FeCu Dual-Single-Atom Catalyst Promotes Gradient H2O2 Activation for Enhanced Methane Oxidation to Methanol

FeCu Dual-Single-Atom Catalyst Promotes Gradient H2O2 Activation for Enhanced Methane Oxidation to 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 FeCu Dual-Single-Atom Catalyst Promotes Gradient H 2 O 2 Activation for Enhanced Methane Oxidation to Methanol Wenting Wu, Haonan Zhang, Shuai Wang, Yang Li, Hongjie Qin, Mingwang Wang, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7017740/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 05 Mar, 2026 Read the published version in Nature Communications → Version 1 posted You are reading this latest preprint version Abstract Hydrogen peroxide is an attractive and sustainable oxidant, yet its effective application in inert alkane oxidation is limited by the inability to precisely match the distribution, concentration, and reactivity of generated oxygen species with substrate activation requirements. Herein, a dual single-atom catalyst, FeCu/ZSM-CI, in which atomically dispersed Fe and Cu are spatially separated within the microporous framework of ZSM-5, with Fe located in the inner channels and Cu on the external surface, thereby enabling a controlled H 2 O 2 activation gradient. This spatial configuration induces differentiated reactive oxygen species evolution: high-valent Fe = O and •OOH species form in the interior to activate methane into CH 3 OOH, while surface Cu sites selectively convert CH 3 OOH into methanol, mitigating overoxidation pathways. The optimized FeCu/ZSM-CI catalyst achieves a methanol yield of 20.20 mmol g cat −1 h − 1 with 90.1% selectivity and a remarkable H 2 O 2 utilization efficiency of 74.6%. Mechanistic studies combining kinetic isotope effects, scavenger assays, in-situ EPR/DRIFTS, and DFT calculations reveal that the rate-determining step shifts from H 2 O 2 activation to C-H bond activation due to synergistic Fe-Cu interactions. These findings establish a generalizable strategy for manipulating ROS spatial distribution via dual single-atom engineering, offering new insights for designing advanced catalysts for selective hydrocarbon oxidation under ambient conditions. Earth and environmental sciences/Environmental sciences/Environmental chemistry/Environmental monitoring Earth and environmental sciences/Biogeochemistry/Carbon cycle Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Introduction Hydrogen peroxide (H 2 O 2 ) is a commonly used oxidant in chemical synthesis and is regarded as one of the top 100 most important chemicals globally due to its effectiveness and eco-friendliness ( 1 – 4 ). However, improving both selectivity and rate simultaneously can be challenging, particularly for selectively oxidizing inert alkane ( 5 – 7 ). Excessive use of H 2 O 2 is often employed to enhance the conversion rate, but this reduces the selectivity and efficiency of H 2 O 2 utilization ( 8 – 11 ). This rises from two main issues: first, single reactive oxygen species (ROS) cannot effectively activate and selectively convert C-H bonds of inert alkane independently, despite many excellent works have been devoted into the selective conversion of H 2 O 2 into specific ROS, such as superoxide radicals (•O 2 − /•OOH), hydroxyl radicals (•OH) and high valent metal-oxygen species (M-O) ( 9 , 12 , 13 ). For example, •OH and high-valent metal-oxygen sites have a strong ability to activate C-H bonds in alkanes, and have the ability to selective conversion C-H bond at low concentration ( 14 ), but they tend to over-oxidize into acid or CO 2 if their concentration increases for enhancing the reaction rate ( 15 – 17 ). This leads to the second issue that high concentrations of H 2 O 2 or ROS do not always match those of reactants ( 18 ). To date, almost no strategy has been proposed to systematically solve the matching problem of the distribution, concentration and kinds of ROS with reactants. The fast expansion of renewable energy facilitates a shift from natural gas, a conventional energy source, to chemical feedstocks ( 19 – 21 ). Since methane (primary component of natural gas) is usually located in distant and dispersed areas, it is better to directly oxidize it into methanol with low boiling point and easy separation for convenient transportation and storage, rather than using the conventional method of reforming it into syngas at high temperatures and then Fischer-Tropsch synthesis ( 22 – 24 ). Molecular sieves are crucial catalysts (e.g. methane conversion) due to their diverse pore structures, which provide distinct reaction sites and ways to regulate reactant concentration ( 25 – 27 ). ZSM-5, for example, possesses both inner small and external large pore structures. According to Fick’s law, H 2 O 2 diffuses more in external surface with higher concentrations and less in inner pores with lower concentrations ( 28 , 29 ). Therefore, by placing functional metal sites more precisely within the pores, ROS concentration can be controlled through diffusion rather than only adjusting H 2 O 2 amounts. What metal sites can efficiently promote H 2 O 2 evolution for activating C-H bonds and selectively converting methane? Non-noble metal iron (Fe) nanoparticles or clusters incorporated within the nanopores of ZSM-5 can react with H 2 O 2 and are prone to generate •OH for the activation of C-H bond ( 30 ). Reducing Fe site size to binuclear Fe or individual Fe atom could promote the decomposition of H 2 O 2 from •OH to high valent Fe-O, significantly enhancing methane activation ( 31 , 32 ). This may be due to the longer intrinsic lifetime of high valent Fe-O compared to •OH (100 ns), providing more reaction time to activate C-H bond ( 23 ). In addition, extra-framework Fe sites in ZSM-5 pores via a template-free synthesis strategy show over 5 times higher methane conversion rate than that Fe sites in the framework of ZSM-5, which provide good reference for precise fabrication of Fe sites to activate C-H bond into •CH 3 ( 33 ). At this juncture, a new challenge arises: how to control H 2 O 2 evolution to improve product selectivity, particularly in the conversion of methane into CH 3 OH? Gradient H 2 O 2 evolution into mild ROS (e.g. •OOH) is preferable for selectively converting methane into CH 3 OOH instead of risking over-oxidation with •OH that reacts with •CH 3 and easily form CH 3 OH, HCOOH and CO 2 ( 34 , 35 ). To enhance the product selectivity, it is better to separate the distribution of •OOH and •OH. This allows for CH 3 OOH to diffuse into a milder condition for subsequent conversion into CH 3 OH. Hutchings and Yu et al. found that Cu ions impregnated into molecular sieve (e.g. Fe/ZSM-5) can mildly and selectively convert H 2 O 2 into •OH, significantly increasing methanol yield up to 85%, providing a good suggestion for selective conversion of CH 3 OOH ( 30 , 36 ). However, the efficiency of H 2 O 2 conversion is only 3.39%, and the significant residual amounts of H 2 O 2 easily cause over oxidation. Therefore, there is much room left for improvement in both CH 3 OH selectivity and H 2 O 2 utilization efficiency ( 37 ). By optimizing the combination of Fe active sites anchored in the extra framework of inner small pores using the crystal seed method and Cu anchored in the external large pores of ZSM-5 via impregnation methods, CH 3 OH yield reaches 20.20 mmol g cat −1 h − 1 with a selectivity of 90.1% in direct oxidation of methane, representing a breakthrough in simultaneously enhancing selectivity and reaction rate. More importantly, the utilization efficiency of H 2 O 2 reached 74.6%, much higher than most reported results. Experiments and theoretical calculations show that Fe is more reactive with H 2 O 2 , forming high-valent Fe-O and •OOH species that generate CH 3 OOH for efficient H 2 O 2 utilization in inner small pores. Cu has lower reactivity but selectively converts CH 3 OOH into CH 3 OH, promoting selective conversion to methanol in external larger pores at higher H 2 O 2 concentrations. Combining H 2 O 2 diffusion and functional metal site distribution can improve gradient H 2 O 2 evolution to increase both methane conversion rate and selectivity, which provide a new perspective to enhance the selective conversion and efficient utilization of H 2 O 2 . Results and discussion Catalytic Performance in Direct and Selective Methane Oxidation To achieve gradient H 2 O 2 decomposition and improve utilization efficiency, we confined Fe species inside the porous channels of ZSM-5 via an in-situ seed-assisted synthesis method (Noted: C), while loading Cu species on the external surface through impregnation (Noted: I), constructing a spatially segregated FeCu/ZSM-CI catalyst. For comparison, a series of FeCu catalysts were prepared using different synthetic approaches (see Supplementary Information). Methane directly oxidation to methanol (DOM) was employed as a model reaction to investigate the gradient H 2 O 2 activation mechanism. To evaluate the catalytic performance of FeCu/ZSM-CI, direct oxidation of methane was conducted using H 2 O 2 as the oxidant in a 50 mL autoclave reactor at 80°C. Control experiments confirmed that no reaction occurred with alternative oxidants (e.g., O 2 ) or in the absence of H 2 O 2 , CH₄, or the catalyst (Table S1 ), demonstrating that both H 2 O 2 and the catalyst are indispensable for methane conversion. After optimizing key parameters (Fig. S1 -3), including H 2 O 2 concentration, reaction temperature, methane pressure, catalyst dosage, and time, the best performance was achieved under the following conditions: 20 mL of 0.1 M H 2 O 2 , 10 mg of catalyst, 80°C, 3.5 MPa CH₄ pressure, and a 3 hour reaction time. Under these conditions, FeCu/ZSM-CI exhibited exceptional activity, producing CH 3 OH at a yield of 20.20 mmol g cat −1 h − 1 with 90.1% selectivity (Fig. 1 A). To study the influence of metal type on the catalysis performance, monometallic decorated H-ZSM-5 catalysts were employed under the optimal reaction conditions mentioned above (Fig. 1 A). When catalyzed by Fe/ZSM-I (Fe primarily located on the external surface of ZSM-5), the yield of total C 1 oxidation was 12.11 mmol g cat −1 h − 1 , higher than those of Cu/ZSM-I (2.22 mmol g cat −1 h − 1 ) and pure H-ZSM-5 (0.64 mmol g cat −1 h − 1 ). Similar results could also be observed in Fe/ZSM-C (16.12 mmol g cat −1 h − 1 ) and Cu/ZSM-C (1.89 mmol g cat −1 h − 1 ). This suggests that the metal active site plays a crucial role in CH 4 conversion, and Fe is more effective than Cu regardless of whether the catalyst was prepared through impregnation or crystal seed method. However, when catalyzed by Fe/ZSM-I, HCOOH was the main liquid product, and the selectivity of CH 3 OH was only 18.4%, which is much lower than that of Cu/ZSM-I (98.6%). When the Fe site was changed from external surface to inner pores in Fe/ZSM-C, the selectivity of CH 3 OH increased to 41.6%, but it still remained lower than that of Cu/ZSM-C (96%). It indicates that Cu could maintained high methanol selectivity, and metal location could also influence methanol selectivity. Therefore, combining both Fe and Cu may improve both the yield and selectivity of methanol. Further studies were conducted to investigate the influence of Fe and Cu location on catalytic performance. FeCu/ZSM-CC (simultaneous in-situ growth of Fe and Cu metals) achieved 89.1% selectivity for CH 3 OH, but the yield was only 10.36 mmol g cat −1 h − 1 (Fig. 1 A). This low yield may be due to competitive adsorption of CH 4 and H 2 O 2 at Fe and Cu sites within a confined space. The unsatisfactory CH 3 OH yield (9.57 mmol g cat −1 h − 1 and 77.1%) observed for FeCu/ZSM-II (simultaneous impregnation of metals Fe and Cu) may also be attributed to this reason. Additionally, FeCu/ZSM-II has lower yield and selectivity for CH 3 OH than FeCu/ZSM-CC, suggesting different locations in H-ZSM-5 may have distinct reaction processes. As Fe promotes methanol conversion and Cu enhances methanol selectivity, the presence of both Fe and Cu in different locations may increase the yield and selectivity of methanol simultaneously. The yield and selectivity of CH 3 OH for FeCu/ZSM-IC ( in-situ growth of Cu and then impregnation anchoring of Fe) was only 69.3% and 7.86 mmol g cat −1 h − 1 . In contrast, FeCu/ZSM-CI ( in-situ growth of Fe and impregnation anchoring of Cu) exhibited significant improvement with a much higher yield and selectivity of CH 3 OH at 90.1% and 20.20 mmol g cat −1 h − 1 , surpassing other catalysts. Generally, H 2 O 2 and CH 4 follow Fick’s diffusion law in ZSM-5 pores, with lower concentration in the inner pores than the external surface. Therefore, Fe with higher methanol conversion ability was placed in inner pores with lower concentrations of CH 4 and H 2 O 2 , while Cu with lower methanol conversion ability but higher CH 3 OH selectivity was placed on external surface with higher concentrations of CH 4 and H 2 O 2 . This arrangement facilitates gentle and effective utilization of H 2 O 2 while preventing overoxidation. The utilization efficiency of H 2 O 2 is estimated to reach 74.6%. To ensure a fair comparison of methanol selectivity among the FeCu/ZSM-CI, FeCu/ZSM-CC, FeCu/ZSM-II, and FeCu/ZSM-IC samples, evaluations were conducted at an equivalent activity level (~ 25–27 mmol g cat −1 h − 1 , Fig. S4). FeCu/ZSM-CI exhibited outstanding methanol selectivity, exceeding 90%, which is significantly higher than that of the other catalysts. This effectively demonstrates the advantage of the configuration where Fe species are located inside the zeolite framework and Cu species are distributed on the external surface in enhancing methanol selectivity. Subsequently, kinetic measurements were performed to investigate the origin of the activity differences (Fig. 1 B). FeCu/ZSM-CI exhibited the lowest apparent activation energy (E a ) of 78.4 kJ mol − 1 , followed by FeCu/ZSM-II (83.8 kJ mol − 1 ), FeCu/ZSM-CC (85.9 kJ mol − 1 ), and FeCu/ZSM-IC (99.8 kJ mol − 1 ). These results indicate that precise spatial positioning of Fe and Cu dual atoms not only ensures high catalytic activity but also significantly enhances methanol selectivity. To verify the heterogeneous nature and stability of the catalyst, a series of control experiments were conducted. In the absence of catalyst, as well as in the presence of iron acetylacetonate, FeCl 2 , Cu(NO 3 ) 2 , or their mixtures, no catalytic activity was observed (Table S3). Hot filtration tests further confirmed the heterogeneous nature of the catalytic system, as no additional product formation was detected after 1 hour of reaction following catalyst removal (Fig. S5). Moreover, FeCu/ZSM-CI demonstrated excellent recyclability, with no significant loss in CH 3 OH yield or selectivity over eight consecutive reaction cycles (Fig. 1 C). Inductively coupled plasma (ICP) analysis revealed negligible leaching of Fe and Cu species after the reaction (Table S4), further confirming the structural robustness of the catalyst. Overall, FeCu/ZSM-CI exhibits high stability under reaction conditions for methanol production, and its catalytic performance surpasses that of most previously reported catalysts (Fig. 1 D, E). Characterization of FeCu/ZSM-CI Catalyst To elucidate the structural properties of the as-prepared catalysts, comprehensive characterizations were conducted. The XRD pattern of FeCu/ZSM-CI (Fig. S6) retains characteristic ZSM-5 framework peaks, confirming high dispersion of Fe and Cu species within the zeolite matrix. Consistent with this, HRTEM and SEM-EDS mapping (Fig. S7-S10) revealed no detectable nanoparticles or clusters, indicating atomic-scale anchoring of metals on H-ZSM-5. Strikingly, atomic-resolution AC-HAADF-STEM imaging of Fe/ZSM-C, Cu/ZSM-I, and FeCu/ZSM-CI (Fig. 2 A-C) unveiled a distinct spatial arrangement: Fe species predominantly reside within internal zeolite channels, while Cu species enrich the external surface. To quantify this distribution, semi-quantitative SEM-EDS mapping measured surface Fe and Cu contents at 0.08 wt% and 0.49 wt%, respectively. In contrast, bulk ICP-AES analysis yielded 0.67 wt% Fe and 0.50 wt% Cu (Table S3). The significant disparity in Fe content (surface vs. bulk) strongly supports the encapsulation of Fe within internal channels, while the consistent Cu concentration indicates its predominant surface anchoring. As the electronic properties of active sites are determined by their structures and coordination environments, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy were applied for further investigation (Fig. S11-13). XPS revealed that Fe is present in the + 3 oxidation state, as indicated by peaks at 711.3 eV and 724.5 eV corresponding to Fe2p 3/2 and Fe2p 1/2 , respectively ( 38 , 39 ) (Fig. S11). The Cu valence state was found to be between + 1 and + 2 based on a peak centered at 933.5 eV in the Cu2p 3/2 spectra (Fig. S12), which is higher than that of Cu + but lower than Cu 2+ ( 40 , 41 ). For further exploring the coordination environment of Fe and Cu species, XAFS analysis was performed (Fig. S13A), Fe K-edge of X-ray Absorption Near Edge Structure (XANES) showed that the Fe absorption edge at 7115 eV is similar to that of Fe 2 O 3 , indicating the valent state of Fe is + 3. At the same time, the peak corresponding to the characteristic leading edge of the Fe element at 7114 eV attributed to Fe 2 O 3 is not obvious, indicating that its structure does not conform to that of a binuclear iron tetrahedron of Fe 2 O 3 ( 42 ). Simultaneously, it was demonstrated that the Fe sites did not substitute for aluminum during the synthesis process, thereby preserving the integrity of the molecular sieve framework; instead, they were situated externally to the structure. The coordination environment was analyzed using EXAFS curve fitting techniques, which revealed two prominent peaks relating to Fe-O scattering at distances of 1.6 Å and 2.6 Å (Fig. S14) with coordination numbers of 3.1 and 2.8 respectively (Table S5); no peaks associated with Fe-Fe or Fe-O-Fe scattering were detected (Fig. S13B). The Fourier Transform (FT) K 3 -weighted extended EXAFS spectrum for iron was analyzed using the Fe-O backscattering path (Fig. S14). The optimal fitting results indicate that the Fe-O bond corresponding to a coordination number of 3.1 at a distance of 1.6 Å pertains to Fe-O-H, which corresponds to the peaks of 715.7 eV and 728.0 eV attributed to Fe(OH)x (where x = 1, 2, or 3) shown in the XPS spectra (Fig. S11) ( 38 ). While the bond corresponding to a coordination number of 2.8 at a distance of 2.6 Å is attributed to Fe-O-Al. It can be seen that the Fe within the FeCu/ZSM-CI catalyst is classified as extra-framework mononuclear iron, exhibiting a total coordination number of 6, specifically anchored to the inner pores in the form of a single atom. Similarly, the XANES spectrum of the Cu element reveals that the absorption edge for Cu (Fig. 13C) is situated between that of Cu 2 O and CuO. Notably, there is no discernible peak at 8977 eV, indicating that the copper present in FeCu/ZSM-CI does not exhibit a high oxidation state. This observation aligns with the XPS data phase revealing Cu 𝛿+ (1 < 𝛿 < 2) (Fig. S12). Additionally, in the EXAFS spectrum (Fig. 13D) corresponding to the Cu site, a characteristic peak related to the Cu-O bond can be identified, with its value measured at 1.57 Å. Upon fitting the Cu-O backscattering path, it was determined that the coordination number of cupric ions is 3 (Fig. S14, Table S5). The presence of Fe and Cu as isolated single atoms was further confirmed by wavelet transform (WT) analysis (Fig. S15-S16). Additionally, a series of characterizations (XRD, UV, IR and XANES) of the reaction after reaction (Fig. S17-21), reveals that the Fe and Cu sites within the catalyst are still anchored within molecular sieve channels after cycling experiments since there were no observed changes in their structure or morphology. In summary, The FeCu/ZSM-CI catalyst achieves precise spatial control of atomically dispersed Fe (inside) and Cu (outside) sites through a combined seed-impregnation synthesis. The resulting dual monatomic structure, characterized by its distinct spatial metal sites, facilitates efficient utilization of the H 2 O 2 gradient while optimizing the reaction pathway for methane. Ultimately, this leads to enhanced selectivity and yield in converting methane to methanol. Catalytic Mechanism Identification of the Active Species During the activation of H 2 O 2 , the metal site catalyzes the homolysis or heterolysis of H 2 O 2 , generating reactive species such as •OH, •OOH radicals, and high-valent metal-oxo compounds. To identify the reactive species in the FeCu/ZSM-CI and H 2 O 2 system, electron paramagnetic resonance (EPR) analysis was conducted. As shown in Fig. 3 A, when 2,2-dimethyl-1-oxido-3,4-dihydropyrrol-1-ium (DMPO) was used as the trapping agent, only the signals of DMPO-OH and DMPO-•O 2 − adducts were observed in the aqueous solution. In the absence of H 2 O 2 , no •OH or •CH 3 were generated under any experimental conditions tested (Fig. S22). When H 2 O 2 was added without the catalyst (Fig. 3 B), and the signal of •OH was detected. After introducing methane, only the •OH signal remained. However, when the catalyst was added, signals corresponding to both •OH and •CH 3 appeared, indicating that methane activation is not dominated by •OH and that the cleavage of the C-H bond relies on FeCu metal species. Since •OH can oxidize dimethyl sulfoxide (DMSO) to DMSO-OH, while high-valent metals (Fe = O) can oxidize DMSO to DMSO 2 (Fig. S23) ( 43 ). In the DMSO oxidation system (Fig. 3 C), both Fe/ZSM-C and FeCu/ZSM-CI catalysts are capable of oxidizing DMSO to DMSO 2 , whereas the H 2 O 2 and the Cu/ZSM-I catalyst alone cannot. This indicates that Fe is oxidized to a high-valent Fe = O species during the process. Subsequently, scavenging experiments were conducted to identify the primary reactive species involved in the reaction (Fig. 3 D). Salicylic acid was used to quench the •OH, p-benzoquinone as a scavenger for •O 2 − , and DMSO was employed to quench high-valent metal-oxo species ( 44 , 45 ). Upon addition of DMSO, the total methanol yield over FeCu/ZSM-CI decreased significantly from 22.40 mmol g cat −1 h − 1 (without DMSO) to 7.40 mmol g cat −1 h − 1 , indicating the critical role of high-valent metal-oxo species. Complementary in-situ CV revealed characteristic redox peaks at 0.5–0.7 V for Fe/ZSM-C and FeCu/ZSM-CI following H 2 O 2 addition (Fig. 3 E, S24), which were absent in the Cu/ZSM-I sample. These distinct electrochemical responses provide direct evidence for the dynamic valence state cycling of Fe species during catalysis. The addition of other scavengers also led to notable reductions in liquid product yield. Meanwhile, in-situ EPR analysis revealed a much stronger •CH 3 signal over the Fe/ZSM-C catalyst compared to Cu/ZSM-I (Fig. S25) ( 46 ), suggesting that high-valent Fe centers are the primary active sites for C-H bond activation, while •OH and •O 2 − radicals play essential roles in methanol formation. With the assistance of H 2 O 2 , metal sites within molecular sieves can generate high-valent metal-oxo species and produce •OH/•O 2 − radicals, both of which are capable of activating the C-H bond in methane and promoting methanol formation through subsequent radical-mediated pathways. To optimize C-H activation efficiency and product selectivity, it is essential to elucidate the mechanisms of H 2 O 2 activation at different metal sites and establish correlations between reaction selectivity and the nature of the generated radical species. The Influence of Fe, Cu Sites on Selective H 2 O 2 Evolution into ROS Next, how Fe and Cu sites affect the selective generation of free radicals was carefully studied. Coumarin reacts with •OH to produce 7-hydroxycoumarin, a highly fluorescent species ( 44 ). Plotting fluorescent luminescence (FL)-t curves can assist in semi-quantifying the Cu and Fe sites’ catalyzed •OH generation rate (Fig. 3 E). The catalysts containing Cu (FeCu/ZSM-CI, Cu/ZSM-I and Cu/ZSM-C) exhibit similar PL intensity, significantly greater than that of only containing Fe catalyst (Fe/ZSM-C and Fe/ZSM-I), indicating that •OH primarily originates from H 2 O 2 conversion at the Cu site. Subsequently, the production rate of •OOH was quantified by plotting the conversion of nitrotetrazolium chloride blue (NBT)-t curves (Fig. 3 F) ( 23 ). Fe containing catalyst (e.g. FeCu/ZSM-CI, Fe/ZSM-C and Fe/ZSM-I) show the higher slope than that of only Cu containing catalyst (Cu/ZSM-I and Cu/ZSM-C), suggesting that •OOH primarily originates from the H 2 O 2 conversion at the Fe site (Fig. 3 G). When the ratio of Fe and Cu is adjusted from 3:1 to 1:2.5, the highest content of •OH and •O 2− /•OOH occurs at a ratio of 1:1 (Fig. S26). Furthermore, the position of metal active site (e.g. inside and outside) were also important for efficient utilization of H 2 O 2 and selective conversion of CH 4 . When quantifying different free radicals using benzoic acid and NBT, •OH is preferentially detected (Fig. S26D). This is because that the concentration gradient of H 2 O 2 decreases from the o outside to the inside during diffusion in the molecular sieve. Cu sites have a slower H 2 O 2 conversion rate, but can balance •OH production in the outside with higher H 2 O 2 concentration. Fe sites have a fast H 2 O 2 conversion rate and efficient utilization of H 2 O 2 into •O 2 − /•OOH when in the inside with lower H 2 O 2 concentration. This distribution of Fe and Cu prevents over-oxidation by maintaining appropriate concentrations of •O 2 − /•OOH and •OH. The FeCu catalyst demonstrated exceptional H 2 O 2 utilization efficiency (74.6%) (Fig. S27), the highest among all tested catalysts. This dual-metal promoted gradient decomposition of H 2 O 2 not only enhances methanol selectivity but also significantly improves the overall oxidant utilization efficiency. The synergistic effect between Fe and Cu sites facilitates a controlled decomposition pathway, minimizing unproductive H 2 O 2 dissociation while maximizing its conversion to active oxygen species for selective methanol formation (Fig. 3 I). Theoretical Investigation on the Evolution Path from Methane to Methanol In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy ( in-situ DRIFTS) was employed to identify methane oxidation intermediates catalyzed by FeCu/ZSM-Cl at 80°C during selective methane conversion (Fig. 4 A). After introducing water vapor with H 2 O 2 , peaks at 3365 cm − 1 , 3227 cm − 1 , and 1624 cm − 1 , corresponding to •OOH, •OH, and •OH 2 , gradually strengthened ( 47 ). Upon adding methane continuously, the peak at 1458 cm − 1 belonging to •CH 3 became apparent along with strong characteristic peaks attributed to •OCH 3 and •COOH observed at 2823 cm − 1 and 3576 cm − 1 respectively ( 48 ). As the reaction progressed, these two characteristic peaks increased less while those at 1061 cm − 1 corresponding to C-O bond in CH 3 OH continued increasing ( 33 , 48 ). Associated with 1 H-NMR results that show trace amounts of CH 3 OOH in the product (Fig. S28), it indicates that CH 3 OH is converted from the intermediates of CH 3 OOH ( 22 ). The hydroxyl group in CH 3 OH may form through two distinct mechanisms: ( 1 ) direct coupling between •CH 3 and •OOH/•OH radicals generated from H 2 O 2 decomposition, or ( 2 ) direct insertion of O* species into the C-H bond. To elucidate the reaction pathway, isotopic labeling experiments were conducted using D 2 O + H 2 O 2 + CH 4 and H 2 O + H 2 O 2 + CD 4 systems (Fig. S29). The experimental results unambiguously show that the hydrogen in methanol's hydroxyl group exclusively originates from H 2 O 2 , demonstrating that the hydroxyl formation proceeds via active oxygen species from H 2 O 2 decomposition rather than through direct O* insertion into C-H bonds. Identifying the rate-determining step (RDS) in a reaction is crucial for precisely enhancing the overall reaction rate. The kinetic isotope effect (KIE) of CH 3 OH product reveals that the k H /k D value is 1.15 for Fe/ZSM-C and 1.31 for Cu/ZSM-I (Fig. 4 B-E), both close to 1. This suggests that C-H bond activation has minimal influence on the reaction rate, confirming that H 2 O 2 activation is the RDS for both Fe/ZSM-C and Cu/ZSM-I. In contrast, FeCu/ZSM-CI exhibits a significantly higher k H /k D value of 2.32, indicating that C-H bond activation plays a more dominant role in catalytic activity. This confirms that C-H bond activation is the RDS for FeCu/ZSM-CI. A similar phenomenon was observed in the KIE (HCOOH) studies (Fig. S30, S31). Overall, due to the synergistic interaction between Fe and Cu dual single atoms, the RDS shifts from H 2 O 2 activation to C-H bond activation. The enhanced generation of reactive oxygen species via H 2 O 2 activation provides more active sites for methane oxidation, thereby boosting catalytic performance. After confirming the important intermediates of CH 3 OOH, DFT calculation were used to study the activation and transformation processes of CH 4 at functional Fe, Cu sites, respectively (Fig. 5 A, B, S32, S33). The reaction can be divided into three stages due to the spatial and functional differences between