THE DISTRIBUTION OF ACTIVATION-ENERGY FOR HYDROGEN DESORPTION OVER SILICA-SUPPORTED NICKEL-CATALYSTS DETERMINED FROM TEMPERATURE-PROGRAMMED DESORPTION SPECTRA

A method has been developed that can calculate the distribution of activation energy for desorption of hydrogen from temperature-programmed desorption (TPD) spectra for characterizing the heterogeneity of the surfaces of supported metal catalysts. This method is based on the idea of Hashimoto et al. [Stud. Surf. Sci. Catal. 28 (1986) 503] who determined the distribution of acid strength of solid acid catalysts from the TPD spectra of ammonia. The surface of a catalyst is regarded as a collection of groups of desorption sites with identical activation energy in each group. These groups are experimentally sampled from a series of TPD spectra and a set of desorption kinetic parameters are determined for each group. An overall TPD spectrum is given by the summation of the contribution from each group characterized by a particular activation energy. The fitting of a calculated spectrum to an experimental one determines the activation energy distribution. This method has been applied to study the surfaces of silica-supported nickel catalysts in the present work. The surface state of the catalysts is influenced by various preparation variables, and their influence is expressed in terms of the distribution of activation energy for hydrogen desorption.