Visualization of Frequent Desorption/Re-Adsorption Events for Sorbate at the External Surface of Microporous Crystals by Hyperpolarized Xe-129 2D NMR Exchange Spectroscopy

Many types of porous membranes and catalyst particles contain microporous crystals, which are interconnected by larger meso- and macropores. Transport of guest molecules through the external surface of microporous crystals can significantly affect the overall rate of transport in membranes and catalysts. Here we report a new experimental methodology that was developed to study how often desorption of sorbate molecules from a microporous crystal is followed by fast re-adsorption into the same crystal. The rates of desorption and re-adsorption processes are also investigated. The experimental approach is based on application of continuous flow hyperpolarized Xe-129 2D NMR exchange spectroscopy (2D EXSY). First results of the study of desorption/re-adsorption events of Xe from/to NaY zeolite crystals will be presented and discussed. The experimental data will be compared with the corresponding results of the dynamic Monte Carlo simulations.