Heterogeneous Fe3 single-cluster catalyst for ammonia synthesis via an associative mechanism

Electrocatalytic CN Coupling: Advances in Urea Synthesis and Opportunities for Alternative Products

Urea is an essential fertilizer produced through the industrial synthesis of ammonia (NH3) via the Haber-Bosch process, which contributes ≈1.2% of global annual CO2 emissions. Electrocatalytic urea synthesis under ambient conditions via CN coupling from CO2 and nitrogen species such as nitrate (NO3 -), nitrite (NO2 -), nitric oxide (NO), and nitrogen gas (N2) has gained interest as a more sustainable route. However, challenges remain due to the unclear reaction pathways for urea formation, competing reactions, and the complexity of the resulting product matrix. This review highlights recent advances in catalyst design, urea quantification, and intermediate identification in the CN coupling reaction for electrocatalytic urea synthesis. Furthermore, this review explores future prospects for industrial CN coupling, considering potential nitrogen and carbon sources and examining alternative CN coupling products, such as amides and amines.

Theoretical study of ammonia synthesis catalysed by trimetallic clusters with or without a sumanene support

DFT calculations were utilized to explore the electrocatalytic nitrogen reduction reaction (NRR) mechanisms catalyzed by trimetallic clusters M3 (M = Ti, Zr, V, and Nb), both unsupported and supported by bowl-shaped sumanene. The substrate enhanced N2 adsorption and activation but hindered hydrogenation due to more negative adsorption energies. The substrate promoted hydrogenation of nitrogen, reducing the interference of the hydrogen evolution reaction (HER) and enhancing the NRR selectivity. Three fundamental and three mixed pathways were investigated, and the rate-determining step (RDS) was identified for each pathway. Through a consecutive pathway, V3 exhibits the best catalytic performance with the free energy change of the RDS (ΔGRDS) as 0.82 eV, while the optimal supported catalyst, Nb3 supported on sumanene, has a ΔGRDS of 1.43 eV. The introduction of the substrate generally increased ΔGRDS by 0.3-0.8 eV. The substrate can effectively regulate the distance between metal atoms and reduce the change in geometric structures of M3 clusters during the reaction process, thereby enhancing the structural stability of the active sites in the NRR process. The substrate can reduce the reactivity differences among catalysts with different metal types. This so-called blurring effect allows cheap metals to partially replace noble metals while maintaining catalyst performance. A linear correlation between charge changes on M3 or M3 together with the substrate and ΔG was observed, providing a potential method for optimizing the catalyst performance and designing new catalysts.

Ammonia Synthesis over Transition Metal Catalysts: Reaction Mechanisms, Rate-Determining Steps, and Challenges

Ammonia synthesis remains a cornerstone of global chemical manufacturing, essential for fertilizer production, energy storage, and emerging carbon capture technologies. This overview examines recent developments in the understanding of elementary reaction mechanisms in heterogeneous catalysis, with emphasis on transition metal thermocatalysts operating under the Haber-Bosch process. Traditionally, the dissociative adsorption of nitrogen (N2) has been considered the rate-determining step. However, recent studies challenge this view, revealing possible shifts in rate-determining steps and suggesting that alternative mechanistic pathways may be operative. The discussion critiques studies that adhere strictly to the classic dissociative mechanism-often inferred from the reaction order of N2-while overlooking alternative pathways that could offer more efficient catalytic routes and deeper mechanistic insight into ammonia synthesis. These insights offer a pathway toward more rational catalyst design and improved process efficiency in ammonia synthesis.

Site-Specific Spin State Modulation in Spinel Oxides for Enhanced Nonradical Oxidation

Spinel oxides hold tremendous potential for driving advanced oxidation processes, yet the underlying mechanism for maximizing their activity remains unclear. In this study, we leverage tetrahedral and octahedral site interactions in MnxCo3-xO4 to modulate the spin states, specifically spin alignment and spin moment, thereby enhancing periodate (PI) activation and catalytic performance in contaminant degradation. Through combined experimental and density functional theory (DFT) analyses, we elucidate the role of spin alignment at synergetic tetrahedral and octahedral sites in facilitating quantum spin exchange interactions (QSEI) with an efficient electronic spin channel for charge transfer. Meanwhile, the engineered high spin configuration in CoMn2O4 raises the d-band center, favoring stable PI* surface complex formation and accelerating the rate-determining desorption of IO3 - with a lower-ICOHP value during the catalytic degradation of ciprofloxacin. As a result, the fine-tuned spin state of CoMn2O4 leads to enhanced overall reaction kinetics, with a 2.5-fold increase compared to MnCo2O4 and up to 22-fold increase compared to the octahedrally-active only catalysts. Such a site-specific modulation has been found applicable to other spinel oxides, enlightening fine-tuned electronic structure for maximizing catalytic performance.

Efficient Photoelectrocatalytic Synthesis of Ammonia by Superionic Conductor with Mixed Ion/Electron Conduction

Photoelectrochemical (PEC) nitrate reduction shows substantial potential for solar-to-ammonia (NH3) conversion. However, low electron density and disordered electron conduction of conventional catalysts result in limited performance and low Faraday efficiency. Herein, a FePS2.66Li0.87 superionic conductor (SIC) is developed by introducing lithium ions into van der Waals immobile layered of FePS3 catalyst. This layered crystal framework facilitates high-concentration lithium ions confinement and long-range diffusion at room temperature, transitioning the conduction mechanism from electronic to mixed ionic/electronic. The typical nanofluidic ion transport leads to a high ionic conductivity of 16.4 mS cm-1 at room temperature and enhanced electronic conductivity of 5 × 10-6 S cm-1. Furthermore, mobile lithium ions within interlayers enhance the interaction between the low-lying 3dyz orbitals of Fe interacting with 2a2 empty antibonding orbitals of NO3 -. An excellent PEC ammonia production of 134.18 µmol cm-2 h-1 with 96.95% Faradaic efficiency is achieved, and the corresponding solar-to-NH3 efficiency of 57.13% offers a promising pathway toward sustainable ammonia production.

Accelerating the global search of adsorbate molecule positions using machine-learning interatomic potentials with active learning

We present an algorithm for accelerating the search of a molecule's adsorption sites based on global optimization of surface adsorbate geometries. Our approach uses a machine-learning interatomic potential (moment tensor potential) to approximate the potential energy surface and an active learning algorithm for the automatic construction of an optimal training dataset. To validate our methodology, we compare the results across various well-known catalytic systems with surfaces of different crystallographic orientations and adsorbate geometries, including CO/Pd(111), NO/Pd(100), NH3/Cu(100), C6H6/Ag(111), and CH2CO/Rh(211). In all the cases, we observed an agreement of our results with the literature.

Highly Active and Air-Stable Iron Phosphide Catalyst for Reductive Amination of Carbonyl Compounds Enabled by Metal-Support Synergy

Iron has long been recognized as an ideal catalytic material for sustainable chemistry. However, conventional iron catalysts employed in liquid-phase hydrogenation reactions suffer from poor activity and air instability, severely restricting their wide applicability in practical use. Herein, we present the development of highly active and air-stable iron phosphide nanocrystal immobilized on zirconia (Fe2P NC/ZrO2) for the reductive amination of aldehydes and ketones. The Fe2P NC/ZrO2 catalyst demonstrated broad substrate applicability, high recyclability, and scalability in both gram-scale and continuous-flow processes. This catalyst leverages the synergistic metal-support effect of Fe2P NCs and ZrO2 support, leading to activity 313 times higher than that of conventional iron nanoparticle catalysts. In-depth mechanistic studies elucidated that the distinctive interplay between Fe2P and ZrO2 significantly accelerates ammonolysis of Schiff bases, a key step for boosting reaction efficiency. This study sets a new benchmark for iron-based catalysis, offering a robust alternative to precious metals, thereby contributing significantly to sustainable chemical manufacturing and green organic synthesis.

