Understanding the Activity of Single-Atom Catalysis from Frontier Orbitals

Modulation of Photocatalytic CO2 Reduction by n-p Codoping Engineering of Single-Atom Catalysts

Transition metal (TM) single-atom catalysts (SACs) have been widely applied in photocatalytic CO2 reduction. In this work, n-p codoping engineering is introduced to account for the modulation of photocatalytic CO2 reduction on a two-dimensional (2D) bismuth-oxyhalide-based cathode by using first-principles calculation. n-p codoping is established via the Coulomb interactions between the negatively charged TM SACs and the positively charged Cl vacancy (VCl) in the dopant-defect pairs. Based on the formation energy of charged defects, neutral dopant-defect pairs for the Fe, Co, and Ni SACs (PTM0) and the -1e charge state of the Cu SAC-based pair (PCu-1) are stable. The electrostatic attraction of the n-p codoping strengthens the stability and solubility of TM SACs by neutralizing the oppositely charged VCl defect and TM dopant. The n-p codoping stabilizes the electron accumulation around the TM SACs. Accumulated electrons modify the d-orbital alignment and shift the d-band center toward the Fermi level, enhancing the reducing capacity of TM SACs based on the d-band theory. Besides the electrostatic attraction of the n-p codoping, the PCu-1 also accumulates additional electrons surrounding Cu SACs and forms a half-occupied dx2-y2 state, which further upshifts the d-band center and improves photocatalytic CO2 reduction. The metastability of Cl multivacancies limits the concentration of the n-p pairs with Cl multivacancies (PTM@nCl (n > 1)). Positively charged centers around the PTM@nCl (n > 1) hinders the CO2 reduction by shielding the charge transfer to the CO2 molecule.

Steering sp-Carbon Content in Graphdiynes for Enhanced Two-Electron Oxygen Reduction to Hydrogen Peroxide

Compared to sp2-hybridized graphene, graphdiynes (GDYs) composed of sp and sp2 carbon are highly promising as efficient catalysts for electrocatalytic oxygen reduction into oxygen peroxide because of the high catalytic reactivity of the electron-rich sp-carbon atoms. The desired catalytic capacity of GDY, such as catalytic selectivity and efficiency, can theoretically be achieved by strategically steering the sp-carbon contents or the topological arrangement of the acetylenic linkages and aromatic bonds. Herein, we successfully tuned the electrocatalytic activity of GDYs by regulating the sp-to-sp2 carbon ratios with different organic monomer precursors. As the active sp-carbon atoms possess electron-sufficient π orbitals, they can donate electrons to the lowest unoccupied molecular orbital (LUMO) orbitals of O2 molecules and initiate subsequent O2 reduction, GDY with the high sp-carbon content of 50 at % exhibits excellent capability of catalyzing O2 reduction into H2O2. It demonstrates exceptional H2O2 selectivity of over 95.0 % and impressive performance in practical H2O2 production, Faraday efficiency (FE) exceeding 99.0 %, and a yield of 83.3 nmol s-1 cm-2. Our work holds significant importance in effectively steering the inherent properties of GDYs by purposefully adjusting the sp-to-sp2 carbon ratio and highlights their immense potential for research and applications in catalysis and other fields.

DFT Study on Effect of Metal Type and Coordination Environment on CO2 ECR to C1 Products over M-N-C Catalysts

Electrocatalytic reduction (ECR) of CO2 to chemical products is an important carbon emission reduction method. This work uses DFT to study the stability of N-doped graphene-supported four metal single-atom catalysts (M-N-C) and the effects of the coordination environment and metal centers on the selectivity of CO2 ECR to C1 products. The results show that Fe, Co, Ni, and Cu have good stability. The coordination environment has a significant modulating effect on product selectivity, and the change of the number of ligand nitrogen atoms will affect the size of the potential-limiting step of each product. When the number of nitrogen ligands is the same, the different metal centers of the M-N-C catalyst have a significant effect on the selectivity of different products. In addition, the introduction of nitrogen atom ligands can adjust the electronic structure of the graphene-supported metal center, increase the d-band center of most metals, and improve the reaction activity.

