Photooxidation and dark thermal oxidation of 1-butene on cationic forms of zeolite Y: a spectroscopic study

Hydrocarbon oxidation and aldol condensation over basic zeolite catalysts

“…The band at 3636 cm À1 was very weak, indicating that hydrated CsX has very weak or almost no acidity. The dark, thermal oxidation of 1-butene on CaY and SrY was studied by Tang et al [2]. They also observed the formation of water during the oxidation reaction, which agrees well with our results.…”

“…Researchers proposed that the strong stabilization of a hydrocarbon RH + -O 2 À charge-transfer pair inside a zeolite cage is due to the interaction of its large dipole with the high electrostatic field near alkali or alkaline earth cations [7]. Interestingly, the dark thermal oxidation of hydrocarbons was catalyzed by zeolites X and Y at low temperature (353 K) [1,2,6], and those reactions were assumed to proceed via the same mechanism as the photoassisted oxidation, i.e. electron transfer involving the superoxide anion radical [2].…”

“…For example, hydrocarbon oxidation reactions induced by photons within zeolite structures have been extensively studied over recent years. Researchers have achieved oxidation of ethane, propane, isobutene and 1-butene with high selectivity under irradiation with visible light as well as under dark thermal conditions in cation-exchanged zeolites, such as NaY, CaY, SrY, and BaY [1][2][3]. A proposed mechanism by Frei and coworkers in Expression (1) involves a radical cation and O 2 À by activating dioxygen and hydrocarbon with electron transfer from the hydrocarbon to the oxygen molecule.…”

“…Interestingly, the dark thermal oxidation of hydrocarbons was catalyzed by zeolites X and Y at low temperature (353 K) [1,2,6], and those reactions were assumed to proceed via the same mechanism as the photoassisted oxidation, i.e. electron transfer involving the superoxide anion radical [2]. Vanoppen et al found that activity decreased in the order CaY > SrY > BaY > NaY during cyclohexane autoxidation, which provided further evidence that the electrostatic field plays an important role in determining the extent of hydrocarbon oxidation in zeolites [8].…”

“…A proposed mechanism by Frei and coworkers in Expression (1) involves a radical cation and O 2 À by activating dioxygen and hydrocarbon with electron transfer from the hydrocarbon to the oxygen molecule. The produced hydrocarbon radical cations have strong acidity and therefore readily donate the proton (H + ) to À O 2 to yield R (alkyl or allyl) and HOO [1,2,4].…”