Fe and Cu sites: ( 1 ) diffusion and evolution of H 2 O 2 , ( 2 ) effective activation and conversion of methane, ( 3 ) migration and conversion of intermediates. ( 1 ) When H 2 O 2 diffuse through the molecular sieve from the outside to the inside, it passes by Cu and Fe sites in succession, resulting in a gradient reduction of H 2 O 2 concentration. Both Cu and Fe sites require a similar energy barrier (Fe : 0.26 eV / Cu : 0.29 eV) to absorb H 2 O 2 , but Cu only needs to overcome an additional energy barrier of 0.07 eV to decompose H 2 O 2 into •OH, which is much higher than that required for decomposition into •OOH (-0.3 eV) catalyzed by Fe. Due to spatial priority, Cu weakly decomposes H 2 O 2 into •OH, making the concentration of •OH radical in the external large pores enrich slowly. The residual H 2 O 2 concentration decreases significantly after diffusing into the inner small pores, leading to slower interaction with the Fe site and selective generation of mild ROS, specifically •OOH species. ( 2 ) H 2 O 2 decomposes at the mental site and forms a high-valence Fe-O bond. Both the initial energy required for the adsorption of CH 4 at the Fe and Cu sites (Fe : 0.23 eV / Cu : 0.32 eV) and the corresponding free energy change during the subsequent release of •CH 3 (Fe : -0.03 eV / Cu : 0.92 eV) indicate that methane activation is more favorably influenced by Fe sites compared to Cu sites. Therefore, methane activation occurs primarily at the Fe site, where it is effectively abstract H on the Fe = O site, leading to C-H bond dissociation and resulting in •CH 3 free radicals as shown in TS3 (Fig. 5 B). The released •CH 3 free radicals accumulate and react with significant number of •OOH species along with a smaller quantity of migrating •OH free radicals present in solution to form CH 3 OOH and CH 3 OH. ( 3 ) Cu’s high electron density causes it to adsorb the terminal O in CH 3 OOH and break the bond of O-O easily, resulting in •OCH 3 . This then reacts with an H proton to form CH 3 OH as a product. Compared to the 0.32 eV energy needed for CH 4 adsorption and activation on Cu sites, only a 0.19 eV energy barrier must be overcome for effective CH 3 OOH adsorption. Additionally, only 1.11 eV of energy input is required to advance into the rate-limiting step TS2. This approach offers significant advantages in terms of efficiency and variations in free energy profiles. Additionally, the re-adsorption of CH 3 OH at the Cu site poses significant challenges, and achieving effective deep oxidation of CH 3 OH solely with •OH remains difficult. Ultimately, all produced CH 3 OH is fully desorbed from the molecular sieve into the solution system, resulting in high yield and selectivity for CH 3 OH products (Fig. 5 C). Conclusions This work demonstrates that spatially engineering dual single-atom Fe and Cu sites within the hierarchical pore network of ZSM-5 enables gradient-controlled H 2 O 2 activation, allowing for both efficient C-H bond activation and selective methanol production from methane under mild conditions. By decoupling ROS evolution across pore domains high-valent Fe = O species and •OOH in the micropores for methane activation, and Cu-mediated •OH reactions on the external surface for CH 3 OH formation overoxidation is suppressed while maximizing H 2 O 2 utilization. The FeCu/ZSM-CI catalyst achieves a rare combination of high activity, selectivity, and oxidant efficiency. Mechanistic insights from isotopic, spectroscopic, and theoretical studies reveal a shift in the rate-determining step from oxidant activation to C-H activation due to Fe-Cu synergy. These findings establish spatial site isolation as a general and scalable strategy for regulating ROS pathways in alkane oxidation, offering new design principles for sustainable catalytic conversions of inert molecules. Materials and Chemicals Iron acetylacetonate (Fe(C 5 H 7 O 2 ) 3 , AR, 99%, Macklin) and Copper (II) nitrate Gerhardite (Cu(NO 3 ) 2 3H 2 O, AR, 99%, Macklin) were used as metal precursors. Sodium aluminum oxide (Al 2 Na 2 O 4 , AR, 98%, Macklin), Sodium hydroxide (NaOH, 95%, graininess, Macklin) Silicasol (Silica content: 29% ~ 31%, Macklin) and Ammonium chloride (NH 4 Cl, AR, 99.99%, Macklin) were used as a raw material for the synthesis of H-ZSM-5. Hydrogen peroxide (H 2 O 2 , AR, 30%, Macklin) was used as the oxidizing agent. Methane (99.999 vol.%, Qingdao Xin ke yuan) was used as the feedstock gases. All chemicals were used as received without any further purification. Deionized water was used throughout the research. Catalyst Synthesis. Fe acetylacetone was chosen as the source to incorporate Fe into inner small pores due to its similar size and ability to be confined in the micropores. The stable coordination structure of Fe acetylacetone reduces its reaction with Si and Al sources, while the residual Fe acetylacetone in the external large pores can be eliminated by washing away because of its slightly solubility in water. Fe species were grown in-situ using the crystal seed method and then calcined to produce Fe/ZSM-C. Cu species were added through impregnation, resulting in FeCu/ZSM-CI, where C and I denote the sequence of crystal seed method and impregnation method for Fe and Cu respectively. To conduct control experiments, a series of catalysts decorated with different combinations of metals (e.g., Fe/ZSM-C, Cu/ZSM-I, CuFe/ZSM-CI) were obtained by varying metal types, ratios and introduction methods. Initially, Fe site was grown in-situ using the crystal seed method to fix it in the inner small pores of ZSM-5. To achieve this, Fe acetylacetone was chosen as its size is similar to that of the micropore. Residual Fe present in external large pores (such as mesoporous) was mostly eliminated by washing with water after hydrothermal synthesis. The above precursor was then obtained through calcination and named Fe/ZSM-C (C refers to crystal seed method). Next, Cu(NO 3 ) 2 solution was used for impregnation on Fe/ZSM-C under controlled conditions resulting in a catalyst called FeCu/ZSM-CI (I stands for impregnated method). Synthesis of Fe/ZSM-C. Fe/ZSM-C was synthesized using crystal seed method. This synthetic procedure comprised two steps: the synthesis of ZSM-5 seeds and the synthesis of Fe-ZSM-5. In the first step, 15 g of Silica sol was dissolved in 7 mL of a NaOH solution (1 mol/L) under constant stirring at 100°C for 1 h. Simultaneously, a solution was prepared by dissolving 0.45 g of sodium aluminate oxide in 7 mL of a NaOH solution (1 mol/L). The amalgamation of these two solutions resulted in the formation of a synthetic aluminosilicate gel with a molar composition of 4Na 2 O : 1Al 2 O 3 : 36SiO 2 : 460H 2 O. The gel underwent stirred vigorously at 100°C for 2 h and was then transferred to a stainless-steel autoclave for crystallization at 180°C for 48 h. The resultant crystals were collected by filtration, cleaned with deionized water until the pH of the filtrate is neutral. Subsequently, the obtained crystals were dried at 100°C to produce the ZSM-5 seeds. In the second step, a synthetic aluminosilicate gel was prepared using the same method as described in the first step. 2 mL of an aqueous solution containing 0.21 g of iron acetylacetonate and 0.06 g of seeds were added sequentially to the gel, followed by 30 min of stirring. The mixture was then transferred to an autoclave for crystallization at 180°C for 48 h. After crystallization, the hydrothermal catalyst was placed in a beaker, to which 200 mL of deionized water was added. The mixture was at 80 ℃ for 12 h to remove the residual iron acetylacetone. The catalyst was washed and filtered with a large amount of deionized water until the filtrate presents a clear color, and the present of Fe ions are determined using KSCN. Washing and filtration were stopped when no iron acetylacetone was detected in the filtrate. The filter cake was dried at 80 ℃ to obtain the synthesized Fe/ZSM-C. Finally, Fe/ZSM-C was converted to H-type Fe/ZSM-C through ion exchange with ammonium chloride at 80°C, followed by calcination in air at 550°C for 6 h. The Fe loading was determined by ICP-OES to be approximately 0.6 wt%. In the synthesis of H-ZSM-5, the only deviation from the standard procedure was the omission of iron acetylacetonate in the second step, while all other steps and conditions remained unchanged. The obtained H-ZSM-5 was used in the following other catalyst synthesis. Synthesis of Cu/ZSM-I. H-ZSM-5, synthesized using the seed method above, was used as the molecular sieve carrier. To prepared the catalyst, 1 g of synthetic H-ZSM-5 was suspended in 50 mL deionized water and fully stirred to obtain solution A. A certain amount of Copper (II) nitrate was dissolved in 10 mL deionized water, followed by ultrasonic treatment for 5 mins to ensure complete dissolution. The pH value of the solution was then adjusted to 3–4. The prepared copper nitrate solution was slowly added into solution A at a rate of 0.5 mL/min, followed by continuous stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The obtained catalyst was dried at 80°C, and then calcined at 550°C in the Muffle furnace for 6 h to obtain Cu/ZSM-I. Synthesis of FeCu/ZSM-CI. FeCu/ZSM-CI was prepared by introducing copper into Fe/ZSM-C as a precursor by the impregnation adsorption method. The procedure can be divided into two main steps. Take the metal load Fe / Cu (0.6 wt% / 0.6 wt%) as an example: First, the precursor Fe/ZSM-C was synthesized following the same method as described for Fe/ZSM-C above. After that, 1 g of the synthesized Fe/ZSM-C was placed in 50 mL deionized water and stirred thoroughly to obtain solution B. Then 0.02 g of Copper (II) nitrate was dissolved in 10 mL deionized water and ultrasonically treated for 5 mins to ensure complete dissolution. The pH of the solution to 3–4. The prepared copper nitrate solution was added into B solution at the rate of 0.5 mL/min, followed by stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The obtained catalyst was dried at 80 ℃ and then calcined at 550°C in muffle furnace for 6 hours to obtain FeCu/ZSM-CI. Synthesis of FeCu/ZSM-CC. The synthesis procedure is the same as Fe/ZSM-C, but the difference is that Iron acetylacetonate and Copper (II) nitrate are added at the same time. Synthesis of FeCu/ZSM-IC. The precursor of Cu-ZSM-5-C was synthesized using Copper (II) nitrate instead of Iron acetylacetonate, followed by the adsorption and impregnation of Fe. The procedure follows the same steps as described above. Synthesis of FeCu/ZSM-II. H-ZSM-5, synthesized using the seed method described above, was used as the molecular sieve carrier. 1.00 g of synthetic H-ZSM-5 was placed in 50 mL deionized water and stirred thoroughly to obtain solution C. A specific amount of Iron acetylacetonate and Copper (II) nitrate were dissolved in 10 mL deionized water, then ultrasonicated for 5 mins to ensure complete dissolution. The pH of the solution was adjusted to 3–4. The prepared copper nitrate solution was then added uniformly into solution A at 0.5 mL/min, followed by stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The resulting catalyst was dried at 80°C and then calcined at 550 ℃ in the muffle furnace for 6 h to obtain FeCu/ZSM-II. Catalyst Testing. The selective oxidation of methane experiment was carried out in a 50 mL high-pressure reactor. The catalyst (10 mg) was uniformly dispersed in 20 mL of distilled water and sonicated for 15 minutes. A specific amount of H 2 O 2 was added and the reactor was sealed. The reactor was purged with argon gas 3–5 times to replace the air. Then, methane was injected into the reactor to reach the required pressure. The reaction was carried out in an oil bath for 3 h. After the reaction, the reactor was cooled to below 10 ℃ using an ice bath, and both the gas and liquid were collected. Catalyst Characterization. X-ray Diffraction (XRD) was performed by the diffractometer (X’Pert PRO MPD, PANalytical, Netherland) with Cu Kα radiation (40 kV, 100 mA, λ = 0.154 nm). The morphology of materials was observed by Scanning electron microscope (SEM), whose model is JSM-7500F scanning electron microscopes (Japan). High-Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-ray Spectroscopy-mapping (EDS-mapping) images were captured using Tecni G30 instrument (FEI, USA). The morphology of the samples was further observed by Aberration Corrected High-Angle Annular Dark Field Scanning Transmission Electron Microscope (AC-HAADF-STEM, Themis Z, Thermo Scientific, USA). UV-Vis diffuse reflectance spectra were obtained from the spectrometer (UV-2700, Shimadzu, Japan) furnished with an integrating sphere device. Solid-state 27 Al Magic-Angle Spinning NMR ( 27 Al NMR MAS) cross polarization spectroscopy was measured on a JEOL ECA-600 spectrometer at a resonance frequency of 156.4 MHz using a 4 mm sample rotor with a spinning rate of 15.0 kHz. The 27 Al chemical shift was referenced to -0.54 ppm of AlNH 4 (SO 4 ) 2 ·12H 2 O. The information on the electronic states of the material surface was collected via the X-ray Photoelectron Spectrometer (XPS, ESCALAB 250Xi, Thermo Scientific, USA). The metal site structure of the catalyst materials was determined by X-ray Absorption Spectroscopy (XAS), whose date for Fe K-edge and Cu K-edge were collected at the 1W1B station of the Beijing Synchrotron Radiation Facility (BSRF), where the storage rings operated at 2.5 GeV with a maximum current of 250 mA. For Fe-containing and Cu-containing references (i.e., Fe foil, FeO, Fe 2 O 3 , Cu foil, Cu 2 O and CuO), data were collected in transmission mode using an ionization chamber, while for Fe-containing zeolites and Cu-containing zeolites, data were obtained in fluorescence excitation mode using a Lytle detector. The X-ray Absorption Near Edge Structure (XANES) and Fourier-transformed Extended X-ray Absorption Fine Structure (EXAFS) data were analyzed using ATHENA and ARTEMIS software, respectively, and MATLAB software was employed for the analysis of wavelet-transformed EXAFS data. In-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements were measured on the instrument (VERTEX70, Bruker, Germany), the mercury cadmium telluride (MCT) detector was adopted, and Ar was bubbled into H 2 O 2 when the temperature was raised and stabilized to 80°C. The background correction was stabilized, and CH 4 replaced Ar for testing. Electron Paramagnetic Resonance (EPR) spectra was measured on CIQTEK EPR200M (CIQTEK Co., Ltd.) with continuous-wave X band frequency, with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the radical trap. The samples were dispersed in H 2 O 2 aqueous solution dissolved CH 4 to detect •CH 3 , •O 2 − and •OH. Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES, Agilent 730, USA) was used to determine the metal contents. Temperature-Programmed Desorption measurements were carried out on Micromeritics AutoChemHP-2950. The Fluorescence Spectra were collected by the fluorescence spectrophotometer (RF-6000, Shimadzu, Japan). The gas chromatography (Scion 456C, Tianmei, China) is equipped with a thermal conductivity detector (TCD), two flame ionization detectors (FID), a methanizer, and a headspace autosampler (DK-5001A, Beijing Zhongxing, China), were used to quantify gaseous and CH 3 OH and CO 2 products. High-performance liquid chromatography (HPLC, Prominence-i, LC-2030 Plus, Japan) equipped with a Refractive Index Detector (RID) was used to quantify HCOOH products. UV-Vis diffuse reflectance spectra (UV-2700, Shimadzu, Japan) was used to quantify HCHO products. This combination of sophisticated techniques provided comprehensive information about the structure, composition, and catalytic behavior of the materials under study. Low temperature selective oxidation of methane. The methane carbonylation experiment was carried out in a 50 mL high-pressure reactor (Shi ji shen lang). The catalyst (10 mg) was uniformly dispersed in 20 mL of distilled water and sonicated for 15 minutes. A certain amount of H 2 O 2 was added and the reactor was sealed. The reactor was purged with argon gas to replace the air for 3–5 times. Then, methane was injected at the required pressure. The reaction was carried out in an oil bath for 3 h. After the reaction, the reactor was cooled to below 10 ℃ in an ice bath, and the gas and liquid were collected. Cyclic experiment. The recycle test followed the same procedure. After each run, the spent catalyst was separated, washed with a large amount of H 2 O then dried at 80 ℃ in the vacuum oven for the next cycle. The same amount of catalyst was used and repeated experiments were carried out under the same experimental conditions to verify the stability of the catalyst. Declarations Acknowledgments This work was supported by National Natural Science Foundation of China (22322815, 22179146, and 22138013), National Key Research and Development Program of China (NO.2019YFA0708700), the Fundamental Research Funds for Central Universities (18CX07009A), Independent Innovation Research Project (Science and Engineering) (20CX06072A). Author Contributions M.W. and W.W. conceived and supervised the project. 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Petroleum, Qingdao 266580","correspondingAuthor":false,"prefix":"","firstName":"chaoqun","middleName":"","lastName":"gu","suffix":""},{"id":485018709,"identity":"b80abef6-2364-444c-8ad1-2eec95aae03d","order_by":11,"name":"Yunyun Li","email":"","orcid":"","institution":"State Key Laboratory of Heavy Oil Processing, College of Chemistry and Chemical Engineering","correspondingAuthor":false,"prefix":"","firstName":"Yunyun","middleName":"","lastName":"Li","suffix":""},{"id":485018710,"identity":"f1055cb6-a261-4c82-9b4b-397a06d99307","order_by":12,"name":"qi hua","email":"","orcid":"","institution":"State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580","correspondingAuthor":false,"prefix":"","firstName":"qi","middleName":"","lastName":"hua","suffix":""},{"id":485018711,"identity":"37b37b46-3b05-4cc8-933f-85d1a7b956e1","order_by":13,"name":"Mingbo Wu","email":"","orcid":"https://orcid.org/0000-0003-0048-778X","institution":"China University of Petroleum (East China)","correspondingAuthor":false,"prefix":"","firstName":"Mingbo","middleName":"","lastName":"Wu","suffix":""}],"badges":[],"createdAt":"2025-07-01 08:22:03","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7017740/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7017740/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s41467-026-70179-8","type":"published","date":"2026-03-05T05:00:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":86742682,"identity":"9d79470f-2357-4620-8a7d-22a064fc9db7","added_by":"auto","created_at":"2025-07-15 07:13:26","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":414506,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCatalytic performances for direct oxidation of methane. \u003c/strong\u003e(A) Liquid product yields and methanol selectivity on different catalysts. (B) Arrhenius plots for CH\u003csub\u003e4\u003c/sub\u003e oxidation over FeCu/ZSM-CI, FeCu/ZSM-CC, FeCu/ZSM-II, and FeCu/ZSM-IC. (C) Cyclic experiment. Reaction Condition: 10 mg catalysts dispersed in 20 mL of 0.1 mol/L H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e aqueous solution, 80 °C and 35 bar CH\u003csub\u003e4\u003c/sub\u003e. (D-E) Comparisons with the representative catalytic performances for methanol yield and selectivity. Numbers in square brackets correspond to the entry numbers in Table S2.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/bd574eb77167c271bc555da3.png"},{"id":86742684,"identity":"54d0e490-7025-40c1-ae7c-52ed719becd1","added_by":"auto","created_at":"2025-07-15 07:13:26","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":321396,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCharacterization of FeCu/ZSM-CI.\u003c/strong\u003e (A-C) Atomic-resolution AC-HAADF-STEM image and HRTEM-EDS mapping of the Fe/ZSM-C, Cu/ZSM-I, and FeCu/ZSM-CI. (D) XANES spectra at Fe K-edge of FeCu/ZSM-CI in comparison with Fe foil, FeO and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. (E) Fourier transform (FT) k\u003csup\u003e3\u003c/sup\u003e-weighted EXAFS spectra of FeCu/ZSM-CI in comparison with Fe foil, FeO and Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. (F) XANES spectra at Cu K-edge of FeCu/ZSM-CI in comparison with Cu foil, Cu\u003csub\u003e2\u003c/sub\u003eO and CuO. (G) Fourier transform (FT) k\u003csup\u003e3\u003c/sup\u003e-weighted EXAFS spectra of FeCu/ZSM-CI in comparison with Cu foil, Cu\u003csub\u003e2\u003c/sub\u003eO and CuO. (h) Models of FeCu/ZSM-CI.\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/b23b3ba67b083815311853d5.png"},{"id":86743343,"identity":"a310c015-42df-473e-af8b-e89404088ad2","added_by":"auto","created_at":"2025-07-15 07:21:26","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":310593,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eActivation of methane and the Evolution of H\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eO\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e2\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e into ROS. \u003c/strong\u003e(A) EPR spectra of FeCu/ZSM-CI. (B) EPR spectra of FeCu/ZSM-CI under different reaction conditions. (C) \u003csup\u003e1\u003c/sup\u003eH-NMR spectrum of DMSO oxidation. (D) Quenching experiments. (E) \u003cem\u003eIn-situ\u003c/em\u003e CV tests of catalysts for H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation. (F) PL spectra of 7-hydroxycoumarin by •OH under different catalysts. (G) NBT degradation experiment spectra by •O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e under different catalysts. (H) The ratio of •O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e and •OH generated on FeCu/ZSM-CI. (I) Decomposition pathways of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at FeCu/ZSM-CI metal sites.\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/a23a1d573842d2e9a8156ef7.png"},{"id":86742687,"identity":"458efa35-8ec6-4b33-9e3b-40fd5df52257","added_by":"auto","created_at":"2025-07-15 07:13:26","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":470436,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe conversion of CH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003e to CH\u003c/strong\u003e\u003csub\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003c/sub\u003e\u003cstrong\u003eOH over FeCu/ZSM-CI. \u003c/strong\u003e(a) \u003cem\u003eIn-situ\u003c/em\u003e Diffuse Reflectance Infrared Fourier Transform Spectroscopy (\u003cem\u003ein-situ\u003c/em\u003e DRIFTS) spectra of CH\u003csub\u003e4\u003c/sub\u003e on FeCu/ZSM-CI catalyst at 80 ℃. (B-D) Kinetic isotope effect experiment of CH\u003csub\u003e4\u003c/sub\u003e oxidation to CH\u003csub\u003e3\u003c/sub\u003eOH over Fe/ZSM-C, Cu/ZSM-I and FeCu/ZSM-CI. (E) Kinetic isotope effect experiment of CH\u003csub\u003e3\u003c/sub\u003eOH production over as-prepared catalysts.\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/0c9380614c8bc28004d08b94.png"},{"id":86744351,"identity":"12c126be-73fd-405a-994c-b842ae67db02","added_by":"auto","created_at":"2025-07-15 07:29:26","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":665637,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTheoretical research on the selective production of methanol from methane. \u003c/strong\u003e(A) Energy profiles for the conversion of CH\u003csub\u003e4\u003c/sub\u003e to CH\u003csub\u003e3\u003c/sub\u003eOOH over Fe sites. (B) Energy profiles for the conversion of CH\u003csub\u003e3\u003c/sub\u003eOOH to CH\u003csub\u003e3\u003c/sub\u003eOH over Cu sites. (C) Diagram of the process of low temperature and high selectivity conversion of methane to methanol.\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/9d88d9567f9e14ef5192c15b.png"},{"id":107130547,"identity":"2ab14ebf-cf34-48a4-aa9d-6ee54e16be2f","added_by":"auto","created_at":"2026-04-17 07:07:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3062475,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/28c9772b-efbc-40c3-8416-87731d69b9de.pdf"},{"id":86743344,"identity":"d05ad23c-3934-4600-8acb-533a0a4bfc9d","added_by":"auto","created_at":"2025-07-15 07:21:26","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":11077149,"visible":true,"origin":"","legend":"Supplementary Information","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-7017740/v1/a05ee762f8433310b2892e5d.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"\u003cp\u003eFeCu Dual-Single-Atom Catalyst Promotes Gradient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e Activation for Enhanced Methane Oxidation to Methanol\u003c/p\u003e","fulltext":[{"header":"Introduction","content":"\u003cp\u003eHydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e) is a commonly used oxidant in chemical synthesis and is regarded as one of the top 100 most important chemicals globally due to its effectiveness and eco-friendliness (\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e). However, improving both selectivity and rate simultaneously can be challenging, particularly for selectively oxidizing inert alkane (\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e). Excessive use of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is often employed to enhance the conversion rate, but this reduces the selectivity and efficiency of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization (\u003cspan additionalcitationids=\"CR9 CR10\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). This rises from two main issues: first, single reactive oxygen species (ROS) cannot effectively activate and selectively convert C-H bonds of inert alkane independently, despite many excellent works have been devoted into the selective conversion of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into specific ROS, such as superoxide radicals (\u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e/\u0026bull;OOH), hydroxyl radicals (\u0026bull;OH) and high valent metal-oxygen species (M-O) (\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e). For example, \u0026bull;OH and high-valent metal-oxygen sites have a strong ability to activate C-H bonds in alkanes, and have the ability to selective conversion C-H bond at low concentration (\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e), but they tend to over-oxidize into acid or CO\u003csub\u003e2\u003c/sub\u003e if their concentration increases for enhancing the reaction rate (\u003cspan additionalcitationids=\"CR16\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e). This leads to the second issue that high concentrations of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e or ROS do not always match those of reactants (\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e). To date, almost no strategy has been proposed to systematically solve the matching problem of the distribution, concentration and kinds of ROS with reactants.\u003c/p\u003e\u003cp\u003eThe fast expansion of renewable energy facilitates a shift from natural gas, a conventional energy source, to chemical feedstocks (\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e). Since methane (primary component of natural gas) is usually located in distant and dispersed areas, it is better to directly oxidize it into methanol with low boiling point and easy separation for convenient transportation and storage, rather than using the conventional method of reforming it into syngas at high temperatures and then Fischer-Tropsch synthesis (\u003cspan additionalcitationids=\"CR23\" citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e). Molecular sieves are crucial catalysts (e.g. methane conversion) due to their diverse pore structures, which provide distinct reaction sites and ways to regulate reactant concentration (\u003cspan additionalcitationids=\"CR26\" citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e). ZSM-5, for example, possesses both inner small and external large pore structures. According to Fick\u0026rsquo;s law, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e diffuses more in external surface with higher concentrations and less in inner pores with lower concentrations (\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e). Therefore, by placing functional metal sites more precisely within the pores, ROS concentration can be controlled through diffusion rather than only adjusting H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e amounts.