Ammonia Loading Detection of Zeolite SCR Catalysts using a Radio Frequency based Method

Ammonia adsorption on the catalyst surface is a crucial step in the selective catalytic reduction of nitrogen oxides over zeolites with NH₃ as the reducing agent. In this study, two small pore zeolites with chabazite frameworks, H-SSZ-13 and Cu exchanged SSZ-13, are examined. Adsorption of NH₃ on the zeolite causes changing electrical properties of the material. They can be detected by a radio frequency based technique. We have found that with this method it is possible to determine the amount of adsorbed NH₃ on these catalysts, examining both the influences of temperature and NH₃/NO feed gas ratio. At constant temperature, a fairly linear correlation between the resonance frequency and the amount of adsorbed ammonia was observed. Furthermore, this method also allows differentiation between some of the NH₃ adsorption sites.