A theoretical study of single-atom catalysis of CO oxidation using Au embedded 2D h-BN monolayer: a CO-promoted O₂ activation

Theoretical study on the interaction between acetone and BN monolayer doped with Ni for the clinical diagnosis of diabetes mellitus

Endogenous volatile organic compounds (VOCs) in human exhaled gases can reflect human health status and be used for clinical diagnosis and health monitoring. Acetone is the sign VOC gases of diabetes mellitus. In order to find a potential material for the detection of acetone in the application of the clinical diagnosis of diabetes mellitus. The adsorption properties, including adsorption energy, adsorption distance, charge transfer, density of states, electron localization function and electrons density difference, of acetone on BN monolayer doped with Ni were comprehensively investigated based on density functional theory. The results show that there could be chemisorption between acetone and Ni-BN monolayer and Ni-BN monolayer is probably suitable gas sensitive material for the detection of acetone in the application of diabetes mellitus monitoring and clinical diagnosis.

Performance Regulation of Single-Atom Catalyst by Modulating the Microenvironment of Metal Sites

Metal-based catalysts, encompassing both homogeneous and heterogeneous types, play a vital role in the modern chemical industry. Heterogeneous metal-based catalysts usually possess more varied catalytically active centers than homogeneous catalysts, making it challenging to regulate their catalytic performance. In contrast, homogeneous catalysts have defined active-site structures, and their performance can be easily adjusted by modifying the ligand. These characteristics lead to remarkable conceptual and technical differences between homogeneous and heterogeneous catalysts. As a recently emerging class of catalytic material, single-atom catalysts (SACs) have become one of the most active new frontiers in the catalysis field and show great potential to bridge homogeneous and heterogeneous catalytic processes. This review documents a brief introduction to SACs and their role in a range of reactions involving single-atom catalysis. To fully understand process-structure-property relationships of single-atom catalysis in chemical reactions, active sites or coordination structure and performance regulation strategies (e.g., tuning chemical and physical environment of single atoms) of SACs are comprehensively summarized. Furthermore, we discuss the application limitations, development trends and future challenges of single-atom catalysis and present a perspective on further constructing a highly efficient (e.g., activity, selectivity and stability), single-atom catalytic system for a broader scope of reactions.

MP2-Based Correction Scheme to Approach the Limit of a Complete Pair Natural Orbitals Space in DLPNO-CCSD(T) Calculations

The domain-based local pair natural orbital (PNO) coupled-cluster DLPNO-CCSD(T) method has been proven to provide accurate single-point energies at a fraction of the cost of canonical CCSD(T) calculations. However, the desired "chemical accuracy" can only be obtained with a large PNO space and extended basis set. We present a simple yet accurate and efficient correction scheme based on a perturbative approach. Here, in addition to DLPNO-CCSD(T) energy, one calculates DLPNO-MP2 correlation energy with the same settings as in the preceding coupled-cluster calculation. In the next step, the canonical MP2 correlation energy is obtained in the same orbital basis. This can be efficiently performed for essentially all molecule sizes accessible with the DLPNO-CCSD(T) method. By taking the difference between the canonical MP2 and DLPNO-MP2 energies, we obtain a correction term that can be added to the DLPNO-CCSD(T) correlation energy. This way, one can obtain the total correlation energy close to the limit of the complete PNO space (cPNO). The presented approach allows us to significantly increase the accuracy of the DLPNO-CCSD(T) method for both closed- and open-shell systems. The latter are known to be especially challenging for locally correlated methods. Unlike the previously developed PNO extrapolation procedure by Altun, Neese, and Bistoni ( J. Chem. Theory Comput. 2020, 16, 6142-6149), this strategy allows us to get the DLPNO-CCSD(T) correlation energy at the cPNO limit in a cost-efficient way, resulting in a minimal overall increase in calculation time as compared to the uncorrected method.

