The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol

The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol Haojie Geng, Yanling Gao, Haobo Zhao, Yi Wang, Nian Bing Li, Jingyu Ran This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7370917/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Feb, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract The direct oxidation of methane to methanol holds significant industrial value. In the methane-assisted oxidation and one-step methanol synthesis reaction, the oxidants or oxygen-containing groups are highly prone to deeply oxidize the dissociated methane molecules, making it difficult to control the reaction proces. This study, based on dual-atom catalysts, we regulate the reaction process by separating active sites at a short distance and constraining the activity of oxygen intermediates, enabling methanol formation through the oxygen insertion. Aiming at the precise construction of dual sites, we innovatively developed an encapsulated pyrolysis strategy and successfully synthesized Rh–Cu heteronuclear dual-atom catalysts (RhCu DACs) over nitrogen-doped graphite carbon supports, forming an Rh–Cu–N 6 structural catalyst (Rh–Cu bond length = 2.42 Å). The electronic coupling between the bimetallic sites induces a significant charge polarization effect, enhancing the activation efficiency of reactant molecules. The introduction of the second metal, Cu, captures active oxygen species, generating a “restraint” effect on oxygen species. This restraint effectively inhibits excessive oxygen insertion, thereby inhibiting the complete oxidation of methane. The methanol selectivity is as high as 81% and the catalytic activity is three times than that of the single-atom Rh catalyst. In-situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrate that the rhodium-copper bimetallic centers form stable oxygen-bridged intermediate structure (Rh-O-O-Cu or Rh-O-Cu). The rhodium site acts as an electron acceptor for methyl groups (*CH 3 ) to stabilize the formation of hydrocarbon intermediates, while the copper site restricts the activity of adjacent oxygen species and guides oxygen insertion into C-H bonds for methanol synthesis. Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis Physical sciences/Chemistry/Catalysis/Catalytic mechanisms Methane Methanol Dual-atom Catalyst Catalytic Oxidation Kinetics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 1. Introduction The one-step oxidation of CH 4 to CH3OH is widely regarded as the "Holy Grail" during catalytic reactions [ 1 – 3 ] . CH 4 molecules have a symmetrical tetrahedral structure and a high C − H bond dissociation enthalpy of 440 kJ·mol − 1 , which makes the C − H bond difficult to polarize [ 4 , 5 ] . The highly reactive methyl radical (·CH 3 ) is prone to further C − H bond cleavage or side reactions with active oxygen, which reduces methanol selectivity and the economic viability of the process [ 6 , 7 ] . This contradiction of "efficient activation and high selectivity being hard to reconcile" essentially stems from the insufficient ability of catalysts to precisely control the reaction pathway. Active sites need to have an appropriate electronic state to polarize and break the C − H bond while providing multiple stable sites for carbon-hydrogen intermediates and oxygen-containing groups to inhibit over oxidation. Traditional catalytic systems fail to meet these dual requirements simultaneously. In recent years, single-atom catalysts (SACs) have attracted widespread attention due to their high atomic utilization and unique electronic structure [ 8 , 9 ] . However, the singularity of their active sites limits the multidimensional control of reaction pathways [ 10 , 11 ] . When oxygen is used as the oxidant, the single metal site is unable to flexibly regulate the utilization of active oxygen species, making it challenging to balance the dual requirements of methane activation and intermediate stabilization [ 12 , 13 ] . To overcome these limitations, dual-atom catalysts (DACs) have shown breakthrough advantages through the spatial proximity and electronic coupling effects of dual metal sites [ 14 ] . The introduction of two active sites not only changes the energy band structure but also adjusts the d-center and work function [ 15 ] . The synergistic effect of the dual sites can achieve charge distribution polarization and an increase in electronic states near the Fermi level, significantly enhancing the adsorption capacity for reactant methane and intermediates [ 16 – 18 ] , thereby improving methane activation. More importantly, the adjacent dual-metal centers can cooperatively promote the adsorption and activation of both O 2 and CH 4 [ 19 ] , while providing differentiated stable sites for carbon-hydrogen intermediates and oxygen-containing groups, fundamentally inhibiting deep dehydrogenation and overoxidation side reactions, which greatly aligns with the reaction demands for methane-to-methanol conversion [ 20 – 22 ] . Compared with single-metal centers, the introduction of a second metal facilitate the capture of active oxygen to form coordination restraints, weakening the excessive binding of active oxygen to reactive carbon-hydrogen intermediates during methane activation, thus effectively preventing deep oxidation and dehydrogenation [ 23 , 24 ] . However, the controllable synthesis of DACs still faces challenges in precise construction at the nanoscale: first, the stability of the dual-metal sites is highly dependent on the metal-support interaction, requiring precise control of the bonding mode to prevent the migration or aggregation of active centers [ 25 ] ; second, due to differences in the chemical properties and coordination environments of heteronuclear dual-metal atoms, they are difficult to arrange directionally and tend to form inactive aggregates [ 26 ] . To address these challenges, this study innovatively adopts an encapsulated pyrolysis method to design and construct a heteronuclear Rh-Cu dual-metal catalytic system (Rh-Cu DACs). This catalyst, using a high surface area nitrogen-doped two-dimensional graphene support, successfully achieves the precise construction of spatially proximal and functionally cooperative Rh-Cu dual-metal centers. Kinetic studies show that when O 2 is used as the oxidant, the CH 4 conversion rate reaches 232 mol/(mol cat ·s), with a methanol selectivity of 81%, approximately 3 times higher than that of the single Rh atomic catalyst. The products shift from CO 2 -dominated to CH 3 OH, demonstrating excellent catalytic performance and application prospects. Theoretical calculations further reveal that the RhCu bimetallic centers catalyze methane oxidation through a synergistic effect: the Rh sites attack and activate the C-H bonds of methane, breaking its stable tetrahedral structure; the Cu sites, on the other hand, form a coordination constraint on the adsorbed oxygen species, preventing their deep insertion during methane oxidation, thereby forming the key intermediate *CH 3 O, which ultimately combines with active hydrogen to generate the target product CH 3 OH. 2. Experimental Section 2.1 Synthesis of RhCu DACs This study successfully constructed a Rh–Cu dual-atom synergistic catalytic system using a host-guest confinement strategy (Fig. 1 d). The preparation of the precursor and Rh 3+ confinement encapsulation process begins with the self-assembly of Zn 2+ , Cu 2+ , and 2-methylimidazole as ligands to synthesize ZnCu-MOF (200 mg) as the precursor. Using the heteronuclear metal nodes and the multilevel pore structure of the MOF (with a pore size of approximately 0.55 nm, Figure S15 ), the MOF was ultrasonically dispersed in 30 mL of n-hexane. Next, 100 µL of RhCl 3 ·xH 2 O solution (10 mg·mL − 1 ) was added dropwise to the dispersion and sonicated for 30 minutes at room temperature, followed by stirring for 2 hours. This process encapsulates Rh 3+ species, smaller than 0.5 nm, within the MOF cavities. The encapsulated sample was then centrifuged, vacuum-dried overnight at 333 K to obtain Rh@ZnCu-MOF. The next step involves high-temperature pyrolysis and structural reconstruction. The Rh@ZnCu-MOF was placed in a nitrogen atmosphere and pyrolyzed at 1173 K for 2 hours. During this process, Zn volatilized preferentially, inducing the formation of a gradient pore structure in the skeleton and driving the MOF to restructure into nitrogen-doped graphene. The remaining Cu 2+ ions strongly coordinate with the pyridine-type nitrogen atoms in the carbon substrate, forming stable Cu-N 3 anchoring sites. The Rh 3+ species pre-constrained in the cavities of the MOF migrate toward the adjacent Cu-N 3 sites under the stress induced by the contraction of the carbon layer. Ultimately, the synergistic interaction between Rh and Cu atoms forms a stable RhCu-N 6 heteronuclear bimetallic active configuration on the carbon substrate. To validate the dual-metal synergistic effect, Rh single-atom catalysts (Rh SACs) were prepared using ZIF-8 without Cu 2+ as the precursor, following the same confinement encapsulation and pyrolysis steps. Meanwhile, Cu single-atom catalysts (Cu SACs) were obtained by directly pyrolyzing ZnCu-MOF without encapsulating Rh 3+ . 2.2 Characterization The phase composition and crystal structure of the catalysts were analyzed using a powder X-ray diffractometer (XD-6 model, Cu Kα). The specific surface area and pore size distribution were measured using a physical adsorption instrument (Micromeritics ASAP 2020 PLUS HD88) under liquid nitrogen, with calculations based on the BET equation. The microscopic structure and elemental distribution were characterized by transmission electron microscopy (FEI Talos F200X, 200 kV) combined with HAADF-STEM and EDS, and high-resolution structural images were obtained using a Hitachi HD3000C microscope (200 kV). X-ray photoelectron spectroscopy (XPS) was performed on a SPECS analyzer (MCD-10 analyzer, Al Kα, hv = 1486.6 eV). In situ X-ray absorption spectroscopy (XAS) was conducted at the Beijing Synchrotron Radiation Facility 8-ID and 8-BM beamlines, encompassing XANES and EXAFS information to analyze the metal's electronic state and local structure. In situ Fourier-transform infrared (FTIR) spectroscopy was measured using a PerkinElmer FTIR spectrometer (MCT detector, resolution 0.2 cm − 1 ), combined with CO adsorption studies to examine catalytic active sites. Raman spectroscopy was conducted on a confocal Raman system (Xplora Plus, HORIBA Scientific, excitation source: 532 nm) and calibrated with a silicon wafer for Raman shifts. Hydrogen temperature-programmed reduction (H 2 -TPR) experiments were carried out on a Micromeritics Auto Chem II 2920 (USA) to investigate the reduction behavior and hydrogen adsorption capacity of the catalyst. Electron paramagnetic resonance (EPR) spectroscopy was performed using an EMX plus 10/12 (Bruker, Germany) instrument to detect defect information, such as nitrogen vacancies. 