Sulfur oxides poisoning, mechanism

Poisoning of iron catalysts during ammonia synthesis by sulfur compounds has received relatively little attention (154, 240-244). Nevertheless, the previous work provides information on the poisoning mechanism and interesting examples of how oxide promoters may influence the sulfur poisoning behavior of a catalytic metal. 

If one accepts the above mechanism for the WGS reaction, poisoning of the catalyst by SO2 must either block the oxidation of reduced ceria by water (Reaction (2)) or decrease the rate at which adsorbates on the metal can be oxidized by ceria (Reaction (3)). In either case, it is necessary to understand how SO2 interacts with ceria in any attempt 10 synthesize sulfur-tolerant catalysts. 

The study which we have conducted shows that the support material has an effect on the soot combustion characteristics of a supported catalyst, with the best support being a novel support. Comparing base metal to noble metal catalysts w,e have found that certain base metal catalysts (i.e, CuO or C Og) are poisoned by sulfur, do not promote complete combustion of the soot, and initiate soot combustion at a higher temperature than noble metal catalysts. These results are consistent with a soot combustion mechanism in which the metal (especially the noble metals) initiates oxidation of easily combusted adsorbed hydrocarbons and thereby provides local exotherms which initiate the oxidation of the soot. 

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