Nuclear Magnetic Resonance Spectroscopy in Studies of Catalysts

Abstract

During the last decades nuclear magnetic resonance (nmr) spectroscopy has found widespread application in the field of heterogeneous catalysis. Its success is a consequence of the world-wide introduction of zeolites as catalysts and selective adsorbents since their well-defined structure as porous crystallites corresponding to specific surface areas of up to 1000 m²/g allows the application of nmr spectroscopy in spite of its relatively poor sensitivity compared with infrared spectroscopy or particle beam methods. In the following, at first basic principles of nmr spectroscopy including typical examples for their applicability in studies of solid catalysts and molecules adsorbed thereon are given. Then in the second paragraph the unique possibilities of the ¹H mas nmr method are demonstrated to characterize quantitatively Broensted acidity of catalysts and finally in the third paragraph principles of the pulsed field gradient nmr method and its application to study molecular diffusion in porous crystallites are presented including the so-called nmr tracer desorption technique which is a unique method to measure transport resistances at the outer surfaces of porous crystallites.