far. This work offers new insights into the utilization of diverse single-atom catalysts for the RWGS reaction and other crucial catalytic processes, paving the way for the further exploration and application of SACs in various industrial endeavors. [ABSTRACT FROM AUTHOR]

Single atom (SA)-embedded nitrogen-doped carbon has shown great potential in environmental remediation. Nowadays, engineered nanomaterials (ENMs) have attracted great research interests in recent years. Metal-organic framework (MOF) derived SAs show the advantages of tunable topology and averaged separated active sites. SAs bridge the gap between homogeneous and heterogeneous catalysts. The reaction efficiency can be significantly improved by designing the MOFs derived from carbon and SAs. In this review, the research advanced in MOFs-derived carbon and SAs in advanced oxidation process (AOP) in water were summarized. Major strategies to fabricate the SAs derived from MOFs were discussed, including the mixed/single metal strategy, metal-containing linker strategy, pore confinement strategy, thermal diffusion strategy, and pyrolysis MOFs with bulk metals. Advanced characterization technologies have been introduced, including electron microscopy and spectroscopic methods. To explain the catalytic mechanism for various applications, the relationship between the performance and the atomic configuration was systematically discussed. Recent applications of the MOFs derived from carbon and SAs have been summarized. A series of the latest work on effectively removing pollutants by SAs are also listed. Based on the fundamental knowledge and recent practical application of MOFs-derived carbon and SAs, some perspectives on the further directions were presented. This review offers guidance for applying novel engineered nanomaterials in the water treatment field. [ABSTRACT FROM AUTHOR]

Photocatalytic generation of •OH from O3 is an intriguing avenue for aqueous organics degradation due to the high utilization of photogenerated electrons, but ambiguous information about charge transfer and surface‐active sites hinders the optimization of photocatalysts. In this work, a series of cobalt single‐atom catalysts (SACs) anchored on graphitic carbon nitride to improve •OH generation from O3 via electron reduction and catalytic activation dual pathway is synthesized. Various characterization and density functional theory calculations reveal that cobalt single atoms can introduce trap states for holes, which improve the light‐harvesting ability and accelerate the transfer of electrons and holes. Meanwhile, Co single atoms can also act as active sites to accelerate ozone decomposition and produce •OH directly. Particularly, the influence of different surface densities of Co single atoms on photogenerated electron supply and surface reaction is disclosed. A higher density of Co provided more active sites for O3 catalytic activation, but the narrowed distance between oxidation and reduction centers reduces the supply of available electrons by worsening the charge recombination. This work offers an atomic‐level correlation of the isolated metal density and photocatalytic properties, and can scientifically guide the design of high‐performance photocatalysts for organic synthesis and water purification. [ABSTRACT FROM AUTHOR]

In recent years, non-Pt-based ORR catalysts have been developing rapidly and have achieved performance comparable to or even surpassing Pt precious metal catalysts in specific reactions, offering new possibilities for Pt-based catalyst replacement and showing great promise for application. This paper reviews the recent research progress of non-Pt-based fuel cell ORR catalysts. The latest research progress of non-Pt-based ORR SACs (including single metal active site ORR SACs, multi-metal active site ORR SACs, and non-Pt-based noble metal catalyst ORR SACs), non-metallic ORR catalysts, alloy-based ORR catalysts, high-entropy alloy ORR catalysts, and other non-Pt-based fuel cell ORR catalysts are presented in detail. This paper discusses in detail the synthesis methods, characterization means, optimization of performance, and application prospects of these non-Pt-based ORR catalysts. In addition, this review details the excellent performance of these catalysts in terms of compositional and structural controllability, electrical conductivity, and chemical stability, as well as their ability to exhibit ORR activity comparable to that of commercial Pt/C catalysts. This field is full of opportunities and challenges. In summary, non-Pt-based fuel cells show great potential in ORR. With the continuous improvement of preparation and characterization technologies, catalysts have broad application and market prospects. In addition, the development trend of non-precious metal fuel cell catalysts is reviewed. [ABSTRACT FROM AUTHOR]

