A MONTE-CARLO STUDY OF TEMPERATURE-PROGRAMMED DESORPTION FROM SUPPORTED-METAL CATALYSTS

The extent to which metal particle geometry and adsorbate spillover in fluence the temperature-programmed desorption spectra for the desorpti on of hydrogen from supported-metal catalysts has been studied by Mont e Carlo simulation. By including a mechanism for adsorbate spillover a nd surface diffusion it is shown that spillover of the adsorbate onto the catalyst support can result in the differences observed experiment ally between desorption spectra obtained from single crystals and supp orted-metal catalysts. An isosteric Arrhenius analysis of the TPD spec tra has been used to demonstrate that, at low surface coverage, the ac tivation energy characterising surface diffusion of adsorbates on the catalyst support can be obtained from the desorption spectrum.