Reaction mechanism of preferential oxidation of carbon monoxide on Pt, Fe, and Pt-Fe/mordenite catalysts

We have investigated the preferential oxidation (PROX) of carbon monoxide at Pt/mordenite (Pt/M), Fe/mordenite (Fe/M), and Pt-Fe/mordenite (Pt-Fe/M) for a purification of reformates to supply polymer electrolyte fuel cells (PEFCs). Pt-Fe/M exhibited remarkable PROX activity up to an extremely high space velocity (i.e., ca. 100% selectivity, SV=∼105h−1) even at 50 °C, although Pt/M and Fe/M had negligibly small PROX activity. CO, H2, and O2 chemisorption measurements demonstrated that Pt sites act as adsorption sites for CO and/or H2 and Fe (dominantly FeO) sites only for O2, so that the addition of Fe to Pt/M can preserve O2 adsorption sites for the PROX reaction even in CO/excess H2 gas flow. The poor reactivity of Pt/M and Fe/M can be ascribed to the lack of CO and/or O2 adsorption as the essential requisite for the Langmuir-Hinshelwood mechanism. We propose the so-called “bifunctional mechanism” for the distinctive performance at Pt-Fe/M, where the Pt site acts as a CO adsorption site and the Fe site acts as an O2 dissociative-adsorption site and enhances the surface reaction between the reactants on the neighboring sites.