ESR studies of the effect of zeolite structures on motional dynamics of NO2

Electron spin resonance (ESR) spectroscopy was used to study the effect of zeolite structure on the motional dynamics of NO2 adsorbed on the zeolites. The temperature-dependent ESR spectral line shapes were quantitatively ana lyzed using the slow-motion ESR theory. It was observed that the motional d ynamics of NO2 is strongly dependent on the structure of the zeolite (Beta- type, ZSM-5, mordenite, L-type and ferrierite zeolites). The following impo rtant observations were made. (1) In zeolites with similar channel structur es, the diffusion rate of NO2 is proportional to the channel size, and the order of the diffusion rates is Beta-type > ZSM-5 > ferrierite and L-type > mordenite. (2) The diffusion of NO2 is faster in the zeolites with multi-d imensional channels (Beta-type, ZSM-5 and ferrierite) than that in those wi th uni-dimensional channels (L-type and mordenite). (C) 1999 Elsevier Scien ce B.V. All rights reserved.