\u003c/p\u003e\u003cp\u003eWhat metal sites can efficiently promote H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e evolution for activating C-H bonds and selectively converting methane? Non-noble metal iron (Fe) nanoparticles or clusters incorporated within the nanopores of ZSM-5 can react with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and are prone to generate \u0026bull;OH for the activation of C-H bond (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e). Reducing Fe site size to binuclear Fe or individual Fe atom could promote the decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e from \u0026bull;OH to high valent Fe-O, significantly enhancing methane activation (\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e). This may be due to the longer intrinsic lifetime of high valent Fe-O compared to \u0026bull;OH (100 ns), providing more reaction time to activate C-H bond (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). In addition, extra-framework Fe sites in ZSM-5 pores via a template-free synthesis strategy show over 5 times higher methane conversion rate than that Fe sites in the framework of ZSM-5, which provide good reference for precise fabrication of Fe sites to activate C-H bond into \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eAt this juncture, a new challenge arises: how to control H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e evolution to improve product selectivity, particularly in the conversion of methane into CH\u003csub\u003e3\u003c/sub\u003eOH? Gradient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e evolution into mild ROS (e.g. \u0026bull;OOH) is preferable for selectively converting methane into CH\u003csub\u003e3\u003c/sub\u003eOOH instead of risking over-oxidation with \u0026bull;OH that reacts with \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e and easily form CH\u003csub\u003e3\u003c/sub\u003eOH, HCOOH and CO\u003csub\u003e2\u003c/sub\u003e (\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e, \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e). To enhance the product selectivity, it is better to separate the distribution of \u0026bull;OOH and \u0026bull;OH. This allows for CH\u003csub\u003e3\u003c/sub\u003eOOH to diffuse into a milder condition for subsequent conversion into CH\u003csub\u003e3\u003c/sub\u003eOH. Hutchings and Yu et al. found that Cu ions impregnated into molecular sieve (e.g. Fe/ZSM-5) can mildly and selectively convert H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into \u0026bull;OH, significantly increasing methanol yield up to 85%, providing a good suggestion for selective conversion of CH\u003csub\u003e3\u003c/sub\u003eOOH (\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e). However, the efficiency of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e conversion is only 3.39%, and the significant residual amounts of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e easily cause over oxidation. Therefore, there is much room left for improvement in both CH\u003csub\u003e3\u003c/sub\u003eOH selectivity and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization efficiency (\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eBy optimizing the combination of Fe active sites anchored in the extra framework of inner small pores using the crystal seed method and Cu anchored in the external large pores of ZSM-5 via impregnation methods, CH\u003csub\u003e3\u003c/sub\u003eOH yield reaches 20.20 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a selectivity of 90.1% in direct oxidation of methane, representing a breakthrough in simultaneously enhancing selectivity and reaction rate. More importantly, the utilization efficiency of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e reached 74.6%, much higher than most reported results. Experiments and theoretical calculations show that Fe is more reactive with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, forming high-valent Fe-O and \u0026bull;OOH species that generate CH\u003csub\u003e3\u003c/sub\u003eOOH for efficient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization in inner small pores. Cu has lower reactivity but selectively converts CH\u003csub\u003e3\u003c/sub\u003eOOH into CH\u003csub\u003e3\u003c/sub\u003eOH, promoting selective conversion to methanol in external larger pores at higher H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentrations. Combining H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e diffusion and functional metal site distribution can improve gradient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e evolution to increase both methane conversion rate and selectivity, which provide a new perspective to enhance the selective conversion and efficient utilization of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cb\u003eCatalytic Performance in Direct and Selective Methane Oxidation\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo achieve gradient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposition and improve utilization efficiency, we confined Fe species inside the porous channels of ZSM-5 via an \u003cem\u003ein-situ\u003c/em\u003e seed-assisted synthesis method (Noted: C), while loading Cu species on the external surface through impregnation (Noted: I), constructing a spatially segregated FeCu/ZSM-CI catalyst. For comparison, a series of FeCu catalysts were prepared using different synthetic approaches (see Supplementary Information). Methane directly oxidation to methanol (DOM) was employed as a model reaction to investigate the gradient H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation mechanism.\u003c/p\u003e\u003cp\u003eTo evaluate the catalytic performance of FeCu/ZSM-CI, direct oxidation of methane was conducted using H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e as the oxidant in a 50 mL autoclave reactor at 80\u0026deg;C. Control experiments confirmed that no reaction occurred with alternative oxidants (e.g., O\u003csub\u003e2\u003c/sub\u003e) or in the absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, CH₄, or the catalyst (Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e), demonstrating that both H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and the catalyst are indispensable for methane conversion. After optimizing key parameters (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e-3), including H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration, reaction temperature, methane pressure, catalyst dosage, and time, the best performance was achieved under the following conditions: 20 mL of 0.1 M H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, 10 mg of catalyst, 80\u0026deg;C, 3.5 MPa CH₄ pressure, and a 3 hour reaction time. Under these conditions, FeCu/ZSM-CI exhibited exceptional activity, producing CH\u003csub\u003e3\u003c/sub\u003eOH at a yield of 20.20 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with 90.1% selectivity (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA).\u003c/p\u003e\u003cp\u003eTo study the influence of metal type on the catalysis performance, monometallic decorated H-ZSM-5 catalysts were employed under the optimal reaction conditions mentioned above (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). When catalyzed by Fe/ZSM-I (Fe primarily located on the external surface of ZSM-5), the yield of total C\u003csub\u003e1\u003c/sub\u003e oxidation was 12.11 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, higher than those of Cu/ZSM-I (2.22 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and pure H-ZSM-5 (0.64 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). Similar results could also be observed in Fe/ZSM-C (16.12 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) and Cu/ZSM-C (1.89 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). This suggests that the metal active site plays a crucial role in CH\u003csub\u003e4\u003c/sub\u003e conversion, and Fe is more effective than Cu regardless of whether the catalyst was prepared through impregnation or crystal seed method. However, when catalyzed by Fe/ZSM-I, HCOOH was the main liquid product, and the selectivity of CH\u003csub\u003e3\u003c/sub\u003eOH was only 18.4%, which is much lower than that of Cu/ZSM-I (98.6%). When the Fe site was changed from external surface to inner pores in Fe/ZSM-C, the selectivity of CH\u003csub\u003e3\u003c/sub\u003eOH increased to 41.6%, but it still remained lower than that of Cu/ZSM-C (96%). It indicates that Cu could maintained high methanol selectivity, and metal location could also influence methanol selectivity. Therefore, combining both Fe and Cu may improve both the yield and selectivity of methanol.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eFurther studies were conducted to investigate the influence of Fe and Cu location on catalytic performance. FeCu/ZSM-CC (simultaneous \u003cem\u003ein-situ\u003c/em\u003e growth of Fe and Cu metals) achieved 89.1% selectivity for CH\u003csub\u003e3\u003c/sub\u003eOH, but the yield was only 10.36 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA). This low yield may be due to competitive adsorption of CH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e at Fe and Cu sites within a confined space. The unsatisfactory CH\u003csub\u003e3\u003c/sub\u003eOH yield (9.57 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 77.1%) observed for FeCu/ZSM-II (simultaneous impregnation of metals Fe and Cu) may also be attributed to this reason. Additionally, FeCu/ZSM-II has lower yield and selectivity for CH\u003csub\u003e3\u003c/sub\u003eOH than FeCu/ZSM-CC, suggesting different locations in H-ZSM-5 may have distinct reaction processes. As Fe promotes methanol conversion and Cu enhances methanol selectivity, the presence of both Fe and Cu in different locations may increase the yield and selectivity of methanol simultaneously.\u003c/p\u003e\u003cp\u003eThe yield and selectivity of CH\u003csub\u003e3\u003c/sub\u003eOH for FeCu/ZSM-IC (\u003cem\u003ein-situ\u003c/em\u003e growth of Cu and then impregnation anchoring of Fe) was only 69.3% and 7.86 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. In contrast, FeCu/ZSM-CI (\u003cem\u003ein-situ\u003c/em\u003e growth of Fe and impregnation anchoring of Cu) exhibited significant improvement with a much higher yield and selectivity of CH\u003csub\u003e3\u003c/sub\u003eOH at 90.1% and 20.20 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, surpassing other catalysts. Generally, H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and CH\u003csub\u003e4\u003c/sub\u003e follow Fick\u0026rsquo;s diffusion law in ZSM-5 pores, with lower concentration in the inner pores than the external surface. Therefore, Fe with higher methanol conversion ability was placed in inner pores with lower concentrations of CH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, while Cu with lower methanol conversion ability but higher CH\u003csub\u003e3\u003c/sub\u003eOH selectivity was placed on external surface with higher concentrations of CH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e. This arrangement facilitates gentle and effective utilization of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e while preventing overoxidation. The utilization efficiency of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e is estimated to reach 74.6%.\u003c/p\u003e\u003cp\u003eTo ensure a fair comparison of methanol selectivity among the FeCu/ZSM-CI, FeCu/ZSM-CC, FeCu/ZSM-II, and FeCu/ZSM-IC samples, evaluations were conducted at an equivalent activity level (~\u0026thinsp;25\u0026ndash;27 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, Fig. S4). FeCu/ZSM-CI exhibited outstanding methanol selectivity, exceeding 90%, which is significantly higher than that of the other catalysts. This effectively demonstrates the advantage of the configuration where Fe species are located inside the zeolite framework and Cu species are distributed on the external surface in enhancing methanol selectivity. Subsequently, kinetic measurements were performed to investigate the origin of the activity differences (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB). FeCu/ZSM-CI exhibited the lowest apparent activation energy (E\u003csub\u003ea\u003c/sub\u003e) of 78.4 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, followed by FeCu/ZSM-II (83.8 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), FeCu/ZSM-CC (85.9 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e), and FeCu/ZSM-IC (99.8 kJ mol\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e). These results indicate that precise spatial positioning of Fe and Cu dual atoms not only ensures high catalytic activity but also significantly enhances methanol selectivity.\u003c/p\u003e\u003cp\u003eTo verify the heterogeneous nature and stability of the catalyst, a series of control experiments were conducted. In the absence of catalyst, as well as in the presence of iron acetylacetonate, FeCl\u003csub\u003e2\u003c/sub\u003e, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e, or their mixtures, no catalytic activity was observed (Table S3). Hot filtration tests further confirmed the heterogeneous nature of the catalytic system, as no additional product formation was detected after 1 hour of reaction following catalyst removal (Fig. S5). Moreover, FeCu/ZSM-CI demonstrated excellent recyclability, with no significant loss in CH\u003csub\u003e3\u003c/sub\u003eOH yield or selectivity over eight consecutive reaction cycles (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eC). Inductively coupled plasma (ICP) analysis revealed negligible leaching of Fe and Cu species after the reaction (Table S4), further confirming the structural robustness of the catalyst. Overall, FeCu/ZSM-CI exhibits high stability under reaction conditions for methanol production, and its catalytic performance surpasses that of most previously reported catalysts (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eD, E).\u003c/p\u003e\u003cp\u003e\u003cb\u003eCharacterization of FeCu/ZSM-CI Catalyst\u003c/b\u003e\u003c/p\u003e\u003cp\u003eTo elucidate the structural properties of the as-prepared catalysts, comprehensive characterizations were conducted. The XRD pattern of FeCu/ZSM-CI (Fig. S6) retains characteristic ZSM-5 framework peaks, confirming high dispersion of Fe and Cu species within the zeolite matrix. Consistent with this, HRTEM and SEM-EDS mapping (Fig. S7-S10) revealed no detectable nanoparticles or clusters, indicating atomic-scale anchoring of metals on H-ZSM-5. Strikingly, atomic-resolution AC-HAADF-STEM imaging of Fe/ZSM-C, Cu/ZSM-I, and FeCu/ZSM-CI (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eA-C) unveiled a distinct spatial arrangement: Fe species predominantly reside within internal zeolite channels, while Cu species enrich the external surface.\u003c/p\u003e\u003cp\u003eTo quantify this distribution, semi-quantitative SEM-EDS mapping measured surface Fe and Cu contents at 0.08 wt% and 0.49 wt%, respectively. In contrast, bulk ICP-AES analysis yielded 0.67 wt% Fe and 0.50 wt% Cu (Table S3). The significant disparity in Fe content (surface vs. bulk) strongly supports the encapsulation of Fe within internal channels, while the consistent Cu concentration indicates its predominant surface anchoring.