Framework zinc-substituted zeolites: Synthesis, and core-level and valence-band XPS

A proof of framework substitution of T atoms of faujasite by divalent zinc is obtained by high-resolution X-ray photoelectron spectroscopy (XPS). Distinct and systematic XPS binding energy shifts between cationic and framework zinc are reported for both the core-levels and the valence-band Zn3d emission. A strong preference of T-atom substitution with zinc for silicon rather than aluminum is observed. Synthesis of a zinc-containing faujasite gives rise to a clean embedding of zinc into the framework. A subsequent postsynthesis modification by aqueous solution of zinc oxide in sodium hydroxide further enhances the framework zinc concentration. In the present investigation, a total of 15% Si atoms substituted by zinc yielded over a 2-fold enhancement of the monovalent cation-exchange capacity of faujasite.