Abstract
Direct methane functionalization and, in particular, the selective partial oxidation to methanol, remains an eminent challenge and a field of competitive research. The conversion of methane to methanol over transition-metal-containing zeolites using molecular oxygen is a promising and extensively studied process. Herein, we scrutinize some oft-cited assumptions in this topic—which include the labelling of the process as biomimetic, the debate regarding the industrial viability of direct methane-oxidation systems and the claim that methane is difficult to activate—and delineate the extent to which these are scientifically robust. We highlight both the merits and pitfalls of such statements and point out the hazards associated with their improper use. By examining these misconceptions, we build an outlook for future research, highlighting the need to optimize materials and process conditions for the stepwise approach and to further explore catalytic processes that explicitly employ strategies for the preservation of methanol.
Similar content being viewed by others
Data availability
The authors declare that the data supporting the findings of this study are available within the paper.
References
Nisbet, E. G., Dlugokencky, E. J. & Bousquet, P. Methane on the rise—again. Science 343, 493–495 (2014).
Alvarez-Galvan, M. C. et al. Direct methane conversion routes to chemicals and fuels. Cataly. Today 171, 15–23 (2011).
Tang, P., Zhu, Q., Wu, Z. & Ma, D. Methane activation: the past and future. Energy & Environ. Science 7, 2580–2591 (2014).
Choudhary, T. V. & Choudhary, V. R. Energy‐efficient syngas production through catalytic oxy‐methane reforming reactions. Angew. Chem. Int. Ed. 47, 1828–1847 (2008).
Dybkjær, I. & Aasberg‐Petersen, K. Synthesis gas technology large‐scale applications. Can. J. Chem. Eng. 94, 607–612 (2016).
Foster, N. R. Direct catalytic oxidation of methane to methanol—a review. Appl. Catal. 19, 1–11 (1985).
Lange, J. P., De Jong, K. P., Ansorge, J. & Tijm, P. J. A. in Studies in Surface Science and Catalysis Vol. 107 81–86 (Elsevier, 1997).
Ahlquist, M., Nielsen, R. J., Periana, R. A. & Goddard, W. A. III. Product protection, the key to developing high performance methane selective oxidation catalysts. J. Am. Chem. Soc. 131, 17110–17115 (2009).
Hammond, C., Conrad, S. & Hermans, I. Oxidative methane upgrading. ChemSusChem 5, 1668–1686 (2012).
Kondratenko, E. V. et al. Methane conversion into different hydrocarbons or oxygenates: current status and future perspectives in catalyst development and reactor operation. Catal. Sci. Technol. 7, 366–381 (2017).
Ravi, M., Ranocchiari, M. & van Bokhoven, J. A. The direct catalytic oxidation of methane to methanol-a critical assessment. Angew. Chem. Int. Ed. 56, 16464–16483 (2017).
Kulkarni, A. R., Zhao, Z.-J., Siahrostami, S., Nørskov, J. K. & Studt, F. Cation-exchanged zeolites for the selective oxidation of methane to methanol. Catal. Sci. Technol. 8, 114–123 (2018).
Lance, D. & Elworthy, E. G. Process for the manufacture of methyl-alcohol from methane. French patent 352,687 (1905).
Periana, R. A. et al. A mercury-catalyzed, high-yield system for the oxidation of methane to methanol. Science 259, 340–343 (1993).
Periana, R. A. et al. Platinum catalysts for the high-yield oxidation of methane to a methanol derivative. Science 280, 560–564 (1998).
Muehlhofer, M., Strassner, T. & Herrmann, W. A. New catalyst systems for the catalytic conversion of methane into methanol. Angew. Chem. Int. Ed. 41, 1745–1747 (2002).
Hashiguchi, B. G. et al. Main-group compounds selectively oxidize mixtures of methane, ethane, and propane to alcohol esters. Science 343, 1232–1237 (2014).
Ravi, M. & van Bokhoven, J. A. Homogeneous copper‐catalyzed conversion of methane to methyl trifluoroacetate in high yield at low pressure. ChemCatChem 10, 2383–2386 (2018).
Hammond, C. et al. Direct catalytic conversion of methane to methanol in an aqueous medium by using copper‐promoted Fe‐ZSM‐5. Angew. Chem. Int. Ed. 51, 5129–5133 (2012).
