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

1990; Volume: 36; Issue: 4 Linguagem: Inglês

10.1007/bf01914061

0368-4466

B. Hunger, J. Hoffmȧnn, Olaf Heitzsch, Michael Hunger,

Advanced Chemical Physics Studies

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 (Β andγ peak). Parts of the ammonia desorbed can be attributed to SiOHAl groups considering also1H-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 micro-calorimetrically.