2.3 Assessment This study focuses on the catalytic performance of single-atom and dual-atom catalysts, evaluated using a self-built fixed-bed tubular reactor system for gas-solid reactions ( Figure S8 ). The experimental setup uses a quartz tube reactor with an outer diameter of 10 mm and a wall thickness of 1 mm. The reaction gas mixture consists of fuel gas (CH 4 /Ar), synthetic air (O 2 /N 2 ), and high-purity N 2 as a diluent. To ensure accurate gas flow control, a soap film flow meter is used to calibrate the feed gas flow, and the calibrated values are applied during the experiment to maintain precision. A total of 100 mg of catalyst sample is uniformly mixed with quartz sand at a 1:1 mass ratio and loaded into the isothermal section of the reactor, with quartz wool isolating both ends. Prior to the reaction, the catalyst undergoes pretreatment under a high-purity N 2 flow of 100 sccm: the temperature is ramped to 200°C at a rate of 5°C/min and maintained for 1 hour to remove surface-adsorbed impurities. After pretreatment, the temperature is increased to the target value at the same rate and held for 1 hour to activate the catalyst. Upon completion of activation, the reactant gases, mixed in controlled proportions, are introduced into the system with a total flow rate of 100 sccm. The effluent gases are collected after condensation in a cold trap and quantitatively analyzed by gas chromatography (GC). By optimizing the catalyst particle size (100–200 mesh) and total gas flow rate (100 sccm), both internal and external diffusion limitations are eliminated, ensuring that the reaction is controlled by intrinsic kinetics ( Figure S9 ). Product analysis is performed using an Agilent 8890 GC system equipped with a hydrogen flame ionization detector (FID) and a thermal conductivity detector (TCD), with high-purity N 2 as the carrier gas. TCD is connected to an HP-MOLESIEVE column to detect CH 4 , CO 2 , and Ar; FID is connected to an HP-PLOT/Q capillary column for the quantitative analysis of CH 3 OH (methanol) products. All gaseous products are analyzed in online mode. 2.4 DFT Calculations All density functional theory (DFT) calculations in this study were performed using the Vienna Ab-initio Simulation Package (VASP) [ 27 ] . The exchange-correlation energy was described using the Perdew-Burke-Ernzerhof (PBE) function within the generalized gradient approximation (GGA) [ 28 ] , and the electron-ion interactions were described using projector augmented-wave (PAW) pseudopotentials [ 29 , 30 ] . A plane-wave energy cutoff of 450 eV was used in the calculations. The geometry optimization was carried out with strict convergence criteria, including a maximum force of 0.05 eV/Å, maximum pressure of 0.1 GPa, maximum displacement of 1×10 − 3 Å, single-atom energy change no greater than 1×10 − 5 eV, and a self-consistent field (SCF) convergence threshold of 1×10 − 5 eV [ 31 ] . Transition states were searched using the climbing image elastic band method (CI-NEB) [ 32 ] , and the transition state structures were validated through imaginary frequency calculations. For the construction of the computational models, the heteronuclear bimetallic system embedded in N-doped graphene (NC) was based on a p(6×6) single-layer graphene structure, while the single-metal system embedded in the NC substrate used a p(5×5) single-layer structure. A vacuum layer of 15 Å was applied in the vertical direction of the two-dimensional monolayer to eliminate interactions between periodic images. K-point sampling was performed using the Monkhorst-Pack grid, with geometry optimization carried out on a 3×3×1 grid, Gibbs free energy calculations on a 4×4×1 grid, and projected density of states (PDOS) analysis on a 6×6×1 grid [ 33 ] . The electronic structure calculations were analyzed for charge transfer using the Bader charge analysis method, and post-processing was performed using VASPKIT [ 34 ] . 3. Result and discussion 3.1 Structural Characterizations The XRD results indicate that after introducing Cu and Rh species into ZIF-8, Rh@ZnCu-MOF still retains a crystallographic structure similar to ZIF-8 ( Figure S13 ) [ 35 ] . In the XRD pattern of RhCu DACs, two broad carbon characteristic peaks are observed at approximately 22.8° and 43.6° ( Figure S14 ) [ 36 ] , and no characteristic crystalline peaks of metals, metal oxides, or metal carbides are detected, suggesting the absence of metal particle formation [ 37 ] . The pore size of bimetallic RhCu DACs has increased compared to that of other single - atom catalysts such as Rh SACs ( Figure S16, Table S2 ). Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the metal Rh and Cu are atomically dispersed and evenly distributed on the carbon substrate (Figs. 1 a, 1 b, 1 c). Due to the different scattering abilities of Rh (atomic number Z = 45) and Cu (atomic number Z = 29) elements in HAADF-STEM imaging, they appear with different brightness. Using this property, we can visually observe the formation of RhCu paired sites. Randomly selected different bright spots were measured, and the average distance between them was found to be 2.46 Å (Figs. 1 b 1 , 1c 1 ), indicating the possible formation of metal-metal bonds. Energy dispersive X-ray spectroscopy (EDS) results ( Figure S18 ) show that Rh, Cu, N, and C are uniformly distributed throughout the structure. Furthermore, the metallic Rh in the Rh SACs catalyst exists in an atomic - scale dispersed state ( Figures S16, S19 ). The H 2 -TPR results of Rh SACs and RhCu DACs exhibit distinct reduction behaviors ( Fig. 2 a ) . Specifically, the Rh SACs catalyst shows a higher reducibility, with its reduction peak appearing in a lower temperature range. In contrast, the reduction peak of the RhCu DACs catalyst shifts to a significantly higher temperature, which indicates that the interaction between rhodium and copper modifies the reducibility of the species. X-ray photoelectron spectroscopy (XPS) confirmed the coexistence of C, N, O, Rh, and Cu elements in the RhCu dual-atom catalyst (RhCu DACs). The C 1s high-resolution spectrum ( Figure S20 ) reveals three carbon species corresponding to C–C, C = N, and C–N, demonstrating the successful doping of nitrogen atoms into the carbon framework. The C–C component in RhCu DACs is lower than that in Rh SACs and Cu SACs, indicating a reduction in the sp 2 hybridization degree of its carbon structure. The N 1s spectrum ( Figure S21 ) can resolve four nitrogen species: pyridine nitrogen, metal-coordinated nitrogen, graphitic nitrogen, and oxidized nitrogen [ 38 ] . The metal–N coordination peak (399.07 eV) is significantly higher in RhCu DACs than in Rh SACs, indicating the formation of stable M–N (M = Rh, Cu) structures in DACs, while pyridine and graphitic nitrogen together form a nitrogen-doped network, providing electronic environment support for metal anchoring. The high-resolution Rh 3d and Cu 2p spectra (Figs. 2 b, 2 c) show that in the reduced state, Rh and Cu mainly exist in high oxidation states [ 39 , 40 ] , while in the reaction state, Rh tends toward a low oxidation state, and Cu further oxidizes. This charge behavior suggests that Rh remains more stable during the reaction, while Cu may be involved in the transfer of oxygen species. Further analysis of the local coordination environment was performed using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XANES results show that the K-edge absorption energy (E 0 ) of reduced Rh lies between metallic Rh 0 and oxidized Rh, indicating that it is partially oxidized with a positive charge (Figs. 2 d). In the reaction state, E 0 is closer to Rh 0 , indicating that Rh tends to maintain a reduced state during the reaction. Similarly, Cu exists as Cu + in the reduced state (E 0 between Cu 0 and Cu 2+ ), while it further oxidizes under reaction conditions (Figs. 2 e). EXAFS fitting (Figs. 2 f, Figs. 2 g, Figure S23 ) reveals that the main peak of Rh is located at 1.95 Å, corresponding to Rh–N coordination, and the secondary peak at 2.45 Å corresponds to Rh–Cu coordination, indicating that Rh atoms are anchored on nitrogen-doped carbon and form atomically adjacent Rh–Cu bimetallic structures. The main peak of Cu at 1.92 Å is attributed to Cu–N, and a secondary peak also appears at 2.45 Å, matching the Rh–Cu bond, further supporting the stable presence of Rh–Cu dual-atom sites. The small bond length difference (ΔR = 0.03 Å) between Rh–N and Cu–N suggests that the Rh–N bond has stronger covalent characteristics, while the 2.45 Å Rh–Cu metal bond reflects significant electronic coupling between the two atoms. Raman spectroscopy (Fig. 2 h, Figure S22 ) further reveals the structural ordering and defect characteristics of the carbon support. RhCu DACs show distinct peaks at 1335 cm − 1 (D-band) and 1580 cm − 1 (G-band). The intensity ratio (ID/IG = 1.01) is higher than that of Rh SACs and the NC support. This indicates that the synergistic doping of bimetallic atoms disrupts the ordering of the sp 2 carbon framework. It induces structural distortion. It also leads to the generation of sp 3 defects. This significantly enhances the defect density. Electron paramagnetic resonance (EPR) spectroscopy (Fig. 2 i) was used to analyze the metal–support interactions and defect structures. The nitrogen-doped carbon support (NC) shows a strong EPR signal at g = 2.003, corresponding to nitrogen vacancy (NV)-related paramagnetic defects. After introducing Rh SACs and RhCu DACs, the EPR signal gradually weakens, indicating that metal atoms preferentially coordinate with nitrogen vacancies to form the Rh–Nx–Cu structure, effectively passivating free electrons and reducing defect states. In conclusion, RhCu DACs achieve dual-atom synergy by constructing a stable Rh–N–Cu–N bridged structure, demonstrating advantages in charge state regulation and defect structure optimization, which provide a structural foundation for their high activity in CH 4 selective oxidation reactions. 3.2 Reaction Kinetics Figure 3 a shows that as oxygen partial pressure ( \(\:{P}_{{O}_{2}}\) ) increases, the methane catalytic reaction exhibits distinct kinetic regimes. In Region A ( \(\:{P}_{{O}_{2}}\) < 0.12 kPa), the CH 4 conversion rate increases linearly with \(\:{P}_{{O}_{2}}\) , consistent with first-order reaction kinetics. During this stage, oxygen adsorption on the active sites adopts a bridging configuration (Rh-O*-O*-Cu or Rh-O*-Cu). When \(\:{P}_{{O}_{2}}\) exceeds the optimal value (Region B), the catalyst surface active sites gradually become saturated with adsorbed oxygen (Rh-O 2 * + Cu-O 2 *), weakening the interaction between the metal sites and the C-H bond, leading to a decrease in the methane conversion. Figure 3 b illustrates the influence of oxygen partial pressure and reaction regime on the product distribution. The primary product in Region A is methanol. Comparing rate constants, CH 3 OH selectivity reaches 81.0%, superior to some literature reports ( Table S6 ). Compared to the inferior methane conversion efficiency and CO 2 as the main product observed on single-atom Rh catalysts ( Figure S25 ), this indicates that single active sites struggle to control the oxidation reaction pathway. The introduction of Cu sites provides a coordination confinement effect on the oxygen species, restricting the attack by molecular oxygen or active oxygen monomers on the C-H bond, resulting in methanol as the partially oxidized product. After oxygen adsorption saturation (Region B), the regulatory role of Cu diminishes, causing a rapid decline in methanol yield and a sharp increase in CO 2 production. Ultimately, under surface oxygen oversaturation coverage, the reaction rate becomes uncorrelated with oxygen pressure and proportional only to methane partial pressure ( Figure S24 ). Figure 3 c presents the activation energy barriers for the two reaction regimes: Ea = 18.9 kJ/mol (Region A) and Ea = 89.7 kJ/mol (Region B). Under unsaturated oxygen adsorption on the active site surface, the bonding and coordination of oxygen are primarily facilitated by the Cu site. This allows the Rh site to possess stronger electronic potential for activating the C-H bond of methane, thereby lowering the activation barrier. Conversely, when the metal sites become saturated, their activation capability decreases, leading to a significant increase in the reaction activation energy. Figure 3 d reveals the variation of RhCu DACs catalytic activity with temperature and \(\:{P}_{{O}_{2}}\) . Across different reaction temperatures, a positive correlation regime exists between the production rate and \(\:{P}_{{O}_{2}}\) . As the reaction temperature increases, the optimal inflection point for oxygen partial pressure also shifts to higher values. This is likely because high activity rapidly depletes surface oxygen, maintaining an unsaturated surface oxygen state. Figure 3 e displays the kinetics of oxygen exchange and its isotope ( 18 O 2 ) on the dual-atom catalyst. With fixed 16 O 2 partial pressure (0.01 mbar), the 18 O 2 