Shan, J., Li, M., Allard, L. F., Lee, S. & Flytzani-Stephanopoulos, M. Mild oxidation of methane to methanol or acetic acid on supported isolated rhodium catalysts. Nature 551, 605–608 (2017).
Mehta, P. K., Mishra, S. & Ghose, T. K. Methanol accumulation by resting cells of Methylosinus trichosporium (I). J. Gen. Appl. Microbiol. 33, 221–229 (1987).
Sugimori, D., Takeguchi, M. & Okura, I. Biocatalytic methanol production from methane with methylosinus trichosporium OB3b: an approach to improve methanol accumulation. Biotechnol. Lett. 17, 783–784 (1995).
Kim, H. G., Han, G. H. & Kim, S. W. Optimization of lab scale methanol production by methylosinus trichosporium OB3b. Biotechnol. Bioprocess Eng. 15, 476–480 (2010).
Duan, C., Luo, M. & Xing, X. High-rate conversion of methane to methanol by methylosinus trichosporium OB3b. Bioresour. Technol. 102, 7349–7353 (2011).
Sushkevich, V. L., Palagin, D., Ranocchiari, M. & van Bokhoven, J. A. Selective anaerobic oxidation of methane enables direct synthesis of methanol. Science 356, 523–527 (2017).
Wang, X. et al. Copper-modified zeolites and silica for conversion of methane to methanol. Catalysts 8, 545 (2018).
Narsimhan, K., Iyoki, K., Dinh, K. & Román-Leshkov, Y. Catalytic oxidation of methane into methanol over copper-exchanged zeolites with oxygen at low temperature. ACS Cent. Sci. 2, 424–429 (2016).
Starokon, E. V., Parfenov, M. V., Pirutko, L. V., Abornev, S. I. & Panov, G. I. Room-temperature oxidation of methane by α-oxygen and extraction of products from the FeZSM-5 surface. J. Phys. Chem. C. 115, 2155–2161 (2011).
Starokon, E. V. et al. Oxidation of methane to methanol on the surface of FeZSM-5 zeolite. J. Catal. 300, 47–54 (2013).
Groothaert, M. H., Smeets, P. J., Sels, B. F., Jacobs, P. A. & Schoonheydt, R. A. Selective oxidation of methane by the bis (μ-oxo) dicopper core stabilized on ZSM-5 and mordenite zeolites. J. Am. Chem. Soc. 127, 1394–1395 (2005).
Beznis, N. V., Weckhuysen, B. M. & Bitter, J. H. Cu-ZSM-5 zeolites for the formation of methanol from methane and oxygen: Probing the active sites and spectator species. Catal. Lett. 138, 14–22 (2010).
Alayon, E. M., Nachtegaal, M., Ranocchiari, M. & van Bokhoven, J. A. Catalytic conversion of methane to methanol over Cu–mordenite. Chem. Commun. 48, 404–406 (2012).
Vanelderen, P. et al. Spectroscopic definition of the copper active sites in mordenite: selective methane oxidation. J. Am. Chem. Soc. 137, 6383–6392 (2015).
Zhao, Z.-J., Kulkarni, A., Vilella, L., Norskov, J. K. & Studt, F. Theoretical insights into the selective oxidation of methane to methanol in copper-exchanged mordenite. ACS Catal. 6, 3760–3766 (2016).
Li, G. et al. Stability and reactivity of copper oxo-clusters in ZSM-5 zeolite for selective methane oxidation to methanol. J. Catal. 338, 305–312 (2016).
Sheppard, T., Daly, H., Goguet, A. & Thompson, J. M. Improved efficiency for partial oxidation of methane by controlled copper deposition on surface‐modified ZSM‐5. ChemCatChem 8, 562–570 (2016).
Grundner, S. et al. Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol. Nat. Commun. 6, 7546 (2015).
Yumura, T., Hirose, Y., Wakasugi, T., Kuroda, Y. & Kobayashi, H. Roles of water molecules in modulating the reactivity of dioxygen-bound Cu-ZSM-5 toward methane: a theoretical prediction. ACS Catal. 6, 2487–2495 (2016).