Global warming has been mainly attributed to the excessive release of carbon dioxide (CO 2) to the atmosphere. Several CO 2 capture and conversion technologies have been developed in the past few decades with their own merits and limitations. Electrochemical conversion of CO 2 is one of the most attractive techniques for combating CO 2 emissions. However, the efficacy of the electrochemical reduction of CO 2 hinges on the efficiency of the utilized materials (i.e., electrocatalysts). Metal organic frameworks (MOFs)-based materials have recently emerged as attractive tools for various applications, including the electrochemical conversion of CO 2. Although there are some review articles on CO 2 capture and conversion using different materials, reviews focusing specifically on the electrochemical conversion of CO 2 using MOFs-based materials are still comparatively lacking. Additionally, the field of electrochemical conversion of CO 2 into valuable chemicals is currently gaining high momentum, requiring comprehensive and recent reviews, which would provide researchers/professionals with a quick and easy access to the recent developments in this rapidly evolving research area. Accordingly, this article comprehensively reviews recent studies on the electrochemical conversion of CO 2 using pristine/modified/functionalized MOFs as well as composite materials containing MOFs. Additionally, single atom catalysts (SACs) derived from MOFs and their applications for the electrochemical conversion of CO 2 has also been reviewed. Furthermore, obstacles, challenges, limitations, and remaining research gaps have been identified, and future works to tackle them have been highlighted. Overall, this review article provides valuable discussion and insights into the recent advancements in the field of electrochemical conversion of CO 2 into chemicals using MOFs-based materials. [Display omitted] • Electrocatalytic conversion of CO 2 using MOFs-based materials is extensively reviewed. • CO 2 conversion using pristine and MOFs modified using various materials are covered. • CO 2 conversion using single atom catalysts (SACs) derived from MOFs is also discussed. • Obstacles and challenges are identified, and future work to address them is proposed. [ABSTRACT FROM AUTHOR]

Developing highly efficient single-atom catalysts (SACs) for electrocatalytic carbon dioxide reduction reaction (CO 2 RR) is a promising approach to promoting carbon neutrality. However, challenges such as low activity, selectivity and high costs hinder industrial scaling, attributed to the lack of innate activity or insufficient transition metal (TM) active site density in current catalysts. Therefore, the focus of CO 2 RR research remains on developing SACs with intrinsic catalytic activity, high TM coverage and cost-effectiveness. This study presents the design of carbon-based materials with ultra-high TM coverage (TM 2 C 12) (TM = Mo, Ru, Rh, W, Re, Os and Ir) as electrocatalyst SACs for CO 2 RR using density functional theory calculations. Among these materials, W 2 C 12 (W represents tungsten) demonstrates superior selectivity and catalytic activity for CO 2 RR to carbon monoxide (CO) products with overpotentials of 0.45 V and a W coverage of up to 71.84 wt%. To further enhance its catalytic activity, non-metallic (NM) coordination modification (NM = B, N, O, P doping and C vacancy) was explored on W 2 C 12. The results indicate that N-doped W 2 C 12 (N-W 2 C 12) can significantly improve selectivity and catalytic activity, achieving an extremely low overpotential of 0.34 V. This research offers valuable insights into designing SACs with high activity, selectivity and stability for CO 2 RR and other catalytic reactions. [Display omitted] • The M 2 C 12 catalysts possesses ultra-high coverage of TM active sites (57.11–72.73 wt%). • W 2 C 12 shows impressive intrinsic CO 2 RR activity, with a low overpotential of 0.45 V. • N doping optimizes positive charge density and overcomes selectivity and activity challenges. • N-W 2 C 12 exhibits exceptional selectivity and activity with an overpotential of only 0.34 V. • Designing descriptors based on intrinsic characteristics for CO 2 RR. [ABSTRACT FROM AUTHOR]

The architecture of heterogeneous single-atom catalysts (SACs) is deemed as an ultimate goal for the chemical industry and for materials catalysis research for many years. The design of these materials is intended in the first place to maximize the cost-efficiency of precious metals used in catalytic applications and related fields. Furthermore, SACs are highly interesting from a fundamental point of view because of their better-defined active site ensembles which facilitate the investigation of reaction mechanisms on heterogeneous catalysts, a highly debated subject since the introduction of the concept 'active sites' by H.S. Taylor. Metal-organic frameworks (MOFs) are highly attractive platforms for this purpose not only because of their exceptionally large specific surface area and structural diversity, but also because they are crystalline materials with regular structure which facilitate the elucidation of the structure of "active sites". Having these features combined in one single material is very meritorious for both fundamental and applied aspects. This review highlights the distinctive attributes of MOFs in the context of heterogeneous catalysis and outlines strategies for their use to prepare heterogeneous SACs. We discussed selected examples focusing on their catalytic applications, limitations, and future perspectives for the expansion of these materials in catalytic applications. First, we discussed concepts related to SACs, active sites, and surface reactivity. Afterwards, we gave a concise description of the buildup of MOFs and approaches to use them for the synthesis of MOF-SACs. This is followed by discussing key examples of MOF-SACs including non-noble (Cu, Fe, Ni) and noble (Pt, Rh and Au) metal centers. In addition, we highlighted strategies and examples for the use of MOF as sacrificial templates for the synthesis of highly dispersed metal-SAC composites. Finally, we discussed general perspectives and considerations for the development of these materials. [Display omitted] • Challenges for the design of heterogeneous single-atom catalysts (SACS). • Metal-organic frameworks as ideal support for the architecture of SACs. • MOF-based SACS: Ideal platform for precise mechanistic studies. • Synthesis scaling up of MOF-SACs necessity for industrial applications. [ABSTRACT FROM AUTHOR]

