Confinement Effects at the External Surface of Delaminated Zeolites (ITQ-2): An Inorganic Mimic of Cyclodextrins

Novel delaminated ITQ-2 zeolite has a remarkably large accessible external surface area (∼800 m2 g-1) and reduced microporosity (0.009 cm-3 g-1) and has attracted interest as an alternative to conventional zeolites or mesoporous MCM-41 (Corma, A.; Fornés, V.; Pergher, S. B.; Maesen, T. L. M.; Buglass, J. G. Nature 1998, 396, 353−356). α,ω-Diphenyl polyenes have been used as molecular probes to check the ability of ITQ-2 zeolite to generate organic radical cations. Of these probes, only t,t-1,4-diphenyl-1,3-butadiene (DPB) is transformed into a persistent reaction intermediate upon adsorption on ITQ-2. The process occurs in the “cup”-like cavities open to the exterior since selective silylation of the cups inhibits completely the generation of this reaction intermediate. Detection of 1-phenylnaphthalene as reaction product, EPR spectroscopy, and alternative laser flash photolysis generation strongly support 1-phenylnaphthalene radical cation as the intermediate formed after the adsorption of DPB onto ITQ-2. This contrasts with the behavior of conventional zeolites ZSM-5 and mordenite in which DPB•+ is the only species formed and demonstrates the uniqueness of the behavior of ITQ-2 as result of its unprecedented topology.