The selective oxidation of fragrant C-H bonds has drawn important consideration in each industrial and tremendous chemistry as a result of its essential position in changing readily- and cheaply-available fragrant hydrocarbons into high-value-added oxygenated merchandise for numerous fields corresponding to biology, drugs, perfume, and agriculture.
The standard strategies of acetophenone (ACP) manufacturing endure from quite a few limitations, corresponding to the usage of carcinogenic substrates, unrecyclable catalysts, harsh response situations, and low product yields. By intensive explorations, solvent-free selective ethylbenzene (EB) oxidation with molecular oxygen has been achieved utilizing cobalt naphthenate as a benchmark homogeneous catalyst.
As compared with homogeneous catalysis, heterogeneous catalysis reveals unparalleled benefits in catalyst recycling and product separation and is extra appropriate for industrial manufacturing. Eligible heterogeneous catalysts for EB-to-ACP conversion are being pursued, which stays a key problem in selective oxidation catalysis.
An in situ ligand-protected hydrothermal route was employed to encapsulate cobalt complexes (Co-DETA) within the faujasite matrix. Subsequently, Co@Y catalyst, consisting of cobalt ions confined in zeolite Y, was obtained by way of the removing of natural ligands upon calcination and was examined for the solvent- and additive-free selective EB oxidation to ACP.
Characterization outcomes from XRD, STEM, UV-vis, and SSNMR reveal that the single-site Co2+ had been stably confined in zeolite Y by way of interplay with framework oxygen atoms, which had been additional recognized because the lively websites for EB oxidation. Comparative research of EB oxidation over varied cobalt-containing zeolites and cobalt naphthenate catalysts had been performed to elucidate the essential position of single-site Co2+ confined in Co@Y.
Co@Y exhibited superior efficiency than different catalysts underneath an identical response situations. The new filtration take a look at of Co@Y signifies no leaching of Co species throughout the response, confirming the heterogeneous nature of EB oxidation catalyzed by Co@Y. Furthermore, after a number of recycles, the construction and catalytic efficiency of Co@Y remained practically unchanged, revealing its excellent stability.
Notably, the self-accelerating phenomenon was noticed throughout the progress of EB oxidation. Comparative assessments of EB oxidation with the addition of benzaldehyde or 1-phenylethanol reveal that benzaldehyde or 1-phenylethanol can modulate the catalytic behaviors of Co@Y, decreasing the obvious activation vitality for EB oxidation.
The mechanism of the EB oxidation on the single-site Co2+ in Co@Y catalyst and the origin of the self-acceleration phenomenon had been systematically studied by the first-principles density practical concept (DFT) calculations. It’s revealed that hint benzaldehyde or 1-phenylethanol generated within the response can promote EB oxidation to ACP, bypassing the normal pathway of ethylbenzene to 1-phenylethanol and eventually to acetophenone.
The self-acceleration phenomenon in EB oxidation was attributed to the technology of the reactive oxygen species (O*) on the single-site Co2+, which acted as an ‘initiator’ to advertise the next chain reactions.
In abstract, this work from a analysis group led by Prof. Landong Li from Nankai College, China, gives helpful insights into the experimental phenomena and the catalytic mechanisms concerned within the oxidation of fragrant C-H bonds over single-site cobalt catalysts, opening a brand new avenue for catalyst design.
The outcomes had been printed within the Chinese language Journal of Catalysis.
Extra info:
Jian Dang et al, Self-adjusted response pathway permits environment friendly oxidation of fragrant C–H bonds over zeolite-encaged single-site cobalt catalyst, Chinese language Journal of Catalysis (2024). DOI: 10.1016/S1872-2067(23)64579-6
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Chinese language Academy of Sciences
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Self-adjusted response pathway permits environment friendly oxidation of fragrant C-H bonds over Co@Y catalyst (2024, April 19)
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