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Yasuyuki Yamada, Akiko Sakata, Yuka Toyoda, Chaoqi Chen, Satoshi Muratsugu, Yutaka Hitomi, Kin‐ichi Oyama, Akiyoshi Kuzume, [Koji Harano](https://orcid.org/0000-0001-6800-8023), Mizuki Tada, Kentaro Tanaka

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[Efficient Room‐Temperature Methane Oxidation by μ‐Nitrido‐Bridged Iron Phthalocyanine Dimer Deposited on Conductive Carbon Black](https://mdr.nims.go.jp/datasets/f52eddf9-5fe4-4566-8c95-f199f9891359)

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Efficient Room‐Temperature Methane Oxidation by μ‐Nitrido‐Bridged Iron Phthalocyanine Dimer Deposited on Conductive Carbon BlackChemCatChem RESEARCH ARTICLEEfficient Room-Temperature Methane Oxidation by µ-Nitrido-Bridged Iron Phthalocyanine Dimer Deposited on Conductive Carbon Black Yasuyuki Yamada1 , 2 , 3 Akiko Sakata2 Yuka Toyoda2 Chaoqi Chen1 , 2 Satoshi Muratsugu1 , 3 Yutaka Hitomi4 Kin-ichi Oyama2 Akiyoshi Kuzume5 Koji Harano6 , 7 Mizuki Tada1 , 2 , 3 Kentaro Tanaka1 , 3 , 8 1 Department of Chemistry, Graduate School of Science, Nagoya University, Nagoya, Japan 2 Research Center for Materials Science, Nagoya University, Nagoya, Japan 3 Integrated Research Consortium on Chemical Sciences, Nagoya University, Nagoya, Japan 4 Department of Molecular Chemistry and Biochemistry, Graduate School of Science and Engineering, Doshisha University, Kyotanabe, Kyoto, Japan 5 Clean Energy Research Centre, University of Yamanashi, Yamanashi, Japan 6 Center for Basic Research on Materials, National Institute for Materials Science, Tsukuba, Japan 7 Research Center for Autonomous Systems Materialogy (ASMat), Institute of Integrated Research, Institute of Science Tokyo, Yokohama, Japan 8 Research Institute for Quantum and Chemical Innovation, Institute of Innovation for Future Society, Nagoya University, Nagoya, Japan Correspondence: Yasuyuki Yamada ( yamada.yasuyuki.i6@f.mail.nagoya-u.ac.jp) Kentaro Tanaka ( kentaro@chem.nagoya-u.ac.jp) Received: 3 September 2025 Revised: 21 December 2025 Accepted: 12 January 2026 Keywords: μ-nitrido-bridged dimer | carbon substrate | iron phthalocyanine | methane oxidation | room temperature ABSTRACT Appropriate deposition of metal complex-based catalysts on solid carriers sometimes results in considerably higher catalytic activity than that of the metal complex alone, due to interactions between the complex and the solid. These catalysts could be a part of single-molecule catalysts (SMCs) or site-isolated molecular complex catalysts (SIMCs). Herein, we report a solid-supported metal complex catalyst for CH4 oxidation at room temperature. Specifically, μ-nitrido-bridged iron phthalocyanine dimer deposited on conductive carbon black can oxidatively activate the chemically stable C ─H bond of CH4 with high efficiency even at 25◦C in an aqueous solution containing H2 O2 as an oxidant. Its catalytic activity for CH4 oxidation is much higher than that of the commonly used Fenton reaction with Fe2 + and H2 O2 under the same conditions. Such high catalytic oxidizing activity is attributable to the interaction between the specific surface sites of carbon black and the high-valent iron-oxo species of the catalyst molecule.                 1 Introduction By atomically dispersing isolated metal ions on solid carriers,single-atom catalysts (SACs) have shown outstanding activity ina variety of reactions due to their high density of active sites [ 1–7 ].Similarly, single-molecule catalysts (SMCs) [ 8 ] and site-isolatedmolecular complex catalysts (SIMCs) [ 9 ] can be constructed bydispersing and immobilizing metal complexes on solid carriers. Inthese catalysts, the metal center coordinated by ligands functionsas a “single site.” There are two practical ways to tune thecatalytic activity of SMCs and SIMCs: (i) ligand design of theThis is an open access article under the terms of the Creative Commons Attribution License, which permcited. © 2026 The Author(s). ChemCatChem published by Wiley-VCH GmbH ChemCatChem , 2026; 18:e01356 https://doi.org/10.1002/cctc.202501356metal complex deposited on the solid surface, and (ii) tuningthe electronic state of the metal center through interaction withthe solid support. An appropriate combination of coordinating ligand and solid support in SMCs or SIMCs would result in abetter catalytic performance than that of the conventional metalcomplex-based homogeneous catalysts. In particular, carbon- based supports are extremely promising for SMCs or SIMCs dueto their mechanical and electrochemical stability, high specific surface area, porous structure, and easy introduction of defectsor substituents, including