Temperature-programmed desorption (TPD) of ammonia from HZSM-5 zeolites

Abstract

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.

Dexterous template-free synthesis of ferrisilicate with MFI morphology using rice husk ash

“…The band at 557 cm − 1 portrays the zeolite framework while the bands at 455 and 557 cm − 1 clearly confirms the purity and well ordered formation of the zeolites [29]. The band at 920 cm − 1 is observed for all the samples attributed to iron-perturbed T-O-T component and the intensity of this peak decreases with Si/Fe ratio, whereas the intensity of all other bands increases with Si/Fe ratio [30]. This band proves the presence of Fe in the framework.…”

“…Three peaks at 97, 202 and 437°C is attributed to NH 3 desorption. The peak at 97°C is assigned to physisorbed NH 3 , 202°C is due to ammonia adsorbed on weak acid sites, while the peak at 437°C could account for strong Brønsted acid sites [30]. The intensity of peaks at 97 and 202°C decreases with decreasing iron content in the catalyst.…”

Comparative study of sulfur-free nickel and palladium catalysts in hydrodeoxygenation of different fatty acid feedstocks for production of biofuels

“…For Ni/H-Y-80 the TPR showed the first broad peak appearing in the temperature range of 160°C -230°C, which is originated from reduction of oxidized Ni reported to to reduced at 222°C [36] . [36] at 362°C. [36] at 362°C.…”

Adsorption of water on zeolites of different types

“…For that thermoanalytical methods are frequently used to characterize their hydrophobic properties (e.g., [1][2][3]). However, non-isothermal investigations allow detailed information with respect to the strength of interaction of molecules with different adsorption sites, as it was shown for other systems (e.g., [4][5][6]). Therefore, we have performed temperature-programmed desorption (TPD) of water on Na+-ion exchanged zeolites of different types in order to characterize their adsorption properties with respect to water as probe molecule in more details.…”