Bioinspired methane oxidation in a zeolite

doi:10.1126/science.abj4734

GSTDTAP > 气候变化

DOI	10.1126/science.abj4734
	Bioinspired methane oxidation in a zeolite
	Susannah L. Scott
	2021-07-16
发表期刊	Science
出版年	2021
英文摘要	Fundamental advances have enhanced our understanding of how to activate the very stable C–H bonds in methane ([ 1 ][1]), but its conversion into useful chemicals such as methanol through simple, cost-effective, modular processes is still an unsolved problem ([ 2 ][2]). Living systems oxidize hydrocarbons, including methane, at near-ambient temperatures using enzymes that contain Earth-abundant metals (typically iron and copper). However, their electronic structures favor single-electron transfers that generate highly reactive radical intermediates ([ 3 ][3]). Escape of these radicals from the vicinity of an enzyme's active site must be scrupulously avoided to prevent damage to nearby biological structures. On page 327 of this issue, Snyder et al. ([ 4 ][4]) demonstrate how one of nature's strategies can be mimicked in an iron-containing zeolite that promotes radical formation and capture in rapid succession. This gating of molecular transport regenerates the active sites while limiting the propensity of radicals to deactivate active sites located in other zeolite pores. ![Figure][5] Different rebounding abilities The fate of methyl radicals in zeolites depends on the cage aperture size. In microporous zeolites such as chabazite (CHA) and beta (BEA), extra-framework ferrous (FeII) ions are oxidized to ferryl (FeIVO) ions that can abstract a hydrogen atom from a methane molecule. GRAPHIC: N. DESAI/ SCIENCE Enzymes functionalize normally unreactive saturated hydrocarbons such as methane selectively by using a “rebound” mechanism ([ 5 ][6]). In heme-based P450 and peroxidase enzymes, as well as nonheme iron dioxygenases, a highly oxidized iron site (Fe=O, ferryl) abstracts a hydrogen atom from the organic molecule and creates an organic radical. The oxygen atom becomes a hydroxyl (Fe-OH) that must recapture the organic radical by forming a stable C–O bond before the radical can diffuse away. Thus, the environment around the active site of an enzyme determines the reaction outcome by restricting the transport of molecules in the vicinity of the active site ([ 6 ][7]). Zeolites are a diverse family of robust, microporous aluminosilicate materials that are widely used as catalysts in hydrocarbon processing on an industrial scale. The ion-exchanged metal sites in iron- and copper-containing zeolites resemble key structural components of the active sites in enzymes ([ 2 ][2]). Snyder et al. installed the same active iron sites in the pores of two zeolites. Both have similar silicon-to-aluminum ratios, iron loadings, and cage diameters, and might be expected to have nearly identical activities toward methane. However, the zeolite structures differ in the accessibility of their iron sites. Beta zeolite (BEA) has a system of interconnected pores composed of “large” 12-rings (Si12O12), and no smaller constrictions ([ 7 ][8]). Although chabazite (CHA) cages have the same diameter, entry into the cages must occur through smaller 8-ring apertures (Si8O8) ([ 7 ][8]). Methane hydroxylation in these zeolites was studied as a sequence of stoichiometric reactions at room temperature. First, the reduced Fe(II) sites were activated by the oxidant, N2O, which installs reactive α-O atoms (see the figure). When one of the activated Fe(IV)O sites abstracts a hydrogen atom from methane, a methyl radical and a hydroxy site, Fe(III)OH, are simultaneously created in the same zeolite cage. If rebound of the methyl radical to the colocated Fe(III)OH site ensues, the Fe(II) site is regenerated and can perform the reaction sequence again. If the methyl radicals diffuse away, they can be trapped by neighboring ferryl sites, which are converted to inert methoxy sites, Fe(III)OCH3. Although a C–O bond is formed in both types of reaction, radical trapping at a ferryl site is unproductive because neither of the resulting Fe(III) sites (hydroxy or methoxy) can be reoxidized by N2O under mild conditions. The ratio of radical