Selective Orbital Coupling: An Adsorption Mechanism in Single-Atom Catalysis

Quantitative understanding of the chemisorption on single-atom catalysts (SACs) by their electronic properties is crucial for the catalyst design. However, the physical mechanism is still under debate. Here, the CO catalytic oxidation on single transition metal (i.e., Sc, Ti, V, Cr, Mn, Fe, Co, Ni) dopants is used as a theoretical model to explore the correlations between the characteristics of electronic structures and the chemisorption on SACs. For these metal dopants, their atomic d orbitals form several nondegenerate and localized electronic states that are found to be selectively coupled with the π* orbital of the adsorbed O2, which we defined as selective orbital coupling. Based on the selective orbital coupling, we find that the alignment between the selected d state and the π* state determines the bond strength, regardless of the electron occupation number of the selected d states; the electron transfer to form M-O bonding can be provided by the support. Such electron transfer can be related with the electronic metal-support interaction. We attribute the origin of the chemisorption mechanism to the coexistence of the localized orbital of the single transition metal and the continuous energy band of the Au support. Finally, we illustrate how this mechanism dominates the variation trend of the reaction barriers. Our results unravel a fundamental adsorption mechanism in SAC systems.

Origin of Interfacial Orbital Reconstruction in Perovskite Superlattices

The competition between on-site electronic correlation and local crystal field stands out as a captivating topic in research. However, its physical ramifications often get overshadowed by influences of strong periodic potential and orbital hybridization. The present study reveals this competition may become more pronounced or even dominant in two-dimensional systems, driven by the combined effects of dimensional confinement and orbital anisotropy. This leads to electronic orbital reconstruction in certain perovskite superlattices or thin films. To explore the emerging physics, we investigate the interfacial orbital disorder-order transition with an effective Hamiltonian and how to modulate this transition through strains.

Descriptor for C2N-Supported Single-Cluster Catalysts in Bifunctional Oxygen Evolution and Reduction Reactions

Developing highly active cluster catalysts for the bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is significant for future renewable energy technology. Here, we employ first-principles calculations combined with a genetic algorithm to explore the activity trends of transition metal clusters supported on C2N. Our results indicate that the supported clusters, as bifunctional catalysts for the OER and the ORR, may outperform single-atom catalysts. In particular, the C2N-supported Ag6 cluster exhibits outstanding bifunctional activity with low overpotentials. Mechanistic analysis indicates that the activity of the cluster is related to the number of atoms in the active site as well as the interaction between the intermediate and the cluster. Accordingly, we identify a descriptor that links the intrinsic properties of the clusters with the activity of both the OER and the ORR. This work provides guidelines and strategies for the rational design of highly efficient bifunctional cluster catalysts.

Investigating the role of undercoordinated Pt sites at the surface of layered PtTe2 for methanol decomposition

Transition metal dichalcogenides, by virtue of their two-dimensional structures, could provide the largest active surface for reactions with minimal materials consumed, which has long been pursued in the design of ideal catalysts. Nevertheless, their structurally perfect basal planes are typically inert; their surface defects, such as under-coordinated atoms at the surfaces or edges, can instead serve as catalytically active centers. Here we show a reaction probability > 90 % for adsorbed methanol (CH3OH) on under-coordinated Pt sites at surface Te vacancies, produced with Ar+ bombardment, on layered PtTe2 - approximately 60 % of the methanol decompose to surface intermediates CHxO (x = 2, 3) and 35 % to CHx (x = 1, 2), and an ultimate production of gaseous molecular hydrogen, methane, water and formaldehyde. The characteristic reactivity is attributed to both the triangular positioning and varied degrees of oxidation of the under-coordinated Pt at Te vacancies.

High Catalytic Activity of Co-centered 2D Metal Organic Frameworks toward Bifunctional Oxygen Evolution and Reduction Reactions: Rationalized by Spin Polarization Effect

CoX4 (X = NH, S, and O) motifs have demonstrated their high catalytic activity in the platforms of metal organic frameworks (MOFs), however, the underlying reason is still unrevealed. Herein, we propose monolayers constructed by linking TMNxO4-x motifs (TM = Fe, Co, Ni, Cu) with trioxotriangulenes (TOTs) as suitable models to clarify the structure-property-performance relationship of 2D MOFs for the oxygen evolution/reduction reaction (OER/ORR). The highly robust catalytic activity of CoNxO4-x for both the OER and the ORR has been confirmed, even surpassing that of most previously reported 2D MOFs and SACs. This activity is attributed to the moderate interaction between Co and the key intermediate species, which can be modulated by the coordinating atoms. We reveal spin momentum as a reliable activity descriptor in rationalizing the OER/ORR activity, which can be extended to many other 2D MOFs. The elucidated structure-activity relationship is significant for the development of effective bifunctional OER/ORR electrocatalysts.

