Time-dependent xenon diffusion measurements in microporous silicon imidonitrides by pulsed field gradient NMR spectroscopy

We present time-dependent xenon diffusion measurements over a wide range of diffusion times in three different silicon imidonitrides, a new class of m icroporous catalysts, by PFG NMR spectroscopy. Our experimental data show t hat for short diffusion times Delta a sharp decrease of the diffusion coeff icient D with increasing Delta occurs, while in the long-time regime D appr oaches a constant value. We correlate the differences in the diffusional be haviour with the pore structure of the material. Additionally, we found tha t for these materials there is a linear correlation between the chemical sh ift of the Xe-129 resonances and the corresponding long-time diffusion coef ficient. (C) 1999 Elsevier Science B.V. All rights reserved.