XAFS characterization of Pt-Fe/zeolite catalysts for preferential oxidation of CO in hydrogen fuel gases

We have developed a new Pt-Fe/mordenite (Pt-Fe/M) catalyst which shows remarkably high activity and selectivity for the oxidation of CO in H-2-rich gas compared with Pt/M. In the present work, to understand the role and structure of Pt and Fe in the Pt-Fe/M catalyst, the states of metallic components in ion-exchanged, H-2 pre-treated and post-PROX (preferential oxidation of CO) samples have been studied by means of XAFS. It was confirmed that Pt forms the metallic clusters after H-2 pretreatment or the PROX experiment, whereas a large part of Fe exists as oxides even after the H-2 treatment. At post-analysis of the catalysts used for the PROX experiment, an increase in coordination number of Fe-O was observed. Pt clusters in the Pt-Fe(2:1 weight ratio)/M catalyst, which showed the highest PROX performance, were found to have a different electronic structure from the other catalysts. Additionally, preferential CO adsorption onto Pt sites at Pt-Fe/M was clearly demonstrated by infrared spectroscopy analysis in a stream of 1% CO containing H-2. Based on these results, the superior PROX mechanism was discussed.