CHARACTERIZATION OF SIOHAL GROUPS ON HNAY ZEOLITES BY MEANS OF TEMPERATURE-PROGRAMMED DESORPTION (TPD)

The temperature-programmed desorption (TPD) of ammonia, belonging to t he SiOHAl groups of HNaY zeolites, yields a well structured course of desorption. This can be described by a distribution function for the d esorption energy. The dependence of the desorption energy on the cover age, calculated by this assumption, agrees well with microcalorimetric ally determined heats of adsorption in dependence on the ammonia cover age. Thus, the distribution function can be used as a reasonable quant itative measure for the acid strength distribution of SiOHAl groups in zeolites. Further investigations on partially dehydroxylated samples allow refined characterization about changes of the acid properties.