甲烷作為天然氣、頁岩氣與生質氣中的主要成分，也是目前最豐富但尚未被充分利用的重要碳資源。若能將其直接轉化為甲醇、甲醛及甲酸等含氧有機化合物，不僅可提升碳資源利用效率，亦可增加其應用價值。然而，甲烷分子結構穩定且C–H鍵能高，傳統熱催化常需在高溫或高壓條件下進行，容易造成目標產物過度氧化及積碳生成。因此，本研究利用介電質常壓電漿（dielectric barrier discharge, DBD）結合後電漿催化系統（post-plasma catalysis, PPC），進行甲烷部分氧化反應，並探討不同沸石孔道結構及金屬物種對反應活性與產物選擇性的影響。
本研究以CHA型沸石SAPO-34與SSZ-13作為主要觸媒載體，分別透過離子交換法負載銅與銀活性物種，並與MFI型ZSM-5及BEA型沸石進行比較。結果顯示，金屬導入後沸石骨架大致仍維持完整，其中銅物種均勻分散於沸石顆粒中，而銀物種則主要分布於觸媒外表面。於電漿輔助甲烷部分氧化反應中，CHA型沸石相較於MFI與BEA型沸石展現較高之含氧有機化合物選擇性及較低之積碳生成量，顯示其八圓環（8-membered ring, 8-MR）孔道侷限效應有助於穩定反應中間體並調控後續轉化路徑。其中，Cu/SAPO-34與Cu/SSZ-13展現最佳之甲烷轉化率與含氧有機化合物選擇性，且於五次短期循環測試中仍維持良好的催化穩定性；相較之下，銀的導入則使產物分布由甲醇逐漸轉向甲醛。綜合而言，本研究證實DBD電漿結合Cu、Ag修飾CHA型沸石，可於溫和反應條件下有效促進甲烷部分氧化生成含氧有機化合物，並證實沸石孔道侷限效應與金屬物種特性為調控產物選擇性的關鍵因素。

Methane is an abundant carbon resource, but its direct conversion into value-added chemicals remains challenging because of its strong C–H bond and the tendency toward deep oxidation under conventional thermal conditions. In this study, a dielectric barrier discharge (DBD) post-plasma catalysis (PPC) system combined with Cu- and Ag-modified zeolite catalysts was developed for the selective partial oxidation of methane to light oxygenates under mild reaction conditions. CHA-type zeolites (SAPO-34 and SSZ-13) were selected as catalyst supports and compared with larger-pore MFI (ZSM-5) and BEA zeolites to investigate the influence of pore structure on catalytic performance. Catalyst characterization confirmed that the zeolite frameworks remained intact after metal loading, while Cu species were highly dispersed and Ag species were mainly distributed on the external surface of the zeolites. Catalytic results demonstrated that CHA-type zeolites exhibited superior oxygenate selectivity and lower coke formation owing to their 8-membered-ring confinement effect. Furthermore, Cu favored methanol formation, whereas Ag promoted formaldehyde production without significantly changing methane conversion. The Cu-modified CHA catalysts also exhibited stable catalytic performance during short-term recycling tests. These findings demonstrate that combining DBD plasma with properly designed CHA zeolite catalysts provides an effective strategy for low-temperature methane upgrading and offers valuable insights into plasma-assisted catalytic methane conversion.

[1] D. Saha, H. A. Grappe, A. Chakraborty, and G. Orkoulas, "Postextraction separation, on-board storage, and catalytic conversion of methane in natural gas: A review," Chem. Rev., vol. 116, no. 19, pp. 11436-11499, 2016/10/12 2016, doi: 10.1021/acs.chemrev.5b00745.
[2] L. Sun, Y. Wang, N. Guan, and L. Li, "Methane activation and utilization: Current status and future challenges," Energy Technol., vol. 8, no. 8, p. 1900826, 2020, doi: https://doi.org/10.1002/ente.201900826.
[3] M. Muehlhofer, T. Strassner, and W. A. Herrmann, "New catalyst systems for the catalytic conversion of methane into methanol," Angew. Chem. Int. Ed., vol. 41, no. 10, pp. 1745-1747, 2002, doi: https://doi.org/10.1002/1521-3773(20020517)41:10<1745::AID-ANIE1745>3.0.CO;2-E.