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAs the electronic properties of active sites are determined by their structures and coordination environments, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure (XAFS) spectroscopy were applied for further investigation (Fig. S11-13). XPS revealed that Fe is present in the +\u0026thinsp;3 oxidation state, as indicated by peaks at 711.3 eV and 724.5 eV corresponding to Fe2p\u003csub\u003e3/2\u003c/sub\u003e and Fe2p\u003csub\u003e1/2\u003c/sub\u003e, respectively (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e, \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e) (Fig. S11). The Cu valence state was found to be between +\u0026thinsp;1 and +\u0026thinsp;2 based on a peak centered at 933.5 eV in the Cu2p\u003csub\u003e3/2\u003c/sub\u003e spectra (Fig. S12), which is higher than that of Cu\u003csup\u003e+\u003c/sup\u003e but lower than Cu\u003csup\u003e2+\u003c/sup\u003e(\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e, \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eFor further exploring the coordination environment of Fe and Cu species, XAFS analysis was performed (Fig. S13A), Fe K-edge of X-ray Absorption Near Edge Structure (XANES) showed that the Fe absorption edge at 7115 eV is similar to that of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, indicating the valent state of Fe is +\u0026thinsp;3. At the same time, the peak corresponding to the characteristic leading edge of the Fe element at 7114 eV attributed to Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e is not obvious, indicating that its structure does not conform to that of a binuclear iron tetrahedron of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e). Simultaneously, it was demonstrated that the Fe sites did not substitute for aluminum during the synthesis process, thereby preserving the integrity of the molecular sieve framework; instead, they were situated externally to the structure. The coordination environment was analyzed using EXAFS curve fitting techniques, which revealed two prominent peaks relating to Fe-O scattering at distances of 1.6 \u0026Aring; and 2.6 \u0026Aring; (Fig. S14) with coordination numbers of 3.1 and 2.8 respectively (Table S5); no peaks associated with Fe-Fe or Fe-O-Fe scattering were detected (Fig. S13B). The Fourier Transform (FT) K\u003csup\u003e3\u003c/sup\u003e-weighted extended EXAFS spectrum for iron was analyzed using the Fe-O backscattering path (Fig. S14). The optimal fitting results indicate that the Fe-O bond corresponding to a coordination number of 3.1 at a distance of 1.6 \u0026Aring; pertains to Fe-O-H, which corresponds to the peaks of 715.7 eV and 728.0 eV attributed to Fe(OH)x (where x\u0026thinsp;=\u0026thinsp;1, 2, or 3) shown in the XPS spectra (Fig. S11) (\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e). While the bond corresponding to a coordination number of 2.8 at a distance of 2.6 \u0026Aring; is attributed to Fe-O-Al. It can be seen that the Fe within the FeCu/ZSM-CI catalyst is classified as extra-framework mononuclear iron, exhibiting a total coordination number of 6, specifically anchored to the inner pores in the form of a single atom.\u003c/p\u003e\u003cp\u003eSimilarly, the XANES spectrum of the Cu element reveals that the absorption edge for Cu (Fig.\u0026nbsp;13C) is situated between that of Cu\u003csub\u003e2\u003c/sub\u003eO and CuO. Notably, there is no discernible peak at 8977 eV, indicating that the copper present in FeCu/ZSM-CI does not exhibit a high oxidation state. This observation aligns with the XPS data phase revealing Cu\u003csup\u003e\u0026#120575;+\u003c/sup\u003e (1 \u0026lt; \u0026#120575; \u0026lt; 2) (Fig. S12). Additionally, in the EXAFS spectrum (Fig.\u0026nbsp;13D) corresponding to the Cu site, a characteristic peak related to the Cu-O bond can be identified, with its value measured at 1.57 \u0026Aring;. Upon fitting the Cu-O backscattering path, it was determined that the coordination number of cupric ions is 3 (Fig. S14, Table S5). The presence of Fe and Cu as isolated single atoms was further confirmed by wavelet transform (WT) analysis (Fig. S15-S16).\u003c/p\u003e\u003cp\u003eAdditionally, a series of characterizations (XRD, UV, IR and XANES) of the reaction after reaction (Fig. S17-21), reveals that the Fe and Cu sites within the catalyst are still anchored within molecular sieve channels after cycling experiments since there were no observed changes in their structure or morphology.\u003c/p\u003e\u003cp\u003eIn summary, The FeCu/ZSM-CI catalyst achieves precise spatial control of atomically dispersed Fe (inside) and Cu (outside) sites through a combined seed-impregnation synthesis. The resulting dual monatomic structure, characterized by its distinct spatial metal sites, facilitates efficient utilization of the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e gradient while optimizing the reaction pathway for methane. Ultimately, this leads to enhanced selectivity and yield in converting methane to methanol.\u003c/p\u003e\u003cp\u003e\u003cb\u003eCatalytic Mechanism\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eIdentification of the Active Species\u003c/b\u003e\u003c/p\u003e\u003cp\u003eDuring the activation of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, the metal site catalyzes the homolysis or heterolysis of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, generating reactive species such as \u0026bull;OH, \u0026bull;OOH radicals, and high-valent metal-oxo compounds. To identify the reactive species in the FeCu/ZSM-CI and H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e system, electron paramagnetic resonance (EPR) analysis was conducted. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA, when 2,2-dimethyl-1-oxido-3,4-dihydropyrrol-1-ium (DMPO) was used as the trapping agent, only the signals of DMPO-OH and DMPO-\u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e adducts were observed in the aqueous solution. In the absence of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, no \u0026bull;OH or \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e were generated under any experimental conditions tested (Fig. S22). When H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added without the catalyst (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB), and the signal of \u0026bull;OH was detected. After introducing methane, only the \u0026bull;OH signal remained. However, when the catalyst was added, signals corresponding to both \u0026bull;OH and \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e appeared, indicating that methane activation is not dominated by \u0026bull;OH and that the cleavage of the C-H bond relies on FeCu metal species. Since \u0026bull;OH can oxidize dimethyl sulfoxide (DMSO) to DMSO-OH, while high-valent metals (Fe\u0026thinsp;=\u0026thinsp;O) can oxidize DMSO to DMSO\u003csub\u003e2\u003c/sub\u003e (Fig. S23) (\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e). In the DMSO oxidation system (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eC), both Fe/ZSM-C and FeCu/ZSM-CI catalysts are capable of oxidizing DMSO to DMSO\u003csub\u003e2\u003c/sub\u003e, whereas the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and the Cu/ZSM-I catalyst alone cannot. This indicates that Fe is oxidized to a high-valent Fe\u0026thinsp;=\u0026thinsp;O species during the process.\u003c/p\u003e\u003cp\u003eSubsequently, scavenging experiments were conducted to identify the primary reactive species involved in the reaction (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eD). Salicylic acid was used to quench the \u0026bull;OH, p-benzoquinone as a scavenger for \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e, and DMSO was employed to quench high-valent metal-oxo species (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e, \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e). Upon addition of DMSO, the total methanol yield over FeCu/ZSM-CI decreased significantly from 22.40 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e (without DMSO) to 7.40 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, indicating the critical role of high-valent metal-oxo species. Complementary \u003cem\u003ein-situ\u003c/em\u003e CV revealed characteristic redox peaks at 0.5\u0026ndash;0.7 V for Fe/ZSM-C and FeCu/ZSM-CI following H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e addition (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE, S24), which were absent in the Cu/ZSM-I sample. These distinct electrochemical responses provide direct evidence for the dynamic valence state cycling of Fe species during catalysis. The addition of other scavengers also led to notable reductions in liquid product yield. Meanwhile, \u003cem\u003ein-situ\u003c/em\u003e EPR analysis revealed a much stronger \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e signal over the Fe/ZSM-C catalyst compared to Cu/ZSM-I (Fig. S25) (\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e), suggesting that high-valent Fe centers are the primary active sites for C-H bond activation, while \u0026bull;OH and \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e radicals play essential roles in methanol formation.\u003c/p\u003e\u003cp\u003eWith the assistance of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, metal sites within molecular sieves can generate high-valent metal-oxo species and produce \u0026bull;OH/\u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e radicals, both of which are capable of activating the C-H bond in methane and promoting methanol formation through subsequent radical-mediated pathways. To optimize C-H activation efficiency and product selectivity, it is essential to elucidate the mechanisms of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation at different metal sites and establish correlations between reaction selectivity and the nature of the generated radical species.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003cb\u003eThe Influence of Fe, Cu Sites on Selective H\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e\u003cb\u003eO\u003c/b\u003e\u003csub\u003e\u003cb\u003e2\u003c/b\u003e\u003c/sub\u003e \u003cb\u003eEvolution into ROS\u003c/b\u003e\u003c/p\u003e\u003cp\u003eNext, how Fe and Cu sites affect the selective generation of free radicals was carefully studied. Coumarin reacts with \u0026bull;OH to produce 7-hydroxycoumarin, a highly fluorescent species (\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e). Plotting fluorescent luminescence (FL)-t curves can assist in semi-quantifying the Cu and Fe sites\u0026rsquo; catalyzed \u0026bull;OH generation rate (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eE). The catalysts containing Cu (FeCu/ZSM-CI, Cu/ZSM-I and Cu/ZSM-C) exhibit similar PL intensity, significantly greater than that of only containing Fe catalyst (Fe/ZSM-C and Fe/ZSM-I), indicating that \u0026bull;OH primarily originates from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e conversion at the Cu site. Subsequently, the production rate of \u0026bull;OOH was quantified by plotting the conversion of nitrotetrazolium chloride blue (NBT)-t curves (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eF) (\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e). Fe containing catalyst (e.g. FeCu/ZSM-CI, Fe/ZSM-C and Fe/ZSM-I) show the higher slope than that of only Cu containing catalyst (Cu/ZSM-I and Cu/ZSM-C), suggesting that \u0026bull;OOH primarily originates from the H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e conversion at the Fe site (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eG). When the ratio of Fe and Cu is adjusted from 3:1 to 1:2.5, the highest content of \u0026bull;OH and \u0026bull;O\u003csup\u003e2\u0026minus;\u003c/sup\u003e/\u0026bull;OOH occurs at a ratio of 1:1 (Fig. S26).\u003c/p\u003e\u003cp\u003eFurthermore, the position of metal active site (e.g. inside and outside) were also important for efficient utilization of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e and selective conversion of CH\u003csub\u003e4\u003c/sub\u003e. When quantifying different free radicals using benzoic acid and NBT, \u0026bull;OH is preferentially detected (Fig. S26D). This is because that the concentration gradient of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decreases from the o outside to the inside during diffusion in the molecular sieve. Cu sites have a slower H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e conversion rate, but can balance \u0026bull;OH production in the outside with higher H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration. Fe sites have a fast H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e conversion rate and efficient utilization of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e/\u0026bull;OOH when in the inside with lower H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration. This distribution of Fe and Cu prevents over-oxidation by maintaining appropriate concentrations of \u0026bull;O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e/\u0026bull;OOH and \u0026bull;OH.\u003c/p\u003e\u003cp\u003eThe FeCu catalyst demonstrated exceptional H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization efficiency (74.6%) (Fig. S27), the highest among all tested catalysts. This dual-metal promoted gradient decomposition of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e not only enhances methanol selectivity but also significantly improves the overall oxidant utilization efficiency. The synergistic effect between Fe and Cu sites facilitates a controlled decomposition pathway, minimizing unproductive H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e dissociation while maximizing its conversion to active oxygen species for selective methanol formation (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eI).