Noble Metal Nanoparticles Decorated Boron Nitride Nanotubes for Efficient and Selective Low-Temperature Catalytic Reduction of Nitric Oxide with Carbon Monoxide

Parallel to CO₂ emission, NO_x emission has become one of the menacing problems that seek a simple, durable, and high-efficiency deNO_x catalyst. Herein, we demonstrated simple syntheses of platinum group metal nanoparticle-decorated f-BNNT (PGM = Pd, Pt, and Rh, and f-BNNT stands for -OH-functionalized boron nitride nanotubes) as a catalyst for efficient and selective reduction of NO by CO at low-temperature conditions. PGM/f-BNNT with a low amount of noble metal nanoparticles (0.7-0.8 wt %) presents very efficient catalytic activity for NO reduction as well as CO oxidation during their removal process. The removal efficiencies of NO and CO with Pd/f-BNNT, Pt/f-BNNT, and Rh/f-BNNT catalysts were investigated under various temperatures, flow rates, and reaction times, respectively. For most cases, NO catalytic reduction with CO reaction was >99% at a temperature as low as ∼200 °C. The catalyst robustness and efficiency were also verified by presenting almost 100% conversion of NO using a Rh/f-BNNT catalyst, which was aged under humid air at 600 and 700 °C for 24 h, respectively. The synergic effect of the catalytic efficacy of the well-dispersed noble metal nanoparticles and the excellent surface properties of BNNT are reasons for the high selectivity and catalytic property at a low temperature. On the basis of this investigation, we demonstrated that the noble metal nanoparticle-decorated f-BNNT catalysts are possible to save expensive PGM catalysts, such as Pt, Pd, and Rd, as much as 100 times while presenting similar or better catalytic performance for simultaneous NO and CO removals.

Tuning low-temperature CO oxidation activities via N-doping on graphene-supported three-coordinated nickle single-atom catalysts

Nitrogen doping is identified as an intriguing way to regulate graphene-supported single-atom catalysts (SACs) for heterogeneous catalysis. However, little theoretical effort has been directed towards exploring the activity trend in terms of N-doping level. In this study, we systematically investigated the N-doping effect on CO oxidation activities for graphene-supported three-coordinated Ni SACs (Ni-N_xC_3-x) in virtue of density functional theory (DFT) calculations and microkinetic modeling. We found that N-doping will shift the d-band center of single-atom Ni upwards, enhance the adsorption of intermediates, and tune the activation barrier to the overall reaction activities. Ni-N₁C₂ exhibits excellent catalytic performance with the highest total reaction rate comparable to that of noble metal SACs. These findings are helpful for understanding the N-doping influence and rationalizing the art of designing novel SACs for CO oxidation at low temperatures.

Coadsorption Interfered CO Oxidation over Atomically Dispersed Au on h-BN

Similar to the metal centers in biocatalysis and homogeneous catalysis, the metal species in single atom catalysts (SACs) are charged, atomically dispersed and stabilized by support and substrate. The reaction condition dependent catalytic performance of SACs has long been realized, but seldom investigated before. We investigated CO oxidation pathways over SACs in reaction conditions using atomically dispersed Au on h-BN (AuBN) as a model with extensive first-principles-based calculations. We demonstrated that the adsorption of reactants, namely CO, O₂ and CO₂, and their coadsorption with reaction species on AuBN would be condition dependent, leading to various reaction species with different reactivity and impact the CO conversion. Specifically, the revised Langmuir–Hinshelwood pathway with the CO-mediated activation of O₂ and dissociation of cyclic peroxide intermediate followed by the Eley–Rideal type reduction is dominant at high temperatures, while the coadsorbed CO-mediated dissociation of peroxide intermediate becomes plausible at low temperatures and high CO partial pressures. Carbonate species would also form in existence of CO₂, react with coadsorbed CO and benefit the conversion. The findings highlight the origin of the condition-dependent CO oxidation performance of SACs in detailed conditions and may help to rationalize the current understanding of the superior catalytic performance of SACs.

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

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

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.

Understanding Single-Atom Catalysis in View of Theory

In the past decade, isolated single atoms have been successfully dispersed on various substrates, with their potential applications being intensively investigated in different reactions. While the essential target of research in single-atom catalysis is the precise synthesis of stable single-atom catalysts (SACs) with clear configurations and impressive catalytic performance, theoretical investigations have also played important roles in identifying active sites, revealing catalytic mechanisms, and establishing structure-activity relationships. Nevertheless, special attention should still be paid in theoretical works to the particularity of SACs. In this Perspective, we will summarize the theoretical progress made on the understanding of the rich phenomena in single-atom catalysis. We focus on the determination of local structures of SACs via comparison between experiments and simulations, the discovery of distinctive catalytic mechanisms induced by multiadsorption, synergetic effects, and dynamic evolutions, to name a few, the proposal of criteria for theoretically designing SACs, and the extension of original concepts of single-atom catalysis. We hope that this Perspective will inspire more in-depth thinking on future theoretical studies of SACs.