[4] P. Tomkins, M. Ranocchiari, and J. A. van Bokhoven, "Direct conversion of methane to methanol under mild conditions over Cu-zeolites and beyond," Acc. Chem. Res., vol. 50, no. 2, pp. 418-425, 2017/02/21 2017, doi: 10.1021/acs.accounts.6b00534.
[5] E. M. Turan, E. van Steen, and K. P. Möller, "Comparison of mechanisms for the direct, gas phase, partial oxidation of methane to methanol," Chem. Eng. Sci., vol. 241, p. 116718, 2021/09/21/ 2021, doi: https://doi.org/10.1016/j.ces.2021.116718.
[6] J. Tian et al., "Direct conversion of methane to formaldehyde and CO on B2O3 catalysts," Nat. Commun., vol. 11, no. 1, p. 5693, 2020/11/10 2020, doi: 10.1038/s41467-020-19517-y.
[7] T. Akiyama, R. Sei, and S. Takenaka, "Partial oxidation of methane to formaldehyde over copper–molybdenum complex oxide catalysts," Catal. Sci. Technol., 10.1039/D1CY00511A vol. 11, no. 15, pp. 5273-5281, 2021, doi: 10.1039/D1CY00511A.
[8] A. Matsuda et al., "Bismuth phosphate nanoparticle catalyst for direct oxidation of methane into formaldehyde," Catal. Sci. Technol., 10.1039/D3CY00590A vol. 13, no. 18, pp. 5180-5189, 2023, doi: 10.1039/D3CY00590A.
[9] P. Schwach, X. Pan, and X. Bao, "Direct conversion of methane to value-added chemicals over heterogeneous catalysts: Challenges and prospects," Chem. Rev., vol. 117, no. 13, pp. 8497-8520, 2017/07/12 2017, doi: 10.1021/acs.chemrev.6b00715.
[10] R. Horn and R. Schlögl, "Methane activation by heterogeneous catalysis," Catal. Lett., vol. 145, no. 1, pp. 23-39, 2015/01/01 2015, doi: 10.1007/s10562-014-1417-z.
[11] V. Arutyunov, "Low-scale direct methane to methanol – Modern status and future prospects," Catal. Today, vol. 215, pp. 243-250, 2013/10/15/ 2013, doi: https://doi.org/10.1016/j.cattod.2012.12.021.
[12] L. Sun, Y. Wang, C. Wang, Z. Xie, N. Guan, and L. Li, "Water-involved methane-selective catalytic oxidation by dioxygen over copper zeolites," Chem, vol. 7, no. 6, pp. 1557-1568, 2021/06/10/ 2021, doi: https://doi.org/10.1016/j.chempr.2021.02.026.
[13] X. Zhang et al., "Ambient catalyst-free conversion of methane to methanol by water radical cations," Sci. Adv., vol. 11, no. 31, p. eadw0584, 2025, doi: doi:10.1126/sciadv.adw0584.
[14] N. Sánchez-Bastardo, R. Schlögl, and H. Ruland, "Methane Pyrolysis for Zero-Emission Hydrogen Production: A Potential Bridge Technology from Fossil Fuels to a Renewable and Sustainable Hydrogen Economy," Industrial & Engineering Chemistry Research, vol. 60, no. 32, pp. 11855-11881, 2021/08/18 2021, doi: 10.1021/acs.iecr.1c01679.
[15] T. Nozaki and K. Okazaki, "Non-thermal plasma catalysis of methane: Principles, energy efficiency, and applications," Catal. Today, vol. 211, pp. 29-38, 2013/08/01/ 2013, doi: https://doi.org/10.1016/j.cattod.2013.04.002.
[16] L. Wang, Y. Yi, C. Wu, H. Guo, and X. Tu, "One-step reforming of CO2 and CH4 into high-value liquid chemicals and fuels at room temperature by plasma-driven catalysis," Angew. Chem. Int. Ed., vol. 56, no. 44, pp. 13679-13683, 2017, doi: https://doi.org/10.1002/anie.201707131.
[17] H. M. Nguyen, A. Omidkar, and H. Song, "Technical challenges and prospects in sustainable plasma catalytic ammonia production from methane and nitrogen," ChemPlusChem, vol. 88, no. 7, p. e202300129, 2023, doi: https://doi.org/10.1002/cplu.202300129.
