NOx Adsorption in ZSM-5 Films - Experimental studies and mathematical modeling

Licentiatavhandling, 2006

This work dealt with studies of NOx adsorption in films of ZSM-5. The study was interesting due to its significant contribution to develop a detailed understanding of NOx transport and adsorption in ZSM-5 which is of interest for catalyst or membrane applications. The adsorption study was focused on developing a mechanistic understanding of NOx adsorption in ZSM-5 films. NOx adsorption measurements and temperature programmed desorption (TPD) were carried out in a continuous flow reactor using binder-free ZSM-5 films grown on a cordierite monolith. The TPD measurements were used to determine the thermal stability of the various adsorbed species. To obtain more information about the character of the adsorbed species formed, in-situ diffuse reflectance infrared spectroscopy experiments were also carried out. It was found that various NOx adsorbed species with different thermal stabilities were present in the ZSM-5 depending on the counter-ions present and adsorption temperature. Also, mass transport resistance was observed to be of importance during transient adsorptions. In addition to the experimental work, mathematical modeling of NOx adsorption in a ZSM-5 film supported on a monolith support was also addressed, where both adsorption kinetics and mass transport resistances are important issues. A proposed adsorption mechanism combined with a transport model was able to reproduce the observed NOx adsorption-desorption phenomena which in turn offered a better insight into the NOx adsorption process in a thin ZSM-5 film.