Characterization of Acidic OH Groups in Y-Type Zeolites by Means of Different Methods of Temperature-Programmed Desorption (TPD) of Ammonia

The acidic properties of HNaY zeolites with different degrees of exchange have been studied by means of two complementary techniques of temperature-programmed desorption (TPD) of ammonia, namely, FTIR-TPD and conventional TPD. In HNaY zeolites with low exchange levels only a single type of OH group is observed. The analysis of the spectra in the region of NH bending modes during NH3-FTIR-TPD on zeolites with higher proton content (40% or higher) shows that ammonia is bound in two different adsorption states. This assessment is further confirmed by evaluation of the OH stretching region. Furthermore, desorption energy distribution functions for the different types of OH groups have been calculated using a numerical regularization method.