Submitted Successfully!
To reward your contribution, here is a gift for you: A free trial for our video production service.
Thank you for your contribution! You can also upload a video entry or images related to this topic.
Version Summary Created by Modification Content Size Created at Operation
1 -- 1558 2022-11-08 02:16:55 |
2 format correct -3 word(s) 1555 2022-11-08 03:36:11 | |
3 format correct Meta information modification 1555 2022-11-08 03:41:21 |

Video Upload Options

Do you have a full video?


Are you sure to Delete?
If you have any further questions, please contact Encyclopedia Editorial Office.
Mao, M.;  Liu, L.;  Liu, Z. Cu-Based Catalytic Sites for Methane to Methanol. Encyclopedia. Available online: (accessed on 22 April 2024).
Mao M,  Liu L,  Liu Z. Cu-Based Catalytic Sites for Methane to Methanol. Encyclopedia. Available at: Accessed April 22, 2024.
Mao, Min, Lingmei Liu, Zhaohui Liu. "Cu-Based Catalytic Sites for Methane to Methanol" Encyclopedia, (accessed April 22, 2024).
Mao, M.,  Liu, L., & Liu, Z. (2022, November 08). Cu-Based Catalytic Sites for Methane to Methanol. In Encyclopedia.
Mao, Min, et al. "Cu-Based Catalytic Sites for Methane to Methanol." Encyclopedia. Web. 08 November, 2022.
Cu-Based Catalytic Sites for Methane to Methanol

Direct conversion of methane to methanol is an effective and practical process to improve the efficiency of natural gas utilization. Copper (Cu)-based catalysts have attracted great research attention, due to their unique ability to selectively catalyze the partial oxidation of methane to methanol at relatively low temperatures. Many different catalysts have been studied to achieve a high conversion of methane to methanol, including the Cu-based enzymes, Cu-zeolites, Cu-MOFs (metal-organic frameworks) and Cu-oxides.

methane to methanol copper active site structure characterization

1. Introduction

Nowadays, extensive consumption of energy for transportation, electricity and heat are continuously increasing due to the fast growth of global population and industrial production. However, the primary energy resources are still fossil fuels, even if there are also some alternative renewable energy sources [1][2][3][4][5]. With the sustainability and environmental concerns, considerable efforts have been devoted to the progressive exploration of renewable energy sources. Methane, as a greenhouse gas and an earth-abundant carbon feedstock, is mainly reserved in natural gas [6]. However, the wide application and effective utilization of methane meet the access and transportation challenges. Therefore, the effective catalytic conversion of methane to value-added chemicals has drawn considerable attention [7][8][9][10][11][12].
Because the C−H bonds in methane are quite stable (438.8 kJ/mol), the conversion of methane under moderate reaction conditions is a long-standing challenge [13]. However, its valuable products are readily converted to CO and CO2 at high temperatures. The dilemma thus makes the upgrading of methane more complicated [14]. Methanol is thought of as one green raw material for biodiesel and a very important chemical feedstock as well, which can be converted to many different commodities via well-developed techniques [15][16][17]. In the current industrial route, methanol can be formed from methane through a syngas intermediate. However, this indirect process requires high-temperature and high-pressure conditions, requiring large energy consumption [18]. Therefore, the partial oxidation of methane to methanol directly was proposed as the holy grail in chemistry [19]. Many observations and conclusions on the direct conversion of methane to methanol have been reported. Recently, several valuable review articles have already been published, which focused on biological methane oxidation [20] and zeolite-supported metal catalysts for methane conversion [21][22].

2. Cu-Based Enzymes

Methanotrophs, a kind of methane-consuming bacteria living in nature, have the ability to oxidize methane to methanol with their methane monooxygenases (MMOs) at an ambient temperature and pressure. Two kinds of MMOs exist in bacterium; a copper-based particulate membrane-bound enzyme (pMMO) and an iron-based soluble cytoplasmic enzyme (sMMO). The active structure of sMMO is a diiron active site, but the catalytic site of pMMO has remained unclear. Recently, many scientists have devoted their efforts to unveiling the structure of pMMO and its biochemistry on methane oxidation [23][24][25].

