A New Quantitative Analysis Of The Surface Energetic Heterogeneity Of Catalyst
A NEW QUANTITATIVE ANALYSIS OF THE SURFACE ENERGETIC HETEROGENEITY OF CATALYST
AND ADSORBENT SURFACES BASED ON THE STATISTICAL RATE THEORY OF INTERFACIAL TRANSPORT
W. Rudziński1, T. Borowiecki2, T. Pańczyk1, A. Dominko2
1Department of Theoretical Chemistry
2Department of Chemical Technology, Faculty of Chemistry Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 3, 20-031Lublin, Poland
Ph.: +48 81 5375633, Fax: +48 81 5375685,
e-mail: rudzinsk@hermes.umcs.lublin.pl
So far, attempts to draw quantitative information about surface energetic heterogeneity of adsorbents and catalysts from experimental TPD spectra, have been based on applying the ART (Absolute Rate Theory) approach, used to describe the adsorption/desorption kinetics. Meanwhile, the shortcomings, or even paradoxes accompanying the use of ART to describe the adsorption/desorption kinetics on (from) heterogeneous solid surfaces, have been more and more clearly realised.
Recently we have proposed a new method to generate information about the surface energetic heterogeneity of solids from TPD spectra, based on employing the Statistical Rate Theory of Interfacial Transport (SRTIT). [1,2,3] SRTIT is a new theoretical approach linking the rate of adsorption/desorption kinetics to the chemical potential of the adsorbed molecules and the molecules in the gas phase.
By assuming that transport between two phases at thermal equilibrium results primarily from single molecular events, the equation for the rate of transport between gas and a solid phase was developed by Ward and Findlay using a first-order perturbation analysis of the Schroedinger equation and the Boltzmann definition of entropy, [4,5] Where mg and ms are the chemical potentials of the adsorbate in the gas phase (g), and in the adsorbed (surface) phase (s), respectively. Then is a constant describing the rate of the elementary adsorption/desorption processes at equilibrium.
One of the most important advantages of this new approach is that it involves using the same thermodynamic quantities which appear in theoretical description of adsorption equilibria. Such terms like the "activation energy for adsorption and desorption" are not longer used in the new theoretical analysis of thermodesorption spectra.
In a recent series of papers we have shown, how the SRTIT approach can be applied to describe thermodesorption from energetically heterogeneous surfaces. The purpose of the present paper is to show our most recent results in this field.
References
1. W. Rudzinski, T. Borowiecki, A. Dominko, T. Panczyk, Langmuir, 13(1997)3445.
2. W. Rudzinski, T. Borowiecki, T. Panczyk, A. Dominko, Langmuir 16(2000)8037.
3. W. Rudzinski, T. Borowiecki, T. Panczyk, A. Dominko, J. Phys. Chem. B, 104(2000)1984.
4. J.A.Elliot, C.A. Ward, J.Chem.Phys. 106(1997)5667.
5. J.A.Elliot, C.A. Ward, J.Chem.Phys., 106(1997)5677.
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