The need to tackle CO2 emissions arising from the continuously rising combustion of fossil fuels has sparked considerable interest in investigating the reverse water gas shift (RWGS) reaction. This reaction holds great promise as an alternative technique for the conversion and utilization of CO2. In this study, a scalable method was employed to synthesize a single-atom Pt catalyst, uniformly dispersed on SiC, where up to 6.4 wt% Pt1 was loaded onto a support based on ligand modification and UV photoreduction. This Pt1/SiC catalyst exhibited a high selectivity (100%) towards the RWGS reaction; 54% CO2 conversion was observed at 900 °C with a H2/CO2 feed-in ratio of 1:1, significantly higher than the conventional Pt nanoparticle counterparts. Moreover, Pt1/SiC displayed a robust stability during the long-term test. The activation energy with as-synthesized Pt1/SiC was further calculated to be 61.6 ± 6.4 kJ/mol, which is much lower than the 91.6 ± 15.9 kJ/mol of the Pt nanoparticle counterpart and other Pt-based catalysts reported so far. This work offers new insights into the utilization of diverse single-atom catalysts for the RWGS reaction and other crucial catalytic processes, paving the way for the further exploration and application of SACs in various industrial endeavors.

Conversion of carbon dioxide (CO2) with the help of an appropriate electrocatalyst with high stability, low onset potential, and exceptional selectivity is still one of the great tasks in the electrocatalytic reduction of CO2 to valuable chemicals. Herein, by means of systematic first-principles simulations, we investigate the CO2 reduction reaction (CO2RR) activity of zirconium-based single-, double-, and triple-atom (Zrn@C2N; n = 1–3) catalysts anchored on a graphitic carbon-nitride monolayer. In tune with the Sabatier principle, our results reveal that a moderate CO2 binding is vital for a low onset potential for the CO2RR. Consequently, based on rigorous free energy calculations, the Zr-based single-atom catalyst (SAC) is found to be most effective to convert CO2 to valuable products such as HCOOH and CH3OH. It is worth noting that CO2 reduction to HCOOH is spontaneous via the *HCOO intermediate on Zr1@C2N and involves a low onset potential of −0.23 V with respect to the reversible hydrogen electrode from the *COOH intermediate. Among all the catalysts evaluated computationally, the Zr SAC further reveals the lowest onset potential of −0.89 V for CH3OH formation. The results show that the Zr-based catalysts especially Zr1@C2N are found to effectively suppress the competitive hydrogen evolution reaction and promote the CO2RR. Moreover, all three catalysts exhibit high kinetic and thermal stability with negligible distortion due to which their structures can be retained very well up to 600 K. Thus, the current work may provide effective catalyst-design strategies for enhancing the electrocatalytic CO2RR performance of Zr-based materials. [ABSTRACT FROM AUTHOR]

Electrochemical nitrogen reduction reaction (eNRR) is one of the most important chemical reactions for the production of ammonia under ambient environment. However, the lack of in-depth understanding of the structure-activity relationship impedes the development of high-performance catalysts for ammonia production. Herein, the density functional theory (DFT) calculations are performed to reveal the structure-activity relationship for the single-atom catalysts (SACs) supported on g-C3N4, which is modified by molecular groups (i.e., H, O, and OH). The computational results demonstrate that the W-based SACs are beneficial to produce ammonia with a low limiting potential (UL). Particularly, the W-OH@g-C3N4 catalyst exhibits an ultralow UL of −0.22 V for eNRR. And the competitive eNRR selectivity can be identified by the dominant *N2 adsorption free energy than that of *H. Our findings provide a theoretical basis for the synthesis of efficient catalysts to produce ammonia. [ABSTRACT FROM AUTHOR]

A template-engaged multistep synthesis process is developed to fabricate ultrathin carbon nanosheets assembled hierarchical nanoboxes embedded with dense Mo-N 4 active sites, which exhibited excellent activity and superb stability for oxygen reduction reaction. [Display omitted] • Unique hierarchical SA-Mo-C nanoboxes were fabricated via a template-engaged multistep synthesis process. • Comprehensive characterizations including EXAFS reveal Mo-N 4 atomic sites were formed and densely dispersed in the SA-Mo-C nanoboxes. • SA-Mo-C nanoboxes exhibited better ORR performance compared to commercial Pt/C catalysts. Construction of single-atom catalysts (SACs) with maximally exposed active sites remains a challenging task mainly because of the lack of suitable host matrices. In this study, hierarchical N -doped carbon nanoboxes composed of ultrathin nanosheets with dispersed atomic Mo (denoted as hierarchical SA-Mo-C nanoboxes) were fabricated via a template-engaged multistep synthesis process. Comprehensive characterizations, including X-ray absorption fine structure analysis, reveal the formation of Mo-N 4 atomic sites uniformly anchored on the hierarchical carbon nanoboxes. The prepared catalysts offer structural and morphological advantages, including ultrathin nanosheet units, unique hollow structures and abundant active Mo-N 4 species, that result in excellent activity with a half-wave potential of 0.86 V vs. RHE and superb stability for the oxygen reduction reaction in 0.1 M KOH; thus, the catalysts are promising air–cathode catalysts for Zn-air batteries with a high peak power density of 157.6 mW cm−2. [ABSTRACT FROM AUTHOR]