2.1. The Trinuclearcopper Sites Found in Enzymes

Extensive efforts have been made to reveal the catalytic center of the pMMO enzyme to understand its working mechanism. Because pMMO is an instable complex membrane protein composite, it is rather difficult to be isolated and purified for characterization. In 2004, Chan et al. proposed that the active sites in pMMO were trinuclear copper clusters, which worked for alkane hydroxylation or electron transfer [26]. They then demonstrated the trinuclear copper clusters by an electron paramagnetic resonance spectroscopic (EPR) test, in which the copper ions for alkane hydroxylation were reduced and the intensity of the CuII EPR signal decreased by increasing the negative potentials [27]. Via a simulation strategy, they confirmed that the EPR signal was assigned to 0.84 CuII ions at the negative potential of −53.0 mV, which consisted of 0.56 type 2 CuII ions and 0.29 trinuclear CuII clusters. At a more negative potential of −121.0 mV, the EPR intensity was only attributed to 0.13 trinuclear CuII clusters. Therefore, these spectroscopic data showed concrete evidence to confirm the presence of trinuclear copper clusters [27]. In addition, they also modeled a minimized trinuclear copper site computationally, considering the side-chain rotomers, hydrogen bonds, and metal–ligand bonds [27]. Via the anaerobic electrospray mass spectrometry, Chen et al. found that the activation of a tri-copper cluster with O2/H2O2 was similar to that of pMMO, also supporting the trinuclear copper cluster theory [28].

2.2. The Dicopper Sites Found in Enzymes

The pMMO comprises three polypeptides that are encoded by pmoB, pmoA and pmoC genes. The isolation and purification process should be much elaborate to keep the original statement of the catalytic centers. It is thus a great challenge to determine the nuclearity, ligation and position of the copper sites in pMMO. Advanced characterization techniques were used to deepen researchers' understanding of the catalytic center of the pMMO enzyme. Besides the above-mentioned EPR technique, the extended X-ray absorption fine structure (EXAFS) spectroscopy was also applied in the study and another proposal on the active site was attributed to a dicopper center in PmoB, based on the obtained evidence [29][30].
In 2003, Rosenzweig and coworkers purified pMMO from methylococcus capsulatus (Bath) and tested its structure by EXAFS [25]. The EXAFS spectra indicated that the purified pMMO contained both CuI and CuII oxidation states and a fitted Cu–Cu bond of 2.57 Å, providing direct evidence for a dicopper-containing cluster in pMMO [25]. Later in 2011, the same group gained more detailed results on different treated pMMO samples [31]. It was seen that the Fourier transform of the EXAFS data for the samples showed two scattering interactions of the nearest-neighbor ligands at around 2 and 2.5 Å. The EXAFS simulations indicate that each sample contains both Cu−O/N and Cu−Cu ligand environments, and the reduced pMMO has an additional Cu−O/N environment. The bond distance of Cu−O/N ligand is a little longer in the reduced sample (2.02 Å) than the isolated (1.97 Å) and oxidized pMMO (1.96 Å). More importantly, the reduced pMMO has a Cu−Cu bond length of 2.64 Å, which is also longer than that in the as-isolated or oxidized pMMO (2.53 Å) and the Cu-reconstituted pMMO (2.52 Å). Excluding the presence of Cu metal, they proposed that the dinuclear metal sites existed in the tested samples as confirmed by the short Cu−Cu interaction, which was also maintained under the reduction treatment [31].

3. Cu-Zeolites

Inspired by enzymology, scientists are taking considerable strides in designing and engineering these similar high-active sites in the catalysis community, which have the ability to convert methane to more valuable products. The crystalline zeolites, which contain various ordered porous frameworks, have been chosen as the potential supports to host the active metal sites [32][33]. In addition, they contain condensing aluminum and silicon tetrahedrons, providing the local coordination environments for copper cations [34]. Therefore, Cu-zeolite is a promising material to mimic the pMMO active site. In this section, researchers provide an overview of the current understanding on the nature of the catalytic Cu sites supported in zeolite for the direct conversion of methane to methanol.

