Effect of Catalysts and Supports

4 Effect of Catalysts and Supports. - Measurable support effects on deactivation by HMDS for otherwise comparable catalysts have been reported. For 

For the Pd catalysts, the results on Pd/AhOs, like Pt/AbOa, indicate the presence of all three types of behaviour about 80% type-A, 5% type-B and 15% type-C. Pd/Si02 and Pd/13X catalysts also show all three types of sites, but with more equal distribution.  

Cullis and Willatt carried out Auger electron spectroscopy on catalysts poisoned or inhibited by HMDS (Table 5). This treatment was found to destroy the methane oxidation activity completely. The results show that silicon and carbon were only present on the outer surface and that removal of 1.5 nm of the surface layer by argon ion bombardment left little trace of these elements on the Pd/Sn02 catalyst. The results also show that the silica had penetrated below the surface of the bead in the case of Pd/(Th02 + VAI2O3) catalyst, but its concentration decreased as successive atomic layers were removed. This is different from the case of Pd/Sn02 bead, in which the silica had only penetrated in the first few atomic layers and argon ion bombardment for 15 seconds removed all the silica as well as carbon.  

Cullis and WillatP also showed that the increased support porosity and metal dispersion provided the best means of increasing the poison resistance of Pt to high molecular weight poisons such as HMDS. The bead form of the catalyst, as 

Auger Electron Spectroscopic Analysis of the surface of powder catalysts and catalytic beads exposed to HMDS in the presence of methane+oxygen mixture (from ref. 3) 

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