Single Dispersion of Fe(H<sub>2</sub>O)<sub>2</sub>-Based Polyoxometalate on Polymeric Carbon Nitride for Biomimetic CH<sub>4</sub> Photooxidation.
basic_science · Level V
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- Record sourced from PubMed, PMID 38771974.
- Also identified by DOI 10.1002/adma.202403101.
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Abstract
Direct methane conversion to value-added oxygenates under mild conditions with in-depth mechanism investigation has attracted wide interest. Inspired by methane monooxygenase, the K<sub>9</sub>Na<sub>2</sub>Fe(H<sub>2</sub>O)<sub>2</sub>{[γ-SiW<sub>9</sub>O<sub>34</sub>Fe(H<sub>2</sub>O)]}<sub>2</sub>·25H<sub>2</sub>O polyoxometalate (Fe-POM) with well-defined Fe(H<sub>2</sub>O)<sub>2</sub> sites is synthesized to clarify the key role of Fe species and their microenvironment toward CH<sub>4</sub> photooxidation. The Fe-POM can efficiently drive the conversion of CH<sub>4</sub> to HCOOH with a yield of 1570.0 µmol g<sub>POM</sub> <sup>-1</sup> and 95.8% selectivity at ambient conditions, much superior to that of [Fe(H<sub>2</sub>O)SiW<sub>11</sub>O<sub>39</sub>]<sup>5-</sup> with Fe(H<sub>2</sub>O) active site, [Fe<sub>2</sub>SiW<sub>10</sub>O<sub>38</sub>(OH)]<sub>2</sub> <sup>14-</sup> and [P<sub>8</sub>W<sub>48</sub>O<sub>184</sub>Fe<sub>16</sub>(OH)<sub>28</sub>(H<sub>2</sub>O)<sub>4</sub>]<sup>20-</sup> with multinuclear Fe-OH-Fe active sites. Single-dispersion of Fe-POM on polymeric carbon nitride (PCN) is facilely achieved to provide single-cluster functionalized PCN with well-defined Fe(H<sub>2</sub>O)<sub>2</sub> site, the HCOOH yield can be improved to 5981.3 µmol g<sub>POM</sub> <sup>-1</sup>. Systemic investigations demonstrate that the (WO)<sub>4</sub>-Fe(H<sub>2</sub>O)<sub>2</sub> can supply Fe═O active center for C-H activation via forming (WO)<sub>4</sub>-Fe<sub>a</sub>-O<sub>t</sub>···CH<sub>4</sub> intermediate, similar to that for CH<sub>4</sub> oxidation in the monooxygenase. This work highlights a promising and facile strategy for single dispersion of ≈1-2 Å metal center with precise coordination microenvironment by uniformly anchoring nanoscale molecular clusters, which provides a well-defined model for in-depth mechanism research.