various heteroatoms such as O, N, andB [ 10–12 ]. its use, distribution and reproduction in any medium, provided the original work is properly 1 of 9https://doi.org/10.1002/cctc.202501356mailto:yamada.yasuyuki.i6@f.mail.nagoya-u.ac.jpmailto:kentaro@chem.nagoya-u.ac.jphttp://creativecommons.org/licenses/by/4.0/https://doi.org/10.1002/cctc.202501356http://crossmark.crossref.org/dialog/?doi=10.1002%2Fcctc.202501356&domain=pdf&date_stamp=2026-01-31FIGURE 1 Catalytic CH4 oxidation by μ-nitrido-bridged iron phthalocyanine-based catalysts. (a) Production of high-valent iron-oxo species ( 1(oxo) ) applicable to CH4 oxidation through the reaction of μ- nitrido-bridged iron phthalocyanine dimer 1 and H2 O2 . (b) Comparison of the initial CH4 oxidation rate based on the effective methane conversion number MCNeff of 1 supported on SiO2 ( 1 /SiO2 ) and graphite ( 1 /G) at 60◦C and 25◦C in an acidic aqueous solution using H2 O2 as an oxidant [ 36 ].                                                               18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative CThis paper reports an efficient room-temperature CH4 oxidationreaction enabled by a highly dispersed metal complex-basedcatalyst on the surface of a conductive carbon support. SinceCH4 is abundant in natural gas, shale gas, and methane hydrate,efficient catalytic activation of its C ─H bond will expand its roleas a carbon source for producing chemicals [ 13–16 ]. Nevertheless,this activation remains difficult because CH4 has a high bonddissociation energy (104.9 kcal/mol), low polarizability, and negli-gible electron affinity. Therefore, although catalysts enabling low-temperature C ─H activation of CH4 are indispensable [ 13–16 ],only a few catalysts have achieved this at room temperature [ 17–25, 30 ]. For instance, Cui et al. demonstrated room-temperatureoxidative C ─H bond activation of CH4 by Fe-carbon-based SAC,using H2 O2 as an oxidizing reagent [ 21 ]. We hypothesize that novel SMCs or SIMCs could be used toprepare efficient catalysts for room-temperature CH4 conversion.Specifically, we chose a μ-nitrido-bridged iron phthalocyaninedimer 1 as the molecular part. The high-valent terminal iron-oxo species 1(oxo) , produced through the reaction of 1 withH2 O2 , is known to possess particularly potent oxidation abilityamong various artificial metal complex-based oxidation catalysts(Figure 1a ) [ 31–33 ]. High-valent iron-oxo species such as 1(oxo)can activate stable C ─H bonds via a proton-coupled electrontransfer (PCET) mechanism, followed by radical recombination2 of 9to afford hydroxylated compounds [ 34, 35 ]. As a result, 1 cancatalytically activate the C ─H bond of CH4 in acidic aqueoussolutions containing excess H2 O2 at below 100◦C to produce theoxidized products (mainly formic acid, and also methanol andformaldehyde) [ 31–33 ]. Moreover, we recently found that stacking1 on a graphite surface ( 1 /G) significantly enhanced its abilityto catalytically oxidize CH4 compared to the silica-supported counterpart ( 1 /SiO2 ), as evidenced by a much higher MCNeff value (to be defined later) of 1.1 × 10− 2 s− 1 for 1 /G versus 1.1 × 10− 4 s− 1 for 1 /SiO2 at 60◦C in an acidic aqueous solution (Figure 1b )[ 36 ]. These results are apparently due to the benefits of SMC (orSIMC). However, the catalytic CH4 oxidation performance of 1 /Gat room temperature (25◦C) was still very low (MCNeff = 4.4 × 10− 4 s− 1 ). Hence, it is desirable to develop a strategy to dramaticallyimprove the catalytic activity of 1 /G. Assuming that the graphite support in 1 /G can tune the catalyticactivity of 1 in this SMC (or SIMC), a different solid support mayimprove the performance. Conductive carbon black is a goodcandidate for this purpose, because it possesses a large π-planesurface for efficient interaction with 1 and 1(oxo) , even thoughits structure is considerably different from that of graphite byincluding a number of defects and substituents such as –COOH,–CHO, and –OH [ 37, 38 ]. Here, we dispersed 1 on conductivecarbon blacks such as Vulcan XC-72R in order to improve thecatalytic C ─H bond activation of CH4 at room temperature. 