\u003c/p\u003e\u003cp\u003e\u003cb\u003eTheoretical Investigation on the Evolution Path from Methane to Methanol\u003c/b\u003e\u003c/p\u003e\u003cp\u003e\u003cem\u003eIn-situ\u003c/em\u003e Diffuse Reflectance Infrared Fourier Transform Spectroscopy (\u003cem\u003ein-situ\u003c/em\u003e DRIFTS) was employed to identify methane oxidation intermediates catalyzed by FeCu/ZSM-Cl at 80\u0026deg;C during selective methane conversion (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA). After introducing water vapor with H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, peaks at 3365 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, 3227 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and 1624 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to \u0026bull;OOH, \u0026bull;OH, and \u0026bull;OH\u003csub\u003e2\u003c/sub\u003e, gradually strengthened (\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e). Upon adding methane continuously, the peak at 1458 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e belonging to \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e became apparent along with strong characteristic peaks attributed to \u0026bull;OCH\u003csub\u003e3\u003c/sub\u003e and \u0026bull;COOH observed at 2823 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 3576 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e respectively (\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e). As the reaction progressed, these two characteristic peaks increased less while those at 1061 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e corresponding to C-O bond in CH\u003csub\u003e3\u003c/sub\u003eOH continued increasing (\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e). Associated with \u003csup\u003e1\u003c/sup\u003eH-NMR results that show trace amounts of CH\u003csub\u003e3\u003c/sub\u003eOOH in the product (Fig. S28), it indicates that CH\u003csub\u003e3\u003c/sub\u003eOH is converted from the intermediates of CH\u003csub\u003e3\u003c/sub\u003eOOH (\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e).\u003c/p\u003e\u003cp\u003eThe hydroxyl group in CH\u003csub\u003e3\u003c/sub\u003eOH may form through two distinct mechanisms: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) direct coupling between \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e and \u0026bull;OOH/\u0026bull;OH radicals generated from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposition, or (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) direct insertion of O* species into the C-H bond. To elucidate the reaction pathway, isotopic labeling experiments were conducted using D\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;CH\u003csub\u003e4\u003c/sub\u003e and H\u003csub\u003e2\u003c/sub\u003eO\u0026thinsp;+\u0026thinsp;H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e\u0026thinsp;+\u0026thinsp;CD\u003csub\u003e4\u003c/sub\u003e systems (Fig. S29). The experimental results unambiguously show that the hydrogen in methanol's hydroxyl group exclusively originates from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, demonstrating that the hydroxyl formation proceeds via active oxygen species from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposition rather than through direct O* insertion into C-H bonds.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eIdentifying the rate-determining step (RDS) in a reaction is crucial for precisely enhancing the overall reaction rate. The kinetic isotope effect (KIE) of CH\u003csub\u003e3\u003c/sub\u003eOH product reveals that the k\u003csub\u003eH\u003c/sub\u003e/k\u003csub\u003eD\u003c/sub\u003e value is 1.15 for Fe/ZSM-C and 1.31 for Cu/ZSM-I (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB-E), both close to 1. This suggests that C-H bond activation has minimal influence on the reaction rate, confirming that H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation is the RDS for both Fe/ZSM-C and Cu/ZSM-I. In contrast, FeCu/ZSM-CI exhibits a significantly higher k\u003csub\u003eH\u003c/sub\u003e/k\u003csub\u003eD\u003c/sub\u003e value of 2.32, indicating that C-H bond activation plays a more dominant role in catalytic activity. This confirms that C-H bond activation is the RDS for FeCu/ZSM-CI. A similar phenomenon was observed in the KIE (HCOOH) studies (Fig. S30, S31). Overall, due to the synergistic interaction between Fe and Cu dual single atoms, the RDS shifts from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation to C-H bond activation. The enhanced generation of reactive oxygen species via H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation provides more active sites for methane oxidation, thereby boosting catalytic performance.\u003c/p\u003e\u003cp\u003eAfter confirming the important intermediates of CH\u003csub\u003e3\u003c/sub\u003eOOH, DFT calculation were used to study the activation and transformation processes of CH\u003csub\u003e4\u003c/sub\u003e at functional Fe, Cu sites, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA, B, S32, S33). The reaction can be divided into three stages due to the spatial and functional differences between Fe and Cu sites: (\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) diffusion and evolution of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, (\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) effective activation and conversion of methane, (\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) migration and conversion of intermediates.\u003c/p\u003e\u003cp\u003e(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e) When H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e diffuse through the molecular sieve from the outside to the inside, it passes by Cu and Fe sites in succession, resulting in a gradient reduction of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration. Both Cu and Fe sites require a similar energy barrier (Fe : 0.26 eV / Cu : 0.29 eV) to absorb H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, but Cu only needs to overcome an additional energy barrier of 0.07 eV to decompose H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into \u0026bull;OH, which is much higher than that required for decomposition into \u0026bull;OOH (-0.3 eV) catalyzed by Fe. Due to spatial priority, Cu weakly decomposes H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e into \u0026bull;OH, making the concentration of \u0026bull;OH radical in the external large pores enrich slowly. The residual H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e concentration decreases significantly after diffusing into the inner small pores, leading to slower interaction with the Fe site and selective generation of mild ROS, specifically \u0026bull;OOH species.\u003c/p\u003e\u003cp\u003e(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e) H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e decomposes at the mental site and forms a high-valence Fe-O bond. Both the initial energy required for the adsorption of CH\u003csub\u003e4\u003c/sub\u003e at the Fe and Cu sites (Fe : 0.23 eV / Cu : 0.32 eV) and the corresponding free energy change during the subsequent release of \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e (Fe : -0.03 eV / Cu : 0.92 eV) indicate that methane activation is more favorably influenced by Fe sites compared to Cu sites. Therefore, methane activation occurs primarily at the Fe site, where it is effectively abstract H on the Fe\u0026thinsp;=\u0026thinsp;O site, leading to C-H bond dissociation and resulting in \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e free radicals as shown in TS3 (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). The released \u0026bull;CH\u003csub\u003e3\u003c/sub\u003e free radicals accumulate and react with significant number of \u0026bull;OOH species along with a smaller quantity of migrating \u0026bull;OH free radicals present in solution to form CH\u003csub\u003e3\u003c/sub\u003eOOH and CH\u003csub\u003e3\u003c/sub\u003eOH.\u003c/p\u003e\u003cp\u003e(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e) Cu\u0026rsquo;s high electron density causes it to adsorb the terminal O in CH\u003csub\u003e3\u003c/sub\u003eOOH and break the bond of O-O easily, resulting in \u0026bull;OCH\u003csub\u003e3\u003c/sub\u003e. This then reacts with an H proton to form CH\u003csub\u003e3\u003c/sub\u003eOH as a product. Compared to the 0.32 eV energy needed for CH\u003csub\u003e4\u003c/sub\u003e adsorption and activation on Cu sites, only a 0.19 eV energy barrier must be overcome for effective CH\u003csub\u003e3\u003c/sub\u003eOOH adsorption. Additionally, only 1.11 eV of energy input is required to advance into the rate-limiting step TS2. This approach offers significant advantages in terms of efficiency and variations in free energy profiles. Additionally, the re-adsorption of CH\u003csub\u003e3\u003c/sub\u003eOH at the Cu site poses significant challenges, and achieving effective deep oxidation of CH\u003csub\u003e3\u003c/sub\u003eOH solely with \u0026bull;OH remains difficult. Ultimately, all produced CH\u003csub\u003e3\u003c/sub\u003eOH is fully desorbed from the molecular sieve into the solution system, resulting in high yield and selectivity for CH\u003csub\u003e3\u003c/sub\u003eOH products (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThis work demonstrates that spatially engineering dual single-atom Fe and Cu sites within the hierarchical pore network of ZSM-5 enables gradient-controlled H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation, allowing for both efficient C-H bond activation and selective methanol production from methane under mild conditions. By decoupling ROS evolution across pore domains high-valent Fe = O species and •OOH in the micropores for methane activation, and Cu-mediated •OH reactions on the external surface for CH\u003csub\u003e3\u003c/sub\u003eOH formation overoxidation is suppressed while maximizing H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization. The FeCu/ZSM-CI catalyst achieves a rare combination of high activity, selectivity, and oxidant efficiency. Mechanistic insights from isotopic, spectroscopic, and theoretical studies reveal a shift in the rate-determining step from oxidant activation to C-H activation due to Fe-Cu synergy. These findings establish spatial site isolation as a general and scalable strategy for regulating ROS pathways in alkane oxidation, offering new design principles for sustainable catalytic conversions of inert molecules.\u003c/p\u003e"},{"header":"Materials and Chemicals","content":"\u003cp\u003eIron acetylacetonate (Fe(C\u003csub\u003e5\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e, AR, 99%, Macklin) and Copper (II) nitrate Gerhardite (Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e 3H\u003csub\u003e2\u003c/sub\u003eO, AR, 99%, Macklin) were used as metal precursors. Sodium aluminum oxide (Al\u003csub\u003e2\u003c/sub\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e, AR, 98%, Macklin), Sodium hydroxide (NaOH, 95%, graininess, Macklin) Silicasol (Silica content: 29% ~ 31%, Macklin) and Ammonium chloride (NH\u003csub\u003e4\u003c/sub\u003eCl, AR, 99.99%, Macklin) were used as a raw material for the synthesis of H-ZSM-5. Hydrogen peroxide (H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e, AR, 30%, Macklin) was used as the oxidizing agent. Methane (99.999 vol.%, Qingdao Xin ke yuan) was used as the feedstock gases. All chemicals were used as received without any further purification. Deionized water was used throughout the research.\u003c/p\u003e\u003cp\u003e\u003cb\u003eCatalyst Synthesis.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eFe acetylacetone was chosen as the source to incorporate Fe into inner small pores due to its similar size and ability to be confined in the micropores. The stable coordination structure of Fe acetylacetone reduces its reaction with Si and Al sources, while the residual Fe acetylacetone in the external large pores can be eliminated by washing away because of its slightly solubility in water. Fe species were grown \u003cem\u003ein-situ\u003c/em\u003e using the crystal seed method and then calcined to produce Fe/ZSM-C. Cu species were added through impregnation, resulting in FeCu/ZSM-CI, where C and I denote the sequence of crystal seed method and impregnation method for Fe and Cu respectively. To conduct control experiments, a series of catalysts decorated with different combinations of metals (e.g., Fe/ZSM-C, Cu/ZSM-I, CuFe/ZSM-CI) were obtained by varying metal types, ratios and introduction methods.\u003c/p\u003e\u003cp\u003eInitially, Fe site was grown \u003cem\u003ein-situ\u003c/em\u003e using the crystal seed method to fix it in the inner small pores of ZSM-5. To achieve this, Fe acetylacetone was chosen as its size is similar to that of the micropore. Residual Fe present in external large pores (such as mesoporous) was mostly eliminated by washing with water after hydrothermal synthesis. The above precursor was then obtained through calcination and named Fe/ZSM-C (C refers to crystal seed method). Next, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e solution was used for impregnation on Fe/ZSM-C under controlled conditions resulting in a catalyst called FeCu/ZSM-CI (I stands for impregnated method).\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of Fe/ZSM-C.\u003c/b\u003e Fe/ZSM-C was synthesized using crystal seed method. This synthetic procedure comprised two steps: the synthesis of ZSM-5 seeds and the synthesis of Fe-ZSM-5.\u003c/p\u003e\u003cp\u003eIn the first step, 15 g of Silica sol was dissolved in 7 mL of a NaOH solution (1 mol/L) under constant stirring at 100°C for 1 h. Simultaneously, a solution was prepared by dissolving 0.45 g of sodium aluminate oxide in 7 mL of a NaOH solution (1 mol/L). The amalgamation of these two solutions resulted in the formation of a synthetic aluminosilicate gel with a molar composition of 4Na\u003csub\u003e2\u003c/sub\u003eO : 1Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e : 36SiO\u003csub\u003e2\u003c/sub\u003e : 460H\u003csub\u003e2\u003c/sub\u003eO. The gel underwent stirred vigorously at 100°C for 2 h and was then transferred to a stainless-steel autoclave for crystallization at 180°C for 48 h. The resultant crystals were collected by filtration, cleaned with deionized water until the pH of the filtrate is neutral.\u003c/p\u003e\u003cp\u003eSubsequently, the obtained crystals were dried at 100°C to produce the ZSM-5 seeds. In the second step, a synthetic aluminosilicate gel was prepared using the same method as described in the first step. 2 mL of an aqueous solution containing 0.21 g of iron acetylacetonate and 0.06 g of seeds were added sequentially to the gel, followed by 30 min of stirring. The mixture was then transferred to an autoclave for crystallization at 180°C for 48 h. After crystallization, the hydrothermal catalyst was placed in a beaker, to which 200 mL of deionized water was added. The mixture was at 80 ℃ for 12 h to remove the residual iron acetylacetone. The catalyst was washed and filtered with a large amount of deionized water until the filtrate presents a clear color, and the present of Fe ions are determined using KSCN. Washing and filtration were stopped when no iron acetylacetone was detected in the filtrate. The filter cake was dried at 80 ℃ to obtain the synthesized Fe/ZSM-C.