Theory of Thermodesorption from Energetically Heterogeneous Surfaces:  Combined Effects of Surface Heterogeneity, Readsorption, and Interactions between the Adsorbed Molecules

Theoretical analysis of thermodesorption from energetically heterogeneous solid surfaces is commonly based on the absolute rate theory in the form of the Wigner−Polanyi (W−P) equation, which neglects readsorption. As a consequence, the results of such analyses contain errors of unknown type and magnitude. Here we show that the application of the statistical rate theory of interfacial transport, instead of the W−P equations, leads to adsorption/desorption rate equations which simplify taking readsorption effects into account. An extensive model investigation is presented to show how neglecting readsorption can affect the theoretical analysis of experimental TPD peaks. Our investigation shows that readsorption can mimic effects which are actually due to surface energetic heterogeneity and/or to interactions between the adsorbed molecules. In addition to illustrative model calculations, the role of readsorption is also demonstrated by a quantitative analysis of spectra of hydrogen thermodesorption from a nickel catalyst.