Stoichiometry catalyst sintering

These results were interpreted in terms of a substantial surface enrichment in Cu, driven by Cu s lower heat of sublimation [23]. The reactivity of these catalysts for CO oxidation, and the clear spectroscopic evidence for surface Pt - CO species indicate that, at least for the heterogeneous systems, particle surface stoichiometries are very sensitive to metal-adsorbate interactions. Similar arguments were presented for the PtAu/silica system, in which monometallic Au particles severely sinter under dendrimer removal conditions. In this case, the retention of small bimetallic particles after activation was attributed to the strength of Pt-silica interactions, which effectively anchored the bimetallic nanoparticles to the support [24],... 

The activity of Uiis type of catalyst in the oxidation of different hydrocarbons in gas mixtures at stoichiometry was next determined in the new or aged state. Irrespective of the natine of the hydrocarbons, their conversion gradually decreases in keeping with the decrease in metal dispersion. This decrease in conversion can be explained by the loss of active sites when sintering takes place. 

The numerator of Equation 11.1 and Equation 11.2 includes the molar stoichiometry (Vsioic) of the metal atoms in the surface metal oxide (MO ) and its molecular weight (MJ. These equations differ in calculation of the denominator Equation 11.1 uses the surface area of the calcined, pure support oxide (no surface oxide), and Equation 11.2 uses the surface area of the calcined composite catalyst. Unless the support oxide shows negligible sintering and the support oxide content is low, ps rfi and psuj(2 are numerically different. 

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