NMR Spectroscopy Applied to Zeolite Catalysis: Progress and Prospects

Abstract

Recent advances in NMR spectroscopy methods for studying zeolites and their catalyzed reactions are briefly reviewed. In-situ NMR spectroscopy, with its controlled atmosphere conditions, is used to characterize the active surface sites of zeolites (highly acidic micro-porous molecular sieves) and to elucidate the hydrocarbon reactions they catalyze. The strong Bronsted acid sites of these catalysts, SiO(H)Al, are accessible to adsorbed molecules via well defined pore systems (0.3 to 1.2 nm). Substantial progress has been made in: obtaining high resolution NMR spectra under conditions (pressure, temperature, reagent flow) similar to real reactor conditions, developing new NMR methods for characterizing quadrupolar nuclei in solids, understanding acidity in solids and evidencing the details (intermediates, pathways, kinetics) of zeolite catalyzed chemical reactions. Some of the practical aspects and limitations in performing these studies are mentioned along with future prospects. Given its high versatility and adeptness for determining: the local structure around selected nuclei (2H, 17O, 27Al, 29Si), and the structure and dynamics of organic molecules (1H, 13C), NMR spectroscopy is destined to attain evermore important and far-reaching application in this field of study.