Photocatalytic oxidative decomposition of fluoroalkenes by titanium dioxide

Abstract

Photoirradiation (>200 nm) of anatase TiO₂ induces decomposition of fluoroalkenes [hexafluoropropene (6FP), tetrafluoroethylene (4FE), 3,3,3-trifluoropropene (3FP), 1,1-difluoroethylene (2FE) and fluoroethylene (1FE)] as well as ethylene (0FE) in air at room temperature. The decomposition requires the coexistence of photoirradiation, air, TiO₂ and water on the catalyst, suggesting that TiO₂-photosensitized oxygenation is operative. Formation of carbon dioxide and hydrogen fluoride was commonly observed. The order of reactivity of the fluoroalkenes is 6FP > 4FE 2FE > 0FE > 3FP = 1FE. The major reaction path of 6FP gave equimolar trifluoroacetic acid and CO₂ as products via oxidative cleavage of the carbon–carbon double bond, while 4FE yielded CO₂ predominantly. The most probable intermediate in these reactions is a dioxetane products via direct addition of superoxide anion radical (O₂˙^–) and/or addition of molecular oxygen following electron injection into the fluoroalkene.