Development and Validation of a Two-Site Kinetic Model for NH3-SCR over Cu-SSZ-13. Part 1. Detailed Global Kinetics Development Based on Mechanistic Considerations

Development of a Nonequilibrium Multisite Kinetic Model for NH3-SCR of NOx on CHA Cu-SAPO-34: Impact of Active Site Configurations and Locations

“…Indeed, at high temperatures, both SCR reactions and NH 3 oxidation can participate to the N 2 formation, while at lower temperatures between 200 and 300 °C, a slower reaction regime is visible. This difference in NH 3 oxidation behavior was previously observed by Gao et al and also taken into consideration in some NH 3 -SCR models developed for Cu-CHA. , Indeed, NH 3 oxidation was previously characterized as promoted by small copper surface clusters on Cu-CHA catalyst, ,, and this activity was also represented in the model regarding the resulting estimated activation energies of NH 3 oxidation on S4 and S3 ( < and < ), allowing a higher NH 3 oxidation intensity on S4 than S3. Accordingly, NH 3 coverage on S4, Figure , drops quickly between 200 and 350 °C.…”

“…However, some assumptions are also made, for example, total storage capacity and redox reactions can take place on the same single active site, which allows faster simulation, as reported by De-La-Torre et al, for steady state SCR process investigations or, as reported by Supriyanto et al, for hydrothermal aging modeling. Nevertheless, for NH 3 adsorption and desorption dynamic at high and low temperatures, at least two sites are generally adopted for better representation. ,, For instance, three sites were employed to model NH 3 storage capacity on Fe-zeolite catalysts, as reported by Skarlis et al, accurately representing the different NH 3 -temperature-programmed desorption (TPD) profiles of weak and strong acidic and nonacidic sites. Olsson et al used also three active sites to simulate the SCR behavior of Cu-CHA and storage capacity.…”

“…Nevertheless, for NH 3 adsorption and desorption dynamic at high and low temperatures, at least two sites are generally adopted for better representation. 38,49,50 For instance, three sites were employed to model NH 3 storage capacity on Fe-zeolite catalysts, as reported by Skarlis et al, 51 accurately representing the different NH 3temperature-programmed desorption (TPD) profiles of weak and strong acidic and nonacidic sites. Olsson et al 39 used also three active sites to simulate the SCR behavior of Cu-CHA and storage capacity.…”

An Aging Model of NH3 Storage Sites for Predicting Kinetics of NH3 Adsorption, Desorption and Oxidation over Hydrothermally Aged Cu-Chabazite

“…The fractional coverages of Z 2 W, ZCu1, ZCu2 and ZB for the degreened sample were, therefore, 0.60, 0.21, 0.12 and 0.07, respectively. The stoichiometry between a certain active site and NH 3 [18,47,56] was lumped into to the reaction rate parameters, similar to the prior literature [30,44]. Figure 5 shows the NH 3 concentration at the outlet of the reactor during NH 3 adsorption, isothermal desorption and TPD along with the fractional coverages obtained using the 4-site transient kinetic model for the degreened Cu-CHA.…”

“…However, it has also been shown that via H 2 -TPR, NH 3 -TPD, DRIFTS [29,30,50] and in situ time-resolved XAS [26] that the NH 3 -TPD profiles of Cu-CHA are much more complicated than proposed in [56]. Additionally, the multi-site kinetic models to predict deNOx performance [30,44,59] suggest that the highest temperature peak of NH 3 -TPD profile of Cu-CHA is associated with NH 3 desorption from ZCu II OH sites residing at the 8MR.…”