Analysis of temperature programmed desorption (TPD) data for the characterisation of catalysts containing a distribution of adsorption sites

Abstract

This paper discusses some methods of analysing TPD data for samples obeying first-order desorption kinetics and proposes several improvements to existing practice. The methods apply in the case when the Arrhenius parameters A and E for each site are independent of coverage, and thus are normally suitable for the characterisation of porous solids. An improved implementation of the condensation approximation method is proposed to gain an initial estimate of the adsorption site distribution. Further, a variation of the method is proposed that can be used when A is a function of E. The initial estimate of the distribution can be used to analyse data obtained by an interrupted TPD experiment, in which heating is halted at a specified temperature. This method provides a reliable method of determining the parameter A for a peak in the distribution. Finally, regularisation procedures for obtaining physically sensible distributions from “noisy” TPD data are discussed. It is shown that a penalty function based on the square of the second derivative of the distribution is normally most suitable for analysing TPD data, at least in the case when the L-curve method is used to select the regularisation parameter.