Marturano, P., Drozdová, L., Kogelbauer, A. & Prins, R. Fe/ZSM-5 prepared by sublimation of FeCl 3: The structure of the Fe species as determined by IR, 27 Al MAS NMR, and EXAFS spectroscopy. J. Catal. 192, 236–247 (2000).
Battiston, A. A. et al. Evolution of Fe species during the synthesis of over-exchanged Fe/ZSM5 obtained by chemical vapor deposition of FeCl 3. J. Catal. 213, 251–271 (2003).
Groothaert, M. H., van Bokhoven, J. A., Battiston, A. A., Weckhuysen, B. M. & Schoonheydt, R. A. Bis (μ-oxo) dicopper in Cu-ZSM-5 and its role in the decomposition of NO: a combined in situ XAFS, UV-Vis-Near-IR, and kinetic study. J. Am. Chem. Soc. 125, 7629–7640 (2003).
Vanelderen, P. et al. Cu-ZSM-5: A biomimetic inorganic model for methane oxidation. J. Catal. 284, 157–164 (2011).
Snyder, B. E. R., Bols, M. L., Schoonheydt, R. A., Sels, B. F. & Solomon, E. I. Iron and copper active sites in zeolites and their correlation to metalloenzymes. Chem. Rev. 118, 2718–2768 (2017).
Rosenzweig, A. C., Frederick, C. A. & Lippard, S. J. Crystal structure of a bacterial non-haem iron hydroxylase that catalyses the biological oxidation of methane. Nature 366, 537–543 (1993).
Sobolev, V. I., Dubkov, K. A., Panna, O. V. & Panov, G. I. Selective oxidation of methane to methanol on a FeZSM-5 surface. Catal. Today 24, 251–252 (1995).
Tomkins, P. et al. Isothermal cyclic conversion of methane into methanol over copper-exchanged zeolite at low temperature. Angew. Chem. Int. Ed. 55, 5467–5471 (2016).
Lee, S. J., McCormick, M. S., Lippard, S. J. & Cho, U.-S. Control of substrate access to the active site in methane monooxygenase. Nature 494, 380–384 (2013).
Lipscomb, J. D. Biochemistry of the soluble methane monooxygenase. Ann. Rev. Microbiol. 48, 371–399 (1994).
Borfecchia, E. et al. Evolution of active sites during selective oxidation of methane to methanol over Cu-CHA and Cu-MOR zeolites as monitored by operando XAS. Catal. Today (2018).
Dalton, H., Smith, D. D. S. & Pilkington, S. J. Towards a unified mechanism of biological methane oxidation. FEMS Microbiol. Rev. 7, 201–207 (1990).
Colby, J. & Dalton, H. Resolution of the methane mono-oxygenase of methylococcus capsulatus (Bath) into three components. Purification and properties of component C, a flavoprotein. Biochem. J. 171, 461–468 (1978).
Friedle, S., Reisner, E. & Lippard, S. J. Current challenges of modeling diiron enzyme active sites for dioxygen activation by biomimetic synthetic complexes. Chem. Soc. Rev. 39, 2768–2779 (2010).
Tinberg, C. E. & Lippard, S. J. Dioxygen activation in soluble methane monooxygenase. Acc. Chem. Res. 44, 280–288 (2011).
Snyder, B. E. R., Vanelderen, P., Schoonheydt, R. A., Sels, B. F. & Solomon, E. I. Second-sphere effects on methane hydroxylation in Cu-zeolites. J. Am. Chem. Soc. 140, 9236–9243 (2018).
Dinh, K. T. et al. Viewpoint on the partial oxidation of methane to methanol using Cu-and Fe-exchanged zeolites. ACS Catal. 8, 8306–8313 (2018).
Solomon, E. I. et al. Copper active sites in biology. Chem. Rev. 114, 3659–3853 (2014).
Beznis, N. V., Van Laak, A. N. C., Weckhuysen, B. M. & Bitter, J. H. Oxidation of methane to methanol and formaldehyde over Co–ZSM-5 molecular sieves: tuning the reactivity and selectivity by alkaline and acid treatments of the zeolite ZSM-5 agglomerates. Microporous Mesoporous Mat. 138, 176–183 (2011).
Grundner, S., Luo, W., Sanchez-Sanchez, M. & Lercher, J. A. Synthesis of single-site copper catalysts for methane partial oxidation. Chem. Commun. 52, 2553–2556 (2016).