Stability and Catalytic Performance of Single-Atom Supported on Ti2 CO2 for Low-Temperature CO Oxidation: A First-Principles Study

Based on first-principles calculations, the potential of Ti₂ CO₂ monolayer (MXene) as a single-atom catalyst (SAC) support for 3d transition metal (TM) atoms (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) is studied for CO oxidation. We first screen the support effect according to the stability of a single metal atom and find that Sc and Ti supported on Ti₂ CO₂ have stronger adsorption energy than the cohesive energy of their bulk counterparts and therefore, we selected Sc and Ti supported on Ti₂ CO₂ for further catalytic reactions. The stability and the potential catalytic reactivity are verified by electronic structure and charge transfer analysis. Both Eley-Rideal (ER) and Langmuir-Hinshelwood (LH) mechanisms are considered in this study, and lower energy barriers of 0.002 and 0.37 eV were found in the ER mechanism compared to the LH mechanism, which are 0.25 and 0.34 eV for Sc and Ti catalysts, respectively. Moreover, kinetic ER and LH mechanisms are favorable for both Sc- and Ti/Ti₂ CO₂ because of the comparable energy barrier to other metals and SAC supported on 2D materials. However, Ti/Ti₂ CO₂ catalyst is thermodynamically unfavorable. Based on these calculations, we propose that Sc supported on Ti₂ CO₂ is the best catalyst for CO-oxidation. The current study not only broadens the scope of the single-atom Sc catalyst but also extends the consideration of MXene support for catalyst optimization.

Significant Role of Oxygen Dopants in Photocatalytic PFCA Degradation over h-BN

The activation of the C(sp³)-F bond is extremely difficult due to its unreactive nature. The importance of this bond activation is recently highlighted because extensive distribution of perfluorocarboxylic acids (PFCAs) (C_nF_2n+1COOH) has emerged as a challenging environmental issue. Photocatalytic degradation of PFCAs over a few semiconducting light absorbers is known to remove these water and soil resilient contaminants but with limited efficiency. This work reports density functional theory calculations, through which we present a detailed mechanistic study of photocatalytic degradation of CF₃COOH (the shortest member of the PFCA family) over hexagonal boron nitride (h-BN). Our results clearly demonstrate that the existence of point defects is necessary to activate the h-BN plane for photocatalytic dissociation of the C-F bond. Specifically, we show that vacancies create strong Lewis acid or base sites (B or N vacancy, respectively) that facilitate the activation of the C(sp³)-F bond considerably. Furthermore, this study presents vivid theoretical evidence for the significant role of oxygen dopants, which mitigate the strength of the active sites and promote PFCA degradation over h-BN. Our calculations suggest that while the very stable intermediates generated during the reaction, in the case of h-BN with B or N vacancies, practically poison the catalyst, oxygen dopants make the degradation much more plausible and controllable. This work thus provides both an explanation for recently observed photocatalytic activity of h-BN to decompose PFCAs and valuable insights for exploring defected two-dimensional materials for activating and removing the fluorine-containing contaminants from water and soil.

Catalytic CO oxidation reaction over N-substituted graphene nanoribbon with edge defects

Density functional theory calculations, including dispersion effects, are used to demonstrate how substitutional nitrogen atoms can improve the catalytic reactivity of graphene nanoribbons (GNR) with edge defects in the CO oxidation process. It is demonstrated that the addition of nitrogen impurities significantly enhances O₂ adsorption on GNR. Carbon atoms near the edges of defects are the most active sites for capturing O₂ molecules. The lower adsorption energy of CO relative to O₂ implies that the N-modified GNR is resistant to CO poisoning. The Eley-Rideal (E-R) mechanism has activation energies as low as 0.38 eV, making it the most energetically relevant pathway for the CO + O₂ reaction. The findings of this study might help in the design of catalysts for metal-free catalysis of CO oxidation.