Tuning Active Site Flexibility by Defect Engineering of Graphene Ribbon Edge-hosted Fe-N3 Sites

Nitrogen-doped, carbon-supported transition metal catalysts are excellent for several reactions. Structural engineering of M-Nx sites to boost catalytic activity is rarely studied. Here, we demonstrate that the structural flexibility of Fe-N3 site is vital for tuning the electronic structure of Fe atoms and regulating the catalytic transfer hydrogenation (CTH) activity. By introducing carbon defects, we construct Fe-N3 sites with varying Fe-N bond lengths distinguishable by X-ray absorption spectroscopy. We investigate the CTH activity by density-functional theory and microkinetic calculations and reveal that the vertical displacement of the Fe atom out of the plane of the support, induced by the Fe-N3 distortion, raises the Fe3 d z 2 ${3{d}_{{z}^{2}}{\rm \ }}$ orbital and strengthens binding. We propose that the activity is controlled by the relaxation of the reconstructed site, which is further affected by Fe-N bond length, an excellent activity descriptor. We elucidate the origin of the CTH activity and principles for high-performing Fe-N-C catalysts by defect engineering.

Electrochemical Potential-Driven Shift of Frontier Orbitals in M-N-C Single-Atom Catalysts Leading to Inverted Adsorption Energies

Electronic structure is essential to understanding the catalytic mechanism of metal single-atom catalysts (SACs), especially under electrochemical conditions. This study delves into the nuanced modulation of "frontier orbitals" in SACs on nitrogen-doped graphene (N-C) substrates by electrochemical potentials. We observe shifts in Fermi level and changes of d-orbital occupation with alterations in electrochemical potentials, emphasizing a synergy between the discretized atomic orbitals of metals and the continuous bands of the N-C based environment. Using O2 and CO2 as model adsorbates, we highlight the direct consequences of these shifts on adsorption energies, unveiling an intriguing inversion of adsorption energies on Co/N-C SAC under negative electrochemical potentials. Such insights are attributed to the role of the dxz and dz2 orbitals, pivotal for stabilizing the π* orbitals of O2. Through this exploration, our work offers insights on the interplay between electronic structures and adsorption behaviors in SACs, paving the way for enhanced catalyst design strategies in electrochemical processes.

Establishing an orbital-level understanding of active origins of heteroatom-coordinated single-atom catalysts: The case of N2 reduction

Heteroatom-coordinated single-atom catalysts (SACs) supported by porous graphene exhibit high activity in electrochemical reduction reactions. However, the underlying active origins are complex and puzzling, hindering the development of efficient catalysts. Herein, we investigate the active origins of heteroatom-coordinated Fe-XmYn SACs (X, Y = B, C, N, O, m + n = 4) toward nitrogen reduction reaction (NRR) as a model reaction, through comprehensive analysis of structural, energetic, and electronic parameters. Specifically, the number and arrangement of heteroatoms are found to significantly affect the degree of d-orbital splitting and magnetic moment of the Fe center. Moreover, d-orbital splitting energy (dSE), rather than the conventional d-band theory, explains the adsorption behavior of intermediates in multi-step electron-proton coupling (EPC) reactions. In addition, both s- and d-orbitals of Fe are found to be important for Fe-N bonding, which promotes charge transfer (CT) and N2 activation. Importantly, CT is thought to influence the Pauli repulsion and orbital interaction. Correspondingly, relationships are unveiled between limiting potential (Ulimit) and adsorption energy ΔE(*NNH), dSE, CT, Fe-N bond. In all, this work provides orbital-level insights into the active origins of Fe-XmYn SACs, contributing to the understanding of intrinsic mechanism and the design of electrocatalysts for multi-step EPC reactions.