2 Results and Discussion 2.1 Preparation and Characterization of Vulcan XC-72R-Supported Catalyst In its neutral form, the μ-nitrido-bridged iron phthalocyanine dimer with no peripheral substituents ( 1 ) is poorly soluble inmany organic solvents, making it difficult to prepare supportedcatalysts. However, we recently developed a method to efficientlyassemble 1 on a graphite surface by using its 1e− -oxidizedmonocationic complex ( 1+ ⋅I− ). Heating graphite (1.0 g) with 1+ ⋅I− (8.0 mg, 5.7 µmol) in pyridine at 80◦C for 24 h quantitativelyproduced the desired catalyst 1 /G, in which 1 was stacked onthe graphite surface [ 36 ]. Pyridine is a good solvent for 1+ ⋅I− because the axial coordination of pyridine with the Fe centerof 1+ ⋅I− prevents aggregation. X-ray photoelectron spectroscopy (XPS) analysis of 1 /G clearly demonstrated that 1+ was reducedby 1e− in graphite to the neutral form 1 on the graphite surface[ 36 ]. Using a similar approach, here we prepared a supportedcatalyst ( 1 /Vul) on Vulcan XC-72R, a well-known conductivecarbon black, as shown schematically in Figure S1a . It shouldbe mentioned that the adsorption of the catalyst molecule onVulcan proceeded quantitatively under these reaction conditions, because the solution was almost colorless after heating Vulcanwith 1+ ⋅I− in pyridine. It was difficult to detect the Fe peaks in the XPS spectrum of 1 /Vul,presumably because Vulcan XC-72R has a much larger surfacearea than graphite (254 vs. 3.9 m2 /g, see Table 1 and Figure S2in the Supporting Information). Instead, we compared the Fe K -edge X-ray absorption near edge structure (XANES) of 1 /Vul, 1deposited on silica gel ( 1 /SiO2 ), solid of 1 , 1+ ⋅I− deposited onChemCatChem, 2026ommons LicenseTABLE 1 Physical properties of carbon supports and the catalytic CH4 oxidation activities of supported catalysts ( 1 /Vul, 1 /KB, 1 /BP, 1 /AB, and 1 /G) at 25◦C for 2 h. Values in parentheses indicate the S.D. of three independent experiments. Carbon support / Catalyst BET surface area [m2 /g] Particle size [nm] [CH3 OH] [mM] [CH3 OOH] [mM] [HCHO] [mM] [HCOOH] [mM] MCNeff for 2 h oxidation Vulcan XC–72R / 1/Vul 254 30 0.18 (0.01) 0.69 (0.03) 0.09 (0.01) 1.13 (0.27) 107 (16) Black Pearls 2000 / 1/BP 1475 15 0.10 (0.01) 0.72 (0.02) 0.04 (0.01) 1.17 (0.11) 117 (6) Acetylene Black / 1/AB 51 35 0.09 (0.00) 0.69 (0.05) 0.02 (0.01) 0.47 (0.06) 72 (6) Ketjen Black EC-DJ600 / 1/KB 1270 30 0.11 (0.01) 0.70 (0.02) 0.03 (0.00) 0.21 (0.05) 61 (3) Graphite / 1/G 3.9 < 75 µm 0.02 (0.00) 0.04 (0.01) 0.00 (0.00) 0.00 (0.01) 4 (0) FIGURE 2 Characterization of the Vulcan XC-72R-supported catalyst ( 1 /Vul). (a) Fe K -edge XANES spectra of 1 /Vul and related materials ( 1 , 1+ ⋅I− , 1 /SiO2 , and 1+ ⋅I− /SiO2 ). Inset: expanded spectra of the pre-edge region. (b) HAADF-STEM image of 1 /Vul. The yellow arrows indicate spots assignable to 1 on the Vulcan support. (c) STEM-EDS mapping of 1 /Vul.                          18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable CreativeSiO2 ( 1+ ⋅I− /SiO2 ), and solid of 1+ ⋅I− . The results are shown inFigure 2a . Their pre-edge peak tops are summarized in TableS1 . The peak of 1 /Vul appears at a lower energy (7113.9 ev)than those of 1+ ⋅I− /SiO2 (7115.4 ev) and solid of 1+ ⋅I− (7115.2 ev)but almost identical to those of 1 /SiO2 (7114.1 ev) and solid of1 (7114.1v). These results indicate that 1+ ⋅I− was reduced byVulcan during heating in pyridine and then deposited on theVulcan surface in its neutral form ( 1 ). The high-angle annulardark-field scanning transmission electron microscopy (HAADF-STEM) image of 1 /Vul contains some bright spots on the layer-by-layer structure of Vulcan, which could be assigned to singleμ-nitrido-bridged iron phthalocyanine dimers (Figure 2b ). STEM-energy dispersive X-ray spectroscopy (EDS) mapping of iron andnitrogen indicated that the μ-nitrido-bridged iron phthalocyanineChemCatChem, 2026dimer was homogeneously dispersed over the carbon particle without forming large aggregates (Figure 2c ). Also note that theEDS signal of iodine was very low ( < 0.01% in atomic fractionbased on the EDS spectrum), further supporting that 1+ ⋅I− wasreduced by Vulcan to 1 (Figure S3 ). It should also be noted thatEDS analysis indicated trace Fe in pristine Vulcan XC-72R (Femass fraction = 0.078 ± 0.019). After deposition of 1 on Vulcan,the Fe mass fraction tended to get higher (0.145 ± 0.073), althoughthe EDS quantification uncertainties were relatively large (page S7–S8 in the Supporting Information). These results do not alterthe conclusions drawn from the HAADF-STEM/EDS results. It was also confirmed that pristine Vulcan XC-72R exhibitedno apparent CH4 oxidation activity at 25◦C under the presentconditions (vide infra). 