Single-metal-atom catalysts supported on graphdiyne catalyze CO oxidation

Single-metal-atom catalysts supported on graphdiyne (GDY) exhibit great potential for catalyzing low temperature CO oxidation in solving the increasingly serious environmental problems caused by CO emissions due to the high catalytic activity, clear structure, uniform metal distribution and low cost. First principle calculations were employed to study CO oxidation activities of four M@GDY single-atom catalysts (M = Pt, Rh, Cu, and Ni). For each catalyst, five possible reaction mechanisms including bi-molecular and tri-molecular reactions were discussed. According to the calculated reaction barriers, the preferred reaction pathway is via the bi-molecular Langmuir-Hinshelwood (BLH) ((CO + O₂)* → OCOO* → CO₂ + O*) route to yield the first CO₂ molecule with 0.55, 0.51, and 0.53 eV as the energy barriers of the rate-limiting steps of Pt@GDY, Rh@GDY, and Cu@GDY, respectively, whereas for Ni@GDY, it switches to the tri-molecular Eley-Rideal (TER1) ((2CO)* + O₂→ OCOOCO* → 2CO₂) mechanism with the reaction barrier of the rate-limiting step being 1.27 eV. Based on the energy difference in the initial states of the five reaction mechanisms, TER1 is generally viable. No matter it is based on the calculated reaction barrier or the energy of the initial state of each mechanism, the non-noble Cu@GDY is supposed to be an efficient catalyst as the noble ones. The electronic properties are calculated to explain the bonding strength and origin of the catalytic performance. The GDY support plays an important role in the electron transfer process.

The formation and evolution of carbonate species in CO oxidation over mono-dispersed Fe on graphene

Fe is not only the most abundant metal on the planet but is also the key component of many enzymes in organisms that are capable of catalyzing many chemical conversions. Mono-dispersed Fe atoms on carbonaceous materials are single atom catalysts (SACs) that function like enzymes. To take advantage of the outstanding catalytic performance of Fe-based SACs, we extended a CO oxidation reaction network over mono-dispersed Fe atoms on graphene (FeGR) by first-principles based calculations. FeGR-catalyzed CO oxidation is initiated with a revised Langmuir-Hinshelwood pathway through a CO-assisted scission of the O-O bond in peroxide species (OCOO). We showed that carbonate species (CO3), which were previously generally considered as a persistent species blocking reaction sites, may form from CO2 and negatively charged O species. This pathway competes with desorption of CO2 and reduction of the Fe center with gaseous CO, and it is exothermic and inevitable, especially at low temperatures and with high CO2 content. Although direct dissociation of CO3 is demanding on FeGR, further adsorption of CO on Fe in CO3 is plausible and takes place spontaneously. We then showed that adsorbed CO may react with CO3, forming a cyclic-carbonate-like species that dissociates easily to CO2. These findings highlight the reaction condition-dependent formation and evolution of CO3 as well as its contribution to CO conversion, and it may extend the understanding of the performance of SACs in low temperature CO oxidation.

Syngas molecules as probes for defects in 2D hexagonal boron nitride: their adsorption and vibrations

Single-layer, defect-laden hexagonal boron nitride (dh-BN) is attracting a great deal of attention for its diverse applications: catalysis on the one hand, and single photon emission on the other. As possible probes for identifying some common defects in single-layer h-BN, we present results of ab initio calculations for the adsorption and vibrational characteristics of syngas molecules (H₂, CO, CO₂) on dh-BN containing one of four types of defects: nitrogen vacancy (V_N), boron vacancy (V_B), Stone-Wales defect (SW), and nitrogen substituted by boron (B_N). Through a comparative examination of adsorption features, charge transfer, electronic structure, and vibrational spectrum, we obtain a deep understanding of the interaction of these molecules with dh-BN and the role of the defect states. We find that while CO, CO₂ and atomic hydrogen chemisorb, molecular H₂ physisorbs on dh-BN with the four considered defect types. V_N and V_B show strong affinity for CO and CO₂ since the defect states induced by them lie close to the Fermi level. SW does not favor adsorption of these small molecules, as the process for each is endothermic. In the case of B_N, CO adsorbs strongly but CO₂ only weakly. Vibrational frequencies of notable modes localized at the adsorbed molecules are analyzed and suggested as measures for identification of the defect type. Through a simple comparison of adsorption characteristics of the molecules on these defects, we propose dh-BN with V_N to be a good catalyst candidate for CO₂ hydrogenation.