Boron Doping Induced Strong Anchor Effect Between Bimetal NiCo Alloy and Carbon Support for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrochemical reduction of nitrate to ammonia presents a promising alternative to the conventional Haber-Bosch process. In this study, a bimetallic NiCo alloy embedded in metal-organic framework derived carbon layer with B doping electrocatalyst NiCo@BC was first successfully developed, which exhibits excellent electrochemical nitrate reduction to ammonia (ENO3RR) performance. In-depth in situ experiments and a machine-learning potential (MLP)-based simulation reveal that B doping within the carbon layer has a crucial anchor effect that induces strong binding between bimetal NiCo alloy and carbon support. Moreover, B doping leads to a decrease in the coordination numbers around the metals, which results in a reduction of the excessively strong intermediates adsorption in the ENO3RR process, thereby significantly enhancing catalytic activity. The fabrication strategy of this electrocatalyst provides a new avenue on ENO3RR research.

Highly Dispersed Single Clusters Supported Porphyrinic Metal-Organic Frameworks for Synergetic CO2 Electroreduction to CH4

The electrocatalytic CO2 reduction is a promising path toward the carbon-neutral goal but remains a huge challenge due to the high activation barrier for CO2 and poor selectivity. Herein, the highly dispersed triruthenium single cluster (Ru3-SCs) is confined into the nanospace of pyrrole-3-carboxylic acid (PyrA)-modified nickel-porphyrin-based metal-organic framework (Ni-PCN-222-PyrA) to form the composite (Ru3-SCs@Ni-PCN-222-PyrA) through the pre-coordination confinement strategy. The prepared Ru3-SCs@Ni-PCN-222-PyrA can accelerate the selective reduction of CO2 to CH4 via electrocatalysis. Under -1.0 V versus reversible hydrogen electrode (RHE), Ru3-SCs@Ni-PCN-222-PyrA affords CO2 electroreduction to CH4 with a high selectivity of 71.9% Faradaic efficiency. Mechanistic studies reveal that the superior reactivity can be attributed to the ensemble effect and synergistic catalysis of Ru3-SCs, in which one Ru atom is responsible for CO2 reduction to *CO and another Ru atom promotes the water splitting to generate *H, and then the two intermediates of *CO and *H coupled to form the key intermediate of *CHO in a thermodynamically favorable way.

Screened Ni3 single-cluster catalyst supported on graphidyne for high-performance electrocatalytic NO reduction to NH3: A computational study

Electrocatalytic NO reduction (NORR) to NH3 represents a promising approach for converting hazardous NO waste gases into high-value NH3 products under ambient conditions. However, exploring stable, low-cost, and highly efficient catalysts to enhance the NO-to-NH3 conversion process remains a significant challenge. Herein, through systematic computational studies based on density functional theory (DFT), we rationally designed transition metal triatomic cluster supported on graphdiyne (TM3/GDY) as potential single-cluster catalysts for high-performance NORR. The results indicated that the GDY support is incredibly effective at immobilizing these triatomic metal clusters, preventing metal aggregation and dissolution. Furthermore, the TM3/GDY systems exhibit tunable reactivity for NO activation due to the synergistic effect of triple-metal sites. Among all examined candidates, Ni3/GDY demonstrates the highest NORR catalytic performance with a record low limiting potential of -0.05 V. Notably, NO adsorption strength was identified as an effective descriptor to rationalize the NORR activity trend, which is highly dependent on the amount of the carrying charges on the anchored TM3 clusters. Additionally, the hydrogenation steps during NORR are kinetically feasible on Ni3/GDY with a small kinetic barrier of 0.34 V for the rate-determining step, corresponding to an outstanding turnover frequency (3.03 × 10-25) s-1 per site at 300 K for NH3 generation, implying an ultra-fast reaction rate. Our work not only identified promising NORR catalysts but also provided valuable insights for rationally designing atomically precise novel catalysts for the resource utilization of small molecules.

First-Principles Kinetic Monte Carlo Simulations for Single-Cluster Catalysis: Study of CO2 and CH4 Conversion on Pt/HfC

The deposition of small transition metal (TM) clusters on transition metal carbides (TMC) gives rise to bifunctional catalysts with multiple active sites. This family of single-cluster catalysts (SCCs) offers exciting opportunities for enabling a wider range of chemical reactions owing to their strong metal-support interactions, which drastically modify the catalytic properties of the supported metal atoms. In this work, we use first-principles Kinetic Monte Carlo (KMC) simulations to investigate the conversion of CO2 and CH4 on Pt/HfC, which was identified as the most promising TM/TMC combination in a previous DFT-based high-throughput screening study. We analyze the interplay between the Pt clusters and the HfC support, evaluating the catalytic activity, selectivity, and adlayer composition across a broad range of operating conditions (p A , p B , and T) and Pt loadings. This study evaluates five different industrial processes, including the dry reforming (DRM), steam reforming (SRM), and partial oxidation (POM) of methane, as well as the water-gas shift (WGS) reaction and its reverse (RWGS). Our results demonstrate that the deposition of Pt clusters on HfC systematically enhances the catalytic performance, even at a Pt loading as low as ∼0.02 ML. This work illustrates the extensive catalytic benefits of SCCs and highlights the importance of considering diffusion steps and lateral interactions in kinetic modeling.

Stepwise Coordination Engineering of Pt1/Au25 Dual Catalytic Sites with Enhanced Electrochemical Activity and Stability

Dual-site catalysts hold significant promise for accelerating complex electrochemical reactions, but a major challenge remains in balancing high loading with precise dual-site architecture to achieve optimal activity, stability, and specificity simultaneously. Herein, a strategy of stepwise targeted coordination engineering is introduced to co-anchor Pt single atoms (Pt1, 1.41 wt.%) and Au25(SG)18 nanoclusters (Au25, 18.92 wt.%) with high loadings on graphitic carbon nitride (g-C3N4). This approach ensures that Pt1 and Au25 occupy distinct surface sites on the g-C3N4 substrate, providing excellent stability and unprecedented electrochemical activity. In the catalysis of As(III), a sensitivity of 8.32 µA ppb-1 is achieved, more than double the previously reported values under neutral conditions. The enhanced detection limit (0.2 ppb) is crucial for monitoring water quality and protecting public health from arsenic contamination, a significant environmental and health risk. Furthermore, the formation of Pt─As and As─S bonds facilitates the easier breakage of As─O bonds, thereby lowering the reaction barrier energy of the rate-determining step and significantly enhancing arsenious acid catalysis efficiency. These results not only offer an intriguing strategy for constructing highly efficient heterogeneous dual-site catalysts but also reveal the atomic-scale catalytic mechanisms that drive enhanced catalytic efficiency.

Suppressing Jahn-Teller distortion of MnO2 via B-Ni dual single-atoms integration for methane catalytic combustion

Precisely managing electron transfer pathways throughout the catalytic reaction is paramount for bolstering both the efficacy and endurance of catalysts, offering a pivotal solution to addressing concerns surrounding host structure destabilization and cycling life degradation. This paper describes the integration of B-Ni dual single-atoms within MnO2 channels to serve as an electronic reservoir to direct the electron transfer route during methane catalytic combustion. Comprehensive analysis discovers that B atoms weaken the interaction between O and Mn atoms by forming bonds with lattice oxygen atoms. Meanwhile, Ni atoms facilitate electron transfer to achieve the heightened activity of MnO2. The B-Ni dual-sites instead of Mn (IV) could accommodate excess electrons generated during the reaction to inhibit the formation of high spin Mn (III) species, thereby hindering the Jahn-Teller distortion and maintaining the catalyst stability. This work demonstrates an effective modification strategy to substantially prolong the service life of MnO2-based materials.