Clustering-Evolved Frontier Orbital for Low-Temperature CO2 Dissociation

In this study, single Ni2 clusters (two Ni atoms bridged by a lattice oxygen) are successfully synthesized on monolayered CuO. They exhibit a remarkable activity toward low-temperature CO2 thermal dissociation, in contrast to cationic Ni atoms that nondissociatively adsorb CO2 and metallic Ni ones that are chemically inert for CO2 adsorption. Density functional theory calculations reveal that the Ni2 clusters can significantly alter the spatial symmetry of their unoccupied frontier orbitals to match the occupied counterpart of the CO2 molecule and enable its low-temperature dissociation. This study may help advance single-cluster catalysis and exploit the unexcavated mechanism for low-temperature CO2 activation.

Orbital distortion and electric field control of sliding ferroelectricity in a boron nitride bilayer

Recent experiments confirm that two-dimensional boron nitride (BN) films possess room-temperature out-of-plane ferroelectricity when each BN layer is sliding with respect to each other. This ferroelectricity is attributed to the interlayered orbital hybridization or interlayer charge transfer in previous work. In this work, we attempt to understand the sliding ferroelectricity from the perspective of orbital distortion of long-pair electrons. Using the maximally localized Wannier function method and first-principles calculations, the out-of-planep_zorbitals of BN are investigated. Our results indicate that the interlayer van der Waals interaction causes the distortion of the Np_zorbitals. Based on the picture of out-of-plane orbital distortion, we propose a possible mechanism to tune the ferroelectric polarization by external fields, including electric field and stress field. It is found that both the polarization intensity and direction can be modulated under the electric field. The polarization intensity of the system can also be controlled by stress field perpendicular to the plane. This study will provide theoretical help in the device design based on sliding ferroelectrics.

Ullmann-Like Covalent Bond Coupling without Participation of Metal Atoms

Ullmann-like on-surface synthesis is one of the most appropriate approaches for the bottom-up fabrication of covalent organic nanostructures and many successes have been achieved. The Ullmann reaction requires the oxidative addition of a catalyst (a metal atom in most cases): the metal atom will insert into a carbon-halogen bond, forming organometallic intermediates, which are then reductively eliminated and form C-C covalent bonds. As a result, traditional Ullmann coupling involves reactions of multiple steps, making it difficult to control the final product. Moreover, forming the organometallic intermediates will potentially poison the metal surface catalytic reactivity. In the study, we used the 2D hBN, an atomically thin sp²-hybridized sheet with a large band gap, to protect the Rh(111) metal surface. It is an ideal 2D platform to decouple the molecular precursor from the Rh(111) surface while maintaining the reactivity of Rh(111). We realize an Ullmann-like coupling of a planar biphenylene-based molecule, i.e., 1,8-dibromobiphenylene (BPBr₂), on an hBN/Rh(111) surface with an ultrahigh selectivity of the biphenylene dimer product, containing 4-, 6-, and 8-membered rings. The reaction mechanism, including electron wave penetration and the template effect of the hBN, is elucidated by combining low-temperature scanning tunneling microscopy and density functional theory calculations. Our findings are expected to play an essential role regarding the high-yield fabrication of functional nanostructures for future information devices.

Challenges and Opportunities in Engineering the Electronic Structure of Single-Atom Catalysts

Controlling the electronic structure of transition-metal single-atom heterogeneous catalysts (SACs) is crucial to unlocking their full potential. The ability to do this with increasing precision offers a rational strategy to optimize processes associated with the adsorption and activation of reactive intermediates, charge transfer dynamics, and light absorption. While several methods have been proposed to alter the electronic characteristics of SACs, such as the oxidation state, band structure, orbital occupancy, and associated spin, the lack of a systematic approach to their application makes it difficult to control their effects. In this Perspective, we examine how the electronic configuration of SACs can be engineered for thermochemical, electrochemical, and photochemical applications, exploring the relationship with their activity, selectivity, and stability. We discuss synthetic and analytical challenges in controlling and discriminating the electronic structure of SACs and possible directions toward closing the gap between computational and experimental efforts. By bringing this topic to the center, we hope to stimulate research to understand, control, and exploit electronic effects in SACs and ultimately spur technological developments.