partial pressure was varied, and the oxygen exchange rate was measured at different temperatures (270–360°C) using gas chromatography-mass spectrometry (GC-MS). The results show that the oxygen exchange rate constant increases with rising temperature, indicating that high temperature promotes oxygen dissociation and recombination processes. Figure 3f presents the kinetics of the CH 4 –D 2 exchange reaction on both Rh-Cu dual-atom and Rh single-atom surfaces. With methane pressure fixed at 5 kPa, the exchange rate increases similarly on both Rh-Cu DACs and Rh SACs as D 2 pressure rises. This demonstrates that C-H bond activation primarily occurs on the Rh site. While Cu plays a role in confining oxygen species through coordination, it does not contribute significantly to the primary activation of the C-H bond. 3.3 Reaction Mechanism Study As shown in Figure S26 , the two transition metal atoms in RhCu DACs are connected by a metal bond, and the pyridine-type nitrogen atoms in a tridentate coordination form a stable Rh–Cu–N 6 configuration. Previous theoretical studies have indicated that this structure is the most stable form of a metal dimer embedded in N-doped graphene [ 41 ] . The geometric optimization results show that the Rh–Cu bond length is 2.42 Å, which is in excellent agreement with the EXAFS experimental results, verifying the validity of the model construction. In the structures of Rh SACs and Cu SACs, metal atoms in each catalyst are coordinated with four N atoms, respectively. The comparative results show that the RhCu DACs has a lower formation energy, thus exhibiting higher thermodynamic stability ( Table S4 ). The differential charge density ( Figure S27 ) and Bader charge analysis ( Table S5 ) reveal that the Rh–Cu dimer undergoes electron transfer to the coordinated nitrogen atoms, while the nitrogen atoms also gain electrons from the carbon backbone, demonstrating a typical "dual electron donation" effect. The projected density of states (PDOS) analysis (Fig. 4 a) further confirms the electronic coupling characteristics: Rh 4d and Cu 3d orbitals significantly overlap, and both hybridize with the N 2p orbitals, indicating the formation of M–N bonds, consistent with the XPS results. Notably, the d-band center of Rh in RhCu DAC is located at − 0.82 eV, which is significantly downshifted compared to − 0.58 eV in Rh SACs. This phenomenon is attributed to the introduction of Cu, which breaks the high symmetry of Rh–N 4 and forms a lower symmetry Rh–N 3 structure. The downward shift of the d-band center directly weakens the adsorption strength of Rh towards oxygen species, laying the electronic structural foundation for the aforementioned "coordination constraint effect". DFT simulation results reveal significant differences in O 2 adsorption behaviors among RhCu DACs, Rh SACs, and Cu SACs ( Figure S28 ). Specifically, both Rh SACs and Cu SACs stably bind O 2 molecules through end-on adsorption modes (corresponding to Rh SACs-O 2 -b and Cu SACs-O 2 -a configurations, respectively). These configurations exhibit lower adsorption energies, representing their most stable adsorption states (Fig. 4 b). Orbital analysis indicates a distinct coupling effect between the d orbitals of the metal centers and the 2p orbitals of O ( Figure S29 ).In contrast, RhCu DACs possess two types of O 2 adsorption configurations. In the lateral configuration (RhCu-O 2 -a), the Rh-O and Cu-O bond lengths are 1.97 Å and 2.06 Å, respectively, while the O-O bond length increases to 1.36 Å, which is significantly longer than that of free O 2 molecules (1.21 Å). In the vertical configuration (RhCu- O 2 -b), the Rh-O and Cu-O bond lengths are 1.93 Å and 2.50 Å, respectively, with an O-O bond length of 1.31 Å, indicating a lower degree of O 2 activation. Among these, the RhCu- O 2 -a configuration has the lowest adsorption energy (Fig. 4 b), making it the optimal O 2 adsorption configuration for RhCu DACs. Electronic structure analysis ( Figure S30 ) shows that RhCu- O 2 -a transfers 0.63 electrons to O 2 , with a higher electron transfer amount compared to Rh SACs-O₂-b and Cu SACs-O₂-a configurations. This makes O 2 molecules electron-rich and the metal sites electron-deficient, significantly enhancing the metal-oxygen polarization effect. The simulation results of reaction pathways for each catalyst are presented in Figures S32-S42 . For RhCu DACs, under the optimal RhCu-O 2 -a adsorption state, CH 4 undergoes two consecutive adsorption and activation reactions to generate 2 molecules of CH 3 OH. In the initial state (IS), CH 4 reacts with *O 2 to form *OCH 3 and *OH (IM1). After overcoming an energy barrier of 0.76 eV (TS-2), it is converted to CH 3 OH (IM2) with the release of bridge oxygen (Rh-O-Cu). The bridge oxygen then reactivates CH 4 (IM4→IM5), ultimately generating a second molecule of CH 3 OH, which desorbs (FS). The Gibbs free energy change (ΔG) of the overall reaction is < 0, indicating an exothermic process. In contrast, the pathway leading to CO 2 formation requires overcoming a higher energy barrier (0.93 eV, TS-2’), making it a non-preferred pathway. This confirms that the RhCu-O₂-a configuration is more favorable for the selective oxidation of CH 4 to CH 3 OH (Figs. 4 c, 4 d). In contrast, for Rh SACs and Cu SACs, under their optimal O 2 adsorption configurations, the dominant pathway of CH 4 oxidation is towards CO 2 formation. Both catalysts generate *CH 3 and *OOH intermediates, leading to the continuous dehydrogenation of *CH 3 and its final conversion to CO 2 . Fourier-transform infrared (FTIR) spectroscopy results (Fig. 4 a) show that under low oxygen pressure (0.01–0.10 kPa), the CH 4 signal weakens as \(\:{P}_{{O}_{2}}\) increases, and C–O vibration peaks at 1088 cm − 1 (*CH 3 O) and 1042 cm − 1 (*CH 3 OH) appear, confirming the correlation between *OCH 3 and CH 3 OH. Under higher oxygen pressure (0.2–0.4 kPa), the *CH 3 O vibration weakens, and the characteristic vibration peaks of CO 2 (2377 and 2333 cm − 1 ) become stronger, reflecting the oxygen coverage effect and the change in the reaction path ( Figure S43 ). In contrast to Rh SACs, no *OCH 3 vibrations are observed, further confirming that *OCH 3 is a key intermediate for RhCu DACs catalyzed CH 4 oxidation to CH 3 OH. To further understand the reaction mechanism of CH 4 selective oxidation to CH 3 OH catalyzed by RhCu DACs, the following analysis was conducted. The adsorption energy calculation results (Fig. 5 b) show that, compared with Rh SACs and Cu SACs, RhCu DACs have lower adsorption energy for CH 4 and higher adsorption energy for the product CH 3 OH. The diatomic sites exhibit stronger activation ability for CH 4 and, at the same time, are more conducive to the timely desorption of the product CH 3 OH. Partial density of states (PDOS) analysis (Fig. 5 c ) indicates that in the RhCu–O 2 –a configuration, both the 4d orbitals of Rh and the 3d orbitals of Cu hybridize with the 2p orbitals of O, reflecting the synergistic adsorption effect of the bimetallic sites on O 2 . After O 2 adsorption, the d-band center of Rh shifts significantly downward (from − 0.82 eV to − 1.86 eV), while the d-band center of Cu shifts only slightly downward (from − 2.28 eV to − 2.73 eV). The significant downward shift of the Rh d-band center directly leads to a weakened adsorption effect on oxygen species (O 2 , O), which is consistent with the weakly oxygen-adsorbed state (Region A) observed in the previous kinetic study and its characteristics (low activation energy barrier, high methanol selectivity). Crystal orbital Hamilton population (COHP) analysis ( Figure S31 ) further confirms that the interaction strength of the Rh–O bond (–ICOHP = − 2.67 eV) is significantly weaker than that of the Cu–O bond (–ICOHP = − 0.37 eV), indicating that the Rh–O bond has weaker covalency. Bader charge analysis (Fig. 5 d) shows that Rh loses 0.92 e⁻, Cu loses 0.71 e⁻, and the charge transfer is mainly concentrated on one of the O atoms (O1 gains 0.38 e⁻). Rh has stronger electronegativity, and the Rh–O bond has an obvious charge polarization effect, which is consistent with the COHP analysis results. In terms of methane activation and product selectivity control, Cu, relying on its stronger electron transfer ability, effectively exerts a "coordination constraint" effect on oxygen species, stabilizes adsorbed oxygen, and promotes the cleavage of the O-O bond; while Rh, due to the weak adsorption state of oxygen species after the downward shift of its d-band center, can more efficiently activate the C–H bond of methane, triggering its first step of dissociation. This is consistent with the conclusion of the previous CH 4 –D 2 exchange experiment, that is, the activation of the C–H bond is mainly undertaken by the Rh site. On Rh SACs, the key intermediate CH 3 –OOH has insufficient stability because Rh transfers limited electrons to it. The highly active OOH group is prone to decompose to produce H 2 O and react with CH 3 triggering deep dehydrogenation to generate the by-product CO 2 (Fig. 5 e). In the RhCu DACs system (Fig. 5 f), the key intermediates are *OCH 3 and *OH. Differential charge and Bader charge analysis show that Rh transfers 0.36 e⁻ to *OCH 3 , and Cu transfers 0.54 e⁻ to *OH, indicating a stronger interaction between *OH and Cu. In the subsequent reaction, *OCH 3 and *OH directly combine through H atoms to form CH 3 OH and desorb, and *OCH₃ preferentially dissociates from the Rh site (rather than *OH dissociating from Cu to form H₂O). Therefore, the relative stability of the intermediate *OCH 3 on the Rh site is the decisive factor for inhibiting the deep oxidation pathway and achieving high selective generation of CH 3 OH. In summary, the significant advantage of RhCu DACs over single-atom catalysts stems from the unique electronic coupling effect between the bimetallic sites and the charge polarization effect caused by it. This synergistic effect achieves precise functional division: the Cu site implements "coordination constraint" on oxygen species through strong electron transfer, stabilizes adsorbed oxygen, and regulates its activity; the Rh site maintains a weak adsorption state for oxygen species due to the significant downward shift of its d-band center, thus enabling efficient activation of the C-H bond of CH 4 . The synergy of the two sites not only optimizes the adsorption and activation of reactant molecules but, more importantly, stabilizes the key intermediate *OCH 3 and drives its efficient conversion to the target product CH 3 OH. This mechanism effectively inhibits the excessive insertion of active oxygen and the deep combination of reaction intermediates with active oxygen, fundamentally avoiding the occurrence of over-oxidation (generating CO 2 ) 4. Conclusion This study we innovatively developed an encapsulated pyrolysis strategy and successfully synthesized Rh–Cu heteronuclear dual-atom catalysts (Rh-Cu DACs) over nitrogen-doped graphite carbon supports. The Rh-Cu DACs possess both excellent structural stability and significant electronic synergy. In the reaction of one-step oxidation of methane to methanol, the unique spatial arrangement of Rh–Cu sites promotes the formation of a highly active oxygen bridge structure (Rh-O-O-Cu, Rh-O-Cu). The difference in electron affinity for oxygen between Rh and Cu leads to electron density polarization at both ends of the oxygen bridge, and Cu achieves precise capture of oxygen through strong coordination, providing a crucial guarantee for limiting excessive oxygen insertion. The electron-deficient Rh center and electronegative oxygen atoms synergistically activate the C–H bond in CH 4 , forming key intermediates *CH 3 O and *OH. Subsequently, *CH 3 O undergoes hydrogenation and desorption to generate the target product CH₃OH. Kinetic experiments have verified its excellent performance that methanol selectivity can reach 81% under mild conditions. The Rh-Cu DACs have the broad application prospects in methane utilization. Declarations Acknowledgements This work was supported by the Fundamental Research Funds for the Central Universities of China (SWU-KT25006), National Natural Science Foundation of China (22109129), and Project of Science and Technology Research Program of Chongqing Education Commission of China (KJQN202400210). Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. References DAVIDSON E A, MONTEVERDE D R, SEMRAU J D. Viability of enhancing methanotrophy in terrestrial ecosystems exposed to low concentrations of methane [J]. Communications Earth & Environment, 2024, 5(1). SUSHKEVICH V L, PALAGIN D, RANOCCHIARI M, et al. Selective anaerobic oxidation of methane enables direct synthesis of methanol [J]. Science, 2017, 356(6337): 523-7. HO C S, PENG J, YUN U, et al. Impacts of methanol fuel on vehicular emissions: A review [J]. 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The role of surface hydroxyl groups on a single-atomic Rh 1 /ZrO 2 catalyst for direct methane oxidation [J]. Chem Commun (Camb), 2021, 57(13): 1671-4. LI Y, WEI B, ZHU M, et al. Synergistic Effect of Atomically Dispersed Ni–Zn Pair Sites for Enhanced CO 2 Electroreduction [J]. Advanced Materials, 2021, 33(41). Additional Declarations There is NO Competing Interest. Supplementary Files CH4CH3OHSI0814.docx SI-The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol Cite Share Download PDF Status: Published Journal Publication published 28 Feb, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7370917","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":506239537,"identity":"b0da7e63-dd8e-41e0-a6ad-687cca2125e6","order_by":0,"name":"Haojie Geng","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyklEQVRIiWNgGAWjYBACA4YDIMoGwuMhQUsaSVrA4DAJWswZj198XPDrvL3BjQTGB2/bGOTNCWmxbDhTbDyz73bihhsJzIZz2xgMdzYQctiBM2nSvD23E8xuJLBJ87YxJBgcIKwl/Tdvzzl7oBb230RqOX6MmefHAcZtQFuYibWFWZq3ITlx/5mHzZJzzkkYbiCo5cbxh595/tjZS7YnH/zwpsxGnqAtDBJnDBgY20AsxgYQl5B6IOBvf8DA8IcIhaNgFIyCUTByAQAIAkdMWTdRJwAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0003-0208-0190","institution":"Southwest University","correspondingAuthor":true,"prefix":"","firstName":"Haojie","middleName":"","lastName":"Geng","suffix":""},{"id":506239538,"identity":"4a665936-c3bf-4e39-8da2-ce5165c91133","order_by":1,"name":"Yanling Gao","email":"","orcid":"","institution":"Southwest University","correspondingAuthor":false,"prefix":"","firstName":"Yanling","middleName":"","lastName":"Gao","suffix":""},{"id":506239539,"identity":"ce6df404-235f-4645-b4ac-24e3a05f881e","order_by":2,"name":"Haobo Zhao","email":"","orcid":"","institution":"Chongqing University","correspondingAuthor":false,"prefix":"","firstName":"Haobo","middleName":"","lastName":"Zhao","suffix":""},{"id":506239540,"identity":"c90edf9b-0745-4479-a717-12e023ecdd59","order_by":3,"name":"Yi Wang","email":"","orcid":"","institution":"Southwest University","correspondingAuthor":false,"prefix":"","firstName":"Yi","middleName":"","lastName":"Wang","suffix":""},{"id":506239541,"identity":"c7870d5c-7ff0-4814-91fb-8dabba046f6d","order_by":4,"name":"Nian Bing Li","email":"","orcid":"https://orcid.org/0000-0001-6395-2074","institution":"Southwest University","correspondingAuthor":false,"prefix":"","firstName":"Nian","middleName":"Bing","lastName":"Li","suffix":""},{"id":506239542,"identity":"290484e6-05da-4549-a462-c5281f4792e5","order_by":5,"name":"Jingyu Ran","email":"","orcid":"","institution":"Chongqing University","correspondingAuthor":false,"prefix":"","firstName":"Jingyu","middleName":"","lastName":"Ran","suffix":""}],"badges":[],"createdAt":"2025-08-14 07:25:07","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7370917/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7370917/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-026-70182-z","type":"published","date":"2026-02-28T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":90083546,"identity":"7ef82bc0-7142-4cb0-9efa-98f4cb5b7db1","added_by":"auto","created_at":"2025-08-28 09:28:57","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":462129,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Transmission electron microscopy (TEM) image of the RhCu DACs catalyst; \u003cstrong\u003e(b, c)\u003c/strong\u003e High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images, with green circles highlighting isolated single atoms and red boxes indicating Rh–Cu dual-atom sites; (\u003cstrong\u003eb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e, c\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e) Corresponding energy-dispersive X-ray spectroscopy (EDS) elemental maps of the selected regions in (\u003cstrong\u003eb\u003c/strong\u003e) and (\u003cstrong\u003ec\u003c/strong\u003e), confirming the presence of adjacent bimetallic atomic sites; (\u003cstrong\u003ed\u003c/strong\u003e) Schematic illustration of the synthesis strategy for RhCu DACs, showing the confinement-assisted pyrolysis process used to construct spatially adjacent heteronuclear Rh–Cu dual-atom sites.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/1f4473f2acd39c23d654fc4e.png"},{"id":90083544,"identity":"00ec9e08-071d-4a80-adc9-b0e576f2d80c","added_by":"auto","created_at":"2025-08-28 09:28:57","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":311936,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e H₂ temperature-programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR) profiles of Rh SACs and RhCu DACs; \u003cstrong\u003e(b)\u003c/strong\u003e High-resolution X-ray photoelectron spectroscopy (XPS) spectrum of Rh 3d; \u003cstrong\u003e(c)\u003c/strong\u003e High-resolution XPS spectrum of Cu 2p; \u003cstrong\u003e(d, e)\u003c/strong\u003e X-ray absorption near-edge structure (XANES) spectra at the metal L-edge for RhCu DACs and reference samples (metal foils, reactive state, and oxygen-covered state); \u003cstrong\u003e(f, g)\u003c/strong\u003e Fourier-transformed (FT) extended X-ray absorption fine structure (EXAFS) spectra at the L\u003csub\u003e3\u003c/sub\u003e-edge in R space for RhCu DACs, Rh SACs, and Cu SACs; \u003cstrong\u003e(h)\u003c/strong\u003e Electron paramagnetic resonance (EPR) spectra; \u003cstrong\u003e(i)\u003c/strong\u003e Raman spectra of the catalysts.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/1ba6dbb511ed4542b509a431.png"},{"id":90083547,"identity":"18f386c3-d37b-4129-ace2-1781f5e07bd9","added_by":"auto","created_at":"2025-08-28 09:28:57","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":159523,"visible":true,"origin":"","legend":"\u003cp\u003e(a, b) CH₄ conversion rate and product formation rates over RhCu DACs as a function of P\u003csub\u003eO2\u003c/sub\u003e ) (P\u003csub\u003eCH4\u003c/sub\u003e = 1 kPa, N₂ balance, total flow rate = 100 mL·min⁻¹, 300 °C); (c) Apparent activation energies under different oxygen coverage regimes:O*–* region: P\u003csub\u003eCH4\u003c/sub\u003e= 1 kPa, P\u003csub\u003eO2\u003c/sub\u003e = 0.1 kPa, N₂ balance, total flow = 100 mL·min-1；O*-O* region: P\u003csub\u003eCH4\u003c/sub\u003e \u0026nbsp;= 3 kPa, P\u003csub\u003eO2\u003c/sub\u003e= 1.0 kPa, N₂ balance, total flow = 100 mL·min-1; (d) Temperature-dependent CH4 conversion and product formation rates over RhCu DACs P\u003csub\u003eCH4\u003c/sub\u003e \u0026nbsp;= 1 kPa, N2 balance, total flow = 100 mL·min-1, temperature range = 240–360 °C); (e) O2 isotope exchange rate as a function of temperature; (f) CH4–D2 exchange rate over RhCu DACs at varied conditions\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/1ddbcd5f320626bff6870a04.png"},{"id":90083894,"identity":"21655e1d-94b3-4cd5-afcf-72858c853744","added_by":"auto","created_at":"2025-08-28 09:36:57","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":185423,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e In situ FTIR spectra for methane oxidation over RhCu DACs; \u003cstrong\u003e(b)\u003c/strong\u003e Adsorption energies of O\u003csub\u003e2\u003c/sub\u003e on RhCu DACs, Rh SACs, and Cu SACs; \u003cstrong\u003e(c, d)\u003c/strong\u003e Comparative reaction pathways for methane oxidation over RhCu DACs: Red pathway: favorable route toward CH\u003csub\u003e3\u003c/sub\u003eOH formation; Black pathway: less favorable route leading to CO\u003csub\u003e2\u003c/sub\u003e formation.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/f85344c3e308d8b4c943c706.png"},{"id":90083562,"identity":"236982f4-a42a-40c1-b7cf-3e3fa7741464","added_by":"auto","created_at":"2025-08-28 09:28:57","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":268851,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003e(a)\u003c/strong\u003e Projected density of states (PDOS) analysis of RhCu DACs;\u003cstrong\u003e(b)\u003c/strong\u003e Comparative adsorption energies of CH\u003csub\u003e4\u003c/sub\u003e and CH\u003csub\u003e3\u003c/sub\u003eOH on different catalyst structures;\u003cstrong\u003e(c)\u003c/strong\u003e PDOS of O\u003csub\u003e2\u003c/sub\u003e adsorbed on the RhCu–O\u003csub\u003e2\u003c/sub\u003e–a configuration;\u003cstrong\u003e(d)\u003c/strong\u003e Optimized structure and Bader charge distribution of the RhCu–O\u003csub\u003e2\u003c/sub\u003e–a adsorption state;\u003cstrong\u003e(e)\u003c/strong\u003e Differential charge density map of the key intermediate CH\u003csub\u003e3\u003c/sub\u003e–OOH during CH\u003csub\u003e4\u003c/sub\u003e oxidation over Rh SACs (cyan: electron depletion, yellow: electron accumulation), along with the corresponding Bader charge transfer data;\u003cstrong\u003e(f)\u003c/strong\u003e Differential charge density distribution of the key intermediates *CH\u003csub\u003e3\u003c/sub\u003eO and *OH during CH\u003csub\u003e4\u003c/sub\u003e oxidation over RhCu DACs (cyan: electron depletion, yellow: electron accumulation), with associated Bader charge transfer analysis.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/b05c6e443b21e8a1f6f12a21.png"},{"id":106584055,"identity":"95b9e901-c85e-4de8-bf0e-30225d53f186","added_by":"auto","created_at":"2026-04-10 07:22:10","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2054638,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/b65fcfa9-be3b-44d9-9340-c4a562d9b46d.pdf"},{"id":90083564,"identity":"442956ac-2427-4819-862e-e569b4d10b24","added_by":"auto","created_at":"2025-08-28 09:28:57","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":25863942,"visible":true,"origin":"","legend":"SI-The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol","description":"","filename":"CH4CH3OHSI0814.docx","url":"https://assets-eu.researchsquare.com/files/rs-7370917/v1/0181fb4d8ba0714edc363d22.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe one-step oxidation of CH\u003csub\u003e4\u003c/sub\u003e to CH3OH is widely regarded as the \"Holy Grail\" during catalytic reactions \u003csup\u003e[\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]\u003c/sup\u003e. CH\u003csub\u003e4\u003c/sub\u003e molecules have a symmetrical tetrahedral structure and a high C\u0026thinsp;\u0026minus;\u0026thinsp;H bond dissociation enthalpy of 440 kJ\u0026middot;mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which makes the C\u0026thinsp;\u0026minus;\u0026thinsp;H bond difficult to polarize \u003csup\u003e[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e, \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]\u003c/sup\u003e. The highly reactive methyl radical (\u0026middot;CH\u003csub\u003e3\u003c/sub\u003e) is prone to further C\u0026thinsp;\u0026minus;\u0026thinsp;H bond cleavage or side reactions with active oxygen, which reduces methanol selectivity and the economic viability of the process \u003csup\u003e[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. This contradiction of \"efficient activation and high selectivity being hard to reconcile\" essentially stems from the insufficient ability of catalysts to precisely control the reaction pathway. Active sites need to have an appropriate electronic state to polarize and break the C\u0026thinsp;\u0026minus;\u0026thinsp;H bond while providing multiple stable sites for carbon-hydrogen intermediates and oxygen-containing groups to inhibit over oxidation. Traditional catalytic systems fail to meet these dual requirements simultaneously.