Solid-state ion exchange of Fe in small pore SSZ-13 zeolite: Characterization of the exchanged species and their relevance for the NOx SCR reaction

Solid state ion exchange was performed for the successful introduction of Fe cations in the small pore CHA structured SSZ-13 zeolite. The produced catalysts were characterized by IR and UV-Vis spectroscopies and thermally programmed reaction techniques to probe the Fe sites formed during the exchange and the catalytic activity for the NOx SCR reaction. The results indicate that highly dispersed and heterogeneous Fe sites are formed, and the type depends on the Al distribution in the zeolite. Dimeric Fe species are formed preferentially at the start of the exchange on the 6- and 8-member rings that contain at least two Al exchange sites and once these sites are fully saturated the Fe is exchanged as isolated cations.