Theoretical Insights into the Efficient Reduction of Nitrate to Ammonia on Crystalline Carbon Nitride

The nitrate reduction reaction (NO3RR) has emerged as a promising approach for wastewater treatment and ammonia (NH3) synthesis. Poly(triazine imide)/LiCl (PTI/LiCl), a highly crystalline carbon nitride with a well-defined structure, has shown significant potential in this field. In this study, the electronic properties and catalytic performance of PTI/LiCl for NO3RR were investigated through theoretical calculations. Band structure and projected density of states (PDOS) analyses show that the intercalation of Li+ and Cl- ions within the PTI pores enhances electronic conductivity and improves its electronic properties. The reduction of nitrate to NH3 through a series of intermediates on the PTI/LiCl (001) surface shows exothermic free energy changes for each elementary step. The catalyst demonstrates outstanding selectivity and stability, effectively suppressing the competitive hydrogen evolution reaction and byproduct formation. Charge density difference and PDOS analyses confirm the orbital interactions between absorbed NO3 and Li ions. The study highlights the potential of PTI/LiCl as a low-cost, efficient electrocatalyst for NO3RR and provides theoretical and practical insights for the design of environmentally friendly catalysts.

Novel two-dimensional molybdenene as a promising electrocatalyst for the nitrogen reduction reaction: a first-principles prediction

The exploration of two-dimensional (2D) metallenes is driven by their noteworthy attributes, encompassing high conductivity and substantial exposure of metal active sites, facilitating the development of nitrogen reduction reaction (NRR) electrocatalysts characterized by a low overpotential and superior selectivity. Here, employing first-principles swarm-intelligence structural search methods, we predict molybdenene as a novel and stable non-precious metallene, featuring a 2-atom-thick structure. Our findings demonstrate that the basal plane of molybdenene showcases remarkable catalytic activity with an overpotential of 0.27 V. Bader charge analysis reveals that the exposed Mo bonded to NxHy groups not only transfers electrons to these groups but also the remaining Mo transfers electrons to NxHy upon the breaking of NN bonds. This electron transfer mechanism contributes to elevated NRR catalytic activity. Our work broadens the scope of metallenes as promising electrocatalysts for the NRR with the expectation that more attention will be paid to emerging metallenes, thus offering a modest contribution to the theoretical exploration, fundamental understanding and practical application of metallenes.

Phase Engineering of Zirconia Support Promotes the Catalytic Dehydrogenation of Formic Acid by Pd Active Sites

The development of Pd-based catalysts with outstanding activity and stability can further promote the hydrogen storage application of formic acid (FA). Regulating the support structure is an effective strategy for enhancing active sites in heterogeneous catalytic systems. This study prepared three types of nanosized ZrO2 through phase engineering to support Pd metal and investigated the implications of support structure on the microenvironment of active sites, thus revealing the structure-activity relationship of the catalysts. The hollow nanoframes like Pd/ZrO2-F with a moderate t-ZrO2 content exhibit remarkable stability and catalytic performance with a TOF of 1348 h-1 at an ambient temperature. Density functional theory (DFT) calculations verify that the crystal phase of ZrO2 can dramatically affect the metal-support interaction and change the Pd electronic state. Moreover, the dehydrogenation energy profiles reveal the synergy effect between ZrO2 phases on Pd active sites in the reaction. Pd/m-ZrO2 is more conducive to the dissociation of FA, and Pd/t-ZrO2 has energy advantages in hydrogen recombination. This work provides a new perspective for understanding the synergistic effect of the zirconia crystal phase on formic acid dehydrogenation by Pd active sites.

Well-defined asymmetric nitrogen/carbon-coordinated single metal sites for carbon dioxide conversion

Asymmetric nitrogen/carbon-coordinated single metal sites (M-NxC4-x) outperform symmetric M-N4 sites in carbon dioxide (CO2) electroreduction. However, the challenge of crafting well-defined M-NxC4-x sites complicates the understanding of their structure-catalytic performance relationship. In this study, we employ metallized N-confused tetraphenylporphyrin (M-NCTPP) to investigate CO2 conversion on M-N3C1 sites using both density functional theory and experimental methods. The optimal cobalt (Co)-N3C1 site (Co-NCTPP) achieves a current density of 500 mA cm-2 and a carbon monoxide Faraday efficiency exceeding 90 % at -1.25 V vs. the reversible hydrogen electrode, surpassing the performance of Co-N4 (Co-TPP). This research introduces a novel approach for designing and synthesizing high-activity heteroatom-anchored single metal sites, advancing fundamental understanding in the field.

High catalytic activity and abundant active sites in M2C12 monolayer for nitrogen reduction reaction

Developing highly efficient single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) to ammonia production has garnered significant attention in the scientific community. However, achieving high activity and selectivity remains challenging due to the lack of innate activity in most existing catalysts or insufficient active site density. This study delves into the potential of M2C12 materials (M = Cr, Ir, Mn, Mo, Os, Re, Rh, Ru, W, Fe, Cu, and Ti) with high transition metal coverage as SACs for NRR using first-principles calculations. Among these materials, Os2C12 exhibited superior catalytic activity for NRR, with a low overpotential of 0.39 V and an Os coverage of up to 72.53 wt%. To further boost its catalytic activity, a nonmetal (NM) atom doping (NM = B, N, O, and S) and C vacancy modification were explored in Os2C12. It is found that the introduction of O enables exceptional catalytic activity, selectivity, and stability, with an even lower overpotential of 0.07 V. Incorporating the O atom disrupted the charge balance of its coordinating C atoms, effectively increasing the positive charge density of the Os-d-orbit-related electronic structure. This promoted strong d-π* coupling between Os and N2H, enhancing N2H adsorption and facilitating NRR processes. This comprehensive study provides valuable insights into NRR catalyst design for sustainable ammonia production and offers a reference for exploring alternative materials in other catalytic reactions.

A theoretical investigation on the OER and ORR activity of graphene-based TM-N3 and TM-N2X (X = B, C, O, P) single atom catalysts by density functional theory calculations

Single-atom catalysts (SACs) have shown promising activity in electrocatalysis, such as CO2 reduction (CO2RR), the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR). Transition-metal-embedded N-doped graphene (M-N-C) with TM-N4 active sites (where TM represents a transition metal) is a representative SAC family that has attracted the most attention in both experimental and theoretical studies. However, TM-N3 type M-N-C has received less attention than TM-N4, although some experimental studies have reported its excellent activity in OER and CO2RR. To fully explore the electrocatalytic activity of TM-N3 type M-N-C, in this work we systematically investigate the OER and ORR activity of TM-N3 (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu) and TM-N2X (X = B, C, O, P) using density functional theory (DFT) calculation. We examine the formation energies, OER/ORR free energy diagrams, overpotentials, charge density, d-band center and electronic structure of each candidate. Our computational screening shows that CuN3 is a promising bifunctional electrocatalyst for both OER and ORR with low overpotentials of 0.31 V (OER) and 0.44 V (ORR), while CrN3 and CuN2B are predicted to be promising OER catalysts, with overpotentials of 0.26 V and 0.50 V, respectively. A volcano plot derived from the scaling relationships suggests that substituting one nitrogen atom with a hetero atom significantly affects the potential-limiting step in OER/ORR, leading to worse activity in most cases. Density of states and d-band center analyses indicate that the change in OER/ORR activity is strongly correlated with the binding strength of *OH, which is dominated by the location of the d-band center. Our simulation results introduce a comprehensive insight into the activity of the TM-N3 site in TM-N-C, which could benefit the further development of graphene-based SACs for fuel cells and renewable energy applications.

