ABSTRACT
Any catalyzed reaction proceeds in parallel with a variety of molecular mass transfer phenomena, so that in many cases the observed activities and product distributions are linked to the diffusional behavior of the reactant, intermediate, and product molecules. With reference primarily to diffusion studies in zeolitic adsorbent-adsorbate systems, this chapter shows how NMR spectroscopy is a most versatile tool for investigating molecular mass transfer phenomena in heterogeneous catalysis. Information is provided with respect to both microscopic and macroscopic dimensions, involving the observation of molecular distributions as well as the diffusion paths of individual molecules. A most straightforward way of applying NMR to study molecular distributions during dynamic processes such as adsorption, counterdiffusion, or chemical reaction is based simply on the NMR signal intensity being directly proportional to the number of resonating nuclei within the sample coil of the NMR probe head.
