Study of the ammonia–zeolite interaction in modified ZSM-5 by temperature-programmed desorption of ammonia

Abstract

T.p.d. of ammonia is a useful method for investigating the surface behaviour of zeolites. By means of various experimental manipulations it is possible to separate the specific ammonia zeolite interactions in order to give a sensible assignment of the corresponding adsorption sites. The high-temperature peak near 500 °C (h-peak) characterizes acidic Brønsted sites, whereas in the low-temperature desorption range two desorption peaks may appear at ca. 275 and 325 °C (l-peak and l_i-peak, respectively), which are though to be due to the interaction of ammonia especially with framework aluminium (l-peak) and sodium cations in the structure (l_i-peak).