Solid-state defects in calcined CaA zeolite

Abstract

Ca ion-exchanged zeolites have been characterized by electron spin resonance (e.s.r.), ²⁷Al magic-angle spinning nuclear magnetic resonance (MAS n.m.r.), ²⁹Si MAS n.m.r., and diffuse reflectance Fourier transform infrared spectroscopy (i.r.). The presence of the radical species that are assigned to solid-state defects was confirmed in CaA zeolites, and the amount of the radical was dependent on the thermal treatment temperature in air. The present experimental results suggest that the formation of extralattice aluminum in the CaA sodalite cage and the change of calcium species by thermal treatment relate to the formation and disappearance of radical species.