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Abstract:
The acidity of dealuminated hydrogen mordenites (Si/Al = 12-39) is characterized by the temperature-programmed desorption
of ammonia or pyridine which is monitored through a mass spectrometer. Four types of sites are indicated by ammonia
desorption, viz., weak and strong sites of Bronsted and Lewis type, whereas pyridine desorption reveals only the existence
of three types of acidic sites which are tentatively assigned to one sort of Bronsted site and weak and strong Lewis centers.
Evaluation of the desorption spectra provides the temperatures of maximum rate of desorption, the population of the respective sites, the desorption rates as a function of the activation energies of desorption, and, finally, probability functions of the activation energies. The results are discussed in terms of coverage, Si/Al ratio, and accessibility.