Unlocking the Nitrogen Reduction Electrocatalyst with a Dual-Metal-Boron System: From High-Throughput Screening to Machine Learning

Recently, dual-metal catalysts have attracted much attention due to their abundant active sites and tunable chemical properties. On the other hand, metal borides have been widely applied in splitting the inert chemical bonds in small molecules (such as N2) because of their excellent catalytic performances. As a combination of the above two systems, in this work, 11 kinds of transition metal atoms (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mo, and W) were selected to embed in boron-doped graphene (BG) to construct 66 dual-metal-boron systems, and their performances toward the N2 reduction reaction (NRR) were examined using first-principles simulations. Our results revealed that such a dual-TM@BG system exhibits excellent thermodynamic and electrochemical stabilities, which facilitate the experimental synthesis. In particular, Fe-Fe- and Fe-Co-doped BG exhibit excellent performance for NRR, with the limiting potentials of -0.29 and -0.32 V, respectively, and both of them exhibit inhibitory effects on the H2 evolution reaction. Remarkably, the microkinetic modeling analysis revealed that the turnover frequency for the NH3 production on FeFe@BG reaches up to 7.27 × 108 s-1 site-1 at 700 K and 100 bar, which further confirms its ultrafast reaction rate. In addition, the machine learning method was employed to further understand the catalytic mechanism, and it is found that the NRR performances of dual-TM@BG catalysts are closely related to the sum of radii of two TM atoms. Therefore, our work not only proposed two promising electrocatalysts for NRR but also verified the feasibility for the application of a dual-metal-boron system in NRR.

Molybdenum Carbide Catalyst Enables Efficient Conversion of Chlorinated Volatile Organic Waste into Syngas through Catalytic Steam Reforming

Catalytic steam reforming offers a groundbreaking approach for converting industrial chlorinated volatile organic compound (CVOC) waste into valuable syngas (H2 and CO) and recovering HCl. However, the lack of C-Cl bond activation ability in traditional transition metal catalysts results in their insufficient reforming activity toward CVOCs. Herein, a novel molybdenum carbide (β-Mo2C) catalyst is developed and loaded onto a γ-Al2O3 support synthesized through a self-assembly method. The γ-Al2O3 support provides abundant unsaturated coordinated Al3+ ions, which effectively anchor and disperse β-Mo2C nanoparticles. In the catalytic steam reforming reaction at 600 °C, the β-Mo2C/γ-Al2O3 catalyst achieves a conversion efficiency higher than 95% and syngas yields of 82.4-92.3% for various typical industrial CVOCs. The mechanistic research reveals that the coordination between C and Mo atoms in β-Mo2C leads to a slightly electron-deficient state of the Mo sites, accompanied by a high density of unoccupied 4d orbitals. These characteristics are highly advantageous for the adsorption and dechlorination of CVOC molecules. The produced nonchlorinated intermediates can subsequently be oxidized to CO and H2 by hydroxyl radicals on adjacent Mo sites.

Investigation of a Single Atom Iron Catalyst for the Electrocatalytic Reduction of Nitric Oxide to Hydroxylamine: A DFT Study

Hydroxylamine, as an important reducing agent, disinfectant, foaming agent, and biocide, plays a role in both human life and industrial production. However, its synthesis is confronted with challenges, such as high pollution and large consumption. Here, we propose a coordination tailoring strategy to design 47 graphene-supported single iron atom catalysts (SACs), namely, Fe@CxZy (Z = B, N, O, P, and S), for the reduction of nitric oxide to hydroxylamine. Using density functional theory calculations, we demonstrated the great impact of the coordination environment on the stability, catalytic selectivity, and activity of the Fe site. We identified that the experimentally available Fe@N4 possesses an ultralow theoretical limiting potential of -0.32 V compared to that of other catalysts. A comprehensive investigation of the electronic properties elucidates the underlying active origin and reaction mechanism of the nitric oxide reduction reaction to hydroxylamine on Fe@N4. These results not only explain the catalytic origin of synthesized SACs for the NH2OH production but also offer theoretical guidance for further optimizing high-performance catalysts.

One Iron for Two Iron Sites in a Metal-Organic Framework Toward Simultaneous N2-H2 Activation under Mild Conditions

Iron-based catalysts play an important role in the ammonia industry. As one of the most abundant iron minerals, Fe3O4 containing FeII and FeIII sites is widely distributed in the earth's crust and even on exoplanets, theoretically giving it both economic and catalytic potentials in ammonia synthesis. However, in the absence of specific active co-catalyst and harsh conditions, Fe3O4 is impossible to achieve ammonia synthesis alone. Here, we designed to activate the relatively inert FeII and FeIII sites in Fe3O4 with a third FeIII site inlayed in a coordination framework (MIL-101(Fe)) to achieve the unpresented multi-site collaborative catalysis. In-depth mechanism study confirmed the roles of three different Fe sites in N2 activation, H2 activation, and product transfer, respectively. Efficient N2-H2 activation to NH3 on the Fe3O4-based catalytic system has been achieved at extremely mild conditions. Our research provides a theoretical basis and a new strategy for designing efficient non-noble metal-based ammonia synthesis catalyst with minimized energy consumption.

Adjusting oxidation pathways via fine-tuning atomic ratios in window-opening MOF membranes for efficient self-cleaning

Peroxymonosulfate (PMS) can be used as a green oxidant to mitigate catalytic membranes fouling and restore filtration performance through advanced oxidation processes (AOP). However, the adjustment of oxidation pathways and the understanding of underlying mechanisms for efficient cleaning without sacrificing the filtration performance need to be studied systematically. We optimized the membranes microenvironment via thermal modification from 25 °C to 400 °C below the catalyst ZIF-8 framework's decomposition temperature. The modified membranes have a doubled pure water flux (158.3 LMH bar-1) and remain rejection rates due to intact ZIF-8 framework structure with "window-opening" effect. The methyl dissociation and self-catalyzed graphitization were regulated by changing temperature, resulting in adjustable nonradical pathway proportion (correlated with the C/Zn atomic ratio at 0.96). The enhanced nonradical pathway targeted attacks on electron-rich regions of organic compounds, resulting in efficient cleaning and almost complete flux recovery (99.3 %). The theoretical simulations revealed that methyl groups dissociation and graphitization significantly influence the electron density and adsorption energy at active sites for tunable oxidation pathways and enhanced catalytic performance. Our work offers a rational strategy to improve both filtration and catalytic performance in catalytic membranes. The enhanced understanding of oxidation mechanisms guides the design of designing efficient AOP membrane cleaning systems.

Flexible Iron Clusters Promoting Ammonia Synthesis: A Density Functional Theory Prediction

In recent years, significant research has been conducted on supported clusters due to their high dispersion, atomic efficiency, and unsaturated coordination, particularly in ammonia synthesis. This study investigates the catalytic performance of flexible iron clusters embedded in two-dimensional carbon-nitrogen materials for ammonia synthesis. Using density functional theory and ab initio molecular dynamics simulations, we demonstrate that the structural flexibility of these clusters significantly enhances their catalytic activity. The flexibility coefficient, derived from the full width at half maximum of the Fe-Fe radial distribution function, is introduced as a novel descriptor for N2 bond cleavage. Our findings reveal that flexible Fe clusters adaptively modify their structures during the reaction process, lowering energy barriers for N2 activation and subsequent hydrogenation. This study opens new avenues for designing advanced catalytic systems based on structural flexibility to meet the growing demand for sustainable and energy-efficient ammonia production.

