A series of ZSM 5 samples obtained by dealumination is studied by TPD, DTA/DTG, XPS and adsorption measurements. The amount of adsorbed water at p/p0 ≦ 0.1 and the amount of chemisorbed NH3 corresponding to the TPD peak at 693–723 K correlate with the number of framework aluminium atoms per unit cell. At strong dealumination an enrichment of non-framework aluminium in the surface layers of the crystals was found. The HZSM-57 zeolites are transformed into silicalite-like samples during the course of the DTA experiment in the temperature range 973–1273 K.
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