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Various representations of the Sn sites potentially present in Sn-substituted zeolites. (a) Simplistic overview of framework and extra-framework Sn species. (c) The nine distinct crystallographic sites of the β-framework, designated T1–T9. Sites T1–T4 are blue; T5–T6 yellow and T7–T9 green. (b) Open and closed Sn sites, depending on the degree of framework hydrolysis. Reproduced with permission from Hammond [3].