Deciphering the Nitrogen Activation Mechanisms on Group VIII Single Atoms at MoS2

The activation of nitrogen (N2) is vital for sustainable ammonia production and nitrogen fixation technologies. This study employs density functional theory (DFT) to investigate the nitrogen activation and reduction capabilities of Group VIII single-atom catalysts anchored on MoS2. Among these, osmium anchored on MoS2 (Os@MoS2) emerged as the most promising catalyst, exhibiting the highest N2 activation and the lowest nitrogen reduction reaction (NRR) overpotential (0.624 V). A pronounced "electron drift" effect was observed for Os@MoS2, leading to significant charge redistribution that weakens the N ≡ N triple bond, facilitating its activation. The N-N dissociation energy barrier at the *N-NH2 intermediate was calculated to be only 0.82 eV, confirming Os@MoS2's superior catalytic efficiency. Detailed analyses, including electrostatic potential maps, electron localization functions, spin density, and charge transfer, revealed the pivotal role of orbital interactions in driving N2 activation. Interestingly, the trends in adsorbed N2 bond energies and NRR overpotentials showed a consistent diagonal pattern across the Group VIII catalysts, emphasizing the importance of electronic and geometric factors. This work offers valuable insights into nitrogen activation mechanisms and provides a framework for designing efficient catalysts, highlighting Os@MoS2's potential in sustainable ammonia synthesis.

Theoretical Design and Study of a Single-Atom Catalyst in Lithium-Sulfur Batteries: Edge-Type FeN4 Active Site Electron Density Redistribution Driven by Heteroatoms

Lithium-sulfur (Li-S) batteries are considered to be the most promising next-generation high energy density storage systems. However, they still face challenges, such as the shuttle effect of lithium polysulfides (LiPSs) and slow sulfur oxidation-reduction kinetics. In this work, heteroatom (P and S)-doped edge-type Fe single-atom catalytic materials (FeN4S2/P2-DG) for sulfur reduction reactions (SRRs) and sulfur oxidation reactions in Li-S batteries are investigated using density functional theory calculations. Theoretical analysis suggests that compared to planar Fe-N4 fragments, the charge density accumulation around edge-type Fe-N4 fragments in S- or P-doped structures is higher. Furthermore, the doping of P or S reduces the electron filling state of Fe_3d orbitals, leading to a decrease in electron occupancy in the antibonding orbitals, which is beneficial for the formation of d-p orbital hybridization, strengthening the anchoring strength of FeN4P2/S2-DG for S8/LiPSs. Specifically, FeN4P1,2-DG showed the lowest free energy barriers (0.57 eV) for SRRs and reduced the dissociation energy barrier of Li2S from 1.85 eV (for planar FeN4-G) to 0.96 eV during the charging process, demonstrating excellent catalytic ability. Additionally, this theoretical study provides further insights into the application of graphene-supported single-atom catalyst materials as anchoring materials for Li-S batteries.

Inhibition effect of p-d orbital hybridized PtSn nanozymes for colorimetric sensor array of antioxidants

Rational design of peroxidase (POD)-like nanozymes with high activity and specificity still faces a great challenge. Besides, the investigations of nanozymes inhibitors commonly focus on inhibition efficiency, the interaction between nanozymes-involved catalytic reactions and inhibitors is rarely reported. In this work, we design a p-block metal Sn-doped Pt (p-d/PtSn) nanozymes with the selective enhancement of POD-like activity. The p-d orbital hybridization interaction between Pt and Sn can effectively optimize the electronic structure of PtSn nanozymes and thus selectively enhance POD-like activity. In addition, the antioxidants as nanozymes inhibitors can effectively inhibit the POD-like activity of p-d/PtSn nanozymes, which results in the fact that antioxidants absorbed on the p-d/PtSn surface can hinder the adsorption of hydrogen peroxide. The inhibition type (glutathione as a model molecule) is reversible mixed-inhibition with inhibition constants (Ki' and Ki) of 0.21 mM and 0.03 mM. Finally, based on the varying inhibition levels of antioxidant molecules, a colorimetric sensor array is constructed to distinguish and simultaneously detect five antioxidants. This work is expected to design highly active and specific nanozymes through p-d orbital hybrid engineering, and also provides insights into the interaction between nanozymes and inhibitors.

p-d Orbital Hybridization in Ag-based Electrocatalysts for Enhanced Nitrate-to-Ammonia Conversion

Considering the substantial role of ammonia, developing highly efficient electrocatalysts for nitrate-to-ammonia conversion has attracted increasing interest. Herein, we proposed a feasible strategy of p-d orbital hybridization via doping p-block metals in an Ag host, which drastically promotes the performance of nitrate adsorption and disassociation. Typically, a Sn-doped Ag catalyst (SnAg) delivers a maximum Faradaic efficiency (FE) of 95.5±1.85 % for NH3 at -0.4 V vs. RHE and reaches the highest NH3 yield rate to 482.3±14.1 mg h-1 mgcat. -1. In a flow cell, the SnAg catalyst achieves a FE of 90.2 % at an ampere-level current density of 1.1 A cm-2 with an NH3 yield of 78.6 mg h-1 cm-2, during which NH3 can be further extracted to prepare struvite as high-quality fertilizer. A mechanistic study reveals that a strong p-d orbital hybridization effect in SnAg is beneficial for nitrite deoxygenation, a rate-determining step for NH3 synthesis, which as a general principle, can be further extended to Bi- and In-doped Ag catalysts. Moreover, when integrated into a Zn-nitrate battery, such a SnAg cathode contributes to a superior energy density of 639 Wh L-1, high power density of 18.1 mW cm-2, and continuous NH3 production.

Rational Design Strategy for High-Valence Metal-Driven Electronically Modulated High-Entropy Co-Ni-Fe-Cu-Mo (Oxy)Hydroxide as Superior Multifunctional Electrocatalysts

Creating durable and efficient multifunctional electrocatalysts capable of high current densities at low applied potentials is crucial for widespread industrial use in hydrogen production. Herein, a Co-Ni-Fe-Cu-Mo (oxy)hydroxide electrocatalyst with abundant grain boundaries on nickel foam using a scalable coating method followed by chemical precipitation is synthesized. This technique efficiently organizes hierarchical Co-Ni-Fe-Cu-Mo (oxy)hydroxide nanoparticles within ultrafine crystalline regions (<4 nm), enriched with numerous grain boundaries, enhancing catalytic site density and facilitating charge and mass transfer. The resulting catalyst, structured into nanosheets enriched with grain boundaries, exhibits superior electrocatalytic activity. It achieves a reduced overpotential of 199 mV at 10 mA cm2 current density with a Tafel slope of 48.8 mV dec1 in a 1 m KOH solution, maintaining stability over 72 h. Advanced analytical techniques reveal that incorporating high-valency copper and molybdenum elements significantly enhances lattice oxygen activation, attributed to weakened metal-oxygen bonds facilitating the lattice oxygen mechanism (LOM). Synchrotron radiation studies confirm a synergistic interaction among constituent elements. Furthermore, the developed high-entropy electrode demonstrates exceptional long-term stability under high current density in alkaline environments, showcasing the effectiveness of high-entropy strategies in advancing electrocatalytic materials for energy-related applications.

Integrative catalytic pairs for efficient multi-intermediate catalysis

Single-atom catalysts (SACs) have attracted considerable research interest owing to their combined merits of homogeneous and heterogeneous catalysts. However, the uniform and isolated active sites of SACs fall short in catalysing complex chemical processes that simultaneously involve multiple intermediates. In this Review, we highlight an emerging class of catalysts with adjacent binary active centres, which is called integrative catalytic pairs (ICPs), showing not only atomic-scale site-to-site electronic interactions but also synergistic catalytic effects. Compared with SACs or their derivative dual-atom catalysts (DACs), multi-interactive intermediates on ICPs can overcome kinetic barriers, adjust reaction pathways and break the universal linear scaling relations as the smallest active units. Starting from this active-site design principle, each single active atom can be considered as a brick to further build integrative catalytic clusters (ICCs) with desirable configurations, towards trimer or even larger multi-atom units depending on the requirement of a given reaction.