Ipek, B. & Lobo, R. F. Catalytic conversion of methane to methanol on Cu-SSZ-13 using N2O as oxidant. Chem. Commun. 52, 13401–13404 (2016).
Parfenov, M. V., Starokon, E. V., Pirutko, L. V. & Panov, G. I. Quasicatalytic and catalytic oxidation of methane to methanol by nitrous oxide over FeZSM-5 zeolite. J. Catal. 318, 14–21 (2014).
Bozbag, S. E. et al. Methane to methanol over copper mordenite: yield improvement through multiple cycles and different synthesis techniques. Catal. Sci. Technol. 6, 5011–5022 (2016).
Tan, S. H. & Barton, P. I. Optimal dynamic allocation of mobile plants to monetize associated or stranded natural gas, part I: Bakken shale play case study. Energy 93, 1581–1594 (2015).
Conley, B. L. et al. Design and study of homogeneous catalysts for the selective, low temperature oxidation of hydrocarbons. J. Mol. Catal. A: Chem. 251, 8–23 (2006).
Zhang, Y., Sunarso, J., Liu, S. & Wang, R. Current status and development of membranes for CO2/CH4 separation: A review. Int. J. Greenh. Gas. Con. 12, 84–107 (2013).
Morigami, Y., Kondo, M., Abe, J., Kita, H. & Okamoto, K. The first large-scale pervaporation plant using tubular-type module with zeolite NaA membrane. Sep. Purif. Technol. 25, 251–260 (2001).
Liu, Q., Noble, R. D., Falconer, J. L. & Funke, H. H. Organics/water separation by pervaporation with a zeolite membrane. J. Membr. Sci. 117, 163–174 (1996).
Won, W., Feng, X. & Lawless, D. Pervaporation with chitosan membranes: separation of dimethyl carbonate/methanol/water mixtures. J. Membr. Sci. 209, 493–508 (2002).
Sheppard, T., Hamill, C. D., Goguet, A., Rooney, D. W. & Thompson, J. M. A low temperature, isothermal gas-phase system for conversion of methane to methanol over Cu–ZSM-5. Chem. Commun. 50, 11053–11055 (2014).
Wulfers, M. J., Teketel, S., Ipek, B. & Lobo, R. F. Conversion of methane to methanol on copper-containing small-pore zeolites and zeotypes. Chem. Commun. 51, 4447–4450 (2015).
Woertink, J. S. et al. A [Cu2O] 2+ core in Cu-ZSM-5, the active site in the oxidation of methane to methanol. Proc. Natl Acad. Sci. 106, 18908–18913 (2009).
Sushkevich, V. L., Palagin, D. & van Bokhoven, J. A. Effect of active sites structure on activity of copper mordenite in aerobic and anaerobic conversion of methane to methanol. Angew. Chem. Int. Ed. 57, 8906–8910 (2018).
Smeets, P. J., Groothaert, M. H. & Schoonheydt, R. A. Cu based zeolites: A UV–vis study of the active site in the selective methane oxidation at low temperatures. Catal. Today 110, 303–309 (2005).
Borfecchia, E. et al. Revisiting the nature of Cu sites in the activated Cu-SSZ-13 catalyst for SCR reaction. Chem. Sci. 6, 548–563 (2015).
Kulkarni, A. R., Zhao, Z.-J., Siahrostami, S., Nørskov, J. K. & Studt, F. Monocopper active site for partial methane oxidation in Cu-exchanged 8MR Zeolites. ACS Catal. 6, 6531–6536 (2016).
Palagin, D., Knorpp, A. J., Pinar, A. B., Ranocchiari, M. & van Bokhoven, J. A. Assessing the relative stability of copper oxide clusters as active sites of a CuMOR zeolite for methane to methanol conversion: size matters? Nanoscale 9, 1144–1153 (2017).
Ipek, B. et al. Formation of [Cu2O2] 2+ and [Cu2O] 2+ toward C–H Bond Activation in Cu-SSZ-13 and Cu-SSZ-39. ACS Catal. 7, 4291–4303 (2017).
Kwak, J. H., Zhu, H., Lee, J. H., Peden, C. H. F. & Szanyi, J. Two different cationic positions in Cu-SSZ-13? Chem. Commun. 48, 4758–4760 (2012).
