27Al spin-echo, high-speed MAS (nu(rot) = 30 kHz), and MQMAS NMR spectroscopy in magnetic fields of B0 = 9.4, 14.1, and 17.6 T were applied for the study of aluminum species at framework and extra-framework positions in non-hydrated zeolites Y. Non-hydrated gamma-Al2O3 and non-hydrated aluminum-exchanged zeolite Y (Al,Na-Y) and zeolite H,Na-Y were utilized as reference materials. The solid-state 27Al NMR spectra of steamed zeolite deH,Na-Y/81.5 were found to consist of four signals. The broad low-field signal is caused by a superposition of the signals of framework aluminum atoms in the vicinity of bridging hydroxyl protons and framework aluminum atoms compensated in their negative charge by aluminum cations (delta(iso) = 70 +/- 10 ppm, C(QCC) = 15.0 +/- 1.0 MHz). The second signal is due to a superposition of the signals of framework aluminum atoms compensated by sodium cations and tetrahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 65 +/- 5 ppm, C(QCC) = 8.0 +/- 0.5 MHz). The residual two signals were attributed to aluminum cations (delta(iso) = 35 +/- 5 ppm, C(QCC) = 7.5 +/- 0.5 MHz) and octahedrally coordinated aluminum atoms in neutral extra-framework aluminum oxide clusters (delta(iso) = 10 +/- 5 ppm, C(QCC) = 5.0 +/- 0.5 MHz). By chemical analysis and evaluating the relative solid-state 27Al NMR intensities of the different signals of aluminum species occurring in zeolite deH,Na-Y/81.5 in the non-hydrated state, the aluminum distribution in this material was determined.

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The effect of adsorbate molecules on the quadrupolar interaction of framework aluminum atoms with the electric field gradient in dehydrated zeolite H,Na-Y has been studied by (27)Al MAS NMR and (27)Al MQMAS NMR spectroscopy at magnetic fields of 9.4 and 17.6 T. Upon adsorption of molecules interacting with bridging OH groups by hydrogen bonds (acetonitrile and acetone), the quadrupole coupling constant of framework aluminum atoms was found to decrease from 16.0 MHz (unloaded zeolite) to 9.4 MHz. Adsorption of molecules, which cause a proton transfer from the zeolite framework to the adsorbates (ammonia and pyridine), reduces the quadrupole coupling constant to 3.8 MHz for coverages of 0.5-2 molecules per bridging OH group. The experiments indicate that the quadrupole coupling constant of framework aluminum atoms in dehydrated zeolite H,Na-Y reflects the chemical state of adsorbate complexes formed at bridging OH groups. In agreement with earlier investigations it was found that a proton affinity of the adsorbate molecules of PA = 812-854 kJ/mol is necessary to induce a proton transfer from the zeolite framework to the adsorbed compounds. This proton transfer is accompanied by a strong improvement of the tetrahedral symmetry of zeolitic framework AlO(4) tetrahedra and a decrease of the electric field gradient.