[18] E. C. Neyts, K. Ostrikov, M. K. Sunkara, and A. Bogaerts, "Plasma catalysis: Synergistic effects at the nanoscale," Chem. Rev., vol. 115, no. 24, pp. 13408-13446, 2015/12/23 2015, doi: 10.1021/acs.chemrev.5b00362.
[19] Y.-C. Lin, Y.-C. Lin, K.-J. Huang, R.-P. Yeh, F. C.-N. Hong, and Y.-M. Shyu, "Role of reducible and mobile oxygens in methane partial oxidation within a post-plasma catalytic system," ChemistrySelect, vol. 10, no. 12, p. e202405886, 2025, doi: https://doi.org/10.1002/slct.202405886.
[20] P. Xiao et al., "Understanding the effect of spatially separated Cu and acid sites in zeolite catalysts on oxidation of methane," Nat. Commun., vol. 15, no. 1, p. 2718, 2024/03/28 2024, doi: 10.1038/s41467-024-46924-2.
[21] J. Prameswari and Y.-C. Lin, "Innovative catalysis approaches for methane utilization," ACS ES&T Eng., vol. 5, no. 2, pp. 325-343, 2025/02/14 2025, doi: 10.1021/acsestengg.4c00700.
[22] P. Chawdhury, K. V. S. S. Bhargavi, and C. Subrahmanyam, "Enhanced synergy by plasma reduced Pd nanoparticles on in-plasma catalytic methane conversion to liquid oxygenates," Catalysis Communications, vol. 147, p. 106139, 2020/12/01/ 2020, doi: https://doi.org/10.1016/j.catcom.2020.106139.
[23] C. Liu, A. Marafee, R. Mallinson, and L. Lobban, "Methane conversion to higher hydrocarbons in a corona discharge over metal oxide catalysts with OH groups," Applied Catalysis A: General, vol. 164, no. 1-2, pp. 21-33, 1997.
[24] X. Chen et al., "Plasma induced methane conversion: a review on COx-free production of hydrogen, valuable chemicals, and functional carbon materials," EES Catal., 10.1039/D5EY00054H 2026, doi: 10.1039/D5EY00054H.
[25] L. Chen, X. Zhang, L. Huang, and L. Lei, "Application of in-plasma catalysis and post-plasma catalysis for methane partial oxidation to methanol over a Fe2O3-CuO/γ-Al2O3 catalyst," J. Nat. Gas Chem., vol. 19, no. 6, pp. 628-637, 2010/11/01/ 2010, doi: https://doi.org/10.1016/S1003-9953(09)60129-8.
[26] L. Chen, X. Zhang, L. Huang, and L. Lei, "Post-plasma catalysis for methane partial oxidation to methanol: Role of the copper-promoted iron oxide catalyst," Chem. Eng. Technol., vol. 33, no. 12, pp. 2073-2081, 2010, doi: https://doi.org/10.1002/ceat.201000092.
[27] W. Bi et al., "One-step direct conversion of methane to methanol with water in non-thermal plasma," Commun. Chem., vol. 5, no. 1, p. 124, 2022/10/10 2022, doi: 10.1038/s42004-022-00735-y.
[28] N. F. Dummer et al., "Methane oxidation to methanol," Chem. Rev., vol. 123, no. 9, pp. 6359-6411, 2023/05/10 2023, doi: 10.1021/acs.chemrev.2c00439.
[29] E. Agyekum-Oduro, A. Mukhtar, and S. Wu, "Plasma-enabled methane upgrading in a gas-liquid reactor: Optimizing a one-step methanol production process," J. Ind. Eng. Chem., vol. 151, pp. 682-691, 2025/11/25/ 2025, doi: https://doi.org/10.1016/j.jiec.2025.04.038.
[30] V. D. B. C. Dasireddy, D. Hanzel, K. Bharuth-Ram, and B. Likozar, "The effect of oxidant species on direct, non-syngas conversion of methane to methanol over an FePO4 catalyst material," RSC Advances, 10.1039/C9RA02327E vol. 9, no. 53, pp. 30989-31003, 2019, doi: 10.1039/C9RA02327E.
