Mössbauer spectroscopy as a tool to predict the catalytic activity of the Fe3+ sites in an exchanged Fe/hydroxyapatite system

Abstract

Catalytic reactions, with iron species as the active phase, require a specific structural organization to achieve good activity and selectivity. Thus, the presence of isolated Fe3+ ions or nanoclusters, the capacity to produce Fe3+/Fe2+ couples, or certain chemisorb reactive molecules are necessary for different reactions. Therefore, if the presence of these structural properties can be demonstrated, it could be inferred that the system could be active in a determined reaction avoiding the screening of catalytic tests. In the present work, using Mössbauer spectroscopy, we have verified that exchanged Fe in hydroxyapatite can produce Fe3+/Fe2+ redox couples which are necessary to achieve good catalytic performances in the NOx, N2O, and NH3 abatement reactions. Besides, this technique allowed us to verify that isolated Fe3+ sites and Fe(III)xOy nanoclusters were able to chemisorb CO molecules. Therefore, it could be thought that Fe/hydroxyapatite system might be active in catalytic reactions in which adsorption and dissociation of CO are necessary.