Effect of External Electric Field on Nitrogen Activation on a Trimetal Cluster

Efficient nitrogen (N2) fixation and activation under mild conditions are crucial for modern society. External electric fields (Felectric) can significantly affect N2 activation. In this work, the effect of Felectric on N2 activation by Nb3 clusters supported in a sumanene bowl was studied by density functional theory calculations. Four typical systems at different stages of N-N activation were studied, including two intermediates and two transition states. The impact of Felectric on various properties related to N2 activation was investigated, including the N-N bond length, overlap population density of states (OPDOS), total energy of the system, adsorption energy of N2, decomposition of energy changes, and electron transfer. The sumanene not only functions as a support and protective substrate, but also serves as a donor or acceptor under different Felectric conditions. Negative Felectric is beneficial to N-N bond activation because it promotes electron transfer to the N-N region and improves the d-π* orbital hybridization between metals and N2 in the activation process. Positive Felectric improves d-π* orbital hybridization only when the N-N is nearly dissociated. The microscopic mechanism of Felectric's effects provides insight into N2 activation and theoretical guidance for the design of catalytic reaction conditions for nitrogen reduction reactions (NRR).

Ru3@Mo2CO2 MXene single-cluster catalyst for highly efficient N2-to-NH3 conversion

Single-cluster catalysts (SCCs) representing structurally well-defined metal clusters anchored on support tend to exhibit tunable catalytic performance for complex redox reactions in heterogeneous catalysis. Here we report a theoretical study on an SCC of Ru3@Mo2CO2 MXene for N2-to-NH3 thermal conversion. Our results show that Ru3@Mo2CO2 can effectively activate N2 and promotes its conversion to NH3 through an association mechanism, in which the rate-determining step of NH2* + H* → NH3* has a low energy barrier of 1.29 eV. Notably, with the assistance of Mo2CO2 support, the positively charged Ru3 cluster active site can effectively adsorb and activate N2, leading to 0.74 |e| charge transfer from Ru3@Mo2CO2 to the adsorbed N2. The supported Ru3 also acts as an electron reservoir to regulate the charge transfer for various intermediate steps of ammonia synthesis. Microkinetic analysis shows that the turnover frequency of the N2-to-NH3 conversion on Ru3@Mo2CO2 is as high as 1.45 × 10-2 s-1 site-1 at a selected thermodynamic condition of 48 bar and 700 K, the performance of which even surpasses that of the Ru B5 site and Fe3/θ-Al2O3(010) reported before. Our work provides a theoretical understanding of the high stability and catalytic mechanism of Ru3@Mo2CO2 and guidance for further designing and fabricating MXene-based metal SCCs for ammonia synthesis under mild conditions.

Electron Spin Broken-Symmetry of Fe-Co Diatomic Pairs to Promote Kinetics of Bifunctional Oxygen Electrocatalysis for Zinc-Air Batteries

Designing bifunctional catalysts to reduce the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) reaction barriers while accelerating the reaction kinetics is perceived to be a promising strategy to improve the performance of Zinc-air batteries. Unsymmetric configuration in single-atom catalysts has attracted attention due to its unique advantages in regulating electron orbitals. In this work, a seesaw effect in unsymmetric Fe-Co bimetallic monoatomic configurations is proposed, which can effectively improve the OER/ORR bifunctional activity of the catalyst. Compared with the symmetrical model of Fe-Co, a strong charge polarization between Co and Fe atoms in the unsymmetric model is detected, in whom the spin-down electrons around Co atoms are much higher than those spin-up electrons. The seesaw effect occurred between Co atoms and Fe atoms, resulting in a negative shift of the d-band center, which means that the adsorption of oxygen intermediates is weakened and more conducive to their dissociation. The optimized reaction kinetics of the catalyst leads to excellent performance in ZABs, with a peak power density of 215 mW cm-2 and stable cycling for >1300 h and >4000 cycles. Flexible Zinc-air batteries have also gained excellent performance to demonstrate their potential in the field of flexible wearables.

Hydrogen production by NH3 decomposition at low temperatures assisted by surface protonics

Ammonia, which can be decomposed on-site to produce CO2-free H2, is regarded as a promising hydrogen carrier because of its high hydrogen density, wide availability, and ease of transport. Unfortunately, ammonia decomposition requires high temperatures (>773 K) to achieve complete conversion, thereby hindering its practical applicability. Here, we demonstrate that high conversion can be achieved at markedly lower temperatures using an applied electric field along with a highly active and readily producible Ru/CeO2 catalyst. Applying an electric field lowers the apparent activation energies, promotes low-temperature conversion, and even surpasses equilibrium conversion at 398 K, thereby providing a feasible route to economically attractive hydrogen production. Experimentally obtained results and neural network potential studies revealed that this reaction proceeds via HN-NH intermediate formation by virtue of surface protonics.

Optimizing the Lattice Nitrogen Coordination to Break the Performance Limitation of Metal Nitrides for Electrocatalytic Nitrogen Reduction

Metal nitrides (MNs) are attracting enormous attention in the electrocatalytic nitrogen reduction reaction (NRR) because of their rich lattice nitrogen (Nlat) and the unique ability of Nlat vacancies to activate N2. However, continuing controversy exists on whether MNs are catalytically active for NRR or produce NH3 via the reductive decomposition of Nlat without N2 activation in the in situ electrochemical conditions, let alone the rational design of high-performance MN catalysts. Herein, we focus on the common rocksalt-type MN(100) catalysts and establish a quantitative theoretical framework based on the first-principles microkinetic simulations to resolve these puzzles. The results show that the Mars-van Krevelen mechanism is kinetically more favorable to drive the NRR on a majority of MNs, in which Nlat plays a pivotal role in achieving the Volmer process and N2 activation. In terms of stability, activity, and selectivity, we find that MN(100) with moderate formation energy of Nlat vacancy (E vac) can achieve maximum activity and maintain electrochemical stability, while low- or high-E vac ones are either unstable or catalytically less active. Unfortunately, owing to the five-coordinate structural feature of Nlat on rocksalt-type MN(100), this maximum activity is limited to a yield of NH3 of only ∼10-15 mol s-1 cm-2. Intriguingly, we identify a volcano-type activity-regulating role of the local structural features of Nlat and show that the four-coordinate Nlat can exhibit optimal activity and overcome the performance limitation, while less coordinated Nlat fails. This work provides, arguably for the first time, an in-depth theoretical insight into the activity and stability paradox of MNs for NRR and underlines the importance of reaction kinetic assessment in comparison with the prevailing simple thermodynamic analysis.

Confined Growth of Highly Ordered Metal Atomic Arrays for Seawater Oxidation

Metal atom catalysts have been among the most important research objects due to their specific physical and chemical properties. However, precise control of the anchoring of metal atoms is still challenging to achieve. Cobalt and iridium atomic arrays formed sequentially ordered stable arrays in graphdiyne (GDY) triangular cavities depending on their intrinsic chemical properties and interactions. The success of this method was attributed to multifunctional integration of GDY, enabling selective growth from one to several atoms and various atomic densities. The bimetallic atom arrays show several advantages resulting from reducibility of acetylene bonds, space limiting effect, incomplete charge transfer between GDY and metal atoms, and sp-C hybridized triple bond skeleton. This well-designed system exhibits unprecedented oxygen evolution reaction (OER) performance with a mass activity of 2.6 A mgcat. -1 at a low overpotential of 300 mV, which is 216.6 times higher than the state-of-the-art IrO2 catalyst, and long-term stability.