Phosphorene Supported Single-Atom Catalysts for CO Oxidation: A Computational Study

Single-atom catalysts (SACs) have attracted extensive attention owing to their high catalytic activity. The development of efficient SACs is crucial for applications in heterogeneous catalysis. In this article, the geometric configuration, electronic structure, stabilitiy and catalytic performance of phosphorene (Pn) supported single metal atoms (M=Ru, Rh, Pd, Ir, Pt, and Au) have been systematically investigated using density functional theory calculations and ab initio molecular dynamics simulations. The single atoms are found to occupy the hollow site of phosphorene. Among the catalysts studied, Ru-decorated phosphorene is determined to be a potential catalyst by evaluating adsorption energies of gaseous molecules. Various mechanisms including the Eley-Rideal (ER), Langmuir-Hinshelwood (LH) and trimolecular Eley-Rideal (TER) mechanisms are considered to validate the most favourable reaction pathway. Our results reveal that Ru-Pn exhibits outstanding catalytic activity toward CO oxidation reaction via TER mechanism with the corresponding rate-determining energy barrier of 0.44 eV, making it a very promising SAC for CO oxidation under mild conditions. Overall, this work may provide a new avenue for the design and fabrication of two-dimensional materials supported SACs for low-temperature CO oxidation.

Antibacterial and Antiviral Functional Materials: Chemistry and Biological Activity toward Tackling COVID-19-like Pandemics

The ongoing worldwide pandemic due to COVID-19 has created awareness toward ensuring best practices to avoid the spread of microorganisms. In this regard, the research on creating a surface which destroys or inhibits the adherence of microbial/viral entities has gained renewed interest. Although many research reports are available on the antibacterial materials or coatings, there is a relatively small amount of data available on the use of antiviral materials. However, with more research geared toward this area, new information is being added to the literature every day. The combination of antibacterial and antiviral chemical entities represents a potentially path-breaking intervention to mitigate the spread of disease-causing agents. In this review, we have surveyed antibacterial and antiviral materials of various classes such as small-molecule organics, synthetic and biodegradable polymers, silver, TiO2, and copper-derived chemicals. The surface protection mechanisms of the materials against the pathogen colonies are discussed in detail, which highlights the key differences that could determine the parameters that would govern the future development of advanced antibacterial and antiviral materials and surfaces.

Catalytic role of graphitic nitrogen atoms in the CO oxidation reaction over N-containing graphene: a first-principles mechanistic evaluation

The catalytic role of graphitic nitrogen atoms of a series of nitrogen-doped graphene surfaces is explored for low-temperature oxidation of CO using periodic DFT calculations.

Ligand Stabilized Ni1 Catalyst for Efficient CO Oxidation

Supported single transition metal (TM₁ ) catalysts have attracted broad attention in academia recently. Still, their corresponding reactivity and stability under reaction conditions are critical but have not well explored at the fundamental level. Herein, we use density functional theory calculation and ab initio molecular dynamics simulation to investigate the role of reactants and ligands on the reactivity and stability of graphitic carbon nitride (g-C₃ N₄ ) supported Ni₁ for CO oxidation. We find out that supported bare Ni₁ atoms are only metastable on the surface and tend to diffuse into the interlayer of g-C₃ N₄ . Though Ni₁ is catalytically active at moderate temperatures, CO adsorption induced dimerization deactivates the catalyst. Hydroxyl groups not only are able to stabilize the supported Ni₁ atom, but also increase the reactivity by participating directly in the reaction. Our results provide valuable insights on improving the chemical stability of TM₁ by ligands without sacrificing the reactivity, which are helpful for the rational design of highly loaded atomically dispersed supported metal catalysts.