3 of 9 Commons LicenseFIGURE 3 CH4 oxidation activity of 1 /Vul at 25◦C. (a) 1 H-NMR spectrum of CH4 reaction mixture. Reaction conditions: 1 /Vul (19 µM as 1 ), 1.0 MPa of CH4 , D2 O (3.0 mL) containing excess H2 O2 (189 mM) and TFA (51 mM), 25◦C, and 2 h. (b) 13 C-NMR spectra of the reaction mixture using unlabeled CH4 (black) and 13 CH4 (red). Reaction conditions: 1 /Vul (19 µM as 1 ), 0.5 MPa of 13 CH4 or CH4 , D2 O (3.0 mL) containing excess H2 O2 (189 mM) and TFA (51 mM), 25◦C, and 2 h. (c) Stepwise oxidation of CH4 by 1 /Vul in an acidic aqueous solution. Time dependence of (d) the concentration of C1 oxygenated products and (e) MCNeff in the reaction of CH4 over 1 /Vul at 25◦C.                                          18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative2.2 Catalytic CH4 Oxidation by 1/Vul at 25◦C We investigated the catalytic CH4 oxidation activity of 1 /Vul(19 µM as 1 ) at 25◦C in an acidic aqueous solution (3.0 mL)containing 51 mM of trifluoroacetic acid (TFA) and 189 mM ofH2 O2 under a CH4 atmosphere of 1.0 MPa, the same conditionswe previously used to investigate 1 /G [ 36 ]. An acidic conditionis necessary for efficient catalysis when using μ-nitrido-bridgediron phthalocyanine dimers, because this condition enhancesthe production of high-valent iron-oxo species by facilitatingO ─O bond cleavage of the corresponding hydroperoxo species(Scheme S1 ) [ 31–33 ]. The resulting solution was analyzed andquantified using gas chromatography-mass spectrometry (GC-MS) and 1 H-nuclear magnetic resonance (NMR) spectroscopy.Significant amounts of C1 oxygenated products, namely CH3 OH,CH3 OOH, HCHO (observed as CH2 (OH)(OOH) and CH2 (OH)2 inNMR), and HCOOH, were found in the solution as summarizedin Figure 3a,d , and Table S2 . Upon replacing the CH4 atmosphere with N2 , the amount ofC1 oxygenated products became much smaller (see Table S2 ),indicating that they did not originate from the catalyst itself.13 C-NMR spectrum of the reaction mixture using 13 CH4 as asubstrate confirmed that these products came from CH4 insteadof from 1 or Vulcan (Figure 3b ). The use of Vulcan XC-72R4 of 9alone also afforded a very small amount of oxygenated productsunder the same reaction conditions (entries 17 and 18 in TableS2 ). It was also confirmed by the hot filtration experiment thatthe species on the Vulcan support actually showed the room-temperature CH4 oxidation activity (see page S20–S21 in the Supporting Information). All these results suggest that 1 adsorbedon Vulcan efficiently catalyzed the CH4 oxidation reaction. The small amount of oxidized products in the absence of CH4 waspresumably generated from organic solvents adsorbed on Vulcan and/or Vulcan itself (see Table S2 ). The addition of excess Na2 SO3 can effectively quench the reactionby ∙OH, whereas oxidation reactions mediated by high-valent iron-oxo species were reported to be only marginally affectedby Na2 SO3 [ 39–44 ]. However, in the case of CH4 oxidation by1 /Vul, excess Na2 SO3 (100 mM) did not completely quenchthe reaction, even though it decreased the total amount of C1oxygenated products to half of that before addition (entries 15 and16, Table S2 ). We also applied electron paramagnetic resonance(EPR, Figure S4 ) and electrospray ionization time-of-flight massspectrometry (ESI-TOF MS, Figure S8 ) analyses to the reactionmixture for CH4 oxidation by 1 /Vul in the presence of excess 5,5-dimethyl-1-pyrroline (DMPO, 100 mM) as a radical scavenger. Theamount of trapped ∙OH was much smaller compared to that ofthe C1 oxygenated products (Figure S7 ). These results suggestChemCatChem, 2026 Commons License                                                                                              18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Cthat CH4 oxidation via ∙OH is not dominant in this reactionsystem, and that the metal complex-based species should be themain reactive intermediate. Based on our previous MALDI-TOFMS experiment, which clearly showed the high-valent iron-oxospecies of 1 ( 1(oxo) ) after treating 1 deposited on a carbonsurface with H2 O2 [ 36 ], we assumed 1(oxo) on Vulcan to be themost likely candidate for the reactive intermediate in the presentsystem. It is likely that CH4 was oxidized in a stepwise manner inthis acidic aqueous solution, as shown in Figure 3c . To discussthe activities of carbon-supported catalysts, we calculated theeffective methane conversion number [MCNeff , defined in Equa-tions ( 1 ) and ( 2 )] based on the concentrations of C1 oxygenatedproducts in CH4 and N2 atmospheres. MCNeff directly reflects thenumber of C ─H bonds in CH4 dissociated during the reaction. MC 𝑁eff = MC 𝑁(CH 4) −MC 𝑁( 𝑁2) (1)MC 𝑁( CH 4) or MC 𝑁( 𝑁2) = ( 𝐶CH 3OH + 𝐶CH 3OOH + 𝐶HCHO + 𝐶HCOOH ) 𝐶Cat (2)Next, we investigated the time courses of the concentrationof C1 oxygenated products and MCNeff , and the results areshown in Figure 3d,e , respectively. The initial linear increase inMCNeff indicated that 1 /Vul worked stably under these reactionconditions. The gradual saturation of catalytic activity, especiallyafter 2 h, was attributed to three reasons: (i) overoxidation ofHCOOH [ 36, 45 ], (ii) consumption of H2 O2 by the catalasereaction, as confirmed by our titration experiments (for details seeFigure S9 ) [ 36, 46 ], and (iii) gradual deactivation of the catalyst.Regarding catalyst deactivation, we confirmed that after 4 h ofreaction with CH4 , the activity of 1 /Vul decreased to almost26% of the original value. Considering that the XANES spectraindicated that the catalyst after CH4 oxidation retained similaroxidation states and coordination as the original one (FigureS10 ), the decreased catalytic activity afterwards is attributableto partial detachment of adsorbed 1 from the Vulcan surface.This assumption is also supported by the fact that the massfraction of Fe in the catalyst after use (4 h reaction at 25◦C),analyzed by EDS, was apparently decreased compared to thatbefore use (see page S8 in the Supporting Information). Detached1 from the Vulcan surface did not show apparent CH4 oxidationactivity in this reaction condition, as confirmed by the results ofhot filtration experiments (see page S20–S21 in the SupportingInformation). Here, the initial reaction rate over 1 /Vul for the C ─H bondactivation of CH4 at 25◦C reached MCNeff = 1.5 × 10− 2 s− 1 (55 h− 1 ),as shown in Table S2 and Figure 3e . The ability of 1 /Vul tocatalytically activate the C ─H bond in CH4 is considerably highamong molecule-based CH4 oxidation catalysts and even amonggeneral room-temperature CH4 oxidation catalysts reported sofar [ 17–30 ]. More importantly, from the viewpoint of SMCs orSIMCs, here we achieved a high catalytic CH4 oxidation activitythat is impossible for the metal complex or carbon substratealone, by using an appropriate combination of μ-nitrido-bridgediron phthalocyanine dimer with a conductive carbon blacksupport. ChemCatChem, 20262.3 Comparison of Catalytic CH4 Oxidation Activities of 1/Vul and Fenton Reaction Using Fe2 + at 25◦C The Fenton reaction exhibits a high catalytic activity for theoxidative activation of C ─H bonds in various organic pollutantsunder mild conditions. The most common Fenton reaction system uses Fe2 + and H2 O2 in an acidic condition, where Fe2 + actsas a catalyst to produce ∙OH or ferryl iron from H2 O2 as a reactiveintermediate [ 47 ]. This system is both potent and simple becausea strong oxidizing ability is obtained by mixing commerciallyavailable reagents without using any special equipment. Thus, ithas long been used to treat wastewater and contaminated soil as“the last trump card”. Under a condition similar to that of theFenton reaction, we compared the catalytic C ─H bond oxidationability of 1 /Vul with that of the Fenton reaction using Fe2 + , usingCH4 as a substrate. Wastewater treatment using the Fenton reaction of Fe2 + and H2 O2 has an optimal pH of approximately 3 [ 47 ]. H2 SO4 is often usedto control the pH value here, and the catalytic activity tends todecrease at a lower pH. When we investigated the pH dependenceof catalytic CH4 oxidation by 1 /Vul at 25◦C, the optimal pH wasfound to be 2 with TFA as an acid (Figure 4a and Table S5 ). Thisreaction also proceeded in the presence of H2 SO4 as an acid at25◦C, and the catalytic activity was almost comparable to that inthe presence of TFA at pH 3 (Table S6 ). We performed 1 H-NMR measurements to compare the catalytic CH4 oxidation activities of 1 /Vul (19 µM as 1 ) and the Fentonreaction using Fe2 + (326 µM) at pH 3 and 25◦C. Figure 4b showsthe experimental results in D2 O (3.0 mL) solution containingexcess H2 O2 (50 µL of 35% H2 O2 , 189 mM) and H2 SO4 (0.5 mM,pH ≈ 3) under a CH4 pressure of 1.0 MPa for 2 h. In thecase of the Fenton reaction, only a small amount of HCOOH(0.02 mM) was observed afterwards. In contrast, 1 /Vul produceda significant amount of C1 oxygenated compounds (0.11 mMof CH3 OH, 0.62 mM of CH3 OOH, 0.48 mM of HCHO, and2.20 mM of HCOOH, as summarized in Table S6 ), even thoughmuch less catalyst was used (19 µM as 1 versus 326 µM of Fe2 + ).Next, we tested the oxidation of CH3 OH, which is easier thanCH4 oxidation, in the Fenton reaction at 25◦C. The reactionoccurred catalytically (see Figure S11 ), suggesting that ∙OH orferryl ion was actually generated in this condition. Meanwhile,EPR experiments in the presence of excess DMPO indicated thatthe amount of ∙OH trapped by DMPO was much larger in theFenton reaction than in the reaction using 1 /Vul (Figures S5c, S6b ,and S7 ), suggesting that highly reactive species other than ∙OHwere involved in the oxidation by 1 /Vul. More importantly, 1 /Vulshowed more potent C ─H activation than the Fenton reactionunder the same reaction conditions at 25◦C. 2.4 Discussion of the Reaction Mechanism To investigate the