New possibilities of NMR spectroscopy in studies of adsorption and catalysis

By using modern Fourier spectrometers operating at high (about 7 T) magnetic field and having special devices for magic angle spinning (MAS), one can obtain within reasonable periods of time, the NMR spectra for nuclei of various elements present in heterogeneous catalysts, including nuclei with small magnetic moments and low natural abundance, as well as the high resolution spectra of these catalysts and of molecules adsorbed on their surfaces. Some examples of such studies are presented. A comparison of 51V-, 17O-, and 23Na-NMR spectra of vanadium catalysts, for SO2 oxidation to SO3, with those of various reference compounds made it possible to identify some chemical compounds present in the active component of these catalysts. By using 27Al-NMR, it is possible to resolve the lines from aluminium ions in tetrahedral and octahedral positions for various crystalline modifications of Al2O3. For zeolites using 27Al NMR, some of the aluminium was found to escape from tetragonal positions in the lattice and to acquire octahedral coordination in the presence of water. The 29Si-MAS spectra support this conclusion. In 1H-MAS spectra of zeolites, lines from various hydroxyl groups can be resolved. Results obtained for the adsorption of hydrogen, methane, carbon monoxide and propylene on heterogeneous catalysts are presented. (Auth.)