Single-atom catalysts (SACs) as the new frontier in heterogeneous catalysis have attracted increasing attention. However, the rational design of SACs with high catalytic activities for specified reactions still remains challenging. Herein, we report the rational design of a Pd1-PdNPs synergistic structure on 2,6-pyridinedicarbonitrile-derived covalent triazine framework (CTF) as an efficient active site for CO2 hydrogenation to formate under ambient conditions. Compared with the catalysts mainly comprising Pd1 and PdNPs, this hybrid catalyst presented significantly improved catalytic activity. By regulating the ratio of Pd1 to PdNPs, we obtained the optimal catalytic activity with a formate formation rate of 3.66 molHCOOM·molPd−1·h−1 under ambient conditions (30°C, 0.1 MPa). Moreover, as a heterogeneous catalyst, this hybrid catalyst is easily recovered and exhibits about a 20% decrease in the catalytic activity after five cycles. These findings are significant in elucidating new rational design principles for CO2 hydrogenation catalysts with superior activity and may open up the possibilities of converting CO2 under ambient conditions.

With the great adjustment of world industrialization and the continuous improvement of energy consumption requirements, the selective conversion of biomass-based platform molecules to high-value chemicals and biofuels has become one of the most important topics of current research. Catalysis is an essential approach to achieve energy-chemical conversion through the “bond breaking-bond formation” principle, which opens a broad world for the energy sector. Single-atom catalysts (SACs) are a new frontier in the field of catalysis in recent years, and exciting achievements have been made in biomass energy chemistry. This mini-review focuses on catalytic conversion of biomass-based levulinic acid (LA) to γ-valerolactone (GVL) over SACs. The current challenges and future development directions of SACs-mediated catalytic upgrading of biomass-based LA to produce value-added GVL, and the preparation and characterization of SACs are analyzed and summarized, aiming to provide theoretical guidance for further development of this emerging field.

Deciphering the fine structure has always been a crucial approach to unlocking the distinct advantages of high activity, selectivity, and stability in single-atom catalysts (SACs). However, the complex system and unclear catalytic mechanism have obscured the significance of exploring the fine structure. Therefore, we endeavored to develop a three-component strategy to enhance oxygen reduction reaction (ORR), delving deep into the profound implications of the fine structure, focusing on central atoms, coordinating atoms, and environmental atoms. Firstly, the mechanism by which the chemical state and element type of central atoms influence catalytic performance is discussed. Secondly, the significance of coordinating atoms in SACs is analyzed, considering both the number and type. Lastly, the impact of environmental atoms in SACs is reviewed, encompassing existence state and atomic structure. Thorough analysis and summarization of how the fine structure of SACs influences the ORR have the potential to offer valuable insights for the accurate design and construction of SACs., (© 2024 Wiley-VCH GmbH.)

The performance of single-atom catalysts is greatly influenced by the chemical environment surrounding the central atom. Here, a salt-assisted method is employed to transform the tetrahedral coordination structure of zeolitic imidazolate frameworks - 8 (ZIF-8) into a planar square coordination structure without altering the ligands. During the subsequent carbonization process, concurrent with the evaporation of zinc atoms, the structure of the nitrogen and carbon carriers (NC carriers) undergoes a transition from five-membered rings to six-membered rings to preserve the 2D structure. This transition results in the generation of additional defect sites on the 2D-NC substrates. Hence, the Pt single-atom catalysts with planar square coordination symmetries can be precisely prepared via electrodeposition (denoted as 2D-Pt SAC). The Pt loading of 2D-Pt SAC is 0.49 ± 0.03 µg cm -2 , higher than that of 3D-Pt SAC (0.37 ± 0.04 µg cm -2 ). In the context of the hydrogen oxidation reaction electrocatalysis, under an overpotential of 50 mV, these single-atom catalysts with 2D coordination exhibit mass activities of 2396 A g Pt -1 (32 times higher than commercial Pt/C catalyst, 2 times higher than 3D-PtNC)., (© 2024 Wiley‐VCH GmbH.)