reason for the high catalytic oxidation activity of1 /Vul, we prepared other carbon-supported catalysts ( 1 /KB, 1 /BP,and 1 /AB) using similar methods and commercially availableconductive carbon blacks (Ketjen Black EC-DJ600 (KB), Black Pearls 2000 (BP), and Acetylene Black (AB)). In each case,5.7 µmol of 1 was quantitatively adsorbed on 1.0 g of carbon5 of 9ommons LicenseFIGURE 4 Comparison of catalytic CH4 oxidation activities of 1 /Vul and Fenton reaction at 25◦C. (a) pH dependence in the catalytic CH4 oxidation activity of 1 /Vul at 25◦C. The pH values of the solution containing 51 mM of TFA were adjusted by the addition of aqueous NaOH. The details are shown in SI. (b) 1 H-NMR spectra of the CH4 reaction mixtures with 1 /Vul (top) and FeSO4 (bottom) at pH 3. Reaction conditions: 1.0 MPa CH4 , 1 /Vul (19 µM as 1 ) or FeSO4 (326 µM), D2 O (3.0 mL) containing H2 SO4 (0.5 mM) and excess H2 O2 (189 mM), 25◦C, and 2 h. (c) Dependence of the total amount of C1 oxygenated products on the loading amount of 1 on Vulcan. (d) Proposed reaction mechanism of CH4 oxidation over 1 /Vul. Error bars in (a) and (c) indicate the S.D. of three independent experiments.                                   v    18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creativesupport after heating in pyridine, as in the case of 1 /Vul. Thecatalytic CH4 oxidation activities of 1 /Vul, 1 /KB, 1 /BP, 1 /AB, and1 /G are summarized in Table 1 . All of them showed significantlyhigher activity of 1 compared to that of 1 /G. However, the initialreaction rate (at 2 h of oxidation) seemed to depend on thetype of carbon support, even though the loading of 1 was thesame. Table 1 shows no apparent correlation between the catalyticCH4 oxidation activity and the surface area or particle size ofthe carbon support. Rather, the catalytic activity of adsorbed 1could have been affected by different electronic structures of thecarbon blacks owing to variations in their structures. In fact, theRaman spectra indicate that the carbon blacks have considerablydifferent ID / IG ratios from that of graphite (Figure S12 ), which isindicative of their structural differences [ 48 ]. To obtain further insight into the interaction between 1 andVulcan, we prepared catalysts with different loadings of 1 per1.0 g of Vulcan XC-72R and performed CH4 oxidation experimentsat 25◦C. As shown in Figure 4c and Table S7 , the total amountof C1 oxygenated products increased almost linearly at lowerloadings but apparently became saturated at higher loadings. Thehighest catalytic activity was obtained at 11 µmol/g of 1 . Based6 of 9on the Brunauer–Emmett–Teller (BET) surface area of Vulcan (254 m2 /g) and the molecular surface area of 1 (ca. 1.6 nm2 , FigureS13 ), the coverage ( q ) by 1 at this loading was calculated to be 0.05.This result suggests that the high catalytic activity is due to notonly the simple stacking of 1 with the carbon surface but also theinteraction between 1 and particular surface sites on Vulcan. According to our previous density functional theory (DFT)calculations and electrochemical experiments, the stacking inter- action of 1 with the π-surface of carbon material could cause aslight charge transfer due to interaction of the singly occupiedmolecular orbital (SOMO) of 1 with the π-orbital of carbon, whichcan lower the SOMO level of the catalyst [ 36 ]. This may be key toelucidating the role of Vulcan. Figure 4d shows the proposed mechanism of CH4 oxidation by1 /Vul. Considering (1) the different optimal pH values between1 /Vul and Fenton reaction as well as the much higher catalyticCH4 oxidation activity of 1 /Vul with less ∙OH trapped by DMPOand (2) our previous MALDI-TOF MS observation of the high-alent iron-oxo species 1(oxo) on a carbon substrate, the reactionof 1 /Vul could involve 1(oxo) as the dominant reactive inter-ChemCatChem, 2026 Commons License                                                                                18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Cmediate. 