Abstract
Abstract Multinuclear solid-state NMR offers many new insights into the structure and reactivity of zeolite catalysts. 29Si magic-angle-spinning (MAS) NMR reveals the details of Si,Al ordering in the frameworks, while 27Al quadrupole nutation NMR probes the chemical status of aluminium. Dealumination and realumination of the framework can be readily studied by both methods. 1H NMR allows the structure of the Bronsted active site to be determined. The source of 29Si spin-lattice relaxation is the paramagnetic oxygen molecule which can penetrate the intracrystalline space. Spin-lattice relaxation times of 27Al in zeolitic frameworks are between 0.3 and 70 ms depending on temperature; the relaxation is governed by the electric quadrupole interaction with the crystal electric field gradients modulated by translational motion of polar sorbate molecules and charge-compensating cations.
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