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Cation-induced speciation of port-size during mordenite zeolite synthesis

Journal of Material Chemistry A – Sebastian Prodinger, Izar Capel Berdiell, Tomas Cordero-Lanzac, Odd Reidar Bygdnes, Bjørn Gading Solemsli, Karoline Kvande, Bjørnar Arstad, Pablo Beato, Unni Olsbye and Stian Svelle.

Mordenite (MOR) zeolite, an important industrial catalyst exists in two, isostructural variants defined by their port-size, small and large-port. Here we show for the first time how a systematic, single-parameter variation influences the synthesis out-come on the final MOR material leading to distinctly different catalysts. The cation identity has a direct impact on the synthesis mechanism with potassium cations generating the more constrained, small-port MOR variant compared to the large-port obtained with sodium cations. This was expressed by different degrees of accessibility ascertained with a combination of toluene breakthrough and temperature programmed desorption (TPD), propylamine TPD, as well as sterically sensitive isobutane conversion. Rietveld refinement of the X-ray diffractograms elucidated the preferential siting of the smaller sodium cations in the constricted 8-ring, from which differences in Al distribution follow. Note, there are no organic structure directing agents utilized in this synthesis pointing at the important role of inorganic structure directing agents (ISDA).

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