Global Kinetic Model for Ammonia Storage and Desorption

1 Global Kinetic Model for Ammonia Storage and Desorption 

In an earlier study, Olsson et al. [10] fitted the parameters for ammonia adsorption and desorption to an ammonia TPD experiment conducted over Cu-ZSM-5, using coverage dependent activation energy for ammonia desorption, occurring on one storage site SI according to  

The results of the experiment and model are shown in Fig. 12.4. Initially, there is a total uptake of all ammonia for about 10 min. This is followed by a breakthrough of ammonia until saturation is reached. After about 80 min, the ammonia is shut off and some weakly bound ammonia is released. Finally, the temperature is increased and a large ammonia desorption follows. The desorption peak is broad and contains a shoulder. Thus, there are different types of ammonia storage sites available in the catalyst. The model (see Fig. 12.4) describes this broad feature well by a coverage dependent heat of adsorption. It should be mentioned that S1, which is used in the global kinehc model is the total amount of sites that can adsorb ammonia, thus likely covering both Bronstedt acid sites as well as different copper sites. 

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