Abstract Catalytically active metals atomically dispersed on supports presents the ultimate atom utilization efficiency and cost‐effective pathway for electrocatalyst design. Optimizing the coordination nature of metal atoms represents the advanced strategy for enhancing the catalytic activity and the selectivity of single‐atom catalysts (SACs). Here, we designed a transition‐metal based sulfide‐Ni3S2 with abundant exposed Ni vacancies created by the interaction between chloride ions and the functional groups on the surface of Ni3S2 for the anchoring of atomically dispersed Pt (PtSA‐Ni3S2). The theoretical calculation reveals that unique Pt‐Ni3S2 support interaction increases the d orbital electron occupation at the Fermi level and leads to a shift‐down of the d ‐band center, which energetically enhances H2O adsorption and provides the optimum H binding sites. Introducing Pt into Ni position in Ni3S2 system can efficiently enhance electronic field distribution and construct a metallic‐state feature on the Pt sites by the orbital hybridization between S‐3p and Pt‐5d for improved reaction kinetics. Finally, the fabricated PtSA‐Ni3S2 SAC is supported by Ag nanowires network to construct a seamless conductive three‐dimensional (3D) nanostructure (PtSA‐Ni3S2@Ag NWs), and the developed catalyst shows an extremely great mass activity of 7.6 A mg−1 with 27‐time higher than the commercial Pt/C HER catalyst.

Catalytically active metals atomically dispersed on supports presents the ultimate atom utilization efficiency and cost‐effective pathway for electrocatalyst design. Optimizing the coordination nature of metal atoms represents the advanced strategy for enhancing the catalytic activity and the selectivity of single‐atom catalysts (SACs). Here, we designed a transition‐metal based sulfide‐Ni3S2 with abundant exposed Ni vacancies created by the interaction between chloride ions and the functional groups on the surface of Ni3S2 for the anchoring of atomically dispersed Pt (PtSA‐Ni3S2). The theoretical calculation reveals that unique Pt‐Ni3S2 support interaction increases the d orbital electron occupation at the Fermi level and leads to a shift‐down of the d ‐band center, which energetically enhances H2O adsorption and provides the optimum H binding sites. Introducing Pt into Ni position in Ni3S2 system can efficiently enhance electronic field distribution and construct a metallic‐state feature on the Pt sites by the orbital hybridization between S‐3p and Pt‐5d for improved reaction kinetics. Finally, the fabricated PtSA‐Ni3S2 SAC is supported by Ag nanowires network to construct a seamless conductive three‐dimensional (3D) nanostructure (PtSA‐Ni3S2@Ag NWs), and the developed catalyst shows an extremely great mass activity of 7.6 A mg−1 with 27‐time higher than the commercial Pt/C HER catalyst. [ABSTRACT FROM AUTHOR]

Ammonia cracking has been identified as a crucial step to unlocking a sustainable economy. Using the density functional theory, we modeled transition metal single-atom catalysts (SACs) supported on graphene and nitrogen-modified graphene to investigate the catalytic NH 3 cracking process. The results showed that (i) N-modified graphene secures the transition metal atoms (M) stronger than C-matrixes, and (ii) structures with three anchoring nitrogens (MN 3) are more reactive than MN 4 ones. On IrN 3 and RuN 3 SAC models, the N 2 evolution determines the total rate, while, on RhN 3 -SAC, it is the NH 3 dehydrogenation. Temperature-programmed desorption simulations on SACs showed variations compared to extended metal surfaces. Batch reactor simulations were employed to balance the sequence of elementary steps as a function of the temperature, revealing the overall NH 3 cracking activity. Results suggested IrN 3 and RhN 3 are strong candidates for NH 3 cracking at temperatures as low as 230 °C. [Display omitted] • Ammonia and NH X intermediates (x < 3) adsorb preferentially on top of transition metal single-atom catalysts. • Simulated TPD of N 2 and H 2 molecules showed fundamental differences between surfaces and SACs. • SACs' activity towards NH 3 cracking is determined by the metal size and band availability at the Fermi energy. • Analysis of the reaction mechanism indicated Ir, Ru, and Rh single-atom catalysts as promising candidates for NH 3 cracking. • Simulated batch reactors showed NH 3 cracking taking place at temperatures close to the thermodynamic minimum. [ABSTRACT FROM AUTHOR]

Due to the maximal atom utilization, high activity, and selectivity, the two-dimensional (2D) matrix supported single-atom catalysts (SACs) have attracted substantial research interests. In this work, we carried out the theoretical study on the stability, activity for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), and its dependence on the electronic structure of transition metal (TM) anchored on two types of borophene (called β12 and χ3) by density functional theory (DFT) calculations. The results show that the early− and VIII−TM anchored β12 and χ3 borophenes are structurally and thermodynamically stable. The overpotentials of OER (ηOER) over the Ni supported on β12 and χ3 borophene SACs, designated as β12−Ni and χ3−Ni, are 0.38 and 0.35 V, respectively. The ηORR of β12−Ni and χ3−Ni are estimated to be as low as 0.34 and 0.39 V, respectively. The OER/ORR activity of the SACs can be well correlated with their electronic structures. The high ηOER values of early TM supported on borophene SACs correspond to high d-band center of TM. Both β12−Ni and χ3−Ni have a moderate d-band center. Since the overpotentials for OER and ORR on β12−Ni and χ3−Ni are comparable to those of Pt group metals and their oxides, β12−Ni and χ3−Ni can be considered as the promising bifunctional catalysts for OER and ORR. [ABSTRACT FROM AUTHOR]