\u003c/p\u003e\u003cp\u003eIn recent years, single-atom catalysts (SACs) have attracted widespread attention due to their high atomic utilization and unique electronic structure \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]\u003c/sup\u003e. However, the singularity of their active sites limits the multidimensional control of reaction pathways \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. When oxygen is used as the oxidant, the single metal site is unable to flexibly regulate the utilization of active oxygen species, making it challenging to balance the dual requirements of methane activation and intermediate stabilization \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]\u003c/sup\u003e. To overcome these limitations, dual-atom catalysts (DACs) have shown breakthrough advantages through the spatial proximity and electronic coupling effects of dual metal sites \u003csup\u003e[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e. The introduction of two active sites not only changes the energy band structure but also adjusts the d-center and work function \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]\u003c/sup\u003e. The synergistic effect of the dual sites can achieve charge distribution polarization and an increase in electronic states near the Fermi level, significantly enhancing the adsorption capacity for reactant methane and intermediates \u003csup\u003e[\u003cspan additionalcitationids=\"CR17\" citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e, thereby improving methane activation. More importantly, the adjacent dual-metal centers can cooperatively promote the adsorption and activation of both O\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, while providing differentiated stable sites for carbon-hydrogen intermediates and oxygen-containing groups, fundamentally inhibiting deep dehydrogenation and overoxidation side reactions, which greatly aligns with the reaction demands for methane-to-methanol conversion \u003csup\u003e[\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eCompared with single-metal centers, the introduction of a second metal facilitate the capture of active oxygen to form coordination restraints, weakening the excessive binding of active oxygen to reactive carbon-hydrogen intermediates during methane activation, thus effectively preventing deep oxidation and dehydrogenation \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. However, the controllable synthesis of DACs still faces challenges in precise construction at the nanoscale: first, the stability of the dual-metal sites is highly dependent on the metal-support interaction, requiring precise control of the bonding mode to prevent the migration or aggregation of active centers \u003csup\u003e[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e; second, due to differences in the chemical properties and coordination environments of heteronuclear dual-metal atoms, they are difficult to arrange directionally and tend to form inactive aggregates \u003csup\u003e[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eTo address these challenges, this study innovatively adopts an encapsulated pyrolysis method to design and construct a heteronuclear Rh-Cu dual-metal catalytic system (Rh-Cu DACs). This catalyst, using a high surface area nitrogen-doped two-dimensional graphene support, successfully achieves the precise construction of spatially proximal and functionally cooperative Rh-Cu dual-metal centers. Kinetic studies show that when O\u003csub\u003e2\u003c/sub\u003e is used as the oxidant, the CH\u003csub\u003e4\u003c/sub\u003e conversion rate reaches 232 mol/(mol\u003csub\u003ecat\u003c/sub\u003e\u0026middot;s), with a methanol selectivity of 81%, approximately 3 times higher than that of the single Rh atomic catalyst. The products shift from CO\u003csub\u003e2\u003c/sub\u003e-dominated to CH\u003csub\u003e3\u003c/sub\u003eOH, demonstrating excellent catalytic performance and application prospects. Theoretical calculations further reveal that the RhCu bimetallic centers catalyze methane oxidation through a synergistic effect: the Rh sites attack and activate the C-H bonds of methane, breaking its stable tetrahedral structure; the Cu sites, on the other hand, form a coordination constraint on the adsorbed oxygen species, preventing their deep insertion during methane oxidation, thereby forming the key intermediate *CH\u003csub\u003e3\u003c/sub\u003eO, which ultimately combines with active hydrogen to generate the target product CH\u003csub\u003e3\u003c/sub\u003eOH.\u003c/p\u003e"},{"header":"2. Experimental Section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Synthesis of RhCu DACs\u003c/h2\u003e\u003cp\u003eThis study successfully constructed a Rh\u0026ndash;Cu dual-atom synergistic catalytic system using a host-guest confinement strategy (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed). The preparation of the precursor and Rh\u003csup\u003e3+\u003c/sup\u003e confinement encapsulation process begins with the self-assembly of Zn\u003csup\u003e2+\u003c/sup\u003e, Cu\u003csup\u003e2+\u003c/sup\u003e, and 2-methylimidazole as ligands to synthesize ZnCu-MOF (200 mg) as the precursor. Using the heteronuclear metal nodes and the multilevel pore structure of the MOF (with a pore size of approximately 0.55 nm, \u003cb\u003eFigure S15\u003c/b\u003e), the MOF was ultrasonically dispersed in 30 mL of n-hexane. Next, 100 \u0026micro;L of RhCl\u003csub\u003e3\u003c/sub\u003e\u0026middot;xH\u003csub\u003e2\u003c/sub\u003eO solution (10 mg\u0026middot;mL\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) was added dropwise to the dispersion and sonicated for 30 minutes at room temperature, followed by stirring for 2 hours. This process encapsulates Rh\u003csup\u003e3+\u003c/sup\u003especies, smaller than 0.5 nm, within the MOF cavities. The encapsulated sample was then centrifuged, vacuum-dried overnight at 333 K to obtain Rh@ZnCu-MOF. The next step involves high-temperature pyrolysis and structural reconstruction. The Rh@ZnCu-MOF was placed in a nitrogen atmosphere and pyrolyzed at 1173 K for 2 hours. During this process, Zn volatilized preferentially, inducing the formation of a gradient pore structure in the skeleton and driving the MOF to restructure into nitrogen-doped graphene. The remaining Cu\u003csup\u003e2+\u003c/sup\u003e ions strongly coordinate with the pyridine-type nitrogen atoms in the carbon substrate, forming stable Cu-N\u003csub\u003e3\u003c/sub\u003e anchoring sites. The Rh\u003csup\u003e3+\u003c/sup\u003e species pre-constrained in the cavities of the MOF migrate toward the adjacent Cu-N\u003csub\u003e3\u003c/sub\u003e sites under the stress induced by the contraction of the carbon layer. Ultimately, the synergistic interaction between Rh and Cu atoms forms a stable RhCu-N\u003csub\u003e6\u003c/sub\u003e heteronuclear bimetallic active configuration on the carbon substrate. To validate the dual-metal synergistic effect, Rh single-atom catalysts (Rh SACs) were prepared using ZIF-8 without Cu\u003csup\u003e2+\u003c/sup\u003e as the precursor, following the same confinement encapsulation and pyrolysis steps. Meanwhile, Cu single-atom catalysts (Cu SACs) were obtained by directly pyrolyzing ZnCu-MOF without encapsulating Rh\u003csup\u003e3+\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e2.2 Characterization\u003c/h2\u003e\u003cp\u003eThe phase composition and crystal structure of the catalysts were analyzed using a powder X-ray diffractometer (XD-6 model, Cu Kα). The specific surface area and pore size distribution were measured using a physical adsorption instrument (Micromeritics ASAP 2020 PLUS HD88) under liquid nitrogen, with calculations based on the BET equation. The microscopic structure and elemental distribution were characterized by transmission electron microscopy (FEI Talos F200X, 200 kV) combined with HAADF-STEM and EDS, and high-resolution structural images were obtained using a Hitachi HD3000C microscope (200 kV). X-ray photoelectron spectroscopy (XPS) was performed on a SPECS analyzer (MCD-10 analyzer, Al Kα, hv\u0026thinsp;=\u0026thinsp;1486.6 eV). In situ X-ray absorption spectroscopy (XAS) was conducted at the Beijing Synchrotron Radiation Facility 8-ID and 8-BM beamlines, encompassing XANES and EXAFS information to analyze the metal's electronic state and local structure. In situ Fourier-transform infrared (FTIR) spectroscopy was measured using a PerkinElmer FTIR spectrometer (MCT detector, resolution 0.2 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), combined with CO adsorption studies to examine catalytic active sites. Raman spectroscopy was conducted on a confocal Raman system (Xplora Plus, HORIBA Scientific, excitation source: 532 nm) and calibrated with a silicon wafer for Raman shifts. Hydrogen temperature-programmed reduction (H\u003csub\u003e2\u003c/sub\u003e-TPR) experiments were carried out on a Micromeritics Auto Chem II 2920 (USA) to investigate the reduction behavior and hydrogen adsorption capacity of the catalyst. Electron paramagnetic resonance (EPR) spectroscopy was performed using an EMX plus 10/12 (Bruker, Germany) instrument to detect defect information, such as nitrogen vacancies.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e2.3 Assessment\u003c/h2\u003e\u003cp\u003eThis study focuses on the catalytic performance of single-atom and dual-atom catalysts, evaluated using a self-built fixed-bed tubular reactor system for gas-solid reactions (\u003cb\u003eFigure S8\u003c/b\u003e). The experimental setup uses a quartz tube reactor with an outer diameter of 10 mm and a wall thickness of 1 mm. The reaction gas mixture consists of fuel gas (CH\u003csub\u003e4\u003c/sub\u003e/Ar), synthetic air (O\u003csub\u003e2\u003c/sub\u003e/N\u003csub\u003e2\u003c/sub\u003e), and high-purity N\u003csub\u003e2\u003c/sub\u003e as a diluent. To ensure accurate gas flow control, a soap film flow meter is used to calibrate the feed gas flow, and the calibrated values are applied during the experiment to maintain precision. A total of 100 mg of catalyst sample is uniformly mixed with quartz sand at a 1:1 mass ratio and loaded into the isothermal section of the reactor, with quartz wool isolating both ends. Prior to the reaction, the catalyst undergoes pretreatment under a high-purity N\u003csub\u003e2\u003c/sub\u003e flow of 100 sccm: the temperature is ramped to 200\u0026deg;C at a rate of 5\u0026deg;C/min and maintained for 1 hour to remove surface-adsorbed impurities. After pretreatment, the temperature is increased to the target value at the same rate and held for 1 hour to activate the catalyst. Upon completion of activation, the reactant gases, mixed in controlled proportions, are introduced into the system with a total flow rate of 100 sccm. The effluent gases are collected after condensation in a cold trap and quantitatively analyzed by gas chromatography (GC). By optimizing the catalyst particle size (100\u0026ndash;200 mesh) and total gas flow rate (100 sccm), both internal and external diffusion limitations are eliminated, ensuring that the reaction is controlled by intrinsic kinetics (\u003cb\u003eFigure S9\u003c/b\u003e). Product analysis is performed using an Agilent 8890 GC system equipped with a hydrogen flame ionization detector (FID) and a thermal conductivity detector (TCD), with high-purity N\u003csub\u003e2\u003c/sub\u003e as the carrier gas. TCD is connected to an HP-MOLESIEVE column to detect CH\u003csub\u003e4\u003c/sub\u003e, CO\u003csub\u003e2\u003c/sub\u003e, and Ar; FID is connected to an HP-PLOT/Q capillary column for the quantitative analysis of CH\u003csub\u003e3\u003c/sub\u003eOH (methanol) products. All gaseous products are analyzed in online mode.