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
H. Munakata et al., 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, J PHYS CH B, 105(17), 2001, pp. 3493-3501
Density functional theory calculations were performed on an activation of h
ydrogen peroxide over a cluster model of a titanosilicate catalyst. The cal
culation results showed possibility to form the hydrated peroxotitanosilica
lite complex, containing a (Ti)-O-O-(Si) peroxo-moiety, as an oxidizing age
nt. Using this hydrated peroxo-titanosilicalite complex as an oxidizing age
nt, oxidation mechanisms were postulated for ethene epoxidation and for amm
onia oxidation to form hydroxylamine. The ethene molecule was oxidized with
the peroxo-oxygen coordinated to the central Ti atom of the hydrated perox
o-titanosilicalite complex, to form ethylene epoxide. For the ammonia oxida
tion process, ammonia replaced the adsorbed water molecule of the hydrated
peroxo-titanosilicalite complex. The oxidation of the adsorbed ammonia in t
he (ammonia)-peroxotitanosilicalite complex led to the formation of an ammo
nia-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 con
taining a Ti-O-O-Si peroxo-moiety as an active oxidizing agent, the catalyt
ic reaction mechanisms are proposed for ethene epoxidation and for ammonia
oxidation to form hydroxylamine.