1(oxo) can efficiently activate the C ─H bond of CH4 via the PCET mechanism, in which both electrons and protonsare extracted from CH4 in a concerted manner [ 34, 35 ]. Theenhanced catalytic ability of 1 /Vul could be explained by theelectronic interaction with carbon, in particular, a lower SOMOof the high-valent iron-oxo species that promotes PCET withCH4 and efficient formation of ∙CH3 . Nevertheless, it is difficultto discuss the detailed mode of interaction between 1 and theVulcan surface. In total, a series of C1 oxygenated products couldbe produced through oxidation by high-valent iron-oxo speciesinstead of by ∙OH. 3 Conclusions We demonstrated that depositing the μ-nitrido-bridged ironphthalocyanine dimer 1 on an appropriate conductive carbonsupport dramatically enhanced its catalytic oxidation ability. Thesupported catalyst ( 1 /Vul) achieved efficient C ─H activation ofCH4 at 25◦C in acidic aqueous solutions. Its catalytic abilityexceeded that of the Fenton reaction using Fe2 + and H2 O2 , asystem that has long been employed for wastewater treatmentunder the same conditions. We also demonstrated that the highcatalytic activity of 1 /Vul occurs by the interaction of 1 withparticular surface sites on Vulcan. It has been difficult forpure artificial high-valent iron-oxo-based molecular catalysts toachieve such a high CH4 oxidation activity at room temperature.In SMCs or SIMCs, the activity of the molecular catalyst canbe tuned through its interaction with the solid support. Thisstrategy enables the modulation of interactions between thecarbon surface and molecular metal complex-based catalysts tocreate novel catalysts for even more difficult reactions. 4 Experimental Section 4.1 Preparation of Supported Catalysts In a typical experiment, the monocationic μ-nitrido-bridged ironphthalocyanine dimer 1+ ⋅I− (16.3 mg, 11.6 µmol as a pyridineadduct) was dissolved in pyridine (10 mL) to obtain a deep bluesolution (Figure S1b ). After adding a suspension of Vulcan XC-72R (1.93 g, Cabot Corp.) in pyridine (50 mL), the mixture wassonicated for 1 h. The resulting suspension was stirred for 20 hat 80◦C. After filtration, the filtrate was almost colorless (FigureS1c ). The separated solid was successively washed with pyridine(20 mL × 2) and CH2 Cl2 (50 mL × 2) and dried under reducedpressure ( ∼ 1 mmHg) at 80◦C for 1 h. The obtained solid was suspended in H2 O (50 mL) containing5.0 mL of TFA and sonicated for 1 h. Then, the solid was separatedby filtration and washed with H2 O to neutral pH. The purifiedsolid was resuspended in H2 O (50 mL) containing 5.0 mL of TFAand sonicated for 1 h, followed by filtration again. The obtainedsolid was washed with H2 O to neutral pH and then dried underreduced pressure ( ∼ 1 mmHg) at 80◦C overnight. Finally, the solidwas kept in air at room temperature until its weight becameconstant, giving 1 /Vul (1.87 g, Figure S1d ). 1 /KB, 1 /BP, 1 /AB, and1 /G were prepared similarly on different supports. ChemCatChem, 2026When mixing more than 11 µmol of 1+ ⋅I− with 1.0 g of VulcanXC-72R, the color of the filtrate after heating at 80◦C in pyridineremained deep blue. In these cases, the solvent was evapo-rated slowly to maximize the adsorption of remaining catalystmolecules in the solvent on Vulcan. After evaporation, the samewashing procedure was performed as described above. 4.2 CH4 Oxidation Reactions CH4 oxidation was performed in a stainless-steel autoclave with a glass tube. A mixture of a solid-supported catalyst (10 mg,19 µM as 1 ), TFA (12 µL, 51 mM), and 35% H2 O2 aq. (50 µL,189 mM) in H2 O (3.0 mL) was stirred by using a magneticstirring bar at 25◦C in a water bath or an oil bath under a CH4 atmosphere of 1.0 MPa for a given reaction time. After the reac-tion mixture was filtered through a disposable membrane filter(ADVANTEC, DISMIC-13CP), the resulting filtrate was mixed with an appropriate amount of an aqueous isovaleric acid solution(100 mM) and analyzed by GC-MS (system: Shimadzu GCMS-QP2020, detection: EI, column: Agilent DB-WAX UI, external standard: isovaleric acid (5 mM), temperature conditions: initial: 50◦C—hold (1 min)—raise to 220◦C (10◦C/min)— hold (5 min)).The yields of CH3 OH and HCOOH were determined based on theresults of GC-MS. The yield of HCHO was determined using the method reportedby Yu et al. [ 49 ]. Typically, 25 µL of the filtrate obtained fromthe reaction mixture was diluted with 50 mL of H2 O, followedby the addition of an aqueous solution (469 µM) of PFBOA ⋅HCl(3.0 mL). The resulting mixture was stirred for 2 h. Then, sulfuricacid (1 + 1) (0.8 mL), NaCl (20 g), and hexane (5.0 mL) were added,and the mixture was stirred vigorously for 5 min. The separatedorganic layer was dried over anhydrous Na2 SO4 . A mixture of theresulting solution (1.0 mL) and a 1.0 mM 1-chlorodecane/hexanesolution (10.1 µL) was analyzed by GC-MS (Agilent 7890Aequipped with JEOL JMS-T100GCV, detection: EI, column: Agi- lent DB-WAX UI, external standard: 1-chlorodecane (10 µM), temperature conditions: initial: 70◦C—hold (10 min)—raise to 150◦C (10◦C/min)—raise to 240◦C (30◦C/min)—hold (3 min)). In an acidic aqueous solution, HCHO can be hydroxylated toCH2 (OH)2 . In addition, 13 C-NMR study of the reaction mixture of the 13 CH4 oxidation reaction (see Supporting Information ) by the catalysts used in this study indicated