Adsorption of Di - tert - butyl Nitroxide at Monovalent Cations in Zeolite Y As Studied by Electron Spin Resonance Spectroscopy

摘要

One mayor challenge in the research of microporous materials is the spectroscopiccharacterization of acid sites with regard to their acidity, structure and concentration.Regarding these questions one promising approach is the complexation of these acid siteswith paramagnetic probe molecules and the subsequent characterization of the adsorptioncomplex by various electron spin resonance techniques. In this work we used standardcontinuous wave electron spin resonance spectroscopy and modern high resolutionpulsed electron spin echo envelope modulation techniques to study adsorption complexesformed by paramagnetic Di-tert-butyl nitroxide probe molecules and zeolite cations Li~+,Na~+, K~+ and Cs~+ in Y zeolites. These investigations allow a determination of thegeometrical structure of the adsorption complexes and provide information about theinfluence of the electronegativity of the various acid sites on the electron densitydistribution within the probe molecule.