3.1. The Dicopper Sites Supported in Zeolites

In 2005, Groothaert et al. first found that copper supported in zeolites could catalyze methane to methanol, and they observed an obvious decrease in the intensity of a UV–Vis band at 22,700 cm−1 of an O2-activated catalyst during the reaction process of the methane oxidation. This band is best assigned to the bis(µ-oxo)dicopper core ([Cu2-(µ-O)2]2+), which was first proposed as the catalytic center in the copper hosted in zeolites catalysts. Since then, considerable efforts have been taken to analyze the active sites of Cu-zeolite catalytic systems and improve the methanol yield in the reaction of methane upgrading [21].
In 2010, Smeets et al. found a UV–Vis absorption band of ~29,000 cm−1 when pretreating the Cu-ZSM-5 catalyst with an oxidation procedure. However, this band disappeared gradually with the parallel formation of an absorption band at 22,700 cm−1 [35]. Combining the Raman spectra, in which the signals of ν(O-O) and ν(Cu-Cu) were determined at 736 and 269 cm−1, respectively, they thus confirmed that the UV–Vis absorption band of 29,000 cm−1 was assigned to a peroxo species. The UV–Vis absorption changes demonstrated that the side-on bridged [Cu2(O)2]2+ species transferred to the [Cu2O]2+ species. Therefore, they proposed that the active center was the [Cu2O]2+ sites, which was transformed from a precursor of peroxo dicopper(II) species ([Cu2(O)2]2+) in the partial oxidation of methane to methanol [35].

3.2. The Multiple Copper Clusters Supported in Zeolites

In addition to the first discovered dicopper core sites, trimeric ([Cu3(m-O)3]2+) sites and even more copper cores are also proposed as the catalytic sites in Cu-zeolite system. In 2015, exploiting the in situ XAS technique, Grundner et al. unveiled that the trinuclear Cu-oxo clusters ([Cu3(m-O)3]2+) were the exclusively single sites in the activated Cu-MOR catalyst under investigation. In combination with ab initio thermodynamic analysis of DFT results, they confirmed that the trinuclear copper clusters were anchored at the windows of the 8-MR MOR side pockets with the connection to two framework Al atoms [36]. In 2016, Li et al. found that both the binuclear [Cu(µ-O)Cu]2+ sites and trinuclear oxygenated [Cu3(µ-O)3]2+ species were presented in ZSM-5 and the trinuclear copper sites were the most stable clusters in Cu/ZSM-5 under calcination conditions [37]. Mahyuddin et al. suggested that the trinuclear copper clusters in MOR and MAZ differed in reactivity in methane conversion based on DFT calculations [38]. Moreover, Palagin et al. proposed the existence of tetra-/pentamer Cu sites of CunOn2+ and CunOn−12+ in zeolite pores which exhibited higher relative stability than the smaller clusters [39]. Therefore, researchers summarized these works together in this paragraph regarding the catalytic center as the multiple copper core clusters. Researchers believe that these multiple copper clusters could be readily formed and may be preferred in zeolites because of the high mobility of Cu atoms under the thermal treatment.