Precious-Metal-Free Mo-MXene Catalyst Enabling Facile Ammonia Synthesis Via Dual Sites Bridged by H-Spillover

To date, NH3 synthesis under mild conditions is largely confined to precious Ru catalysts, while nonprecious metal (NPM) catalysts are confronted with the challenge of low catalytic activity due to the inverse relationship between the N2 dissociation barrier and NHx (x = 1-3) desorption energy. Herein, we demonstrate NPM (Co, Ni, and Re)-mediated Mo2CTx MXene (where Tx denotes the OH group) to achieve efficient NH3 synthesis under mild conditions. In particular, the NH3 synthesis rate over Re/Mo2CTx and Ni/Mo2CTx can reach 22.4 and 21.5 mmol g-1 h-1 at 400 °C and 1 MPa, respectively, higher than that of NPM-based catalysts and Cs-Ru/MgO ever reported. Experimental and theoretical studies reveal that Mo4+ over Mo2CTx has a strong ability for N2 activation; thus, the rate-determining step is shifted from conventional N2 dissociation to NH2* formation. NPM is mainly responsible for H2 activation, and the high reactivity of spillover hydrogen and electron transfer from NPM to the N-rich Mo2CTx surface can efficiently facilitate nitrogen hydrogenation and the subsequent desorption of NH3. With the synergistic effect of the dual active sites bridged by H-spillover, the NPM-mediated Mo2CTx catalysts circumvent the major obstacle, making NH3 synthesis under mild conditions efficient.

Catalysts with Trimetallic Sites on Graphene-like C2N for Electrocatalytic Nitrogen Reduction Reaction: A Theoretical Investigation

Electrocatalytic nitrogen reduction reaction (NRR) is a green and highly efficient way to replace the industrial Haber-Bosch process. Herein, clusters consisting of three transition metal atoms loaded on C2N as NRR electrocatalysts are investigated using density functional theory (DFT). Meanwhile, Ca was introduced as a promoter and the role of Ca in NRR was investigated. It was found that Ca anchored to the catalyst can act as an electron donor and effectively promote the activation of N2 on M3. In both M3@C2N and M3Ca@C2N (M=Fe, Co, Ni), the limiting potential (UL) is less negative than that of the Ru(0001) surface and has the ability to suppress the competitive hydrogen evolution reaction (HER). Among them, Fe3@C2N is suggested to be the most promising candidate for NRR with high thermal stability, strong N2 adsorption ability, low limiting potential, and good NRR selectivity. The concepts of trimetallic sites and alkaline earth metal promoters in this work provide theoretical guidance for the rational design of atomically active sites in electrocatalytic NRR.

Designing Dual-Site Catalysts for Selectively Converting CO2 into Methanol

The variability of CO2 hydrogenation reaction demands new potential strategies to regulate the fine structure of the catalysts for optimizing the reaction pathways. Herein, we report a dual-site strategy to boost the catalytic efficiency of CO2-to-methanol conversion. A new descriptor, τ, was initially established for screening the promising candidates with low-temperature activation capability of CO2, and sequentially a high-performance catalyst was fabricated centred with oxophilic Mo single atoms, who was further decorated with Pt nanoparticles. In CO2 hydrogenation, the obtained dual-site catalysts possess a remarkably-improved methanol generation rate (0.27 mmol gcat. -1 h-1). For comparison, the singe-site Mo and Pt-based catalysts can only produce ethanol and formate acid at a relatively low reaction rate (0.11 mmol gcat. -1 h-1 for ethanol and 0.034 mmol gcat. -1 h-1 for formate acid), respectively. Mechanism studies indicate that the introduction of Pt species could create an active hydrogen-rich environment, leading to the alterations of the adsorption configuration and conversion pathways of the *OCH2 intermediates on Mo sites. As a result, the catalytic selectivity was successfully switched.

Advancements in Electrocatalytic Nitrogen Reduction: A Comprehensive Review of Single-Atom Catalysts for Sustainable Ammonia Synthesis

Electrocatalytic nitrogen reduction technology seamlessly aligns with the principles of environmentally friendly chemical production. In this paper, a comprehensive review of recent advancements in electrocatalytic NH3 synthesis utilizing single-atom catalysts (SACs) is offered. Into the research and applications of three categories of SACs: noble metals (Ru, Au, Rh, Ag), transition metals (Fe, Mo, Cr, Co, Sn, Y, Nb), and nonmetallic catalysts (B) in the context of electrocatalytic ammonia synthesis is delved. In-depth insights into the material preparation methods, single-atom coordination patterns, and the characteristics of the nitrogen reduction reaction (NRR) are provided. The systematic comparison of the nitrogen reduction capabilities of various SAC types offers a comprehensive research framework for their integration into electrocatalytic NRR. Additionally, the challenges, potential solutions, and future prospects of incorporating SACs into electrocatalytic nitrogen reduction endeavors are discussed.

Steering the Orbital Hybridization to Boost the Redox Kinetics for Efficient Li-CO2 Batteries

The sluggish CO2 reduction and evolution reaction kinetics are thorny problems for developing high-performance Li-CO2 batteries. For the complicated multiphase reactions and multielectron transfer processes in Li-CO2 batteries, exploring efficient cathode catalysts and understanding the interplay between structure and activity are crucial to couple with these pendent challenges. In this work, we applied the CoS as a model catalyst and adjusted its electronic structure by introducing sulfur vacancies to optimize the d-band and p-band centers, which steer the orbital hybridization and boost the redox kinetics between Li and CO2, thus improving the discharge platform of Li-CO2 batteries and altering the deposition behavior of discharge products. As a result, a highly efficient bidirectional catalyst exhibits an ultrasmall overpotential of 0.62 V and a high energy efficiency of 82.8% and circulates stably for nearly 600 h. Meanwhile, density functional theory calculations and multiphysics simulations further elucidate the mechanism of bidirectional activity. This work not only provides a proof of concept to design a remarkably efficient catalyst but also sheds light on promoting the reversible Li-CO2 reaction by tailoring the electronic structure.

Density Functional Theory Study of Triple Transition Metal Cluster Anchored on the C2N Monolayer for Nitrogen Reduction Reactions

The electrochemical nitrogen reduction reaction (NRR) is an attractive pathway for producing ammonia under ambient conditions. The development of efficient catalysts for nitrogen fixation in electrochemical NRRs has become increasingly important, but it remains challenging due to the need to address the issues of activity and selectivity. Herein, using density functional theory (DFT), we explore ten kinds of triple transition metal atoms (M3 = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) anchored on the C2N monolayer (M3-C2N) as NRR electrocatalysts. The negative binding energies of M3 clusters on C2N mean that the triple transition metal clusters can be stably anchored on the N6 cavity of the C2N structure. As the first step of the NRR, the adsorption configurations of N2 show that the N2 on M3-C2N catalysts can be stably adsorbed in a side-on mode, except for Zn3-C2N. Moreover, the extended N-N bond length and electronic structure indicate that the N2 molecule has been fully activated on the M3-C2N surface. The results of limiting potential screen out the four M3-C2N catalysts (Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N) that have a superior electrochemical NRR performance, and the corresponding values are -0.61 V, -0.67 V, -0.63 V, and -0.66 V, respectively, which are smaller than those on Ru(0001). In addition, the detailed NRR mechanism studied shows that the alternating and enzymatic mechanisms of association pathways on Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N are more energetically favorable. In the end, the catalytic selectivity for NRR on M3-C2N is investigated through the performance of a hydrogen evolution reaction (HER) on them. We find that Co3-C2N, Cr3-C2N, Fe3-C2N, and Ni3-C2N catalysts possess a high catalytic activity for NRR and exhibit a strong capability of suppressing the competitive HER. Our findings provide a new strategy for designing NRR catalysts with high catalytic activity and selectivity.

