CHARACTERIZATION OF MASS TRANSPORT AND RELATED PHENOMENA IN POROUS CATALYSTS AND SORBENTS BY NMR IMAGING AND DISPLACEMENT NMR SPECTROSCOPY

摘要

Applications of NMR imaging in heterogeneous catalysis are rapidly gaining popularity. Due to its nondestructive and noninvasive nature, the technique can be successfully employed to characterize many of the essential stages of catalyst preparation and use, including multiple coupled processes. The dynamics of Pt or Pd redistribution and the type of their ultimate macroscopic distributions in supported Pt/alumina (Pd/alumina) catalysts can be mapped indirectly by ~1H NMR imaging. Flow imaging of liquids and gases provides flow velocity maps and can be used to guide the design of shaped structures such as monolithic catalysts. Displacement NMR spectroscopy yields information on the average flow velocities and hydrodynamic dispersion for gases, liquids and solids flowing through porous media. Imaging of drying of porous pellets and beds comprised of such pellets initially saturated with various liquids, as well as imaging of water vapor adsorption by porous pellets and beds, can provide useful and reliable information on mass transport mechanisms within porous media and interphase mass transfer between the catalyst and the flowing gas. Spatially resolved imaging of gas adsorption on supported catalysts can be employed to study the selectivity of adsorption by active components. Finally, NMR imaging can be applied to monitor the progress of heterogeneous catalytic reactions in real time. The examples of such applications are presented and discussed.