Abstract
Photocatalysis driven under visible light allows us to carry out hydrocarbon oxofunctionalization under ambient conditions, using molecular oxygen as a sacrificial reagent, with the absence of hazardous subproducts and the potential use of the Sun as a clean and low-cost source of light. In this work, eight materials—five based on titanium dioxide and three based on bismuth oxyhalides—were used as photocatalysts in the selective oxofunctionalization of cyclohexene. The cyclohexane oxofunctionalization reactions were performed inside of a homemade photoreactor equipped with a 400 W metal halide lamp and injected air as a source of molecular oxygen. In all assayed systems, the main oxygenated products, identified by mass spectrometry, were 1,2-epoxycyclohexane, 2-cyclohexen-1-ol, and 2-cyclohexen-1-one. Titanium dioxide-based materials exhibited higher selectivities for 1,2-epoxycyclohexane than bismuth oxyhalide-based materials. In addition to this, titanium dioxide doped with iron exhibited the best selectivity for 1,2-epoxycyclohexane, demonstrating that iron plays a relevant role in the cyclohexene epoxidation process.
Highlights
The heterogeneous photocatalysis of semiconductors is an advanced oxidation process (AOP)based on the ability of photocatalysts to adsorb photons with an energy equal to or greater than the forbidden energy band of the semiconductor material
There exists an optimum value for the iron amount due to the recombination charge increasing with the dopant concentration; this is because the distance between trapping sites in a particle decreases with the number of dopants
In systems that include iron-doped titanium dioxide photocatalysts, in-situ-generated to generate a peroxo complex. This is supported by the results described by McAteer et al in 2013 [46], H2O2 can interact with Fe to generate a peroxo complex. This is supported by the results described who reported the catalytic oxidation of cyclohexene catalyzed by iron(III)/hydrogen peroxide (H O )
Summary
Based on the ability of photocatalysts to adsorb photons with an energy equal to or greater than the forbidden energy band of the semiconductor material (hν ≥ Ebg ). Due to the high reactivity of these systems, they have mainly been applied in the elimination of pollutants and disinfection of water [1,2,3,4,5,6,7]. Due to their low selectivity, these systems have been rarely applied in the selective conversion of organic compounds [8].
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