[31] M. Chen et al., "Catalytic oxidation of methane for methanol production over copper sepiolite: Effect of noble metals," Chinese Journal of Chemical Engineering, vol. 82, pp. 1-14, 2025/06/01/ 2025, doi: https://doi.org/10.1016/j.cjche.2025.02.006.
[32] P. R. Chandewar and D. Shee, "Synergy between Fe-Co oxide catalysts supported over HZSM-5 for direct conversion of methane to methanol," Molecular Catalysis, vol. 562, p. 114204, 2024/06/01/ 2024, doi: https://doi.org/10.1016/j.mcat.2024.114204.
[33] P. Rajendra Chandewar and D. Shee, "Role of copper and cerium species in Cu/CeZSM catalysts for direct methane to methanol reaction: Insights of structure–activity relationship," Journal of Catalysis, vol. 442, p. 115916, 2025/02/01/ 2025, doi: https://doi.org/10.1016/j.jcat.2024.115916.
[34] P. Fathollahi et al., "Selective oxidation of methane to methanol by NTP plasma: The effect of power and oxygen on conversion and selectivity," Journal of Electrostatics, vol. 112, p. 103594, 2021/07/01/ 2021, doi: https://doi.org/10.1016/j.elstat.2021.103594.
[35] L. Chen, X.-W. Zhang, L. Huang, and L.-C. Lei, "Partial oxidation of methane with air for methanol production in a post-plasma catalytic system," Chem. Eng. Process.: Process Intensif., vol. 48, no. 8, pp. 1333-1340, 2009/08/01/ 2009, doi: https://doi.org/10.1016/j.cep.2009.06.007.
[36] Y. Tang et al., "One-step synthesis of methanol and hydrogen from methane and water using non-thermal plasma and Cu-Mordenite catalyst," Fuel Processing Technology, vol. 244, p. 107722, 2023/06/01/ 2023, doi: https://doi.org/10.1016/j.fuproc.2023.107722.
[37] S. Meng et al., "Enhanced Plasma-Catalytic Steam Reforming of Methane to Methanol on a Hydrophobically Modified Cu/Silicalite-1 Catalyst," Chinese Journal of Chemical Engineering, 2025/12/23/ 2025, doi: https://doi.org/10.1016/j.cjche.2025.12.001.
[38] H. Lv et al., "Plasma-catalytic direct oxidation of methane to methanol over Cu-MOR: Revealing the zeolite-confined Cu2+ active sites," Chem. Eng. J., vol. 496, p. 154337, 2024/09/15/ 2024, doi: https://doi.org/10.1016/j.cej.2024.154337.
[39] P. Chawdhury, D. Kumar, and C. Subrahmanyam, "NTP reactor for a single stage methane conversion to methanol: Influence of catalyst addition and effect of promoters," Chem. Eng. J., vol. 372, pp. 638-647, 2019/09/15/ 2019, doi: https://doi.org/10.1016/j.cej.2019.04.172.
[40] B. Pereda-Ayo, U. De La Torre, M. J. Illán-Gómez, A. Bueno-López, and J. R. González-Velasco, "Role of the different copper species on the activity of Cu/zeolite catalysts for SCR of NOx with NH3," Appl. Catal. B, vol. 147, pp. 420-428, 2014/04/05/ 2014, doi: https://doi.org/10.1016/j.apcatb.2013.09.010.
[41] B. E. R. Snyder et al., "Cage effects control the mechanism of methane hydroxylation in zeolites," Science, vol. 373, no. 6552, pp. 327-331, 2021, doi: doi:10.1126/science.abd5803.
[42] K. Sato, K. Sugimoto, N. Shimotsuma, T. Kikuchi, T. Kyotani, and T. Kurata, "Development of practically available up-scaled high-silica CHA-type zeolite membranes for industrial purpose in dehydration of N-methyl pyrrolidone solution," J. Membr. Sci., vol. 409-410, pp. 82-95, 2012/08/01/ 2012, doi: https://doi.org/10.1016/j.memsci.2012.03.032.
[43] H. Kalipcilar, T. C. Bowen, R. D. Noble, and J. L. Falconer, "Synthesis and separation performance of SSZ-13 zeolite membranes on tubular supports," Chem. Mater., vol. 14, no. 8, pp. 3458-3464, 2002/08/01 2002, doi: 10.1021/cm020248i.