Understanding the Activity of Single-Atom Catalysis from Frontier Orbitals

The d-band center and charge states are often used to analyze the catalytic activity of noble or transition metal surfaces and clusters, but their applicability for single-atom catalysts (SACs) is unsure. This work suggests that the spatial structure and orientation of frontier orbitals which are closest to the Fermi level of SACs play a vital role. Taking adsorption of several molecules and CO oxidization on C_{3}N-supported single-atom Au as examples, we demonstrate that adsorption and catalytic activities are well correlated with the characteristics of frontier orbitals. This work provides an effective guidance for understanding the performance of single-atom catalysts.

Theoretical Calculation of Different Reaction Mechanisms for CO Oxidation on MnN3-Doped Graphene

In recent decades, great expectation has always been placed on catalysts that can convert toxic CO into CO₂ under mild conditions. The catalytic mechanism of CO oxidation by Mn-coordinated N-doped graphene with a single vacancy (MnN₃-SV) and a double vacancy (MnN₃-DV) was studied by density functional theory (DFT) calculations. Molecular dynamics simulations showed that CO₂ on MnN₃-SV could not be desorbed from the substrate and MnN₃-SV was not suitable for use as a CO oxidation catalyst. MnN₃-DV was more suitable for CO oxidation (COOR) and from the electronic structure it was found that the Mn atom was the main active site, which was the reaction site for CO oxidation. At temperatures of 0 and 298.15 K, CO oxidation on MnN₃-DV via the Langmuir-Hinshelwood (LH) mechanism was the best reaction pathway. The rate-determining step using MnN₃-DV as the catalyst for CO oxidation through the LH mechanism was O₂ + CO → OOCO, and the energy barrier was 0.861 eV at 298.15 K. MnN₃-DV was suitable as a catalyst for CO oxidation in terms of both thermodynamics and kinetics. This study provides a comprehensive understanding of the various reaction mechanisms of CO oxidation on MnN₃-DV, which is conducive to guiding the development and design of efficient catalysts for CO oxidation.

Density functional study on the CO oxidation reaction mechanism on MnN2-doped graphene

The CO oxidation mechanisms over three different MnN₂-doped graphene (MnN₂C₂: MnN₂C₂-hex, MnN₂C₂-opp, MnN₂C₂-pen) structures were investigated through first-principles calculations. The vacancy in graphene can strongly stabilize Mn atoms and make them positively charged, which promotes O₂ activation and weakens CO adsorption. Hence, CO oxidation activity is enhanced and the catalyst is prevented from being poisoned. CO oxidation reaction (COOR) on MnN₂C₂ along the Eley–Rideal (ER) mechanism and the Langmuir–Hinshelwood (LH) mechanism will leave one O atom on the Mn atom, which is difficult to react with isolated CO. COOR on MnN₂C₂-opp along the ER mechanism and termolecular Eley–Rideal (TER) mechanism need overcome low energy barriers in the rate limiting step (RLS), which are 0.544 and 0.342 eV, respectively. The oxidation of CO along TER mechanism on MnN₂C₂-opp is the best reaction pathway with smallest energy barrier. Therefore, the MnN₂C₂-opp is an efficient catalysis and this study has a guiding role in designing effective catalyst for CO oxidation.

The various COOR mechanisms on MnN₂-doped graphene (MnN₂C₂: MnN₂C₂-hex, MnN₂C₂-opp, MnN₂C₂-pen) were investigated for the first time.

Probing the Hydrogen Bonding in Microsolvated Clusters of Au1,2-(Solv)n (Solv = C2H5OH, n-C3H7OH; n = 1-3 for Au-; n =1 for Au2-)

The microsolvation of gold anions in different alcohol solvents is demonstrated by the combination of anion photoelectron spectroscopy and quantum chemical calculations on the Au_1,2^-(Solv)_n (Solv = C₂H₅OH, n-C₃H₇OH; n = 1-3 for Au^-; n = 1 for Au₂^-). The microsolvation structures of these clusters and their corresponding neutrals are assigned by comparing calculations with experiments. In terms of overall regularity, the increasing solvation number (n) and carbon chain extension both can increase the stability of the anion. When n ≥ 2, these clusters have low-energy isomers, where conventional hydrogen bonds (HBs) compete with nonconventional HBs (NHBs). NHBs are dominant when n ≤ 2 and when n is increased, vice versa. Interestingly, a variety of theoretical calculations show that after the hydroxy H atom of the ethanol molecule forms a weak ionic HB with Au^-, there are two lowest conformations of ethanol, trans and gauche, which could be coexisting in the molecular beams. Some theoretical methods also suggest that the gauche isomer is more stable than the trans one, which indicates that Au^- may exist as a gold gauche effect similar to fluorine.

