Motional dynamics of NO2 on Na-ZSM-5: an ESR investigation

Electron spin resonance (ESR) was used to study the motional dynamics of NO2 adsorbed on Na-ZSM-5 with different SiO2/Al2O3 ratios at 3–160 K. The temperature dependence of the ESR spectral lineshape was quantitatively analyzed with slow-motion ESR theory. The computer analysis with the Heisenberg spin exchange model reveals that the spin exchange rate of NO2 below 160 K increases quickly as the SiO2/Al2O3 ratio is increased from 23.8 to 70 and to 200. It is concluded that the difference in the amount of Na+ among the various zeolites is the main reason for the observed variation in spin exchange rates.