Carbon monoxide tolerance mechanisms

Carbon monoxide (CO), even at trace amounts such as a few ppm levels, can poison Pt catalysts because it can strongly adsorb on the Pt surface, leaving a very small percentage of the Pt surface (e.g., less than 5% at 80°C in the presence of 10 ppm CO) for the HOR. Pt alloys with ruthenium (Ru) and tin (Sn) possess higher CO tolerance, and are thus popular (especially PtRu) as the anode catalysts when H2 is not CO-free. The mechanisms are mainly the accelerated oxidation of CO on PtRu and the reduction of CO adsorption strength on PtSn, respectively. Reaction 1.23 shows how Ru accelerates the... 

This failure mechanism can have significant impact on the ability of the anode to tolerate adsorbed contaminants. Similar to the impact of carbon corrosion on the cathode, the reduced electrochemically active catalyst surface area becomes very sensitive to the presence of contaminants. This is very important, for example, for operation on reformate where even small amounts of carbon monoxide can result in significant performance loss. 

---