Quasi In Situ 57Fe Mössbauer Spectroscopic Study: Quantitative Correlation between Fe2+ and H2 Concentration for PROX over Ir−Fe/SiO2 Catalyst

In this study, Ir−Fe/SiO2 catalyst was prepared by coimpregnation and investigated for preferential oxidation of CO under the presence of H2. It was found that the presence of H2, even in a slight excess, led to a large increase in the reaction rate for CO oxidation over the Ir−Fe/SiO2 catalyst, which was quite different from the case of Ir/SiO2. To reveal the promotional role of Fe associated with the presence of H2, quasi in situ Mossbauer spectroscopy, in combination with in situ DRIFTS and microcalorimetry, was employed. The results showed that the relative amount of Fe2+ increased with increasing H2 concentration in the reaction stream, well consistent with the trend of reaction rate for CO conversion, strongly suggesting that Fe2+ is the active site for oxygen activation. H2 promoted CO oxidation mainly via maintaining a substantial amount of Fe existing as Fe2+.