Fe Speciation in Iron Modified Natural Zeolites as Sustainable Environmental Catalysts

Natural purified mordenite from Palmarito de Cauto (ZP) deposit, Cuba, was subjected to a hydrothermal ion exchange process in acid medium with Fe 2+ or Fe 3+ salts (Fe 2+ZP and Fe 3+ZP). The set of samples was characterized regarding their textural properties, morphology, and crystallinity, and tested in the NO reduction with CO/C 3H 6. Infrared spectroscopy coupled with NO as a probe molecule was used to give a qualitative description of the Fe species’ nature and distribution. The exchange process caused an increase in the iron loading of the samples and a redistribution, resulting in more dispersed Fe 2+ and Fe 3+ species. When contacted with the NO probe, Fe 2+ZP showed the highest intensity of nitrosyl bands, assigned to NO adducts on isolated/highly dispersed Fe 2+/Fe 3+ extra-framework sites and Fe xO y clusters. This sample is also characterized by the highest NO sorption capacity and activity in NO reduction. Fe 3+ZP showed a higher intensity of nitrosonium (NO +) species, without a correlation to NO storage and conversion, pointing to the reactivity of small Fe xO y aggregates in providing oxygen atoms for the NO to NO + reaction. The same sites are proposed to be responsible for the higher production of CO 2 observed on this sample, and thus to be detrimental to the activity in NO SCR. View Full-Tex