A DFT Study on Peroxo-Complex in Titanosilicate Catalyst: Hydrogen Peroxide Activation on Titanosilicalite-1 Catalyst and Reaction Mechanisms for Catalytic Olefin Epoxidation and for Hydroxylamine Formation from Ammonia

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Abstract

Density functional theory calculations were performed on an activation of hydrogen peroxide over a cluster model of a titanosilicate catalyst. The calculation results showed possibility to form the hydrated peroxo-titanosilicalite complex, containing a (Ti)-O-O-(Si) peroxo-moiety, as an oxidizing agent. Using this hydrated peroxo-titanosilicalite complex as an oxidizing agent, oxidation mechanisms were postulated for ethene epoxidation and for ammonia oxidation to form hydroxylamine. The ethene molecule was oxidized with the peroxo-oxygen coordinated to the central Ti atom of the hydrated peroxo-titanosilicalite complex, to form ethylene epoxide. For the ammonia oxidation process, ammonia replaced the adsorbed water molecule of the hydrated peroxo-titanosilicalite complex. The oxidation of the adsorbed ammonia in the (ammonia)-peroxo-titanosilicalite complex led to the formation of an ammonia-N-oxide complex of the titanosilicalite catalyst model. The (ammonia-N-oxide)-titanosilicalite complex was transformed into the (hydroxylamine)-titanosilicalite complex, with a hydrogen transfer from the nitrogen to the oxygen of the ammonia-N-oxide moiety. The transition states were explored for these reaction processes. Using the peroxo-titanosilicalite complex containing a Ti−O-O-Si peroxo-moiety as an active oxidizing agent, the catalytic reaction mechanisms are proposed for ethene epoxidation and for ammonia oxidation to form hydroxylamine.

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