Single‐atom catalysts (SACs) have emerged as promising materials in heterogeneous catalysis. Previous studies reported controversial results about the relative level in activity for SACs and nanoparticles (NPs). These works have focused on the effect of metal atom arrangement, without considering the oxidation state of the SACs. Here, we immobilized Pt single atoms on defective ceria and controlled the oxidation state of Pt SACs, from highly oxidized (Pt0: 16.6 at %) to highly metallic states (Pt0: 83.8 at %). The Pt SACs with controlled oxidation states were then employed for oxidation of CO, CH4, or NO, and their activities compared with those of Pt NPs. The highly oxidized Pt SACs presented poorer activities than Pt NPs, whereas metallic Pt SACs showed higher activities. The Pt SAC reduced at 300 °C showed the highest activity for all the oxidations. The Pt SACs with controlled oxidation states revealed a crucial missing link between activity and SACs. [ABSTRACT FROM AUTHOR]

The ubiquity of refractory organic matter in aquatic environments necessitates innovative removal strategies. Sulfate radical-based advanced oxidation has emerged as an attractive solution, offering high selectivity, enduring efficacy, and anti-interference ability. Among many technologies, sulfite activation, leveraging its cost-effectiveness and lower toxicity compared to conventional persulfates, stands out. Yet, the activation process often relies on transition metals, suffering from low atom utilization. Here we introduce a series of single-atom catalysts (SACs) employing transition metals on g-C 3 N 4 substrates, effectively activating sulfite for acetaminophen degradation. We highlight the superior performance of Fe/CN, which demonstrates a degradation rate constant significantly surpassing those of Ni/CN and Cu/CN. Our investigation into the electronic and spin polarization characteristics of these catalysts reveals their critical role in catalytic efficiency, with oxysulfur radical-mediated reactions predominating. Notably, under visible light, the catalytic activity is enhanced, attributed to an increased generation of oxysulfur radicals and a strengthened electron donation-back donation dynamic. The proximity of Fe/CN's d-band center to the Fermi level, alongside its high spin polarization, is shown to improve sulfite adsorption and reduce the HOMO-LUMO gap, thereby accelerating photo-assisted sulfite activation. This work advances the understanding of SACs in environmental applications and lays the groundwork for future water treatment technologies., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 The Authors.)

Developing single-atom catalysts (SACs) with superior Fenton-like performance and low-cost via green synthesis strategy is an urgent problem. It was for the first time to prepare the iron single-atom catalyst (Fe-SAC) with highly atomically-dispersion from natural Fe-rich marine algae (Enteromorpha) with iron amount over 1.5 wt%. Iron screening test indicated that the activation performance of Enteromorpha -derived Fe-SACs catalyst was mainly based on Fe-N 4 -C sites, and the roles of radicals accompanying with Fe(IV) and 1O 2 oxidation showed very small contributions. In contrast, the degradation of organic was dominated by the electron-transfer process (ETP), and the ETP mechanism was greatly enhanced by the iron centers in the Enteromorpha -derived Fe-SACs, which could help extract more electrons from the organics to the Fe-N 4 -C/PMS complex, thus facilitating the ETP in catalytic system. In addition, the commercial ceramic membrane (CM) coated with Enteromorpha -derived Fe-SACs catalyst showed superior catalytic activtiy with a stable water flux. [Display omitted] • High-performance and low-cost Fe-SAC was prepared from Fe-rich marine algae. • The iron amount in Fe-SAC with Fe-N 4 -C configuration exceeded over 1.5 wt%. • Fe-N 4 -C sites were determined to be the key sites based on iron screening test. • ETP was greatly enhanced by the iron centers in the Enteromorpha -derived Fe-SACs. • Fe-SACs/CM showed superior catalytic activtiy with a stable water flux. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various single atom catalysts based on yeast-derived biochar were prepared. • Isolated metal site was stabilized by 3N and 1P atoms via tetracoordinate manner. • Mn-SA@YBC exhibited excellent reactivity for the synthesis of quinazolines. • Mn-SA@YBC exhibited good recyclability as the heterogeneous synthesis of quinazolines. The 2-substituted quinazoline moiety is the core structure of many fine chemicals, pharmaceutical agents and functional molecules. The effective synthetic strategies for the 2-substituted quinazolines are highly significant. Herein, we presented a new strategy to prepare various SACs (Mn-SA@YBC, Ni-SA@YBC, Cu-SA@YBC and Co-SA@YBC) supported on yeast-derived biochar materials for the first time. These SACs remained the original morphology of yeasts. The studies of catalytic performance of SACs revealed that Mn-SA@YBC exhibited excellent catalytic performance than the Mn-nano@YBC in the dehydrogenation of 2-aminobenzyl alcohol and aromatic nitriles forming 2-substituted quinazolines. The Mn-SA@YBC exhibited good stability, and still showed high catalytic activity without any significant loss after recycled six times. The atomically dispersed Mn atoms were observed in the aberration-corrected high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM) images of the freshly prepared and recycled Mn-SA@YBC which proved the good stability and reusability of the Mn-SA@YBC. XANES and XPS analysis indicated that the Mn atom of Mn-SA@YBC had the Mn-N 3 P coordination structure which was different from previous reports. A reasonable reaction mechanism had been proposed. It was believed that this work paved a new way for the design and preparation of active single atomic site catalysts on biochar materials. [ABSTRACT FROM AUTHOR]