Paolucci, C. et al. Catalysis in a cage: condition-dependent speciation and dynamics of exchanged Cu cations in SSZ-13 zeolites. J. Am. Chem. Soc. 138, 6028–6048 (2016).
Beale, A. M., Lezcano-Gonzalez, I., Slawinksi, W. A. & Wragg, D. S. Correlation between Cu ion migration behaviour and deNO x activity in Cu-SSZ-13 for the standard NH 3-SCR reaction. Chem. Commun. 52, 6170–6173 (2016).
Newton, M. A. et al. On the mechanism underlying the direct conversion of methane to methanol by copper hosted in zeolites; braiding Cu K-edge XANES and reactivity studies. J. Am. Chem. Soc. 140, 10090–10093 (2018).
Narsimhan, K. Catalytic, low temperature oxidation of methane into methanol over copper-exchanged zeolites PhD thesis, Massachusetts Inst. of Technol. (2017).
Mahyuddin, M. H., Staykov, A., Shiota, Y. & Yoshizawa, K. Direct conversion of methane to methanol by metal-exchanged ZSM-5 zeolite (Metal= Fe, Co, Ni, Cu). ACS Catal. 6, 8321–8331 (2016).
Mahyuddin, M. H., Staykov, A., Shiota, Y., Miyanishi, M. & Yoshizawa, K. Roles of zeolite confinement and Cu–O–Cu angle on the direct conversion of methane to methanol by [Cu2 (μ-O)] 2+-exchanged AEI, CHA, AFX, and MFI zeolites. ACS Catal. 7, 3741–3751 (2017).
Bozbag, S. E. et al. Direct stepwise oxidation of methane to methanol over Cu-SiO2. ACS Catal. 8, 5721–5731 (2018).
Ikuno, T. et al. Methane oxidation to methanol catalyzed by Cu-Oxo clusters stabilized in NU-1000 metal–organic framework. J. Am. Chem. Soc. 139, 10294–10301 (2017).
Le, H. V. et al. Stepwise methane‐to‐methanol conversion on CuO/SBA‐15. Chem.: Eur. J. 24, 12592–12599 (2018).
Kalamaras, C. et al. Selective oxidation of methane to methanol over Cu-and Fe-exchanged zeolites: the effect of Si/Al molar ratio. Catal. Lett. 146, 483–492 (2016).
Arndtsen, B. A., Peterson, T. H. & Mobley, T. A. Selective intermolecular carbon-hydrogen bond activation by synthetic metal complexes in homogeneous solution. Acc. Chem. Res. 28, 154–162 (1995).
Labinger, J. A. Methane activation in homogeneous systems. Fuel Process. Technol. 42, 325–338 (1995).
Latimer, A. A., Kakekhani, A., Kulkarni, A. R. & Nørskov, J. K. Direct methane to methanol: the selectivity–conversion limit and design strategies. ACS Catal. 8, 6894–6907 (2018).
Liu, X., Ryabenkova, Y. & Conte, M. Catalytic oxygen activation versus autoxidation for industrial applications: a physicochemical approach. Phys. Chem. Chem. Phys. 17, 715–731 (2015).
Olivos-Suarez, A. I. et al. Strategies for the direct catalytic valorization of methane using heterogeneous catalysis: challenges and opportunities. ACS Catal. 6, 2965–2981 (2016).
Roduner, E. et al. Selective catalytic oxidation of C–H Bonds with molecular oxygen. ChemCatChem 5, 82–112 (2013).
Zuo, Z., Ramírez, P. J., Senanayake, S. D., Liu, P. & Rodriguez, J. A. Low-temperature conversion of methane to methanol on CeO x/Cu2O catalysts: water controlled activation of the C–H bond. J. Am. Chem. Soc. 138, 13810–13813 (2016).
Tomkins, P. et al. Increasing the activity of copper exchanged mordenite in the direct isothermal conversion of methane to methanol by Pt and Pd doping. Chem. Sci. 10, 167–171 (2019).
Wang, G., Huang, L., Chen, W., Zhou, J. & Zheng, A. Rationally designing mixed Cu–(μ-O)–M (M= Cu, Ag, Zn, Au) centers over zeolite materials with high catalytic activity towards methane activation. Phys. Chem. Chem. Phys. 20, 26522–26531 (2018).