Surface Modification Strategy for Promoting the Performance of Non-noble Metal Single-Atom Catalysts in Low-Temperature CO Oxidation

As a bridge between homogeneous and heterogeneous catalyses, single-atom catalysts (SACs), especially the noble metal atoms, have received extensive attention from both the fundamental and applied perspectives recently. High cost and difficulty in synthesis are considerable factors, however, limiting the development and practical applications of SACs. Thus, seeking for non-noble SACs for substituting the noble ones is not only of vital importance but also a long-standing challenge. Herein, a surface modification strategy by introducing an oppositely charged dopant and inducing the charge transfer between the SAC and the substrate was proposed to improve the stability and catalytic performance of the non-noble Cu SAC. Using first-principles density functional theory (DFT) calculations, it was demonstrated that the introduction of C in the MoS₂ monolayer (C:MoS₂, experimentally available) can assist in stabilizing Cu and make it more positively charged, which will facilitate the adsorption of the reactants and further enhance the activity for CO oxidation. Strikingly, our results show that CO oxidation over Cu-C:MoS₂ is more favorable than over the Pt atom deposited on the pristine MoS₂ (Pt-MoS₂), exhibiting its potential in noble metal substitution and low-temperature CO oxidation. Additionally, Cu-C:MoS₂ was observed to have a response to visible light, which manifests that it may be a promising photocatalyst. The strategy proposed here provides an efficient route to regulate the electronic structures of SACs through charge transfer, which further promotes the reactivity of the non-noble metal SACs. We hope that this strategy can contribute to design more SACs with low cost and high efficiency, which will be beneficial for their practical applications.

Efficient metal overlayer catalysts on the Nb2C monolayer for CO oxidation from first-principles screening

Based on the first-principles calculation, the configurations of different metal overlayers on the monolayer Nb₂C (MXene) (M_ML/Nb₂C) (M  =  Rh, Ir, Pd, Pt, Ag, Au) were studied aiming to find a kind of complex system with high CO-tolerance and high CO conversion efficiency. Combined with the stability of the composite systems and their adsorption properties on small gas molecules, Ag_ML/Nb₂C was screened out and further tested for CO oxidation reaction. By comparing the energy barriers of different reaction pathways, we concluded that CO oxidation reaction could be carried out on Ag_ML/Nb₂C var the LH mechanism with a small energy barrier of 0.35 eV. The rate-determining step was the oxidation of CO by the adsorbed oxygen atom. The Ag_ML/Nb₂C showed good activity for CO oxidation, which would provide a theoretical basis for designing the electrode material for the proton exchange membrane fuel cells (PEMFCs).

Single-Atom Catalytic Materials for Advanced Battery Systems

Advanced battery systems with high energy density have attracted enormous research enthusiasm with potential for portable electronics, electrical vehicles, and grid-scale systems. To enhance the performance of conversion-type batteries, various catalytic materials are developed, including metals and transition-metal dichalcogenides (TMDs). Metals are highly conductive with catalytic effects, but bulk structures with low surface area result in low atom utilization, and high chemical reactivity induces unfavorable dendrite effects. TMDs present chemical adsorption with active species and catalytic activity promotes conversion processes, suppressing shuttle effect and improving energy density. But they suffer from inferior conductivity compared with metal, and limited sites mainly concentrate on edges and defects. Single-atom materials with atomic sizes, good conductivity, and individual sites are promising candidates for advanced batteries because of a large atom utilization, unsaturated coordination, and unique electronic structure. Single-atom sites with high activity chemically trap intermediates to suppress shuttle effects and facilitate electron transfer and redox reactions for achieving high capacity, rate capability, and conversion efficiency. Herein, single-atom catalytic electrodes design for advanced battery systems is addressed. Major challenges and promising strategies concerning electrochemical reactions, theoretical model, and in situ characterization are discussed to shed light on future research of single-atom material-based energy systems.

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.