A new method for the analysis of heterogeneity using a modified temperature-programmed desorption technique

Abstract

A new temperature-programmed desorption (TPD) method is proposed which uses discontinuous heating schedules. New general equations are developed through which activation energies and their relationship with surface covering can be determined in an entirely different way from the classical TPD method. In addition, refinement of experimental energy values is shown to be possible, as the influence of temperature on the pre-exponential factor in Arrhenius law is taken into consideration.

For the sake of completeness, the method, called modified temperature-programmed desorption (MTPD), is tested by studying NH₃ desorption from γ-alumina. Relationships between the desorption activation energy, desorption temperature and surface covering are obtained. The existence of at least three adsorbed states, characterized by homogeneity in energy values, is demonstrated, a result comparable to those of other methods.