CHARACTERIZATION OF THE ACIDIC PROPERTIES OF ZEOLITES BY MEANS OF TEMPERATURE-PROGRAMMED DESORPTION (TPD) OF AMMONIA - CALCULATION OF DISTRIBUTION-FUNCTIONS OF THE DESORPTION ENERGY

Desorption energy distributions were calculated for temperature-progra mmed desorption (TPD) of ammonia from H zeolites of different type by means of regularization. This method does not require any limiting ass umptions about the distribution function. It could be shown that the d esorption energy distributions obtained are nearly independent of the experimental conditions and therefore they should represent a suitable measure for the distribution of the strength of acidic sites. The cal culated desorption energy distributions for the ammonia desorption fro m the isolated bridging SiOHAl groups of H zeolites of different type significantly differ from each other in shape. The increase of the des orption energy of the main range of the distribution functions correla tes well with the increase of the average acid strength of the SiOHAl groups with decreasing Al content of the zeolites.