TEMPO Radicals as EPR Probes to Monitor the Adsorption of Different Species into X Zeolite
Abstract
A computer-aided analysis of the electron paramagnetic resonance (EPR) spectra of TEMPO radicals adsorbed in X zeolites is performed under various experimental conditions, both in the absence and in the presence of various species. In dehydrated NaX zeolites the radical gives rise to two superimposed signals corresponding to species characterized by different mobility and polarity and by a different temperature dependence. Controlled addition of water leads to an increase of mobility up to 4.2 water molecules per supercage. Under conditions of partial hydration, the radicals show an increase, in the correlation time for motion with an increase in the size of the cation in the exchanged zeolites, whereas an increase in mobility is found upon going from NaX to NaY samples. These results are analyzed in terms of the variation of the local electric field at the surface. Dipolar broadening is shown to be responsible for the line shape variations found at TEMPO loadings up to 0.32 molecules per supercage. Heisenberg spin-spin interactions also become relevant at higher loading. Increasing amounts of 2,2,6,6-tetramethylpiperidine induce a restriction of mobility.... NaX zeolites, Electron paramagnetic resonance, Faujasites, Supercage, radicals, Pentane
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 1993
- Accession Number
- ADA269829
Entities
People
- Maria Francesca Ottaviani
- Miguel Garcia-garibay
- Nicholas J. Turro
Organizations
- Columbia University