Correlation between Electronic Descriptor and Proton-Coupled Electron Transfer Thermodynamics in Doped Graphite-Conjugated Catalysts

Graphite-conjugated catalysts (GCCs) provide a powerful framework for investigating correlations between electronic structure features and chemical reactivity of single-site heterogeneous catalysts. GCC-phenazine undergoes proton-coupled electron transfer (PCET) involving protonation of phenazine at its two nitrogen atoms with the addition of two electrons. Herein, this PCET reaction is investigated in the presence of defects, such as heteroatom dopants, in the graphitic surface. The proton-coupled redox potentials, E_PCET, are computed using a constant potential periodic density functional theory (DFT) strategy. The electronic states directly involved in PCET for GCC-phenazine exhibit the same nitrogen orbital character as those for molecular phenazine. The energy ε_LUS of this phenazine-related lowest unoccupied electronic state in GCC-phenazine is identified as a descriptor for changes in PCET thermodynamics. Importantly, ε_LUS is obtained from only a single DFT calculation but can predict E_PCET, which requires many such calculations. Similar electronic features may be useful descriptors for thermodynamic properties of other single-site catalysts.

Rare-Earth Single-Atom Catalysts: A New Frontier in Photo/Electrocatalysis

Single-atom catalysts (SACs) provide well-defined active sites with 100% atom utilization, and can be prepared using a wide range of support materials. Therefore, they are attracting global attention, especially in the fields of energy conversion and storage. To date, research has focused on transition-metal and precious-metal-based SACs. More recently, rare-earth (RE)-based SACs have emerged as a new frontier in photo/electrocatalysis owing to their unique electronic structure arising from the spin-orbit coupling of the 4f and valence orbitals, unsaturated coordination environment, and unique behavior as charge-transport bridges. However, a systematic review on the role of the RE active sites, catalytic mechanisms, and synthetic methods for RE SACs is lacking. Therefore, in this review, the latest developments in RE SACs having applications in photo/electrocatalysis are summarized and discussed. First, the theoretical advantages of RE SACs for photo/electrocatalysis are briefly introduced, focusing on the roles of the 4f orbitals and coupled energy levels. In addition, the most recent research progress on RE SACs is summarized for several important photo/electrocatalytic reactions and the corresponding catalytic mechanisms are discussed. Further, the synthetic strategies for the production of RE SACs are reported. Finally, challenges for the development of RE SACs are highlighted, along with future research directions and perspectives.

A charge transfer framework that describes supramolecular interactions governing structure and properties of 2D perovskites

The elucidation of structure-to-function relationships for two-dimensional (2D) hybrid perovskites remains a primary challenge for engineering efficient perovskite-based devices. By combining insights from theory and experiment, we describe the introduction of bifunctional ligands that are capable of making strong hydrogen bonds within the organic bilayer. We find that stronger intermolecular interactions draw charge away from the perovskite layers, and we have formulated a simple and intuitive computational descriptor, the charge separation descriptor (CSD), that accurately describes the relationship between the Pb-I-Pb angle, band gap, and in-plane charge transport with the strength of these interactions. A higher CSD value correlates to less distortion of the Pb-I-Pb angle, a reduced band gap, and higher in-plane mobility of the perovskite. These improved material properties result in improved device characteristics of the resulting solar cells.

Understanding structure-property relationships is important when designing functional materials. Here, authors propose a descriptor to help understand and predict the electronic properties of two-dimensional lead iodide perovskites for photovoltaic applications.

Screening of transition metal single-atom catalysts supported by a WS2 monolayer for electrocatalytic nitrogen reduction reaction: insights from activity trend and descriptor

The electrocatalytic nitrogen reduction reaction (NRR), as an alternative green technology to the Haber-Bosch process, can efficiently synthesize ammonia under ambient conditions and has a reduced carbon footprint. Here we systematically investigate the NRR activity and selectivity of transition metal (TM) single-atom catalyst (SAC) anchored WS₂ monolayers (TM@WS₂) by means of first-principles calculations and microkinetic modeling. The construction of the reaction activity trend and the identification of an activity descriptor, namely *N₂H adsorption energy, facilitate the efficient screening and rational design of SACs with high activity. Manipulating the adsorption strength of the pivotal *N₂H intermediate is a potential strategy for enhancing NRR activity. Utilizing the limiting potential difference of NRR and the hydrogen evolution reaction (HER) as a selectivity descriptor, we screen three SACs with excellent activity and selectivity toward NRR, i.e., Re@WS₂, Os@WS₂ and Ir@WS₂ with favorable limiting potentials of -0.44 V, -0.38 V and -0.69 V. By using the explicit H₉O₄⁺ model, the kinetic barriers of the rate-determining steps (0.47 eV-1.15 eV) of the solvated proton transfer on the screened SACs are found to be moderate, indicative of a kinetically feasible process. Microkinetic modeling shows that the turnover frequencies of N₂ reduction to NH₃ on Re@WS₂, Os@WS₂ and Ir@WS₂ are 1.52 × 10⁵, 8.21 × 10² and 4.17 × 10^-4 per s per site at 400 K, achieving fast reaction rates. The coexistence of empty and occupied 5d orbitals of candidate SACs is beneficial for σ donation and π* backdonation, endowing them with extraordinary N₂ adsorption and activation. Moreover, the screened SACs possess good dispersity and thermodynamic stability. Our work provides a promising solution for the efficient screening and rational design of high-performance electrocatalysts toward the NRR.

