Unsteady-state Kinetics of the Standard SCR Reaction

The dynamic study of the ammonia SCR reactions was typically addressed by investigating the adsorption-desorption kinetics of ammonia and then the surface reactions. 

Langmuir kinetics have usually been considered for ammonia adsorption-desorption kinetics [48, 51, 52]. On the other hand, Andersson et al. ruled out that 

The results confirm that the adsorption of ammonia is very fast and that ammonia is strongly adsorbed on the catalyst surface. The data were analyzed by a dynamic isothermal plug flow reactor model and estimates of the relevant kinetic parameters were obtained by global nonlinear regression over the entire set of runs. The influences of both intra-particle and external mass transfer limitations were estimated to be negligible, on the basis of theoretical diagnostic criteria. 

The activation energy for ammonia desorption was found to be dose to zero and accordingly a non-activated ammonia adsorption process was considered ( a = 0)  

This is consistent with the spontaneity of adsorption of a basic molecule, such as ammonia, over the acid catalyst surface. 

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