It is now well accepted that the interaction of NH3 with the Brönsted acid sites of zeolites leads to the formation of NH4 + ions that are strongly H-bonded to the basic oxygens of the lattice; nevertheless, unambiguous evidence of their local siting is still lacking. In this contribution we report a detailed assignment of the IR vibrational features of NH4 + ions which reveals that mainly bidentate and tridentate species with various local symmetry are stabilized inside the cages and channels of ZSM-5, MORD, β, SAPO-34, and Y zeolites. Tetradentate species, mainly in MORD, are also found. In addition, it is shown that Fermi-type resonance interactions lead to the appearance of several bands in the ν(NH) stretching region of the vibrational spectrum that do not correspond to different NH oscillators. Finally, the solvation of NH4 + in the presence of excess ammonia is also investigated, and the IR manifestations, observed when reversibly adsorbed NH3 is present in the channels and cavities, are explained in terms of N2H7 + and N2H7 +·nNH3 structures.

The interaction of Brønsted sites of H-β (AH) with bases B with proton affinity (PA) ranging in the 118 (N 2 ) to 204 (NH 3 ) kcal mol -1 interval leads to the formation of 1:1 adducts. The vibrational manifestations of these adducts change considerably as a function of the proton potential. In 1:1 neutral adducts characterized by weak-medium hydrogen bonds, the shift of the ν(AH) mode (∆ν j) is proportional to the shift caused by the same bases on the Si-OH (weak) Brønsted acid used as a standard. As far as the 1:1 adducts formed with ethers and tetrahydrofuran (THF; PA ) 196 kcal mol -1 ), the situation is more complex owing to high ionicity acquired by the hydrogen bond. When stronger bases are used (pyridine, Py), the true proton transfer is observed. The ν(AH‚‚‚B) modes of the medium-strong 1:1 adducts are modulated by Fermi resonances with 2δ and 2γ overtones and with internal modes of A and B moieties. A general review of the phenomenon is given. Also the spectra of the ionic 1:1 adducts formed with Py and NH 3 are modulated by complex Fermi resonance effects. The situation occurring at higher dosages of B is also examined: it is concluded that in the presence of an excess of H 2 O (and CH 3 OH) the originally formed neutral 1:1 adducts are transformed into protonated clusters.

A zeolitic material containing Ti chains activated by light allows a shape-selective transformation of organic compounds; the molecules that can enter into the zeolitic cavities are protected from the light-induced processes, while the other are degraded.

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