Synthesis and thermal stability of the sodalite Na6Zn2[Al6Si6O24](SO4)2 and its reaction with hydrogen

Na6Zn2[Al6Si6O24](SO4)2 was prepared as a stoichiometric phase by reacting zeolite A with ZnSO4 at 700 °C for 8 h. Powder-XRD showed that Na6Zn2[Al6Si6O24](SO4)2 crystallised with the sodalite structure, a = 8.923(1) Å, Z = 1; illustrating that Zn2+ can be substituted for Ca2+ in ideal haüyne, Na6Ca2[Al6Si6O24](SO4)2. Na6Zn2[Al6Si6O24](SO4)2 was shown to be largely immiscible with nosean, Na8[Al6Si6O24]SO4 in the solid-state. Na6Zn2[Al6Si6O24](SO4)2 decomposes above 700 °C, yielding nosean, Na8[Al6Si6O24]SO4; willemite, Zn2SiO4; gahnite, ZnAl2O4; and presumably a glass phase, 2Na2O·9SiO2; with the loss of gaseous SO3. Na6Zn2[Al6Si6O24](SO4)2 was annealed under hydrogen at 700 °C, yielding sphalerite, ZnS and a more voluminous sodalite, Na6[AlSiO4]6 (a = 9.068(1) Å, Z = 1). Solid-state NMR indicates that the aluminosilicate framework remains essentially unchanged (according to the 29Si and 27Al) throughout this reaction, with the largest change observed for 23Na.

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► Na6Zn2[Al6Si6O24](SO4)2 was prepared as a novel sodalite-type phase.
► Na6Zn2[Al6Si6O24](SO4)2 decomposes under air ≳700 °C.
► Na6Zn2[Al6Si6O24](SO4)2 is reduced by H2 to ZnS and sodalite, Na6[AlSiO4]6.
► Na6Zn2[Al6Si6O24](SO4)2 and Na8[Al6Si6O24]SO4 are mutually immiscible.
► Solid-state NMR probes the local environment in the framework.