Park, D. & Lee, J. Biological conversion of methane to methanol. Korean J. Chem. Eng. 30, 977–987 (2013).
Huang, S.-P., Shiota, Y. & Yoshizawa, K. DFT study of the mechanism for methane hydroxylation by soluble methane monooxygenase (sMMO): effects of oxidation state, spin state, and coordination number. Dalton Trans. 42, 1011–1023 (2013).
Da Silva, J. C. S., Pennifold, R. C. R., Harvey, J. N. & Rocha, W. R. A radical rebound mechanism for the methane oxidation reaction promoted by the dicopper center of a pMMO enzyme: a computational perspective. Dalton Trans. 45, 2492–2504 (2016).
Smeets, P. J. et al. Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5. J. Am. Chem. Soc. 132, 14736–14738 (2010).
Markovits, M. A. C., Jentys, A., Tromp, M., Sanchez-Sanchez, M. & Lercher, J. A. Effect of location and distribution of Al sites in ZSM-5 on the formation of Cu-Oxo clusters active for direct conversion of methane to methanol. Top. Catal. 59, 1554–1563 (2016).
Pappas, D. K. et al. Methane to methanol: structure–activity relationships for Cu-CHA. J. Am. Chem. Soc. 139, 14961–14975 (2017).
Le, H. V. et al. Solid-state ion-exchanged Cu/mordenite catalysts for the direct conversion of methane to methanol. ACS Catal. 7, 1403–1412 (2017).
Kim, Y., Kim, T. Y., Lee, H. & Yi, J. Distinct activation of Cu-MOR for direct oxidation of methane to methanol. Chem. Commun. 53, 4116–4119 (2017).
Pappas, D. K. et al. The nuclearity of the active site for methane to methanol conversion in Cu-mordenite: a quantitative assessment. J. Am. Chem. Soc. 140, 15270–15278 (2018).
Acknowledgements
The authors acknowledge the ESI platform, Paul Scherrer Institute and ETH Zurich for financial support. DP is grateful for the Swiss National Supercomputing Centre for providing the computational facilities.
Author information
Authors and Affiliations
Contributions
J.A.vB devised the overall idea of the perspective and M.Rav. wrote the manuscript in close consultation with all the other authors. All authors contributed insights, provided feedback and edited the manuscript. V.S gave specific inputs on aspects of industrial viability, kinetic measurements and benchmarking as discussed in the manuscript. A.J.K. and M.A.N added to the discussion on the biomimetic descriptor and compiled data from literature for computing the space–time yield under Table 1. M.A.N., A.J.K. and A.B.P. contributed to sections of the manuscript that deal with X-ray based techniques and active site structure. D.P. gave inputs on computational methods used in this chemistry. M.Ran. provided inputs on sections of the manuscript that deal with benchmarking and catalytic processes for methane to methanol.
Corresponding author
Ethics declarations
Competing interests
The authors have no competing interests.
Additional information
Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary information
Supplementary Data 1
Calculations of maximal methanol selectivity for chemical looping system based on reaction stoichiometry
Rights and permissions
About this article
Cite this article
Ravi, M., Sushkevich, V.L., Knorpp, A.J. et al. Misconceptions and challenges in methane-to-methanol over transition-metal-exchanged zeolites. Nat Catal 2, 485–494 (2019). https://doi.org/10.1038/s41929-019-0273-z
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1038/s41929-019-0273-z
- Springer Nature Limited
This article is cited by
-
Nearly 100% selective and visible-light-driven methane conversion to formaldehyde via. single-atom Cu and Wδ+
Nature Communications (2023)
-
H2-reduced phosphomolybdate promotes room-temperature aerobic oxidation of methane to methanol
Nature Catalysis (2023)
-
Direct conversion of methane with O2 at room temperature over edge-rich MoS2
Nature Catalysis (2023)
-
Copper-zeolites Prepared by Solid-state Ion Exchange - Characterization and Evaluation for the Direct Conversion of Methane to Methanol
Topics in Catalysis (2023)
-
Oxo dicopper anchored on carbon nitride for selective oxidation of methane
Nature Communications (2022)