The concept of "single-atom catalysis" is first proposed by Tao Zhang, Jun Li, and Jingyue Liu in 2011. Single-atom catalysts (SACs) have a very high catalytic activity and greatly improved atom utilization ratio. At present, SACs have become frontier materials in the field of catalysis. Aerogels are highly porous materials with extremely low density and extremely high porosity. These pores play a key role in determining their surface reactivity and mechanical stability. The alliance of SACs and aerogels can fully reflect their structural advantages and lead to new enhancement effects. Herein, a general concept of "atomic aerogel materials" (AAMs) (or single-atom aerogels (SAAs)) is proposed to describe this interesting new paradigm in both material and catalysis fields. Based on the basic units of "gel," the AAMs can be divided into two categories: carrier-level AAMs (with micro-, nano-, or sub-nanometer pore structures) and atomic-level AAMs (with atomic-defective or oxygen-bridged sub-nanopore structures). The basic unit of the former (i.e., single-atom-functionalized aerogels) is the carrier materials in nanostructures, and the latter (i.e., single-atom-built aerogels) is the single metal atoms in atomic structures. The atomic-defective or oxygen-bridged AAMs will be important development directions in versatile heterogeneous catalytic or noncatalytic fields. The design proposals, latent challenges, and coping strategies of this new "atomic nanosystem" in applications are pointed out as well., (© 2023 Wiley-VCH GmbH.)

Academician Tao Zhang from China and co-workers designed the first Pt 1 /FeO x single-atom catalysts (SACs) in 2011, and they proposed the concept of "single-atom catalysis" in the field of heterogeneous catalysis. Generally, it is easy for active metal single-atom sites on a carrier to migrate and aggregate, which results in poor performance; or the chemical bond between the metal atom and carrier is too strong (immovable), which results in passivation of the active site. Recently, "nano-island" type SACs were designed, in which the active metal atoms are isolated on the "islands", and can move within the respective "island", but the migration across the "island" is blocked, to achieve a dynamic confinement design of single atoms (that is, a "moving but not aggregating" design philosophy). Herein, a new concept of "single-atom nano-islands (SANIs)" is proposed to describe these congeneric "atomic-nano" systems in heterogeneous catalysis fields. Particularly, the SANIs are divided into three categories: "one-island-one-atom", "one-island-multi-atoms", and "island-sea synergism" architectures. The scientific significance and application principles of SANIs in versatile heterogeneous catalysis fields (i.e., thermocatalysis, electrocatalysis, and photocatalysis) are summarized. The challenges and proposals of SANIs are also provided., (© 2023 Wiley-VCH GmbH.)

[Display omitted] • Electrochemical reduction of carbon dioxide into fuels. • Density-functional theory calculations to find new effective electrocatalysts. • Single-atom catalysts show low overpotential and high selectivity. • N-terminated TiN (1 1 1) surface obtained experimentally as substrate. The ever-increasing concentration of carbon dioxide (CO 2) in atmosphere has been resulting in disastrous effect on the nature and environment. Among the various methods for the CO 2 reduction, the electrochemical reduction of CO 2 (e-CO 2 RR) into fuels is considered to be much more effective. In this work, we find that the single atom catalysts (SACs) (SACs = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) can be firmly anchored on the N-terminated TiN(1 1 1) surface because of high binding energies on the basis of density-functional theory calculations. We show that the SACs on the N-terminate of TiN(1 1 1) can greatly reduce the energy barrier for e-CO 2 RR and improve the selectivity of products. SACs, including Sc, Ti, and V, show a high catalytic performance to produce CH 4 with a low limiting potential of 0.68, 0.22, and 0.48 eV, respectively. Both CH 4 and CH 2 O can be obtained on SAC-Ni with the potential-determining step (PDS) of 0.77 eV. SAC-Cu can produce CH 4 and CH 3 OH. Our findings demonstrate that N-terminated surface is suitable for anchoring SACs and the catalytic performance for e-CO 2 RR, such as overpotential and selectivity, can be optimized by using different transition metals, which provides a great way for the convertion CO 2 into fuels. [ABSTRACT FROM AUTHOR]

