Cu dimer anchored on C2N monolayer: low-cost and efficient Bi-atom catalyst for CO oxidation

Revealing the origin of activity in phthalocyanine-based dual-metal sites towards electrochemical nitric oxide reduction

Coordinated ligands play crucial roles in tuning the electrochemical nitrate reduction performance of phthalocyanine (Pc)-based dual atom catalysts. With the assistance of axial O ligands, fast NO to NH3 conversion can be realized on O-Ni2-Pc and O-Cu2-Pc. A 2-N product, N2O, can be synthesized on Co2-Pc, Cr2-Pc, O-Co2-Pc, and O-Fe2-Pc through N-N coupling with high NO coverage. ΔENO can be identified as a valid descriptor to support rational M2-Pc design.

Single transition metal-decorated C4N/MoS2 heterostructure for boosting oxygen reduction, oxygen evolution, and hydrogen evolution

Multifunctional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), and hydrogen evolution (HER) are required preconditions for the development of a highly promising new green energy conversion and storage technology. Herein, a comprehensive computation of the ORR, OER and HER catalytic performance for the pristine and metal-decorated C₄N/MoS₂ (TM-C₄N/MoS₂) is researched using density functional theory. Remarkably, Pd-C₄N/MoS₂ exhibits distinguished bifunctional catalytic performance with lower ORR/OER overpotentials of 0.34/0.40 V. Rh-C₄N/MoS₂ is the prospective trifunctional catalyst with the low ORR/OER/HER overpotentials of 0.48/0.55/-0.16 V, but its electrochemical stability needs to be further improved. Furthermore, the strong correlation between intrinsic descriptor (φ) and adsorption free energy of *OH verifies that the catalytic activity of TM-C₄N/MoS₂ is affected by active metal and surrounding coordination environment. The heap map has summarized the correlations of d-band center, adsorption free energy of reaction species, and φ as the vital parameter for ORR/OER overpotentials of designing catalysts. The electronic structure analysis uncovers the activity enhancement is due to the adjustable adsorption behavior of reaction intermediates on TM-C₄N/MoS₂. This finding paves the way to develop high-activity and multifunctional catalysts, making them suitable for multifunctional applications in the forthcoming critically needed green energy conversion and storage technologies.

High-Throughput Screening of Efficient Biatom Catalysts Based on Monolayer Carbon Nitride for the Nitric Oxide Reduction Reaction

Exploring efficient catalysts for the nitric oxide reduction reaction (NORR) toward NH₃ synthesis is becoming increasingly important for tackling both NH₃ synthesis and NO removal problems. Currently, only a few NORR catalysts have been proposed, which are exclusively concentrated on bulk metals or single-atom catalysts. Here, taking monolayer C₂N as an example, we explore the potential of biatom catalysts (BACs) for direct NO-to-NH₃ conversion by means of high-throughput first-principles calculations. According to a rational five-step screening strategy, a promising BAC of Cr₂-C₂N is successfully screened out, exhibiting high stability, activity, and selectivity and a low kinetic barrier for the NORR toward NH₃ synthesis. Importantly, the adsorption energy of N atoms (ΔE_*N) and the Gibbs free energy of NO adsorption (ΔG_*NO) are identified as effective descriptors for efficient NORR catalysts. In addition, through tuning the NO coverage, the NORR on Cr₂-C₂N could produce different products of NH₃ and N₂O, providing the possibility to realize controllable multiproduct BACs. These findings not only suggest the great potential of BACs for direct NO-to-NH₃ conversion but also help in rationally designing high-performance BACs.

Al-Embedded C2N: a DFT study on a promising catalyst for CO oxidation

Al-C2N catalyst exhibits efficient catalytic performance for CO oxidation.

Multi-atom cluster catalysts for efficient electrocatalysis

This review presents recent developments in the synthesis, modulation and characterization of multi-atom cluster catalysts for electrochemical energy applications.

Role of sulfur vacancies in MoS2 monolayers in stabilizing Co atoms for efficient CO oxidation

By performing first-principles calculations, a MoS₂ monolayer with a Co atom doped at the sulfur defect (Co-^SMoS₂) was investigated as a single-atom catalyst (SAC) for CO oxidation. The Co atom is strongly constrained at the S-vacancy site of MoS₂ without forming clusters by showing a high diffusion energy barrier, ensuring good stability to catalyze CO oxidation. The CO and O₂ adsorption behavior on Co-^SMoS₂ surface and four reaction pathways, namely, the Eley–Rideal (ER), Langmuir–Hinshelwood (LH), trimolecular Eley–Rideal (TER) as well as the New Eley–Rideal (NER) mechanisms are studied to understand the catalytic activity of Co-^SMoS₂ for CO oxidation. The CO oxidation is more likely to proceed through the LH mechanism, and the energy barrier for the rate-limiting step is only 0.19 eV, smaller than that of noble metal-based SACs. Additionally, the NER mechanism is also favorable with a low energy barrier of 0.26 eV, indicating that the Co-^SMoS₂ catalyst can effectively promote CO oxidation at low temperatures. Our investigation demonstrates that the S-vacancy of MoS₂ plays an important role in enhancing the stability and catalytic activity of Co atoms and Co-^SMoS₂ is predicted to be a promising catalyst for CO oxidation.