  1. Primo, A.; Garcia, H. Zeolites as catalysts in oil refining. Chem. Soc. Rev. 2014, 43, 7548–7561.
  2. Taarning, E.; Osmundsen, C.M.; Yang, X.; Voss, B.; Andersen, S.I.; Christensen, C.H. Zeolite-catalyzed biomass conversion to fuels and chemicals. Energy Environ. Sci. 2011, 4, 793–804.
  3. Shaner, M.R.; Davis, S.J.; Lewis, N.S.; Caldeira, K. Geophysical constraints on the reliability of solar and wind power in the United States. Energ. Environ. Sci. 2018, 11, 914–925.
  4. Li, C.; Cao, Q.; Wang, F.; Xiao, Y.; Li, Y.; Delaunay, J.J.; Zhu, H. Engineering graphene and TMDs based van der Waals heterostructures for photovoltaic and photoelectrochemical solar energy conversion. Chem. Soc. Rev. 2018, 47, 4981–5037.
  5. Yangcheng, R.X.; Ran, J.S.; Liu, Z.H.; Cui, Y.T.; Wang, J.J. Phosphoric acid-modified commercial kieselguhr supported palladium nanoparticles as efficient catalysts for low-temperature hydrodeoxygenation of lignin derivatives in water. Green Chem. 2022, 24, 1570–1577.
  6. Aasberg-Petersen, K.; Dybkjaer, I.; Ovesen, C.V.; Schjodt, N.C.; Sehested, J.; Thomsen, S.G. Natural gas to synthesis gas—Catalysts and catalytic processes. J. Nat. Gas Sci. Eng. 2011, 3, 423–459.
  7. Guo, X.; Fang, G.; Li, G.; Ma, H.; Fan, H.; Yu, L.; Ma, C.; Wu, X.; Deng, D.; Wei, M.; et al. Direct, nonoxidative conversion of methane to ethylene, aromatics, and hydrogen. Science 2014, 344, 616–619.
  8. Qi, G.; Davies, T.E.; Nasrallah, A.; Sainna, M.A.; Howe, A.G.R.; Lewis, R.J.; Quesne, M.; Catlow, C.R.A.; Willock, D.J.; He, Q.; et al. Au-ZSM-5 catalyses the selective oxidation of CH4 to CH3OH and CH3COOH using O2. Nat. Catal. 2022, 5, 45–54.
  9. Cui, X.; Huang, R.; Deng, D. Catalytic conversion of C1 molecules under mild conditions. EnergyChem 2021, 3, 100050.
  10. Zichittella, G.; Perez-Ramirez, J. Status and prospects of the decentralised valorisation of natural gas into energy and energy carriers. Chem. Soc. Rev. 2021, 50, 2984–3012.
  11. Razdan, N.K.; Bhan, A. Carbidic Mo is the sole kinetically-relevant active site for catalytic methane dehydroaromatization on Mo/H-ZSM-5. J. Catal. 2020, 389, 667–676.
  12. Morejudo, S.H.; Zanon, R.; Escolastico, S.; Yuste-Tirados, I.; Malerod-Fjeld, H.; Vestre, P.K.; Coors, W.G.; Martinez, A.; Norby, T.; Serra, J.M.; et al. Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor. Science 2016, 353, 563–566.
  13. Periana, R.A.; Taube, D.J.; Evitt, E.R.; Loffler, D.G.; Wentrcek, P.R.; Voss, G.; Masuda, T. A mercury-catalyzed, high-yield system for the oxidation of methane to methanol. Science 1993, 259, 340–343.
  14. Luo, L.; Luo, J.; Li, H.; Ren, F.; Zhang, Y.; Liu, A.; Li, W.X.; Zeng, J. Water enables mild oxidation of methane to methanol on gold single-atom catalysts. Nat. Commun. 2021, 12, 1218–1227.
  15. Olsbye, U.; Svelle, S.; Bjorgen, M.; Beato, P.; Janssens, T.V.; Joensen, F.; Bordiga, S.; Lillerud, K.P. Conversion of methanol to hydrocarbons: How zeolite cavity and pore size controls product selectivity. Angew. Chem. Int. Ed. 2012, 51, 5810–5831.
  16. Hua, J.; Dong, X.; Wang, J.; Chen, C.; Shi, Z.; Liu, Z.; Han, Y. Methanol-to-olefin conversion over small-pore DDR zeolites: Tuning the propylene selectivity via the olefin-based catalytic cycle. ACS Catal. 2020, 10, 3009–3017.
  17. Liu, Z.; Dong, X.; Zhu, Y.; Emwas, A.-H.; Zhang, D.; Tian, Q.; Han, Y. Investigating the influence of mesoporosity in zeolite Beta on its catalytic performance for the conversion of methanol to hydrocarbons. ACS Catal. 2015, 5, 5837–5845.
  18. Usman, M.; Daud, W.M.A.W. Recent advances in the methanol synthesis via methane reforming processes. RSC Adv. 2015, 5, 21945–21972.
  19. Kosinov, N.; Hensen, E.J.M. Reactivity, Selectivity, and Stability of Zeolite-Based Catalysts for Methane Dehydroaromatization. Adv. Mater. 2020, 32, e2002565.
  20. Koo, C.W.; Rosenzweig, A.C. Biochemistry of aerobic biological methane oxidation. Chem. Soc. Rev. 2021, 50, 3424–3436.
  21. Newton, M.A.; Knorpp, A.J.; Sushkevich, V.L.; Palagin, D.; van Bokhoven, J.A. Active sites and mechanisms in the direct conversion of methane to methanol using Cu in zeolitic hosts: A critical examination. Chem. Soc. Rev. 2020, 49, 1449–1486.
