Cyclopentenyl Carbenium Ion Formation in Acidic Zeolites: An in situ NMR Study of Cyclic Precursors

Adsorption of Hydrocarbons and Formation of Carbocations over Zeolites Studied by IR Spectroscopy

“…In the present study, the alkenyl cation is considered to be produced at lower temperatures due to the initial CPE reactant. Thus, we assigned the observed band at 1498 cm -1 to alkenyl cation as previously 31) , as well as the assignment of the band at 1490-1530 cm -1 50) .…”

“…The cyclopentenyl cation was formed by intermolecular addition of propene and dehydration of the conjugated diene species, which formed a ring via intermolecular hydride transfer to form the cyclopentenyl cation (Scheme 1). Cyclopentenyl cation was also produced by cracking of ethene oligomer on H-ZSM-5 zeolite 31) . In addition, alkenyl cations can be formed by protonation of conjugated dienes, α, β-unsaturated ketones, allyl alcohols, and so on at Brønsted acid sites (Scheme 2) 32) .…”

“…Theoretical calculations and UVvisible spectra of allyl cations also supported this interpretation 51) . NMR observation of the reaction of cyclopentanol adsorbed on HY zeolite indicated that the formation of CPE and its oligomerization accompanied by dehydration occurred with heating to form alkenyl species with peaks at 250 and 150 ppm at 323-393 K 31) . In the present study, the alkenyl cation is considered to be produced at lower temperatures due to the initial CPE reactant.…”

“…13 C-NMR of cyclohexanol on H-ZSM-5 showed that a compound (Compound 1) was formed at 373 K 31) . However, in the present study, the skeletal rearrangement from cyclohexyl groups (CHE) to cyclopentyl groups represented by Compound 1 was not confirmed based on the different spectral appearance of Fig.…”

Isomerization of cyclohexane and hexane over silica- embedded triflate derivative catalysts

“…Summarizing, the immobilization of triflate derivative catalysts on silica led to systems able to catalyze the skeletal isomerization of cyclohexane at temperatures much lower than reported for zeolites. 27 The system is comparable with silica-supported aluminum chloride 24 but it is environmentally more friendly. The difference of the catalytic reactivity between cyclohexane and n-hexane is not a thermodynamical one because the free Gibbs energies of the reactions are similar, about -1 kcal/mol in both cases.…”