that H2 C(OH)(OOH)was produced as one of the major C1 oxygenated products.It is considered that both H2 C(OH)(OOH) and H2 C(OH)2 can be converted into the same oxime through the derivatizationreaction with the reaction PFBOA ⋅HCl mentioned above. It was reported that CH3 OOH was difficult to be quantifiedby GC-MS because it can easily be decomposed [ 45 ]. There-fore, CH3 OOH was quantified by using 1 H-NMR measurement as mentioned below: A mixture of a solid-supported catalyst(10 mg, 19 µM as 1 ), TFA (12 µL, 51 mM), and 35% H2 O2 aq. (50 µL, 189 mM) in D2 O (3.0 mL), was stirred by using amagnetic stirring bar at 25◦C in a water bath or an oil bathunder a CH4 atmosphere of 1.0 MPa for a given reaction time.After the reaction mixture was filtered through a disposablemembrane filter (ADVANTEC, DISMIC-13CP), the resulting fil- trate was subjected to 1 H-NMR measurements using a JEOLJNM-ECS400 (400 MHz for 1 H) spectrometer. 3-(Trimethylsilyl)- 7 of 9ommons License                                         A                      18673899, 2026, 3, Downloaded from https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cctc.202501356, Wiley Online Library on [31/01/2026]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative C2,2,3,3-tetradeuteropropionic acid sodium salt (TSP, 10 mM inD2 O) in a glass capillary was used as an external standard.The concentration of CH3 OOH was determined based on theintegration of TSP. The evaluations of the CH4 oxidation reactions using 1 /KB, 1 /BP,1 /AB, 1 /G, and Vulcan XC-72R (with no catalyst molecule) wereperformed in a similar manner. The reactions in the presence of100 mM Na2 SO3 (entries 15 and 16 in Table S2 ) were performed ina similar manner. Acknowledgments We are grateful for fruitful discussions with Dr. Atsushi Ogawa andDr. Yuya Shimizu from Okumura Corporation, Prof. Osami Shoji fromNagoya University, and Prof. Satoru Takakusagi from Hokkaido Uni-versity. We thank Mr. Kouichi Okudaira for his contribution to theHAADF-STEM/EDS analyses. XAFS measurements were performedwith the approval of PF-PAC (Nos. 2023G161 and 2023G162) and theAichi Synchrotron Radiation Center (No. 202304025). KT was financiallysupported by a JSPS KAKENHI Grant-in-Aid for Challenging Research(Exploratory) (No. JP25K22271), and YY was financially supported by aGrant-in-Aid for Scientific Research (B) (No. JP25K01843) and a Grant-in-Aid for Transformative Research Areas (A) “Green Catalysis Science”(No. JP24H01844). MT was financially supported by a Grant-in-Aid forInternational Leading Research (No. JP23K020034). KH was finaciallysupported by a Grant-in-Aid for Transformative Research Areas (A)“Materials Science of Meso-Hierarchy” (No. JP23H04874). This studywas also supported by the Okumura Corporation and “Quantum-BasedFrontier Research Hub for Industry Development”, Nagoya University,Japan. Conflicts of Interest The authors declare no conflict of interest. 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Supporting File: cctc70565-supp-0001-SuppMat.pdf. 9 of 9 Creative Commons Licensehttps://doi.org/10.1126/sciadv.aaz9776https://doi.org/10.1021/jacs.1c07590https://doi.org/10.1002/anie.202016888https://doi.org/10.1038/s41929-023-01030-2https://doi.org/10.1126/science.aat9750https://doi.org/10.1021/jacs.3c01317https://doi.org/10.1038/s42004-022-00803-3https://doi.org/10.1016/j.chempr.2023.02.011https://doi.org/10.1002/anie.201209846https://doi.org/10.1021/acs.accounts.5b00458https://doi.org/10.1039/b804405hhttps://doi.org/10.1021/cr0500030https://doi.org/10.1002/anie.201805511https://doi.org/10.1016/0008-6223(94)90031-0https://doi.org/10.1002/advs.201902126https://doi.org/10.1002/anie.201108706https://doi.org/10.1039/D0NJ04601Ahttps://doi.org/10.1039/D1DT02922Chttps://doi.org/10.1039/D1DT00941Ahttps://doi.org/10.1039/D2CY01980Ahttps://doi.org/10.1039/D3DT04313Dhttps://doi.org/10.1016/j.jcat.2012.03.013https://doi.org/10.1021/ja8043689https://doi.org/10.1016/j.carbon.2005.02.018https://doi.org/10.1021/ac015708q Efficient Room-Temperature Methane Oxidation by -Nitrido-Bridged Iron Phthalocyanine Dimer Deposited on Conductive Carbon Black 1 | Introduction 2 | Results and Discussion 2.1 | Preparation and Characterization of Vulcan XC-72R-Supported Catalyst 2.2 | Catalytic CH4 Oxidation by 1/Vul at 25°C 2.3 | Comparison of Catalytic CH4 Oxidation Activities of 1/Vul and Fenton Reaction Using Fe2+ at 25°C 2.4 | Discussion of the Reaction Mechanism 3 | Conclusions 4 | Experimental Section 4.1 | Preparation of Supported Catalysts 4.2 | CH4 Oxidation Reactions Acknowledgments Conflicts of Interest Supporting Information Data Availability Statement References Supporting Information