  22. Kiani, D.; Sourav, S.; Tang, Y.; Baltrusaitis, J.; Wachs, I.E. Methane activation by ZSM-5-supported transition metal centers. Chem. Soc. Rev. 2021, 50, 1251–1268.
  23. Peng, W.; Qu, X.; Shaik, S.; Wang, B. Deciphering the oxygen activation mechanism at the CuC site of particulate methane monooxygenase. Nat. Catal. 2021, 4, 266–273.
  24. Yu, S.S.F.; Chen, K.H.C.; Tseng, M.Y.H.; Wang, Y.S.; Tseng, C.F.; Chen, Y.J.; Huang, D.S.; Chan, S.I. Production of high-quality particulate methane monooxygenase in high yields from Methylococcus capsulatus (Bath) with a hollow-fiber membrane bioreactor. J. Bacteriol. 2003, 185, 5915–5924.
  25. Lieberman, R.L.; Shrestha, D.B.; Doan, P.E.; Hoffman, B.M.; Stemmler, T.L.; Rosenzweig, A.C. Purified particulate methane monooxygenase from Methylococcus capsulatus (Bath) is a dimer with both mononuclear copper and a copper-containing cluster. Proc. Natl. Acad. Sci. USA 2003, 100, 3820–3825.
  26. Chan, S.I.; Chen, K.H.C.; Yu, S.S.F.; Chen, C.L.; Kuo, S.S.J. Toward delineating the structure and function of the particulate methane monooxygenase from methanotrophic bacteria. Biochemistry 2004, 43, 4421–4430.
  27. Chan, S.I.; Wang, V.C.; Lai, J.C.; Yu, S.S.; Chen, P.P.; Chen, K.H.; Chen, C.L.; Chan, M.K. Redox potentiometry studies of particulate methane monooxygenase: Support for a trinuclear copper cluster active site. Angew. Chem. Int. Ed. 2007, 46, 1992–1994.
  28. Chen, Y.H.; Wu, C.Q.; Sung, P.H.; Chan, S.I.; Chen, P.P.Y. Turnover of a Methane Oxidation Tricopper Cluster Catalyst: Implications for the Mechanism of the Particulate Methane Monooxygenase (pMMO). Chemcatchem 2020, 12, 3088–3096.
  29. Lieberman, R.L.; Rosenzweig, A.C. Crystal structure of a membrane-bound metalloenzyme that catalyses the biological oxidation of methane. Nature 2005, 434, 177–182.
  30. Balasubramanian, R.; Smith, S.M.; Rawat, S.; Yatsunyk, L.A.; Stemmler, T.L.; Rosenzweig, A.C. Oxidation of methane by a biological dicopper centre. Nature 2010, 465, 115–119.
  31. Smith, S.M.; Rawat, S.; Telser, J.; Hoffman, B.M.; Stemmler, T.L.; Rosenzweig, A.C. Crystal Structure and Characterization of Particulate Methane Monooxygenase from Methylocystis species Strain M. Biochemistry 2011, 50, 10231–10240.
  32. Liu, Z.; Hua, Y.; Wang, J.; Dong, X.; Tian, Q.; Han, Y. Recent progress in the direct synthesis of hierarchical zeolites: Synthetic strategies and characterization methods. Mater. Chem. Front. 2017, 1, 2195–2212.
  33. Del Campo, P.; Martinez, C.; Corma, A. Activation and conversion of alkanes in the confined space of zeolite-type materials. Chem. Soc. Rev. 2021, 50, 8511–8595.
  34. Chai, Y.; Dai, W.; Wu, G.; Guan, N.; Li, L. Confinement in a Zeolite and Zeolite Catalysis. Acc. Chem. Res. 2021, 54, 2894–2904.
  35. Smeets, P.J.; Hadt, R.G.; Woertink, J.S.; Vanelderen, P.; Schoonheydt, R.A.; Sels, B.F.; Solomon, E.I. Oxygen precursor to the reactive intermediate in methanol synthesis by Cu-ZSM-5. J. Am. Chem. Soc. 2010, 132, 14736–14738.
  36. Grundner, S.; Markovits, M.A.; Li, G.; Tromp, M.; Pidko, E.A.; Hensen, E.J.; Jentys, A.; Sanchez-Sanchez, M.; Lercher, J.A. Single-site trinuclear copper oxygen clusters in mordenite for selective conversion of methane to methanol. Nat. Commun. 2015, 6, 7546–7554.
  37. Li, G.; Vassilev, P.; Sanchez-Sanchez, M.; Lercher, J.A.; Hensen, E.J.M.; Pidko, E.A. Stability and reactivity of copper oxo-clusters in ZSM-5 zeolite for selective methane oxidation to methanol. J. Catal. 2016, 338, 305–312.
  38. Mahyuddin, M.H.; Tanaka, T.; Shiota, Y.; Staykov, A.; Yoshizawa, K. Methane Partial Oxidation over 2+ and 2+ Active Species in Large-Pore Zeolites. ACS Catal. 2018, 8, 1500–1509.
  39. 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 2017, 9, 1144–1153.
Subjects: Chemistry, Applied
Contributors MDPI registered users' name will be linked to their SciProfiles pages. To register with us, please refer to : , ,
View Times: 510
Revisions: 3 times (View History)
Update Date: 08 Nov 2022