Sulfate-supported metal oxides catalyst appearance

In the absence of SO2, Pt supported on silica and alumina show about the same activity for CO oxidation (blue squares) Upon addition of 20 ppm of SOj in the gas feed, the ignition temperature increases only 5°C during the first run in the alumina-supported sample, compared to 3UC in the case of the silica-supported catalyst. Because both samples have similar metal dispersion, the differences in LOT can only be attributed to the nature of the supports. In the literature, it has been proposed that the presence of SOj leads to the formation of sulfates on the alumina surface, which thus becomes a sulfur trap. This would allow the Pt surface to appear not to be affected as strongly as in the case of the silica support in this short time on stream (T-O-S) run. The increase in LOT is relatively small for the ceria-promoted alumina catalyst, probably for the same reason as for unpromoted alumina. Addition of cerium oxide to Pt/silica significantly decreases the LOT (by 26°C compared to Pt(0.63)/SiO2). In the presence of S, however, the activity is the same as that of the Pt without Ce, indicating poisoning of the Ce promotional effect. 

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