Molybdenum disulfide monolayers with Co atoms embedded in the sulfur vacancies are promising two dimensional non-noble metal-based single-atom catalysts to promote carbon monoxide oxidation.

Single non-noble metal atom doped C2N catalysts for chemoselective hydrogenation of 3-nitrostyrene

Improving the reaction selectivity and activity for challenging substrates such as nitroaromatics bearing two reducible functional groups is important in industry, yet remains a great challenge using traditional metal nanoparticle based catalysts. In this study, single metal atom doped M-C₂N catalysts were theoretically screened for selective hydrogenation of 3-nitrostyrene to 3-vinylaniline with H₂ as the H-source. Among 20 M-C₂N catalysts, the non-noble Mn-C₂N catalyst was found to have excellent reaction selectivity. Importantly, due to the solid frustrated Lewis pair sites in the pores of Mn-C₂N, a low H₂ activation energy is achieved on high-spin Mn-C₂N and the rate-determining step for the hydrogenation reactions is the H diffusion from the metal site to the N site. The unraveled mechanism of the hydrogenation of 3-nitrostyrene using Mn-C₂N enriches the applications of Mn based catalysts and demonstrates its excellent properties for catalyzing the challenging hydrogenation reaction of substrates with two reducible functional groups.

Emerging Dual-Atomic-Site Catalysts for Efficient Energy Catalysis

Atomically dispersed metal catalysts with well-defined structures have been the research hotspot in heterogeneous catalysis because of their high atomic utilization efficiency, outstanding activity, and selectivity. Dual-atomic-site catalysts (DASCs), as an extension of single-atom catalysts (SACs), have recently drawn surging attention. The DASCs possess higher metal loading, more sophisticated and flexible active sites, offering more chance for achieving better catalytic performance, compared with SACs. In this review, recent advances on how to design new DASCs for enhancing energy catalysis will be highlighted. It will start with the classification of marriage of two kinds of single-atom active sites, homonuclear DASCs and heteronuclear DASCs according to the configuration of active sites. Then, the state-of-the-art characterization techniques for DASCs will be discussed. Different synthetic methods and catalytic applications of the DASCs in various reactions, including oxygen reduction reaction, carbon dioxide reduction reaction, carbon monoxide oxidation reaction, and others will be followed. Finally, the major challenges and perspectives of DASCs will be provided.

High-Throughput Screening of Synergistic Transition Metal Dual-Atom Catalysts for Efficient Nitrogen Fixation

Great enthusiasm in single-atom catalysts (SACs) for the nitrogen reduction reaction (NRR) has been aroused by the discovery of metal-N_x as a promising catalytic center. However, the poor activity and low selectivity of available SACs are far away from the industrial requirement. Through the first-principles high-throughput screening, we find that Fe-Fe distributed on graphite carbon nitride (Fe₂/g-CN) can manipulate the binding strength of the target reaction species (compromises the ability to adsorb N₂H and NH₂), therefore achieving the best NRR performance among 23 transition metal (TM) centers. Our results show that Fe₂/g-CN achieves a high theoretical Faradaic efficiency of 100% and, impressively, the lowest limiting potential of -0.13 V. Particularly, multiple-level descriptors shed light on the origin of NRR activity, achieving a fast prescreening among various candidates. Our predictions not only accelerate discovery of catalysts for ammonia synthesis but also contribute to further elucidate the structure-performance correlations.

A Pt3 cluster anchored on a C2N monolayer as an efficient catalyst for electrochemical reduction of nitrobenzene to aniline: a computational study

A Pt3 cluster anchored on h-C2N exhibits ultra-high catalytic activity towards nitrobenzene reduction with a small limiting potential (−0.19 V).

Electrocatalytic nitrogen reduction on the transition-metal dimer anchored N-doped graphene: performance prediction and synergetic effect

Present studies highlight the important role of the heteronuclear members for the development of the double-atom catalysts, and further provide a strategy to design efficient heteronuclear double-atom catalysts from the large chemical composition space for the electrocatalytic NRR.