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e2.4 DFT Calculations\u003c/h2\u003e\u003cp\u003eAll density functional theory (DFT) calculations in this study were performed using the Vienna Ab-initio Simulation Package (VASP) \u003csup\u003e[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e. The exchange-correlation energy was described using the Perdew-Burke-Ernzerhof (PBE) function within the generalized gradient approximation (GGA) \u003csup\u003e[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e, and the electron-ion interactions were described using projector augmented-wave (PAW) pseudopotentials \u003csup\u003e[\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]\u003c/sup\u003e. A plane-wave energy cutoff of 450 eV was used in the calculations. The geometry optimization was carried out with strict convergence criteria, including a maximum force of 0.05 eV/\u0026Aring;, maximum pressure of 0.1 GPa, maximum displacement of 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e \u0026Aring;, single-atom energy change no greater than 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV, and a self-consistent field (SCF) convergence threshold of 1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e eV \u003csup\u003e[\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]\u003c/sup\u003e. Transition states were searched using the climbing image elastic band method (CI-NEB) \u003csup\u003e[\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]\u003c/sup\u003e, and the transition state structures were validated through imaginary frequency calculations. For the construction of the computational models, the heteronuclear bimetallic system embedded in N-doped graphene (NC) was based on a p(6\u0026times;6) single-layer graphene structure, while the single-metal system embedded in the NC substrate used a p(5\u0026times;5) single-layer structure. A vacuum layer of 15 \u0026Aring; was applied in the vertical direction of the two-dimensional monolayer to eliminate interactions between periodic images. K-point sampling was performed using the Monkhorst-Pack grid, with geometry optimization carried out on a 3\u0026times;3\u0026times;1 grid, Gibbs free energy calculations on a 4\u0026times;4\u0026times;1 grid, and projected density of states (PDOS) analysis on a 6\u0026times;6\u0026times;1 grid \u003csup\u003e[\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]\u003c/sup\u003e. The electronic structure calculations were analyzed for charge transfer using the Bader charge analysis method, and post-processing was performed using VASPKIT \u003csup\u003e[\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Result and discussion","content":"\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Structural Characterizations\u003c/h2\u003e\n \u003cp\u003eThe XRD results indicate that after introducing Cu and Rh species into ZIF-8, Rh@ZnCu-MOF still retains a crystallographic structure similar to ZIF-8 (\u003cstrong\u003eFigure S13\u003c/strong\u003e) \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e35\u003c/span\u003e]\u003c/sup\u003e. In the XRD pattern of RhCu DACs, two broad carbon characteristic peaks are observed at approximately 22.8\u0026deg; and 43.6\u0026deg; (\u003cstrong\u003eFigure S14\u003c/strong\u003e) \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e36\u003c/span\u003e]\u003c/sup\u003e, and no characteristic crystalline peaks of metals, metal oxides, or metal carbides are detected, suggesting the absence of metal particle formation \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e37\u003c/span\u003e]\u003c/sup\u003e. The pore size of bimetallic RhCu DACs has increased compared to that of other single - atom catalysts such as Rh SACs (\u003cstrong\u003eFigure S16, Table S2\u003c/strong\u003e). Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) results show that the metal Rh and Cu are atomically dispersed and evenly distributed on the carbon substrate (Figs. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ea, \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eb, \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003ec). Due to the different scattering abilities of Rh (atomic number Z\u0026thinsp;=\u0026thinsp;45) and Cu (atomic number Z\u0026thinsp;=\u0026thinsp;29) elements in HAADF-STEM imaging, they appear with different brightness. Using this property, we can visually observe the formation of RhCu paired sites. Randomly selected different bright spots were measured, and the average distance between them was found to be 2.46 \u0026Aring; (Figs.\u0026nbsp;1\u003cstrong\u003eb\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e, \u003cstrong\u003e1c\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e1\u003c/strong\u003e\u003c/sub\u003e), indicating the possible formation of metal-metal bonds. Energy dispersive X-ray spectroscopy (EDS) results (\u003cstrong\u003eFigure S18\u003c/strong\u003e) show that Rh, Cu, N, and C are uniformly distributed throughout the structure. Furthermore, the metallic Rh in the Rh SACs catalyst exists in an atomic - scale dispersed state (\u003cstrong\u003eFigures S16, S19\u003c/strong\u003e).\u003c/p\u003e\n \u003cp\u003eThe H\u003csub\u003e2\u003c/sub\u003e-TPR results of Rh SACs and RhCu DACs exhibit distinct reduction behaviors \u003cstrong\u003e(\u003c/strong\u003eFig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea\u003cstrong\u003e)\u003c/strong\u003e. Specifically, the Rh SACs catalyst shows a higher reducibility, with its reduction peak appearing in a lower temperature range. In contrast, the reduction peak of the RhCu DACs catalyst shifts to a significantly higher temperature, which indicates that the interaction between rhodium and copper modifies the reducibility of the species.\u003c/p\u003e\n \u003cp\u003eX-ray photoelectron spectroscopy (XPS) confirmed the coexistence of C, N, O, Rh, and Cu elements in the RhCu dual-atom catalyst (RhCu DACs). The C 1s high-resolution spectrum (\u003cstrong\u003eFigure S20\u003c/strong\u003e) reveals three carbon species corresponding to C\u0026ndash;C, C\u0026thinsp;=\u0026thinsp;N, and C\u0026ndash;N, demonstrating the successful doping of nitrogen atoms into the carbon framework. The C\u0026ndash;C component in RhCu DACs is lower than that in Rh SACs and Cu SACs, indicating a reduction in the sp\u003csup\u003e2\u003c/sup\u003e hybridization degree of its carbon structure. The N 1s spectrum (\u003cstrong\u003eFigure S21\u003c/strong\u003e) can resolve four nitrogen species: pyridine nitrogen, metal-coordinated nitrogen, graphitic nitrogen, and oxidized nitrogen \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/sup\u003e. The metal\u0026ndash;N coordination peak (399.07 eV) is significantly higher in RhCu DACs than in Rh SACs, indicating the formation of stable M\u0026ndash;N (M\u0026thinsp;=\u0026thinsp;Rh, Cu) structures in DACs, while pyridine and graphitic nitrogen together form a nitrogen-doped network, providing electronic environment support for metal anchoring. The high-resolution Rh 3d and Cu 2p spectra (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec) show that in the reduced state, Rh and Cu mainly exist in high oxidation states \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan class=\"CitationRef\"\u003e40\u003c/span\u003e]\u003c/sup\u003e, while in the reaction state, Rh tends toward a low oxidation state, and Cu further oxidizes. This charge behavior suggests that Rh remains more stable during the reaction, while Cu may be involved in the transfer of oxygen species.\u003c/p\u003e\n \u003cp\u003eFurther analysis of the local coordination environment was performed using X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The XANES results show that the K-edge absorption energy (E\u003csub\u003e0\u003c/sub\u003e) of reduced Rh lies between metallic Rh\u003csup\u003e0\u003c/sup\u003e and oxidized Rh, indicating that it is partially oxidized with a positive charge (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed). In the reaction state, E\u003csub\u003e0\u003c/sub\u003e is closer to Rh\u003csup\u003e0\u003c/sup\u003e, indicating that Rh tends to maintain a reduced state during the reaction. Similarly, Cu exists as Cu\u003csup\u003e+\u003c/sup\u003e in the reduced state (E\u003csub\u003e0\u003c/sub\u003e between Cu\u003csup\u003e0\u003c/sup\u003e and Cu\u003csup\u003e2+\u003c/sup\u003e), while it further oxidizes under reaction conditions (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee). EXAFS fitting (Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ef, Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eg, \u003cstrong\u003eFigure S23\u003c/strong\u003e) reveals that the main peak of Rh is located at 1.95 \u0026Aring;, corresponding to Rh\u0026ndash;N coordination, and the secondary peak at 2.45 \u0026Aring; corresponds to Rh\u0026ndash;Cu coordination, indicating that Rh atoms are anchored on nitrogen-doped carbon and form atomically adjacent Rh\u0026ndash;Cu bimetallic structures. The main peak of Cu at 1.92 \u0026Aring; is attributed to Cu\u0026ndash;N, and a secondary peak also appears at 2.45 \u0026Aring;, matching the Rh\u0026ndash;Cu bond, further supporting the stable presence of Rh\u0026ndash;Cu dual-atom sites. The small bond length difference (\u0026Delta;R\u0026thinsp;=\u0026thinsp;0.03 \u0026Aring;) between Rh\u0026ndash;N and Cu\u0026ndash;N suggests that the Rh\u0026ndash;N bond has stronger covalent characteristics, while the 2.45 \u0026Aring; Rh\u0026ndash;Cu metal bond reflects significant electronic coupling between the two atoms.\u003c/p\u003e\n \u003cp\u003eRaman spectroscopy (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eh, \u003cstrong\u003eFigure S22\u003c/strong\u003e) further reveals the structural ordering and defect characteristics of the carbon support. RhCu DACs show distinct peaks at 1335 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (D-band) and 1580 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (G-band). The intensity ratio (ID/IG\u0026thinsp;=\u0026thinsp;1.01) is higher than that of Rh SACs and the NC support. This indicates that the synergistic doping of bimetallic atoms disrupts the ordering of the sp\u003csup\u003e2\u003c/sup\u003e carbon framework. It induces structural distortion. It also leads to the generation of sp\u003csup\u003e3\u003c/sup\u003e defects. This significantly enhances the defect density. Electron paramagnetic resonance (EPR) spectroscopy (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ei) was used to analyze the metal\u0026ndash;support interactions and defect structures. The nitrogen-doped carbon support (NC) shows a strong EPR signal at g\u0026thinsp;=\u0026thinsp;2.003, corresponding to nitrogen vacancy (NV)-related paramagnetic defects. After introducing Rh SACs and RhCu DACs, the EPR signal gradually weakens, indicating that metal atoms preferentially coordinate with nitrogen vacancies to form the Rh\u0026ndash;Nx\u0026ndash;Cu structure, effectively passivating free electrons and reducing defect states. In conclusion, RhCu DACs achieve dual-atom synergy by constructing a stable Rh\u0026ndash;N\u0026ndash;Cu\u0026ndash;N bridged structure, demonstrating advantages in charge state regulation and defect structure optimization, which provide a structural foundation for their high activity in CH\u003csub\u003e4\u003c/sub\u003e selective oxidation reactions.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Reaction Kinetics\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea shows that as oxygen partial pressure (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e) increases, the methane catalytic reaction exhibits distinct kinetic regimes. In Region A (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e \u0026lt; 0.12 kPa), the CH\u003csub\u003e4\u003c/sub\u003e conversion rate increases linearly with \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e, consistent with first-order reaction kinetics. During this stage, oxygen adsorption on the active sites adopts a bridging configuration (Rh-O*-O*-Cu or Rh-O*-Cu). When \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e exceeds the optimal value (Region B), the catalyst surface active sites gradually become saturated with adsorbed oxygen (Rh-O\u003csub\u003e2\u003c/sub\u003e* + Cu-O\u003csub\u003e2\u003c/sub\u003e*), weakening the interaction between the metal sites and the C-H bond, leading to a decrease in the methane conversion. