The temperature-programmed desorption (tpd) of the amount of ammonia which is preadsorbed at about 373 K at HZSM-5 zeolites yields a complex desorption curve consisting of two overlapped peaks (fl and ~,lPeak). Parts of the ammonia desorbed can be attributed to SiOHAI groups considering also H-MAS NMR measurements.The course of the desorption of both peaks is describable by a rate equation which considers a dependence of the desorption energy on the degree of coverage or an energy distribution, as could be shown by various methods of evaluation. The calculated dependence of the desorption energy on the ammonia amount adsorbed well agrees with data of literature of adsorption heats determined miero-calorimetrieally.Temperature-programmed desorption (tpd) of bases [3,[4][5][6][7][20][21][22][23][24][25][26][27][28][29][30][31] is, beside of IR spectroscopy [1-9], 1H-MAS-NMR spectroscopy [10][11][12][13][14][15][16] and microcalorimetry [2,8,9,[17][18][19][20] a method frequently used for the characterization of acidic properties of HZSM-5 zeolites.Tpd of ammonia adsorbed at low temperature provides 3 peaks more or less strongly overlapped (a, fl or LT, and 7 or HT peak [7,20]), which are ascribed to acidic centres of different strength. The a peak is ascribed in this case to the physisorption of ammonia. The reason for the ~ peak is the NH3 desorption from strongly acidic OH groups, which can be characterized in the IR spectrum by the vibration band at about 3600 cm -1. The fl peak is explained in different manner by several authors: Tops0e [7] ascribes this peak to desorption from weak acidic centres according to a IR band in the 3720...3740 cm -1 region or to the adsbrption on Na + and Hidalgo [5] to a broad IR band at 3350...3650 cm -1. Lok [3] interpretes the peak by splitting of physisorbed ammonia and Schnabel et al. [6] discuss a desorption from extra-framework aluminium.
Novel preorganized host macrocycles with defined cavity size and t w o convergent carboxylic acid groups extract small alkaline earth metal ions in a liquid two-phase system with high selectivity, in particular Ca2+, unlike the alkali metal ions.
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