[44] J. Zheng et al., "Unraveling the non-classic crystallization of SAPO-34 in a dry gel system towards controlling meso-structure with the assistance of growth inhibitor: Growth mechanism, hierarchical structure control and catalytic properties," Microporous Mesoporous Mater., vol. 225, pp. 74-87, 2016/05/01/ 2016, doi: https://doi.org/10.1016/j.micromeso.2015.12.007.
[45] B. Yu et al., "Silver and copper dual single atoms boosting direct oxidation of methane to methanol via synergistic catalysis," Adv. Sci., vol. 10, no. 26, p. 2302143, 2023, doi: https://doi.org/10.1002/advs.202302143.
[46] J. Epp, "4 - X-ray diffraction (XRD) techniques for materials characterization," in Materials Characterization Using Nondestructive Evaluation (NDE) Methods, G. Hübschen, I. Altpeter, R. Tschuncky, and H.-G. Herrmann Eds.: Woodhead Publishing, 2016, pp. 81-124.
[47] R. Arevalo, "15.23 - Laser Ablation ICP-MS and Laser Fluorination GS-MS," in Treatise on Geochemistry (Second Edition), H. D. Holland and K. K. Turekian Eds. Oxford: Elsevier, 2014, pp. 425-441.
[48] P. Ehiomogue, I. I. Ahuchaogu, and I. E. Ahaneku, "REVIEW OF ADSORPTION ISOTHERMS MODELS," Acta Technica Corviniensis-Bulletin of Engineering, vol. 14, no. 4, 2021.
[49] Z. Qiu et al., "Tailoring the local environment of silver in SSZ-13 zeolites for low-temperature catalytic oxidation of ammonia," Appl. Surf. Sci., vol. 598, p. 153856, 2022/10/01/ 2022, doi: https://doi.org/10.1016/j.apsusc.2022.153856.
[50] Y. Jiang, X. Zhang, W. Li, and L. Yuan, "A novel synthesis strategy of Cu/SAPO-34 catalyst for improving isolated Cu dispersion to boosting continuous direct conversion of methane to methanol," J. Environ. Chem. Eng., vol. 13, no. 6, p. 120417, 2025/12/01/ 2025, doi: https://doi.org/10.1016/j.jece.2025.120417.
[51] D. B. Akolekar and S. K. Bhargava, "Adsorption of NO and CO on silver-exchanged microporous materials," J. Mol. Catal. A, vol. 157, no. 1, pp. 199-206, 2000/06/20/ 2000, doi: https://doi.org/10.1016/S1381-1169(00)00055-8.
[52] W. Shen et al., "A study of the acidity of SAPO-34 by solid-state NMR spectroscopy," Microporous and Mesoporous Materials, vol. 158, pp. 19-25, 2012/08/01/ 2012, doi: https://doi.org/10.1016/j.micromeso.2012.03.013.
[53] C. De Bie, J. van Dijk, and A. Bogaerts, "The Dominant Pathways for the Conversion of Methane into Oxygenates and Syngas in an Atmospheric Pressure Dielectric Barrier Discharge," The Journal of Physical Chemistry C, vol. 119, no. 39, pp. 22331-22350, 2015/10/01 2015, doi: 10.1021/acs.jpcc.5b06515.
[54] D. W. Larkin, L. Zhou, L. L. Lobban, and R. G. Mallinson, "Product selectivity control and organic oxygenate pathways from partial oxidation of methane in a silent electric discharge reactor," Ind. Eng. Chem. Res., vol. 40, no. 23, pp. 5496-5506, 2001/11/01 2001, doi: 10.1021/ie010298h.
[55] M. Karatok, M. G. Sensoy, E. I. Vovk, H. Ustunel, D. Toffoli, and E. Ozensoy, "Formaldehyde selectivity in methanol partial oxidation on silver: Effect of reactive oxygen species, surface reconstruction, and stability of intermediates," ACS Catal., vol. 11, no. 10, pp. 6200-6209, 2021/05/21 2021, doi: 10.1021/acscatal.1c00344.
[56] Y. Yi et al., "Selective oxidation of CH4 to CH3OH through plasma catalysis: Insights from catalyst characterization and chemical kinetics modelling," Appl. Catal. B, vol. 296, p. 120384, 2021/11/05/ 2021, doi: https://doi.org/10.1016/j.apcatb.2021.120384.