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb illustrates the influence of oxygen partial pressure and reaction regime on the product distribution. The primary product in Region A is methanol. Comparing rate constants, CH\u003csub\u003e3\u003c/sub\u003eOH selectivity reaches 81.0%, superior to some literature reports (\u003cstrong\u003eTable S6\u003c/strong\u003e). Compared to the inferior methane conversion efficiency and CO\u003csub\u003e2\u003c/sub\u003e as the main product observed on single-atom Rh catalysts (\u003cstrong\u003eFigure S25\u003c/strong\u003e), this indicates that single active sites struggle to control the oxidation reaction pathway. The introduction of Cu sites provides a coordination confinement effect on the oxygen species, restricting the attack by molecular oxygen or active oxygen monomers on the C-H bond, resulting in methanol as the partially oxidized product. After oxygen adsorption saturation (Region B), the regulatory role of Cu diminishes, causing a rapid decline in methanol yield and a sharp increase in CO\u003csub\u003e2\u003c/sub\u003e production. Ultimately, under surface oxygen oversaturation coverage, the reaction rate becomes uncorrelated with oxygen pressure and proportional only to methane partial pressure (\u003cstrong\u003eFigure S24\u003c/strong\u003e).\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec presents the activation energy barriers for the two reaction regimes: Ea\u0026thinsp;=\u0026thinsp;18.9 kJ/mol (Region A) and Ea\u0026thinsp;=\u0026thinsp;89.7 kJ/mol (Region B). Under unsaturated oxygen adsorption on the active site surface, the bonding and coordination of oxygen are primarily facilitated by the Cu site. This allows the Rh site to possess stronger electronic potential for activating the C-H bond of methane, thereby lowering the activation barrier. Conversely, when the metal sites become saturated, their activation capability decreases, leading to a significant increase in the reaction activation energy.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed reveals the variation of RhCu DACs catalytic activity with temperature and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e. Across different reaction temperatures, a positive correlation regime exists between the production rate and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e. As the reaction temperature increases, the optimal inflection point for oxygen partial pressure also shifts to higher values. This is likely because high activity rapidly depletes surface oxygen, maintaining an unsaturated surface oxygen state. Figure \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ee displays the kinetics of oxygen exchange and its isotope (\u003csup\u003e18\u003c/sup\u003eO\u003csub\u003e2\u003c/sub\u003e) on the dual-atom catalyst. With fixed \u003csup\u003e16\u003c/sup\u003eO\u003csub\u003e2\u003c/sub\u003e partial pressure (0.01 mbar), the \u003csup\u003e18\u003c/sup\u003eO\u003csub\u003e2\u003c/sub\u003e partial pressure was varied, and the oxygen exchange rate was measured at different temperatures (270\u0026ndash;360\u0026deg;C) using gas chromatography-mass spectrometry (GC-MS). The results show that the oxygen exchange rate constant increases with rising temperature, indicating that high temperature promotes oxygen dissociation and recombination processes.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure 3f\u003c/strong\u003e presents the kinetics of the CH\u003csub\u003e4\u003c/sub\u003e\u0026ndash;D\u003csub\u003e2\u003c/sub\u003e exchange reaction on both Rh-Cu dual-atom and Rh single-atom surfaces. With methane pressure fixed at 5 kPa, the exchange rate increases similarly on both Rh-Cu DACs and Rh SACs as D\u003csub\u003e2\u003c/sub\u003e pressure rises. This demonstrates that C-H bond activation primarily occurs on the Rh site. While Cu plays a role in confining oxygen species through coordination, it does not contribute significantly to the primary activation of the C-H bond.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Reaction Mechanism Study\u003c/h2\u003e\n \u003cp\u003eAs shown in \u003cstrong\u003eFigure S26\u003c/strong\u003e, the two transition metal atoms in RhCu DACs are connected by a metal bond, and the pyridine-type nitrogen atoms in a tridentate coordination form a stable Rh\u0026ndash;Cu\u0026ndash;N\u003csub\u003e6\u003c/sub\u003e configuration. Previous theoretical studies have indicated that this structure is the most stable form of a metal dimer embedded in N-doped graphene \u003csup\u003e[\u003cspan class=\"CitationRef\"\u003e41\u003c/span\u003e]\u003c/sup\u003e. The geometric optimization results show that the Rh\u0026ndash;Cu bond length is 2.42 \u0026Aring;, which is in excellent agreement with the EXAFS experimental results, verifying the validity of the model construction. In the structures of Rh SACs and Cu SACs, metal atoms in each catalyst are coordinated with four N atoms, respectively. The comparative results show that the RhCu DACs has a lower formation energy, thus exhibiting higher thermodynamic stability (\u003cstrong\u003eTable S4\u003c/strong\u003e).\u003c/p\u003e\n \u003cp\u003eThe differential charge density (\u003cstrong\u003eFigure S27\u003c/strong\u003e) and Bader charge analysis (\u003cstrong\u003eTable S5\u003c/strong\u003e) reveal that the Rh\u0026ndash;Cu dimer undergoes electron transfer to the coordinated nitrogen atoms, while the nitrogen atoms also gain electrons from the carbon backbone, demonstrating a typical \u0026quot;dual electron donation\u0026quot; effect. The projected density of states (PDOS) analysis (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea) further confirms the electronic coupling characteristics: Rh 4d and Cu 3d orbitals significantly overlap, and both hybridize with the N 2p orbitals, indicating the formation of M\u0026ndash;N bonds, consistent with the XPS results. Notably, the d-band center of Rh in RhCu DAC is located at \u0026minus;\u0026thinsp;0.82 eV, which is significantly downshifted compared to \u0026minus;\u0026thinsp;0.58 eV in Rh SACs. This phenomenon is attributed to the introduction of Cu, which breaks the high symmetry of Rh\u0026ndash;N\u003csub\u003e4\u003c/sub\u003e and forms a lower symmetry Rh\u0026ndash;N\u003csub\u003e3\u003c/sub\u003e structure. The downward shift of the d-band center directly weakens the adsorption strength of Rh towards oxygen species, laying the electronic structural foundation for the aforementioned \u0026quot;coordination constraint effect\u0026quot;.\u003c/p\u003e\n \u003cp\u003eDFT simulation results reveal significant differences in O\u003csub\u003e2\u003c/sub\u003e adsorption behaviors among RhCu DACs, Rh SACs, and Cu SACs (\u003cstrong\u003eFigure S28\u003c/strong\u003e). Specifically, both Rh SACs and Cu SACs stably bind O\u003csub\u003e2\u003c/sub\u003e molecules through end-on adsorption modes (corresponding to Rh SACs-O\u003csub\u003e2\u003c/sub\u003e-b and Cu SACs-O\u003csub\u003e2\u003c/sub\u003e-a configurations, respectively). These configurations exhibit lower adsorption energies, representing their most stable adsorption states (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb). Orbital analysis indicates a distinct coupling effect between the d orbitals of the metal centers and the 2p orbitals of O (\u003cstrong\u003eFigure S29\u003c/strong\u003e).In contrast, RhCu DACs possess two types of O\u003csub\u003e2\u003c/sub\u003e adsorption configurations. In the lateral configuration (RhCu-O\u003csub\u003e2\u003c/sub\u003e-a), the Rh-O and Cu-O bond lengths are 1.97 \u0026Aring; and 2.06 \u0026Aring;, respectively, while the O-O bond length increases to 1.36 \u0026Aring;, which is significantly longer than that of free O\u003csub\u003e2\u003c/sub\u003e molecules (1.21 \u0026Aring;). In the vertical configuration (RhCu- O\u003csub\u003e2\u003c/sub\u003e-b), the Rh-O and Cu-O bond lengths are 1.93 \u0026Aring; and 2.50 \u0026Aring;, respectively, with an O-O bond length of 1.31 \u0026Aring;, indicating a lower degree of O\u003csub\u003e2\u003c/sub\u003e activation. Among these, the RhCu- O\u003csub\u003e2\u003c/sub\u003e-a configuration has the lowest adsorption energy (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003eb), making it the optimal O\u003csub\u003e2\u003c/sub\u003e adsorption configuration for RhCu DACs. Electronic structure analysis (\u003cstrong\u003eFigure S30\u003c/strong\u003e) shows that RhCu- O\u003csub\u003e2\u003c/sub\u003e-a transfers 0.63 electrons to O\u003csub\u003e2\u003c/sub\u003e, with a higher electron transfer amount compared to Rh SACs-O₂-b and Cu SACs-O₂-a configurations. This makes O\u003csub\u003e2\u003c/sub\u003e molecules electron-rich and the metal sites electron-deficient, significantly enhancing the metal-oxygen polarization effect. The simulation results of reaction pathways for each catalyst are presented in \u003cstrong\u003eFigures S32-S42\u003c/strong\u003e. For RhCu DACs, under the optimal RhCu-O\u003csub\u003e2\u003c/sub\u003e-a adsorption state, CH\u003csub\u003e4\u003c/sub\u003e undergoes two consecutive adsorption and activation reactions to generate 2 molecules of CH\u003csub\u003e3\u003c/sub\u003eOH. In the initial state (IS), CH\u003csub\u003e4\u003c/sub\u003e reacts with *O\u003csub\u003e2\u003c/sub\u003e to form *OCH\u003csub\u003e3\u003c/sub\u003e and *OH (IM1). After overcoming an energy barrier of 0.76 eV (TS-2), it is converted to CH\u003csub\u003e3\u003c/sub\u003eOH (IM2) with the release of bridge oxygen (Rh-O-Cu). The bridge oxygen then reactivates CH\u003csub\u003e4\u003c/sub\u003e (IM4\u0026rarr;IM5), ultimately generating a second molecule of CH\u003csub\u003e3\u003c/sub\u003eOH, which desorbs (FS). The Gibbs free energy change (\u0026Delta;G) of the overall reaction is \u0026lt;\u0026thinsp;0, indicating an exothermic process. In contrast, the pathway leading to CO\u003csub\u003e2\u003c/sub\u003e formation requires overcoming a higher energy barrier (0.93 eV, TS-2\u0026rsquo;), making it a non-preferred pathway. This confirms that the RhCu-O₂-a configuration is more favorable for the selective oxidation of CH\u003csub\u003e4\u003c/sub\u003e to CH\u003csub\u003e3\u003c/sub\u003eOH (Figs. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ec, \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ed). In contrast, for Rh SACs and Cu SACs, under their optimal O\u003csub\u003e2\u003c/sub\u003e adsorption configurations, the dominant pathway of CH\u003csub\u003e4\u003c/sub\u003e oxidation is towards CO\u003csub\u003e2\u003c/sub\u003e formation. Both catalysts generate *CH\u003csub\u003e3\u003c/sub\u003e and *OOH intermediates, leading to the continuous dehydrogenation of *CH\u003csub\u003e3\u003c/sub\u003e and its final conversion to CO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e\n \u003cp\u003eFourier-transform infrared (FTIR) spectroscopy results (Fig. \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003ea) show that under low oxygen pressure (0.01\u0026ndash;0.10 kPa), the CH\u003csub\u003e4\u003c/sub\u003e signal weakens as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{P}_{{O}_{2}}\\)\u003c/span\u003e\u003c/span\u003e increases, and C\u0026ndash;O vibration peaks at 1088 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (*CH\u003csub\u003e3\u003c/sub\u003eO) and 1042 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (*CH\u003csub\u003e3\u003c/sub\u003eOH) appear, confirming the correlation between *OCH\u003csub\u003e3\u003c/sub\u003e and CH\u003csub\u003e3\u003c/sub\u003eOH. Under higher oxygen pressure (0.2\u0026ndash;0.4 kPa), the *CH\u003csub\u003e3\u003c/sub\u003eO vibration weakens, and the characteristic vibration peaks of CO\u003csub\u003e2\u003c/sub\u003e (2377 and 2333 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) become stronger, reflecting the oxygen coverage effect and the change in the reaction path (\u003cstrong\u003eFigure S43\u003c/strong\u003e). In contrast to Rh SACs, no *OCH\u003csub\u003e3\u003c/sub\u003e vibrations are observed, further confirming that *OCH\u003csub\u003e3\u003c/sub\u003e is a key intermediate for RhCu DACs catalyzed CH\u003csub\u003e4\u003c/sub\u003e oxidation to CH\u003csub\u003e3\u003c/sub\u003eOH.