Temperature-programmed desorption readsorption

When the simplif3dng assumption that no readsorption on the catalyst surface occurs dining the temperature-programmed desorption is valid, the position of the peak maximum (T ) is independent of the initial surface coverage 6 if adsorption sites are homogeneous. On... 

Kinetic Monte Carlo simulations can be parameterized from DFT calculations and used to model surface processes. We shall demonstrate how they can be used to predict the rate at which NH3 molecules desorb from a surface during a temperature programmed desorption experiment, assuming there is no readsorption of molecules to the surface. 

If readsorption is important part of surface event, its influence on temperature-programmed desorption is that TPD profile broadens towards higher desorption temperatures the same stands for diffusion limitations. Therefore, the task to neglect or minimize the effects of these processes is imposed and it is relatively easy if TPD experiments are performed in UHV setups. The pumping speed should be sufficiently high to prevent readsorption of the desorbed species back onto the surface. However, in the case of flow systems there are many experimental conditions that have to be adjusted even though, the interpretation of data obtained from TPD experiment is not simple—in the estimation of kinetic parameters, those experimental conditions have to be taken into consideration. Therefore, the derivation of kinetic and thermodynamic parameters from the results obtained in UHV and in the flow system will be discussed separately. 

Therefore, it is necessary to select suitable operating conditions that enable to avoid effects that could have influence on temperature-programmed profile. The ways how to find experimental conditions required to obtain reliable activation energies have been discussed in the literature. The recommendations that help to And appropriate sets of experimental parameters for experiments of temperature-programmed desorption [41-43] or other tempetrature-programmed techniques can be found [14, 44]. Once limitations that arrive from diffusion and readsorption are minimized, simplified procedures can be applied to evaluate kinetic parameters. 

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