Journal
ACS CATALYSIS
Volume 9, Issue 6, Pages 5742-5751Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acscatal.9b01284
Keywords
photocatalysis; C-H activation; cyclohexane oxidation; KA oil; titanosilicate; chlorine; layered silicate; partial oxidation
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Funding
- Japan Society for the Promotion of Science (JSPS) KAKENHI [17K17906]
- JSPS Core-to-Core Program
- Center for Functional Nano Oxide at Hiroshima University
- Grants-in-Aid for Scientific Research [17K17906] Funding Source: KAKEN
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Owing to the economic and environmental benefits, photocatalytic organic transformation via C-H activation is a crucially important, while still challenging area. We report a photocatalytic process for partial cyclohexane oxidation with enhanced catalytic activity that exploits chlorine and titanium atoms spatially arranged on a silica substrate. Silica based catalysts bearing grafted titanium that effectively interacts with photochemically adsorbed chlorine were prepared. The catalysts were synthesized by reacting a layered silicate with titanium(IV) acetylacetonate and subsequent chlorination treatment. Characterization by a variety of techniques revealed that the organic ligand of the titanium species that is grafted onto the silicate layer surface is converted into chlorine while maintaining its coordination state. However, upon subsequent hydration, the chlorine existed as HCl. We investigated the performance of the catalyst for the production of cyclohexanol and cyclohexanone from cyclohexane with molecular oxygen under solar light irradiation. The chlorinated layered silicate photocatalyst exhibited a remarkably high production rate (0.7 mmol g(-1) h(-1)) and large amount of product formed (0.8 mmol), while the overoxidation of cyclohexane was inhibited. The enhanced catalytic ability could be explained by the presence of a radical mediator (chlorine) located at a position neighboring an isolated titanium atom. The high surface density of these active species (both titanium and chlorine) on the silicate layer provided suitable electron transfer to form chlorine radicals.
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