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Kinetic parameters from a single thermal desorption spectrum

Abstract:

Analytic expressions for desorption kinetics which follows the Polanyi-Wigner rate formulation, have been derived. These expressions allow the determination of the activation energy, frequency factor and reaction order using parameters obtained from a single peak thermal desorption spectra, such as: temperature, desorption rate, surface coverage, and rate of change of the desorption rate. In order to present the scope and limitations of the method the mathematics of the approach are presented for three different heating schedules (linear, exponential, and hyperbolic). Furthermore, plots obtained for simulated temperature programmed desorption spectra are presented. To study the noise effect, random noise added was fed into the spectrum up to 10% p-p level of the maximum signal ( S N = 10). Excellent results were found for the spectrum without noise (error of 0.1% for the energy and 0.05% for the reaction order). Very good results for a spectrum with noise (error of 3.5% for the energy and 2.1% for the reaction order) were obtained. © 1995.