Iron Modified Natural Zeolite as Sustainable Environmental Catalysts: Correlation between Iron Speciation and Catalytic Activity in NO-Reduction

Abstract

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 3 H 6 . Infrared spectroscopy coupled Prime Archives in Chemistry 3 www.videleaf.com 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 x O 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 x O y aggregates, and 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.