Inhibition of Ammonia Poisoning by Addition of Platinum to Ru/α‐Al 2 O 3 for Preferential CO Oxidation in Fuel Cells

In polymer electrolyte fuel cell (PEFC) systems, small amounts of ammonia (NH 3 ) present in the reformate gas deactivate the supported ruthenium catalysts used for preferential oxidation (PROX) of carbon monoxide (CO). In this study, we investigated how the addition of a small amount of platinum to a Ru/α‐Al 2 O 3 catalyst (Pt/Ru=1:9  w / w ) affected the catalyst’s PROX activity in both the absence and the presence of NH 3 (130 ppm) under conditions mimicking the reformate conditions during steam reforming of natural gas. The activity of undoped Ru/α‐Al 2 O 3 decreased sharply upon addition of NH 3 , whereas Pt/Ru/α‐Al 2 O 3 exhibited excellent PROX activity even in the presence of NH 3 . Ruthenium K‐edge X‐ray absorption near‐edge structure (XANES) spectra indicated that in the presence of NH 3 , some of the ruthenium in the undoped catalyst was oxidized in the presence of NH 3 , whereas ruthenium oxidation was not observed with Pt/Ru/α‐Al 2 O 3 . These results suggest that ruthenium oxidation is retarded by the platinum, so that the catalyst shows high activity even in the presence of NH 3 .