Structural and spectroscopic studies of alkali-metal exchanged stilbites

Abstract

The structural, infrared (IR) and Raman spectroscopic properties of alkali-metal exchanged (Na+, K+, Rb+, Cs+) zeolites with the stilbite (STI) framework have been studied by Rietveld analysis of high-resolution synchrotron X-ray powder diffraction data, micro-Raman and synchrotron IR spectroscopy at ambient conditions. Ordered arrangements of the extra-framework cations (EFCs) and H2O molecules were found at the intersection of the 10- and 8-ring channels as well as framework distortions and deformations of the channel system caused by the EFCs distributions. The T(5)–T(5) distances along the chains of the structural building units range from 8.921(1) to 8.979(5) Å and scale with the size of EFCs in Na-, K-, Rb-, Cs-STI. Furthermore, our spectroscopic studies show a systematic increase of characteristic band frequencies for the 4- and 5-ring breathing vibration modes in the far-IR spectral region with the size of the EFCs. The frequencies of the ring vibrational bands in the IR and Raman spectra are very sensitive to the presence of specific EFCS, and framework distortion.