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À propos de : Oxygen and Structural Effects on Silicalite 29SiSpin−Lattice Relaxation Studied by High-Resolution 29SiSolid-State NMR        

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  • Oxygen and Structural Effects on Silicalite 29SiSpin−Lattice Relaxation Studied by High-Resolution 29SiSolid-State NMR
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  • Monodisperse silicalite crystals (170 μm × 40 μm × 40 μm) have been synthesized andthe 29Si spin−lattice relaxation rates have been measured by high-resolution solid-state NMR.Loading of 5 wt % p-xylene into the silicalite channel system reduces the 29Si spin−latticerelaxation time compared to that of empty silicalite. The relaxation time is unaffected whenp-xylene was replaced by p-xylene-d10 of the same loading. This indicates that dipole−dipolecoupling between protons of guest molecules and silicon atoms does not contribute significantly to the 29Si spin-relaxation time. A novel method employing aromatic endoperoxide is demonstrated for controlled addition of molecular oxygen into silicalite samples. The resultsshowed that interaction with a paramagnetic oxygen molecule is not the only relaxationmechanism for 29Si nuclei, and that zeolite structural changes caused by loaded organicguest molecules also play an important role in determining the 29Si spin−lattice relaxationtime.
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