escape relative to rebound is very high in BEA. By contrast, diffusion of the methyl radical in CHA zeolite is restricted by virtue of the small size of the window through which the radical must escape from the cage where it is generated. This cage effect is reminiscent of radical confinement in enzymes. Using Mössbauer and resonance Raman spectroscopies, Snyder et al. show that the yield of Fe(II) (resulting from radical capture in the same zeolite cage) under single-turnover conditions is ∼40% for CHA, whereas it is near zero in BEA. In CHA, the methanol product migrates spontaneously from the Fe(II) sites to Brønsted acid sites in the zeolite pores, allowing a second reaction cycle to take place. When the isotopic identity of the methane was switched, from 13CH4 in the initial cycle to 12CH4 in a subsequent cycle, the isotopic composition of the methanol changed, which demonstrates that Fe(II) sites in CHA can be reactivated by N2O to produce a second equivalent of methanol. Efficient processes for converting methane to an energy-dense liquid hydrocarbon such as methanol are important not only for making greater use of abundant natural gas resources but also to reduce the need to flare stranded natural gas. Rather than generating the greenhouse gas CO2 unproductively, conversion to methanol would allow transport in a cost-effective way to population centers where its energy, chemical value, or both, could be extracted. However, using the strategy of Snyder et al. to this effect will require the process to become much more efficient. For example, combining the oxidant with methane in the zeolite should allow the reaction sequence to proceed in a single step. However, this approach presents a selectivity challenge. Because the relative difficulty of activating a C–H bond in methane versus methanol is roughly constant, there is a universal, catalyst-independent trade-off between conversion and selectivity ([ 8 ][9]). It is not yet clear how to achieve rapid diffusion of methanol away from the active sites, preventing its further oxidation, while simultaneously confining methyl radicals near the active sites to form methanol and regenerate Fe(II). A second challenge is to replace the N2O oxidant by a less expensive oxidant such as O2. Colocating two iron sites in a ferrierite zeolite was recently shown to facilitate O2 splitting ([ 9 ][10]). However, this geometry will enhance the undesired ferryl trapping of methyl radicals that leads to Fe(III)OH/Fe(III)OCH3 sites. The soluble methane monooxygenase enzyme achieves methane oxidation at diiron active sites linked by bridging oxygens, Fe(IV)2(µ-O)2, but it also produces ferric sites that require an external reductant for reactivation. A useful process for converting stranded methane will need to overcome both of these challenges. 1. [↵][11]1. N. J. Gunsalus et al ., Chem. Rev. 117, 8521 (2017). [OpenUrl][12][CrossRef][13][PubMed][14] 2. [↵][15]1. K. T. Dinh et al ., ACS Catal. 8, 8306 (2018). [OpenUrl][16] 3. [↵][17]1. R. M. Bullock et al ., Science 369, eabc3183 (2020). [OpenUrl][18][Abstract/FREE Full Text][19] 4. [↵][20]1. B. E. R. Snyder et al ., Science 373, 327 (2021). [OpenUrl][21][Abstract/FREE Full Text][22] 5. [↵][23]1. X. Huang, 2. J. T. Groves , J. Biol. Inorg. Chem. 22, 185 (2017). [OpenUrl][24][CrossRef][25][PubMed][26] 6. [↵][27]1. R. Breslow , Acc. Chem. Res. 28, 146 (1995). [OpenUrl][28][CrossRef][29][Web of Science][30] 7. [↵][31]1. C. Baerlocher, 2. W. M. Meier, 3. D. H. Olson , Atlas of Zeolite Framework Types (Elsevier, ed. 6, 2007). 8. [↵][32]1. A. A. Latimer, 2. A. Kakekhani, 3. A. R. Kulkarni, 4. J. K. Nørskov , ACS Catal. 8, 6894 (2018). [OpenUrl][33] 9. [↵][34]1. E. Tabor et al ., Sci. Adv. 6, eaaz9776 (2020). [OpenUrl][35][FREE Full Text][36] Acknowledgments: S.L.S. acknowledges the US Department of Energy, Office of Science, Division of Basic Energy Sciences, under the Catalysis Science Initiative (DE-FG-02-03ER15467) for financial support. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: pending:yes [6]: #ref-5 [7]: #ref-6 [8]: #ref-7 [9]: #ref-8 [10]: #ref-9 [11]: #xref-ref-1-1 "View reference 1 in text" [12]: {openurl}?query=rft.jtitle%253DChem.