Hydrogen Adsorption on Zeolite-Supported Tetrairidium Clusters. Thermodynamic Modeling from Density Functional Calculations

Using energetic and spectral data from density functional calculations on a series of model species, hydrogenated clusters Ir 4 H n with up to n = 12 H atoms on a dehydroxylated zeolite support, we established a thermodynamic model of hydrogen loading on zeolite-supported Ir 4 clusters that accounts for temperature and H 2 pressure. The average number of H ligands, < n >, on the metal moiety was determined as function of temperature and H 2 pressure. These results indicate that species with different hydrogen loading should be observable. Thus, the actual hydrogen loading of supported Ir 4 clusters is predicted to depend strongly on the pretreatment and the conditions at which the system is examined. The reported thermodynamic data should be helpful for controlling the hydrogen loading of such clusters via temperature and H 2 pressure. They also permit one to determine conditions for the total dehydrogenation of the clusters or for preparing species with particularly high hydrogen loading. The latter is especially important for hydrogenation/dehydrogenation processes over supported metal catalysts.