Investigations of structure and protonic conductivity in the so-called tin zeolites

Abstract

‘Tin zeolites’, composites containing a zeolite and SnO₂, have been produced from parent zeolites (mordenite, zeolites X, Y and A) by thermal and microwave methods. Materials characterisation employed X-ray powder diffractometry (XRD), ²⁹Si and ²⁷AL MAS NMR, ¹¹⁹Sn Mössbauer spectroscopy, and ac conductivity investigations. Both XRD and MAS NMR studies show degradation of the zeolite framework in materials prepared by the thermal route. The extent of the damage depends upon the tin salt used in synthesis and is higher for those zeolites with higher Al contents. Mössbauer spectra are dominated by a central peak arising from microdispersed SnO₂, but a second Sn^IV environment is also present in materials prepared thermally from zeolites X, Y and A. All the ‘tin zeolites’ exhibit protonic conductivities greater than those of the parent zeolites, with thermally prepared samples exhibiting conductivities up to an order of magnitude greater than corresponding materials prepared by the microwave method.