Boosting Electrochemical Nitrogen Fixation via Regulating Surface Electronic Structure by CeO2 Hybridization

Electrocatalytic nitrogen reduction reaction (NRR) paves a sustainable way to produce NH3 but suffering from the relatively low NH3 yield and poor selectivity. High-performance NRR catalysts and a deep insight into the structure-performance relationship are higher desired. Herein, a molten-salt approach is developed to synthesize tiny CeO2 nanoparticles anchored by ultra-thin MoN nanosheets as advanced catalysts for NRR. Specifically, a considerably high NH3 yield rate of 27.5 µg h-1 mg-1 with 17.2% Faradaic efficiency (FE) can be achieved at -0.3 V vs (RHE) under ambient conditions. Experimental and density functional theory (DFT) calculations further point out that the incorporation of MoN with CeO2 can promotes the enlargement of the electron deficient area of nitrogen vacancy site. The enlarged electron deficient area contributes to the accommodation of lone pair electrons of N2, which dramatically improves the N2 adsorption/activation and the key intermediates (*NNH and *NH3) generation, thus boosting the NRR performance.

*H migration-assisted MvK mechanism for efficient electrochemical NH3 synthesis over TM-TiNO

The electrochemical NH3 synthesis on TiNO is proposed to follow the Mars-van Krevelen (MvK) mechanism, offering more favorable N2 adsorption and activation on the N vacancy (Nv) site, compared to the conventional associative mechanism. The regeneration cycle of Nv represents the rate-determining step in this process. This study investigates a series of TM (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt)-TiNO to explore the *H migration (from TM to TiNO)-promoted Nv cycle. The screening results indicate that Ni-TiNO exhibits strong H2O decomposition for *H production with 0.242 eV and low *H migration resistance with 0.913 eV. Notably, *H migration from Ni to TiNO significantly reduces the Nv formation energy to 0.811 eV, compared to 1.387 eV on pure TiNO. Meanwhile, in the presence of *H, Nv formation takes precedence over Tiv and Ov. Lastly, electronic performance calculations reveal that the collaborative function provided by Ni and Nv enables highly stable and efficient NH3 synthesis. The *H migration-assisted MvK mechanism demonstrates effective catalytic cycle performance in electrochemical N2 fixation and may have potential applicability to other hydrogenation reactions utilizing water as a proton source.

Encapsulate Co3O4 within ultrathin graphene sheets to enhance peroxymonosulfate activation by tuning surface electronic structures

Heterojunctions composed of cobalt-based materials and carbon materials have been recognized as the efficient catalysts for peroxymonosulfate (PMS) activation to generate reactive oxygen species for the removal of environmental contaminants. However, the role of carbon materials in promoting the heterojunction systems has not been fully understood. This study synthesized a heterojunction material of graphene sheets encapsulating Co3O4 (GCO-500) through the pyrolysis of cobalt MOF and applied it to activate PMS for the removal of lomefloxacin. The results showed a high removal rate of 93.59 % with a degradation rate of k1 = 0.0156 min-1. Co3O4 clusters was encapsulated within ultrathin graphene sheets (<2 nm). DFT calculations revealed that graphene layers improve the electron transfer ability of Co3O4 and increased the d-band center of Co3O4 (-1.61 eV) that promote the adsorption of PMS on GCO-500 (-1.32 eV). In the meanwhile, organic pollutant was enriched in graphene layers with high adsorption energy (-13.08 eV), which greatly enhanced the degradation efficiency of pharmaceuticals. This study provides an effective catalyst for PMS activation and sheds light on the fundamental electronic-level understanding of cobalt-based and carbon heterojunction catalysts in PMS activation.

Advances in Naked Metal Clusters for Catalysis

The properties of sub-nano metal clusters are governed by quantum confinement and their large surface-to-bulk ratios, atomically precise compositions and geometric/electronic structures. Advances in metal clusters lead to new opportunities in diverse aspects of sciences including chemo-sensing, bio-imaging, photochemistry, and catalysis. Naked metal clusters having synergic multiple active sites and coordinative unsaturation and tunable stability/activity enable researchers to design atomically precise metal catalysts with tailored catalysis for different reactions. Here we summarize the progress of ligand-free naked metal clusters for catalytic applications. It is anticipated that this review helps to better understand the chemistry of small metal clusters and facilitates the design and development of new catalysts for potential applications.

Synergistic effect between transition metal single atom and SnS2 toward deep CO2 reduction

The electrochemical reduction of CO2 is an efficient channel to facilitate energy conversion, but the rapid design and rational screening of high-performance catalysts remain a great challenge. In this work, we investigated the relationships between the configuration, energy, and electronic properties of SnS2 loaded with transition metal single atom (TM@SnS2) and analyzed the mechanism of CO2 activation and reduction by using density functional theory. The "charge transfer bridge" promoted the adsorption of CO2 on TM@SnS2, thus enhancing the binding of HCOOH∗ to the catalyst for further hydrogenation and reduction to high-value CH4. The research revealed that the binding free energy of COOH∗ on TM@SnS2 formed a "volcano curve" with the limiting potential of CO2 reduction to CH4, and the TM@SnS2 (TM = Cr, Ru, Os, and Pt) at the "volcano top" exhibited a high CH4 activity.

Electronegative Phosphorus-Integrated Co2+ Active Sites for Enhanced Electrocatalytic Nitrogen Reduction

In the quest for proficient electrocatalysts for ammonia's electrocatalytic nitrogen reduction, cobalt oxides, endowed with a rich d-electron reservoir, have emerged as frontrunners. Despite the previously evidenced prowess of CoO in this realm, its ammonia yield witnesses a pronounced decline as the reaction unfolds, a phenomenon linked to the electron attrition from its Co2+ active sites during electrocatalytic nitrogen reduction reaction (ENRR). To counteract this vulnerability, we harnessed electron-laden phosphorus (P) elements as dopants, aiming to recalibrate the electronic equilibrium of the pivotal Co active site, thereby bolstering both its catalytic performance and stability. Our empirical endeavors showcased the doped P-CoO's superior credentials: it delivered an impressive ammonia yield of 49.6 and, notably, a Faradaic efficiency (FE) of 9.6% at -0.2 V versus RHE, markedly eclipsing its undoped counterpart. Probing deeper, a suite of ex-situ techniques, complemented by rigorous theoretical evaluations, was deployed. This dual-pronged analysis unequivocally revealed CoO's propensity for an electron-driven valence metamorphosis to Co3+ post-ENRR. In stark contrast, P-CoO, fortified by P doping, exhibits a discernibly augmented ammonia yield. Crucially, P's intrinsic ability to staunch electron leakage from the active locus during ENRR ensures the preservation of the valence state, culminating in enhanced catalytic dynamism and fortitude. This investigation not only illuminates the intricacies of active site electronic modulation in ENRR but also charts a navigational beacon for further enhancements in this domain.

Single-atom and cluster catalysts for thermocatalytic ammonia synthesis at mild conditions

Ammonia (NH3) is closely related to the fields of food and energy that humans depend on. The exploitation of advanced catalysts for NH3 synthesis has been a research hotspot for more than one hundred years. Previous studies have shown that the Ru B5 sites (step sites on the Ru (0001) surface uniquely arranged with five Ru atoms) and Fe C7 sites (iron atoms with seven nearest neighbors) over nanoparticle catalysts are highly reactive for N2-to-NH3 conversion. In recent years, single-atom and cluster catalysts, where the B5 sites and C7 sites are absent, have emerged as promising catalysts for efficient NH3 synthesis. In this review, we focus on the recent advances in single-atom and cluster catalysts, including single-atom catalysts (SACs), single-cluster catalysts (SCCs), and bimetallic-cluster catalysts (BCCs), for thermocatalytic NH3 synthesis at mild conditions. In addition, we discussed and summarized the unique structural properties and reaction performance as well as reaction mechanisms over single-atom and cluster catalysts in comparison with traditional nanoparticle catalysts. Finally, the challenges and prospects in the rational design of efficient single-atom and cluster catalysts for NH3 synthesis were provided.