Adsorption study by transient tracing methods. theory and modeling

Abstract

The advantages of transient tracing methods (TTM) in studying heterogeneous catalytic systems have been described by many authors. This chapter presents a new application of TTM for studying adsorption. The basic idea of the new method is that the surface concentrations and the adsorption and desorption rates can be obtained from the measured transient response curves during the transient period. Generally, the temperature programmed desorption (TPD) is used for the characterization of adsorption. From an experimental point of view, the method is simple, but the interpretation of TPD spectra is often complicated because a lot of simultaneous processes are involved. Usually, in transient tracing experiments, gradientless reactors (CSTR) are used to linearize the system and reduce mathematical complexity. In model calculations, the gradientless system is represented by a compartmental network. While the species in the gas phase can be considered homogeneous and can be represented by compartments under proper conditions, there is always an inherent inhomogeneity of the surface states. This inhomogeneity—originated from either the surface sites or from the adsorbate interactions—is the main object of the different types of adsorption studies. © 1993, Elsevier Science & Technology. All rights reserved.