Efficient Heteronuclear Diatom Electrocatalyst for Nitrogen Reduction Reaction: Pd-Nb Diatom Supported on Black Phosphorus

Electrocatalytic N₂ reduction reaction (eNRR) is a promising alternative to the traditional Haber-Bosch method for large-scale ammonia production because of its low pollution and low energy consumption. By means of density functional theory (DFT) calculations, a thermodynamically stable Pd-Nb heteronuclear diatom catalyst supported on 2D black phosphorus (PdNb@BP) is designed, which is predicted to exhibit excellent catalytic activity toward eNRR with an ultralow overpotential (0.20 V) and a small NH₃ desorption free energy (0.17 eV), by combining the advantages of Nb atoms for N₂ activation and of Pd atoms for NH₃ desorption, and a high eNRR selectivity over the competing hydrogen evolution reaction. It is highlighted that the participation of one additional N₂ molecule in the mechanism is important for the catalyst to realize the catalytic process.

C2N: A Class of Covalent Frameworks with Unique Properties

C2N is a unique member of the CnNm family (carbon nitrides), i.e., having a covalent structure that is ideally composed of carbon and nitrogen with only 33 mol% of nitrogen. C2N, with a stable composition, can easily be prepared using a number of precursors. Moreover, it is currently gaining extensive interest owing to its high polarity and good thermal and chemical stability, complementing carbon as well as classical carbon nitride (C3N4) in various applications, such as catalysis, environmental science, energy storage, and biotechnology. In this review, a comprehensive overview on C2N is provided; starting with its preparation methods, followed by a fundamental understanding of structure-property relationships, and finally introducing its application in gas sorption and separation technologies, as supercapacitor and battery electrodes, and in catalytic and biological processes. The review with an outlook on current research questions and future possibilities and extensions based on these material concepts is ended.

Heterogeneous Atomic Catalysts Overcoming the Limitations of Single-Atom Catalysts

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

Fe3 Cluster Anchored on the C2N Monolayer for Efficient Electrochemical Nitrogen Fixation

Under the current double challenge of energy and the environment, an effective nitrogen reduction reaction (NRR) has become a very urgent need. However, the largest production of ammonia gas today is carried out by the Haber–Bosch process, which has many disadvantages, among which energy consumption and air pollution are typical. As the best alternative procedure, electrochemistry has received extensive attention. In this paper, a catalyst loaded with Fe3 clusters on the two-dimensional material C2N (Fe3@C2N) is proposed to achieve effective electrochemical NRR, and our first-principles calculations reveal that the stable Fe3@C2N exhibits excellent catalytic performance for electrochemical nitrogen fixation with a limiting potential of 0.57 eV, while also suppressing the major competing hydrogen evolution reaction. Our findings will open a new door for the development of non-precious single-cluster catalysts for effective nitrogen reduction reactions.

Methane Conversion over C2N-Supported Fe2 Dimers

Methane is a vast hydrocarbon resource around the globe that has the potential to replace petroleum as a raw material and energy source. Therefore, the catalytic conversion of methane into high value-added chemicals is significantly important for the utilization of this hydrocarbon resource. However, this is a great challenge due to the high-energy input required to overcome the reaction barrier. Herein, a highly active catalytic conversion process of methane on an iron dimer anchored on a two-dimensional (2D) C2N monolayer (Fe2@C2N) is reported. Density functional theory calculations reveal that the superior properties of Fe2@C2N can be attributed to the formation of the Fe-O-Fe intermediate with H2O2 as the O-donor molecule, which facilitates the formation of methyl radicals and promotes the conversion of methane. This finding could pave the way toward highly efficient non-precious metal catalysts for methane oxidation reactions.

Metal single-atom coordinated graphitic carbon nitride as an efficient catalyst for CO oxidation

Single-atom catalysts (SACs) often present outstanding activity due to their high ratio of low-coordinated metal atoms and can be applied to the activation of strong chemical bonds such as C[triple bond, length as m-dash]O. Herein, we investigate the potential usage of a single-atom catalyst, in which isolated cobalt atoms are supported on porous graphitic carbon nitride (Co/g-C₃N₄), for CO oxidation. Based on the adsorption/co-adsorption energies of O₂, CO, 2O₂, CO + O₂ and 2CO, the screening criteria and the reaction mechanisms of CO oxidation, including the Eley-Rideal, New Eley-Rideal, Langmuir-Hinshelwood, and termolecular Eley-Rideal mechanisms, are established and compared. In particular, the energy barriers of the rate-limiting steps for the CO oxidation process by all possible reaction pathways are in a range from 0.21 to 0.59 eV, suggesting that the Co/g-C₃N₄ catalyst can boost CO oxidation at low temperature. Moreover, the preparation of the SAC (Co/g-C₃N₄) by using CoCl₂ as an appropriate metal precursor and the stability (up to 600 K) are evaluated by ab initio molecular dynamics simulations. The high stability and excellent activity of the Co/g-C₃N₄ SAC for CO oxidation offer a high possibility of clean energy production.

Pd/Pt embedded CN monolayers as efficient catalysts for CO oxidation

The catalytic performance of Pd/Pt embedded planar carbon nitride for CO oxidation has been investigated via spin-polarized density functional theory calculations.