Nature, strength, and concentration of acid sites of erionite-rich zeolite T determined by ammonia—i.r. spectroscopy

Abstract

HNaK-containing T zeolites with different proton content were synthesized. Subsequently, the samples were characterized by i.r. spectroscopy and temperature-programmed desorption of ammonia. Besides the direct observation of the acid OH groups, ammonia was used as the probe molecule to determine the nature, strength, and concentration of the acid sites. The nature of the acid sites was identified by the different frequencies for ionically bound ammonia (Brönsted sites) and coordinatively bound ammonia (Lewis sites). The different Brönsted sites were characterized by coupling of ammonia—i.r. spectroscopy with a desorption procedure. The temperature-programmed desorption of ammonia was applied as an opportunity for comparison to obtain exact information about the concentration of the different acid sites observed by ammonia—i.r. spectroscopy.