The main factor limiting the high activity of single-atom catalysts (SACs) is the structural instability, which is caused by atomic aggregation or attack of reaction intermediates. In this paper, the single-atom transition metal copper and palladium was riveted between two layers of the monolayer materials (carbon nitride and graphene) respectively to enhance the structural stability, and used C 3 N-TM-C 3 N and GR-TM-C 3 N (TM= Cu, Pd) in the theoretical study of CO 2 reduction to methanol (CO 2 RR). It is found that a single TM atom can be firmly anchored between two C 3 N or GR-C 3 N layers, which can prevent the aggregation of TM atoms (TM= Cu, Pd) in SACs and inhibit the attack of reaction intermediates. The TM atom enhances the catalytic activity of the material system by providing electrons to the protective layer GR/C 3 N. And C 3 N-Cu-C 3 N material has the best performance and the lowest reaction energy barrier in CO 2 RR, which is only 2.094 eV. It provides a feasible method to improve the catalytic activity and maintain the stability for the practical application of SACs systems. [Display omitted] • Highly stable single-atom transition metal riveted bilayer 2D materials were constructed. • CO 2 reduction to methanol was run by C 3 N-TM-C 3 N and GR-TM-C 3 N by using DFT. • C 3 N/GR-TM-C 3 N prevent the aggregation of TM atom in SACs and inhibit the attack of intermediates. • C 3 N-Cu-C 3 N has the best performance and the lowest reaction energy barrier in CO 2 RR. • A feasible method to improve catalytic activity and maintain stability for SACs was proposed. [ABSTRACT FROM AUTHOR]

The discoveries of 2D nanomaterials have made huge impacts on the scientific community. Their unique properties unlock new technologies and bring significant advances to diverse applications. Herein, an unprecedented 2D-stacked material consisting of copper (Cu) on nitro-oxygenated carbon is disclosed. Unlike any known 2D stacked structures that are usually constructed by stacking of separate 2D layers, this material forms a continuously folded 2D-stacked structure. Interestingly, advanced characterizations indicate that Cu atoms inside the structure are in an atomically-dispersed form with extraordinarily high Cu loading up to 15.9 ± 1.2 wt.%, which is among the highest reported metal loading for single-atom catalysts on 2D supports. Facile exfoliation results in thin 2D nanosheets that maximize the exposure of the unique active sites (two neighboring Cu single atoms), leading to impressive catalytic performance, as demonstrated in the electrochemical oxygen reduction reaction., (© 2022 Wiley-VCH GmbH.)

Single-atom catalysts (SACs) as the new frontier in heterogeneous catalysis have attracted increasing attention. However, the rational design of SACs with high catalytic activities for specified reactions still remains challenging. Herein, we report the rational design of a Pd 1 -Pd NPs synergistic structure on 2,6 -pyridinedicarbonitrile-derived covalent triazine framework ( CTF ) as an efficient active site for CO 2 hydrogenation to formate under ambient conditions. Compared with the catalysts mainly comprising Pd 1 and Pd NPs , this hybrid catalyst presented significantly improved catalytic activity. By regulating the ratio of Pd 1 to Pd NPs , we obtained the optimal catalytic activity with a formate formation rate of 3.66 mol HCOOM ·mol Pd -1 ·h -1 under ambient conditions (30°C, 0.1 MPa). Moreover, as a heterogeneous catalyst, this hybrid catalyst is easily recovered and exhibits about a 20% decrease in the catalytic activity after five cycles. These findings are significant in elucidating new rational design principles for CO 2 hydrogenation catalysts with superior activity and may open up the possibilities of converting CO 2 under ambient conditions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Zhai, Zhang, Sun, Sun, Jiang, Yu, Zhai, Liu, Li and Ren.)

With the great adjustment of world industrialization and the continuous improvement of energy consumption requirements, the selective conversion of biomass-based platform molecules to high-value chemicals and biofuels has become one of the most important topics of current research. Catalysis is an essential approach to achieve energy-chemical conversion through the "bond breaking-bond formation" principle, which opens a broad world for the energy sector. Single-atom catalysts (SACs) are a new frontier in the field of catalysis in recent years, and exciting achievements have been made in biomass energy chemistry. This mini-review focuses on catalytic conversion of biomass-based levulinic acid (LA) to γ-valerolactone (GVL) over SACs. The current challenges and future development directions of SACs-mediated catalytic upgrading of biomass-based LA to produce value-added GVL, and the preparation and characterization of SACs are analyzed and summarized, aiming to provide theoretical guidance for further development of this emerging field., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Meng, Jian, Chen, Huang, Zhang and Li.)