Anionic coordination involvement in solid-state ion-exchanged CuH-SAPO-n(n= 5, 11 and 34) molecular sieves

Abstract

High-temperature solid-state ion exchange has been performed with H-SAPO-5 and various copper(II) compounds. Electron paramagnetic resonance (EPR) shows that this technique introduces Cu^II cations by ion exchange into H-SAPO-5, producing (S)Cu_(F)H-SAPO-5 and (S)Cu_(O)H-SAPO-5, where (S) indicates solid-state ion exchange and the subscripts F and O indicate the copper sources CuF₂ and CuO used in the solid-state reaction. The EPR parameters for both hydrated and dehydrated samples of (S)Cu_(F)H-SAPO-5 and (S)Cu_(O)H-SAPO-5 vs.(L)CuH-SAPO-5, where (L) indicates liquid-state ion exchange, show differences which are suggested to be due to anion involvement in the coordination of copper(II). This is supported by electron spin echo modulation data which show that the distances between Cu^II and several adsorbates in (S)Cu_(F)H-SAPO-5 are shorter than those for (L)CuH-SAPO-5 by 0.02–0.04 nm. Similar differences are observed for (S)Cu_(F)H-SAPO-34 and (S)Cu_(Cl)H-SAPO-34 vs.(L)CuH-SAPO-34 and for (S)Cu_(O)H-SAPO-11 vs.(L)CuH-SAPO-11. The g anisotropy also supports a decrease in symmetry owing to anion involvement.