%2BRev.%26rft.volume%253D117%26rft.spage%253D8521%26rft_id%253Dinfo%253Adoi%252F10.1021%252Facs.chemrev.6b00739%26rft_id%253Dinfo%253Apmid%252F28459540%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [13]: /lookup/external-ref?access_num=10.1021/acs.chemrev.6b00739&link_type=DOI [14]: /lookup/external-ref?access_num=28459540&link_type=MED&atom=%2Fsci%2F373%2F6552%2F277.atom [15]: #xref-ref-2-1 "View reference 2 in text" [16]: {openurl}?query=rft.jtitle%253DACS%2BCatal.%26rft.volume%253D8%26rft.spage%253D8306%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [17]: #xref-ref-3-1 "View reference 3 in text" [18]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DBullock%26rft.auinit1%253DR.%2BM.%26rft.volume%253D369%26rft.issue%253D6505%26rft.spage%253Deabc3183%26rft.epage%253Deabc3183%26rft.atitle%253DUsing%2Bnatures%2Bblueprint%2Bto%2Bexpand%2Bcatalysis%2Bwith%2BEarth-abundant%2Bmetals%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.abc3183%26rft_id%253Dinfo%253Apmid%252F32792370%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [19]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjE3OiIzNjkvNjUwNS9lYWJjMzE4MyI7czo0OiJhdG9tIjtzOjIyOiIvc2NpLzM3My82NTUyLzI3Ny5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30= [20]: #xref-ref-4-1 "View reference 4 in text" [21]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DSnyder%26rft.auinit1%253DB.%2BE.%2BR.%26rft.volume%253D373%26rft.issue%253D6552%26rft.spage%253D327%26rft.epage%253D331%26rft.atitle%253DCage%2Beffects%2Bcontrol%2Bthe%2Bmechanism%2Bof%2Bmethane%2Bhydroxylation%2Bin%2Bzeolites%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.abd5803%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [22]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzNzMvNjU1Mi8zMjciO3M6NDoiYXRvbSI7czoyMjoiL3NjaS8zNzMvNjU1Mi8yNzcuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [23]: #xref-ref-5-1 "View reference 5 in text" [24]: {openurl}?query=rft.jtitle%253DJ.%2BBiol.%2BInorg.%2BChem.%26rft.volume%253D22%26rft.spage%253D185%26rft_id%253Dinfo%253Adoi%252F10.1007%252Fs00775-016-1414-3%26rft_id%253Dinfo%253Apmid%252F27909920%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [25]: /lookup/external-ref?access_num=10.1007/s00775-016-1414-3&link_type=DOI [26]: /lookup/external-ref?access_num=27909920&link_type=MED&atom=%2Fsci%2F373%2F6552%2F277.atom [27]: #xref-ref-6-1 "View reference 6 in text" [28]: {openurl}?query=rft.jtitle%253DAcc.%2BChem.%2BRes.%26rft.volume%253D28%26rft.spage%253D146%26rft_id%253Dinfo%253Adoi%252F10.1021%252Far00051a008%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [29]: /lookup/external-ref?access_num=10.1021/ar00051a008&link_type=DOI [30]: /lookup/external-ref?access_num=A1995QM79200009&link_type=ISI [31]: #xref-ref-7-1 "View reference 7 in text" [32]: #xref-ref-8-1 "View reference 8 in text" [33]: {openurl}?query=rft.jtitle%253DACS%2BCatal.%26rft.volume%253D8%26rft.spage%253D6894%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [34]: #xref-ref-9-1 "View reference 9 in text" [35]: {openurl}?query=rft.jtitle%253DScience%2BAdvances%26rft.stitle%253DSci%2BAdv%26rft.aulast%253DTabor%26rft.auinit1%253DE.%26rft.volume%253D6%26rft.issue%253D20%26rft.spage%253Deaaz9776%26rft.epage%253Deaaz9776%26rft.atitle%253DDioxygen%2Bdissociation%2Bover%2Bman-made%2Bsystem%2Bat%2Broom%2Btemperature%2Bto%2Bform%2Bthe%2Bactive%2B%257Balpha%257D-oxygen%2Bfor%2Bmethane%2Boxidation%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fsciadv.aaz9776%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [36]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6MzoiUERGIjtzOjExOiJqb3VybmFsQ29kZSI7czo4OiJhZHZhbmNlcyI7czo1OiJyZXNpZCI7czoxMzoiNi8yMC9lYWF6OTc3NiI7czo0OiJhdG9tIjtzOjIyOiIvc2NpLzM3My82NTUyLzI3Ny5hdG9tIjt9czo4OiJmcmFnbWVudCI7czowOiIiO30=
领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/334348
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Susannah L. Scott. Bioinspired methane oxidation in a zeolite[J]. Science,2021.
APA	Susannah L. Scott.(2021).Bioinspired methane oxidation in a zeolite.Science.
MLA	Susannah L. Scott."Bioinspired methane oxidation in a zeolite".Science (2021).