Synergetic Charge Transfer and Spin Selection in CO Oxidation at Neighboring Magnetic Single-Atom Catalyst Sites

Deciphering the precise physical mechanism of interaction between an adsorbed species and a reactive site in heterogeneous catalysis is crucial for predictive design of highly efficient catalysts. Here, using first-principles calculations we identify that the two-dimensional ferromagnetic metal organic framework of Mn₂C₁₈H₁₂ can serve as a highly efficient single-atom catalyst for spin-triplet O₂ activation and CO oxidation. The underlying mechanism is via "concerted charge-spin catalysis", involving a delicate synergetic process of charge transfer, provided by the hosting Mn atom, and spin selection, preserved through active participation of its nearest neighboring Mn atoms for the crucial step of O₂ activation. The synergetic mechanism is further found to be broadly applicable in O₂ adsorption on magnetic X₂C₁₈H₁₂ (X = Mn, Fe, Co, and Ni) with a well-defined linear scaling dependence between the chemical activity and spin excitation energy. The present findings provide new insights into chemical reactions wherein spin selection plays a vital role.

Influence of Magnetic Moment on Single Atom Catalytic Activation Energy Barriers

Design of the molecular environment of single atom catalysts (SAC) is promising for achieving high catalytic activity without expensive and scarce platinum-group metals (PGM). We utilize a first principles approach to examine how the spin state of the SAC and reactants can affect catalytic energy barriers of V, Fe, Mo, and Ta on two different graphene defects with differing magnetic moments. Spin polarized projected density of states and climbing image nudged elastic band calculations demonstrate relatively lower activation energy barriers for systems with higher spin state asymmetry near the Fermi energy; CO oxidation on Ta and V SAC have decreases in activation barrier energies of 27% and 44%, respectively.

Graphic Abstract

Insights into the activity of single-atom Fe-N-C catalysts for oxygen reduction reaction

Single-atom Fe-N-C catalysts has attracted widespread attentions in the oxygen reduction reaction (ORR). However, the origin of ORR activity on Fe-N-C catalysts is still unclear, which hinder the further improvement of Fe-N-C catalysts. Herein, we provide a model to understand the ORR activity of Fe-N4 site from the spatial structure and energy level of the frontier orbitals by density functional theory calculations. Taking the regulation of divacancy defects on Fe-N4 site ORR activity as examples, we demonstrate that the hybridization between Fe 3dz2, 3dyz (3dxz) and O2 π* orbitals is the origin of Fe-N4 ORR activity. We found that the Fe-O bond length, the d-band center gap of spin states, the magnetic moment of Fe site and *O2 as descriptors can accurately predict the ORR activity of Fe-N4 site. Furthermore, these descriptors and ORR activity of Fe-N4 site are mainly distributed in two regions with obvious difference, which greatly relate to the height of Fe 3d projected orbital in the Z direction. This work provides a new insight into the ORR activity of single-atom M-N-C catalysts.

CO2 Reduction on Single-Atom Ir Catalysts with Chemical Functionalization

As promising catalytic systems, single-atom catalysts (SACs) demonstrate improved catalytic performance for electrochemical reactions. However, the pinning of metal atoms on surfaces usually depends on the adsorption on defects. In...

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.

Theoretical study on the adsorption and electronic properties of toxic gas molecules on single-atom Pt-doped B/N-coordinated graphene

The geometric stability, electronic and magnetic characteristics of the single-atom metal (SAMs) Pt-anchored graphene by controlling the coordinated B and N atoms (xB–yN–graphene-Pt, x + y = 1–3) are studied using first-principles calculations.