\u003c/p\u003e\n \u003cp\u003eTo further understand the reaction mechanism of CH\u003csub\u003e4\u003c/sub\u003e selective oxidation to CH\u003csub\u003e3\u003c/sub\u003eOH catalyzed by RhCu DACs, the following analysis was conducted. The adsorption energy calculation results (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb) show that, compared with Rh SACs and Cu SACs, RhCu DACs have lower adsorption energy for CH\u003csub\u003e4\u003c/sub\u003e and higher adsorption energy for the product CH\u003csub\u003e3\u003c/sub\u003eOH. The diatomic sites exhibit stronger activation ability for CH\u003csub\u003e4\u003c/sub\u003e and, at the same time, are more conducive to the timely desorption of the product CH\u003csub\u003e3\u003c/sub\u003eOH.\u003c/p\u003e\n \u003cp\u003ePartial density of states (PDOS) analysis (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ec\u003cstrong\u003e)\u003c/strong\u003e indicates that in the RhCu\u0026ndash;O\u003csub\u003e2\u003c/sub\u003e\u0026ndash;a configuration, both the 4d orbitals of Rh and the 3d orbitals of Cu hybridize with the 2p orbitals of O, reflecting the synergistic adsorption effect of the bimetallic sites on O\u003csub\u003e2\u003c/sub\u003e. After O\u003csub\u003e2\u003c/sub\u003e adsorption, the d-band center of Rh shifts significantly downward (from \u0026minus;\u0026thinsp;0.82 eV to \u0026minus;\u0026thinsp;1.86 eV), while the d-band center of Cu shifts only slightly downward (from \u0026minus;\u0026thinsp;2.28 eV to \u0026minus;\u0026thinsp;2.73 eV). The significant downward shift of the Rh d-band center directly leads to a weakened adsorption effect on oxygen species (O\u003csub\u003e2\u003c/sub\u003e, O), which is consistent with the weakly oxygen-adsorbed state (Region A) observed in the previous kinetic study and its characteristics (low activation energy barrier, high methanol selectivity). Crystal orbital Hamilton population (COHP) analysis (\u003cstrong\u003eFigure S31\u003c/strong\u003e) further confirms that the interaction strength of the Rh\u0026ndash;O bond (\u0026ndash;ICOHP = \u0026minus;\u0026thinsp;2.67 eV) is significantly weaker than that of the Cu\u0026ndash;O bond (\u0026ndash;ICOHP = \u0026minus;\u0026thinsp;0.37 eV), indicating that the Rh\u0026ndash;O bond has weaker covalency. Bader charge analysis (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ed) shows that Rh loses 0.92 e⁻, Cu loses 0.71 e⁻, and the charge transfer is mainly concentrated on one of the O atoms (O1 gains 0.38 e⁻). Rh has stronger electronegativity, and the Rh\u0026ndash;O bond has an obvious charge polarization effect, which is consistent with the COHP analysis results. In terms of methane activation and product selectivity control, Cu, relying on its stronger electron transfer ability, effectively exerts a \u0026quot;coordination constraint\u0026quot; effect on oxygen species, stabilizes adsorbed oxygen, and promotes the cleavage of the O-O bond; while Rh, due to the weak adsorption state of oxygen species after the downward shift of its d-band center, can more efficiently activate the C\u0026ndash;H bond of methane, triggering its first step of dissociation. This is consistent with the conclusion of the previous CH\u003csub\u003e4\u003c/sub\u003e\u0026ndash;D\u003csub\u003e2\u003c/sub\u003e exchange experiment, that is, the activation of the C\u0026ndash;H bond is mainly undertaken by the Rh site.\u003c/p\u003e\n \u003cp\u003eOn Rh SACs, the key intermediate CH\u003csub\u003e3\u003c/sub\u003e\u0026ndash;OOH has insufficient stability because Rh transfers limited electrons to it. The highly active OOH group is prone to decompose to produce H\u003csub\u003e2\u003c/sub\u003eO and react with CH\u003csub\u003e3\u003c/sub\u003e triggering deep dehydrogenation to generate the by-product CO\u003csub\u003e2\u003c/sub\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ee). In the RhCu DACs system (Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ef), the key intermediates are *OCH\u003csub\u003e3\u003c/sub\u003e and *OH. Differential charge and Bader charge analysis show that Rh transfers 0.36 e⁻ to *OCH\u003csub\u003e3\u003c/sub\u003e, and Cu transfers 0.54 e⁻ to *OH, indicating a stronger interaction between *OH and Cu. In the subsequent reaction, *OCH\u003csub\u003e3\u003c/sub\u003e and *OH directly combine through H atoms to form CH\u003csub\u003e3\u003c/sub\u003eOH and desorb, and *OCH₃ preferentially dissociates from the Rh site (rather than *OH dissociating from Cu to form H₂O). Therefore, the relative stability of the intermediate *OCH\u003csub\u003e3\u003c/sub\u003e on the Rh site is the decisive factor for inhibiting the deep oxidation pathway and achieving high selective generation of CH\u003csub\u003e3\u003c/sub\u003eOH.\u003c/p\u003e\n \u003cp\u003eIn summary, the significant advantage of RhCu DACs over single-atom catalysts stems from the unique electronic coupling effect between the bimetallic sites and the charge polarization effect caused by it. This synergistic effect achieves precise functional division: the Cu site implements \u0026quot;coordination constraint\u0026quot; on oxygen species through strong electron transfer, stabilizes adsorbed oxygen, and regulates its activity; the Rh site maintains a weak adsorption state for oxygen species due to the significant downward shift of its d-band center, thus enabling efficient activation of the C-H bond of CH\u003csub\u003e4\u003c/sub\u003e. The synergy of the two sites not only optimizes the adsorption and activation of reactant molecules but, more importantly, stabilizes the key intermediate *OCH\u003csub\u003e3\u003c/sub\u003e and drives its efficient conversion to the target product CH\u003csub\u003e3\u003c/sub\u003eOH. This mechanism effectively inhibits the excessive insertion of active oxygen and the deep combination of reaction intermediates with active oxygen, fundamentally avoiding the occurrence of over-oxidation (generating CO\u003csub\u003e2\u003c/sub\u003e)\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThis study we innovatively developed an encapsulated pyrolysis strategy and successfully synthesized Rh\u0026ndash;Cu heteronuclear dual-atom catalysts (Rh-Cu DACs) over nitrogen-doped graphite carbon supports. The Rh-Cu DACs possess both excellent structural stability and significant electronic synergy. In the reaction of one-step oxidation of methane to methanol, the unique spatial arrangement of Rh\u0026ndash;Cu sites promotes the formation of a highly active oxygen bridge structure (Rh-O-O-Cu, Rh-O-Cu). The difference in electron affinity for oxygen between Rh and Cu leads to electron density polarization at both ends of the oxygen bridge, and Cu achieves precise capture of oxygen through strong coordination, providing a crucial guarantee for limiting excessive oxygen insertion. The electron-deficient Rh center and electronegative oxygen atoms synergistically activate the C\u0026ndash;H bond in CH\u003csub\u003e4\u003c/sub\u003e, forming key intermediates *CH\u003csub\u003e3\u003c/sub\u003eO and *OH. Subsequently, *CH\u003csub\u003e3\u003c/sub\u003eO undergoes hydrogenation and desorption to generate the target product CH₃OH. Kinetic experiments have verified its excellent performance that methanol selectivity can reach 81% under mild conditions. The Rh-Cu DACs have the broad application prospects in methane utilization.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by the Fundamental Research Funds for the Central Universities of China (SWU-KT25006), National Natural Science Foundation of China (22109129), and Project of Science and Technology Research Program of Chongqing Education Commission of China (KJQN202400210). \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of Competing Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eDAVIDSON E A, MONTEVERDE D R, SEMRAU J D. 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Advanced Materials, 2021, 33(41).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Methane, Methanol, Dual-atom Catalyst, Catalytic Oxidation, Kinetics","lastPublishedDoi":"10.21203/rs.3.rs-7370917/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7370917/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe direct oxidation of methane to methanol holds significant industrial value. In the methane-assisted oxidation and one-step methanol synthesis reaction, the oxidants or oxygen-containing groups are highly prone to deeply oxidize the dissociated methane molecules, making it difficult to control the reaction proces. This study, based on dual-atom catalysts, we regulate the reaction process by separating active sites at a short distance and constraining the activity of oxygen intermediates, enabling methanol formation through the oxygen insertion. Aiming at the precise construction of dual sites, we innovatively developed an encapsulated pyrolysis strategy and successfully synthesized Rh–Cu heteronuclear dual-atom catalysts (RhCu DACs) over nitrogen-doped graphite carbon supports, forming an Rh–Cu–N\u003csub\u003e6\u003c/sub\u003e structural catalyst (Rh–Cu bond length = 2.42 Å). The electronic coupling between the bimetallic sites induces a significant charge polarization effect, enhancing the activation efficiency of reactant molecules. The introduction of the second metal, Cu, captures active oxygen species, generating a “restraint” effect on oxygen species. This restraint effectively inhibits excessive oxygen insertion, thereby inhibiting the complete oxidation of methane. The methanol selectivity is as high as 81% and the catalytic activity is three times than that of the single-atom Rh catalyst. In-situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations demonstrate that the rhodium-copper bimetallic centers form stable oxygen-bridged intermediate structure (Rh-O-O-Cu or Rh-O-Cu). The rhodium site acts as an electron acceptor for methyl groups (*CH\u003csub\u003e3\u003c/sub\u003e) to stabilize the formation of hydrocarbon intermediates, while the copper site restricts the activity of adjacent oxygen species and guides oxygen insertion into C-H bonds for methanol synthesis.\u003c/p\u003e","manuscriptTitle":"The Coordination Restraint of Rh-Cu Di-Atomic Catalyst and Oxygen Insertion into C-H Bond for the Synthesis of Methanol","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-28 09:28:52","doi":"10.21203/rs.3.rs-7370917/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"340faec7-d305-4c82-8368-6e70c7e808b3","owner":[],"postedDate":"August 28th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":53769280,"name":"Physical sciences/Chemistry/Catalysis/Heterogeneous catalysis"},{"id":53769281,"name":"Physical sciences/Chemistry/Catalysis/Catalytic mechanisms"}],"tags":[],"updatedAt":"2026-04-10T07:22:04+00:00","versionOfRecord":{"articleIdentity":"rs-7370917","link":"https://doi.org/10.1038/s41467-026-70182-z","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2026-02-28 05:00:00","publishedOnDateReadable":"February 28th, 2026"},"versionCreatedAt":"2025-08-28 09:28:52","video":"","vorDoi":"10.1038/s41467-026-70182-z","vorDoiUrl":"https://doi.org/10.1038/s41467-026-70182-z","workflowStages":[]},"version":"v1","identity":"rs-7370917","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7370917","identity":"rs-7370917","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}