Tailored pore-confined single-site iron(III) catalyst for selective CH<sub>4</sub> oxidation to CH<sub>3</sub>OH or CH<sub>3</sub>CO<sub>2</sub>H using O<sub>2</sub>.
basic_science · Level V
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- Record sourced from PubMed, PMID 39532873.
- Also identified by DOI 10.1038/s41467-024-54101-8 and PMC identifier 11557979.
- Licence recorded as CC BY-NC-ND.
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Abstract
Direct oxidation of methane to valuable oxygenates like alcohols and acetic acid under mild conditions poses a significant challenge due to high C‒H bond dissociation energy, facile overoxidation to CO and CO<sub>2</sub> and the intricacy of C-H activation/C-C coupling. In this work, we develop a multifunctional iron(III) dihydroxyl catalytic species immobilized within a metal-organic framework (MOF) for selective methane oxidation into methanol or acetic acid at different reaction conditions using O<sub>2</sub>. The active-site isolation of monomeric Fe<sup>III</sup>(OH)<sub>2</sub> species at the MOF nodes, their confinement within the porous framework, and their electron-deficient nature facilitate chemoselective C‒H oxidation, yielding methanol or acetic acid with high productivities of <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>38</mn> <mo>,</mo> <mn>592</mn> <mspace></mspace> <mi>μ</mi> <msub><mrow><mi>mol</mi></mrow> <mrow> <msub><mrow><mi>CH</mi></mrow> <mrow><mn>3</mn></mrow> </msub> <mi>OH</mi></mrow> </msub> <msup> <mrow> <msub><mrow><mi>g</mi></mrow> <mrow><mi>Fe</mi></mrow> </msub> </mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> <msup><mrow><mi>h</mi></mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> </math> and <math xmlns="http://www.w3.org/1998/Math/MathML"><mn>81</mn> <mo>,</mo> <mn>043</mn> <mspace></mspace> <mi>μ</mi> <msub><mrow><mi>mol</mi></mrow> <mrow> <msub><mrow><mi>CH</mi></mrow> <mrow><mn>3</mn></mrow> </msub> <msub><mrow><mi>CO</mi></mrow> <mrow><mn>2</mn></mrow> </msub> <mi>H</mi></mrow> </msub> <msup> <mrow> <msub><mrow><mi>g</mi></mrow> <mrow><mi>Fe</mi></mrow> </msub> </mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> <msup><mrow><mi>h</mi></mrow> <mrow><mo>-</mo> <mn>1</mn></mrow> </msup> </math> , respectively. Experiments and theoretical calculations suggest that methanol formation occurs via a Fe<sup>III</sup>-Fe<sup>I</sup>-Fe<sup>III</sup> catalytic cycle, whereas CH<sub>3</sub>CO<sub>2</sub>H is produced via hydrocarboxylation of in-situ generated CH<sub>3</sub>OH with CO<sub>2</sub> and H<sub>2</sub>, and direct CH<sub>4</sub> carboxylation with CO<sub>2</sub>.