In situ and operando IR study of adsorption sites for NH4+ active species in NOx-SCR via NH3 using a Y zeolite

The infrared characterization of various ammonium species obtained after NH3 adsorption over three different Y type zeolites was obtained by both the detailed analysis of the spectra by second derivative treatment and the use of preadsorbed bulky trimethylamine molecule. The broad delta(NH4+) massif obtained after NH3 saturation could thus be decomposed into individual bands, each one being tentatively associated to an identified species. Following by infrared operando spectroscopy the evolution of the delta(NH) bands during selective catalytic reduction of a mixture of NO and O-2, we were then able to determine the activity ranking between the ammonium species and coordinated ammonia over Lewis sites.