\u003c/p\u003e\u003cp\u003eFinally, Fe/ZSM-C was converted to H-type Fe/ZSM-C through ion exchange with ammonium chloride at 80°C, followed by calcination in air at 550°C for 6 h. The Fe loading was determined by ICP-OES to be approximately 0.6 wt%. In the synthesis of H-ZSM-5, the only deviation from the standard procedure was the omission of iron acetylacetonate in the second step, while all other steps and conditions remained unchanged. The obtained H-ZSM-5 was used in the following other catalyst synthesis.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of Cu/ZSM-I.\u003c/b\u003e H-ZSM-5, synthesized using the seed method above, was used as the molecular sieve carrier. To prepared the catalyst, 1 g of synthetic H-ZSM-5 was suspended in 50 mL deionized water and fully stirred to obtain solution A. A certain amount of Copper (II) nitrate was dissolved in 10 mL deionized water, followed by ultrasonic treatment for 5 mins to ensure complete dissolution. The pH value of the solution was then adjusted to 3–4. The prepared copper nitrate solution was slowly added into solution A at a rate of 0.5 mL/min, followed by continuous stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The obtained catalyst was dried at 80°C, and then calcined at 550°C in the Muffle furnace for 6 h to obtain Cu/ZSM-I.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of FeCu/ZSM-CI.\u003c/b\u003e FeCu/ZSM-CI was prepared by introducing copper into Fe/ZSM-C as a precursor by the impregnation adsorption method. The procedure can be divided into two main steps. Take the metal load Fe / Cu (0.6 wt% / 0.6 wt%) as an example: First, the precursor Fe/ZSM-C was synthesized following the same method as described for Fe/ZSM-C above. After that, 1 g of the synthesized Fe/ZSM-C was placed in 50 mL deionized water and stirred thoroughly to obtain solution B. Then 0.02 g of Copper (II) nitrate was dissolved in 10 mL deionized water and ultrasonically treated for 5 mins to ensure complete dissolution. The pH of the solution to 3–4. The prepared copper nitrate solution was added into B solution at the rate of 0.5 mL/min, followed by stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The obtained catalyst was dried at 80 ℃ and then calcined at 550°C in muffle furnace for 6 hours to obtain FeCu/ZSM-CI.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of FeCu/ZSM-CC.\u003c/b\u003e The synthesis procedure is the same as Fe/ZSM-C, but the difference is that Iron acetylacetonate and Copper (II) nitrate are added at the same time.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of FeCu/ZSM-IC.\u003c/b\u003e The precursor of Cu-ZSM-5-C was synthesized using Copper (II) nitrate instead of Iron acetylacetonate, followed by the adsorption and impregnation of Fe. The procedure follows the same steps as described above.\u003c/p\u003e\u003cp\u003e\u003cb\u003eSynthesis of FeCu/ZSM-II.\u003c/b\u003e H-ZSM-5, synthesized using the seed method described above, was used as the molecular sieve carrier. 1.00 g of synthetic H-ZSM-5 was placed in 50 mL deionized water and stirred thoroughly to obtain solution C. A specific amount of Iron acetylacetonate and Copper (II) nitrate were dissolved in 10 mL deionized water, then ultrasonicated for 5 mins to ensure complete dissolution. The pH of the solution was adjusted to 3–4. The prepared copper nitrate solution was then added uniformly into solution A at 0.5 mL/min, followed by stirring and impregnation for 24 h. After impregnation, the solution was washed and filtered with a large amount of deionized water. The resulting catalyst was dried at 80°C and then calcined at 550 ℃ in the muffle furnace for 6 h to obtain FeCu/ZSM-II.\u003c/p\u003e\u003cp\u003e\u003cb\u003eCatalyst Testing.\u003c/b\u003e The selective oxidation of methane experiment was carried out in a 50 mL high-pressure reactor. The catalyst (10 mg) was uniformly dispersed in 20 mL of distilled water and sonicated for 15 minutes. A specific amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added and the reactor was sealed. The reactor was purged with argon gas 3–5 times to replace the air. Then, methane was injected into the reactor to reach the required pressure. The reaction was carried out in an oil bath for 3 h. After the reaction, the reactor was cooled to below 10 ℃ using an ice bath, and both the gas and liquid were collected.\u003c/p\u003e\u003cp\u003e\u003cb\u003eCatalyst Characterization.\u003c/b\u003e\u003c/p\u003e\u003cp\u003eX-ray Diffraction (XRD) was performed by the diffractometer (X’Pert PRO MPD, PANalytical, Netherland) with Cu Kα radiation (40 kV, 100 mA, λ = 0.154 nm). The morphology of materials was observed by Scanning electron microscope (SEM), whose model is JSM-7500F scanning electron microscopes (Japan). High-Resolution Transmission Electron Microscopy (HRTEM) and Energy Dispersive X-ray Spectroscopy-mapping (EDS-mapping) images were captured using Tecni G30 instrument (FEI, USA). The morphology of the samples was further observed by Aberration Corrected High-Angle Annular Dark Field Scanning Transmission Electron Microscope (AC-HAADF-STEM, Themis Z, Thermo Scientific, USA). UV-Vis diffuse reflectance spectra were obtained from the spectrometer (UV-2700, Shimadzu, Japan) furnished with an integrating sphere device. Solid-state \u003csup\u003e27\u003c/sup\u003eAl Magic-Angle Spinning NMR (\u003csup\u003e27\u003c/sup\u003eAl NMR MAS) cross polarization spectroscopy was measured on a JEOL ECA-600 spectrometer at a resonance frequency of 156.4 MHz using a 4 mm sample rotor with a spinning rate of 15.0 kHz. The \u003csup\u003e27\u003c/sup\u003eAl chemical shift was referenced to -0.54 ppm of AlNH\u003csub\u003e4\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e·12H\u003csub\u003e2\u003c/sub\u003eO. The information on the electronic states of the material surface was collected via the X-ray Photoelectron Spectrometer (XPS, ESCALAB 250Xi, Thermo Scientific, USA).\u003c/p\u003e\u003cp\u003eThe metal site structure of the catalyst materials was determined by X-ray Absorption Spectroscopy (XAS), whose date for Fe K-edge and Cu K-edge were collected at the 1W1B station of the Beijing Synchrotron Radiation Facility (BSRF), where the storage rings operated at 2.5 GeV with a maximum current of 250 mA. For Fe-containing and Cu-containing references (i.e., Fe foil, FeO, Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, Cu foil, Cu\u003csub\u003e2\u003c/sub\u003eO and CuO), data were collected in transmission mode using an ionization chamber, while for Fe-containing zeolites and Cu-containing zeolites, data were obtained in fluorescence excitation mode using a Lytle detector. The X-ray Absorption Near Edge Structure (XANES) and Fourier-transformed Extended X-ray Absorption Fine Structure (EXAFS) data were analyzed using ATHENA and ARTEMIS software, respectively, and MATLAB software was employed for the analysis of wavelet-transformed EXAFS data.\u003c/p\u003e\u003cp\u003e\u003cem\u003eIn-situ\u003c/em\u003e Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) measurements were measured on the instrument (VERTEX70, Bruker, Germany), the mercury cadmium telluride (MCT) detector was adopted, and Ar was bubbled into H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e when the temperature was raised and stabilized to 80°C. The background correction was stabilized, and CH\u003csub\u003e4\u003c/sub\u003e replaced Ar for testing. Electron Paramagnetic Resonance (EPR) spectra was measured on CIQTEK EPR200M (CIQTEK Co., Ltd.) with continuous-wave X band frequency, with 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the radical trap. The samples were dispersed in H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e aqueous solution dissolved CH\u003csub\u003e4\u003c/sub\u003e to detect •CH\u003csub\u003e3\u003c/sub\u003e, •O\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e−\u003c/sup\u003e and •OH.\u003c/p\u003e\u003cp\u003eInductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES, Agilent 730, USA) was used to determine the metal contents. Temperature-Programmed Desorption measurements were carried out on Micromeritics AutoChemHP-2950. The Fluorescence Spectra were collected by the fluorescence spectrophotometer (RF-6000, Shimadzu, Japan).\u003c/p\u003e\u003cp\u003eThe gas chromatography (Scion 456C, Tianmei, China) is equipped with a thermal conductivity detector (TCD), two flame ionization detectors (FID), a methanizer, and a headspace autosampler (DK-5001A, Beijing Zhongxing, China), were used to quantify gaseous and CH\u003csub\u003e3\u003c/sub\u003eOH and CO\u003csub\u003e2\u003c/sub\u003e products. High-performance liquid chromatography (HPLC, Prominence-i, LC-2030 Plus, Japan) equipped with a Refractive Index Detector (RID) was used to quantify HCOOH products. UV-Vis diffuse reflectance spectra (UV-2700, Shimadzu, Japan) was used to quantify HCHO products.\u003c/p\u003e\u003cp\u003eThis combination of sophisticated techniques provided comprehensive information about the structure, composition, and catalytic behavior of the materials under study.\u003c/p\u003e\u003cp\u003e\u003cb\u003eLow temperature selective oxidation of methane.\u003c/b\u003e The methane carbonylation experiment was carried out in a 50 mL high-pressure reactor (Shi ji shen lang). The catalyst (10 mg) was uniformly dispersed in 20 mL of distilled water and sonicated for 15 minutes. A certain amount of H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e was added and the reactor was sealed. The reactor was purged with argon gas to replace the air for 3–5 times. Then, methane was injected at the required pressure. The reaction was carried out in an oil bath for 3 h. After the reaction, the reactor was cooled to below 10 ℃ in an ice bath, and the gas and liquid were collected.\u003c/p\u003e\u003cp\u003e\u003cb\u003eCyclic experiment.\u003c/b\u003e The recycle test followed the same procedure. After each run, the spent catalyst was separated, washed with a large amount of H\u003csub\u003e2\u003c/sub\u003eO then dried at 80 ℃ in the vacuum oven for the next cycle. The same amount of catalyst was used and repeated experiments were carried out under the same experimental conditions to verify the stability of the catalyst.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis work was supported by National Natural Science Foundation of China (22322815, 22179146, and 22138013), National Key Research and Development Program of China (NO.2019YFA0708700), the Fundamental Research Funds for Central Universities (18CX07009A), Independent Innovation Research Project (Science and Engineering) (20CX06072A).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eM.W. and W.W. conceived and supervised the project. H.Z. and S.W. conducted most experiments including synthesis, characterization and testing, as well as data analysis. Y.L. carried out DFT calculations section. H.Q. performed characterization and testing analysis. M.W. conducted spectrum analysis. Q.C. and B.Z. contributed to data analysis of the EPR spectra. S.Z. conducted DRIFTS analysis. P.Z. and C.G. contributed to data analysis of the X-ray absorption spectroscopy (XAS). Y.L. conducted an analysis of the mass spectrometry. Q.H. provided advice and expertise. H.Z., S.W. and W.W. wrote and revised the paper. All authors discussed the paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interest.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLiu R\u003cem\u003e, et al.\u003c/em\u003e Linkage-engineered donor-acceptor covalent organic frameworks for optimal photosynthesis of hydrogen peroxide from water and air. \u003cem\u003eNat. 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Herein, a dual single-atom catalyst, FeCu/ZSM-CI, in which atomically dispersed Fe and Cu are spatially separated within the microporous framework of ZSM-5, with Fe located in the inner channels and Cu on the external surface, thereby enabling a controlled H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation gradient. This spatial configuration induces differentiated reactive oxygen species evolution: high-valent Fe\u0026thinsp;=\u0026thinsp;O and \u0026bull;OOH species form in the interior to activate methane into CH\u003csub\u003e3\u003c/sub\u003eOOH, while surface Cu sites selectively convert CH\u003csub\u003e3\u003c/sub\u003eOOH into methanol, mitigating overoxidation pathways. The optimized FeCu/ZSM-CI catalyst achieves a methanol yield of 20.20 mmol g\u003csub\u003ecat\u003c/sub\u003e\u003csup\u003e\u0026minus;1\u003c/sup\u003e h\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with 90.1% selectivity and a remarkable H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e utilization efficiency of 74.6%. Mechanistic studies combining kinetic isotope effects, scavenger assays, \u003cem\u003ein-situ\u003c/em\u003e EPR/DRIFTS, and DFT calculations reveal that the rate-determining step shifts from H\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e2\u003c/sub\u003e activation to C-H bond activation due to synergistic Fe-Cu interactions. These findings establish a generalizable strategy for manipulating ROS spatial distribution via dual single-atom engineering, offering new insights for designing advanced catalysts for selective hydrocarbon oxidation under ambient conditions.\u003c/p\u003e","manuscriptTitle":"FeCu Dual-Single-Atom Catalyst Promotes Gradient H2O2 Activation for Enhanced Methane Oxidation to Methanol","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-15 07:13:21","doi":"10.21203/rs.3.rs-7017740/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":"266a43b0-5cce-4c20-bed4-99e9e2261082","owner":[],"postedDate":"July 15th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[{"id":51543649,"name":"Earth and environmental sciences/Environmental sciences/Environmental chemistry/Environmental monitoring"},{"id":51543650,"name":"Earth and environmental sciences/Biogeochemistry/Carbon cycle"}],"tags":[],"updatedAt":"2026-04-17T07:07:41+00:00","versionOfRecord":{"articleIdentity":"rs-7017740","link":"https://doi.org/10.1038/s41467-026-70179-8","journal":{"identity":"nature-communications","isVorOnly":false,"title":"Nature Communications"},"publishedOn":"2026-03-05 05:00:00","publishedOnDateReadable":"March 5th, 2026"},"versionCreatedAt":"2025-07-15 07:13:21","video":"","vorDoi":"10.1038/s41467-026-70179-8","vorDoiUrl":"https://doi.org/10.1038/s41467-026-70179-8","workflowStages":[]},"version":"v1","identity":"rs-7017740","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7017740","identity":"rs-7017740","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}