XE-129 NMR-SPECTROSCOPY OF MOLYBDENUM CARBONYLS IN NA-Y ZEOLITE

Xe-129 NMR spectroscopy has been used to characterize the reactions of molybdenum hexacarbonyl in Na-Y zeolite. Upon adsorption of Mo(CO)6 and subsequent dispersion at 323 K, bands of color corresponding to a concentration gradient within the NMR tube are observed. Mo(CO)6 adsorbs and saturates the upper regions of the Na-Y sample, while not saturating lower portions of the sample. From gravimetric measurements, the Mo(CO)6 concentration in the saturated region is approximately 2 molecules/supercharge. Evacuation of the sample at 373 K produces a subcarbonyl species which is an adsorption site for xenon. Further heat treatments produce Mo species which are able to migrate out of the supercages. Oxidation of these Mo clusters is observed at 623 K. Reduction of these oxidized species is possible only at elevated temperatures, and although a color change is observed, there is no change in the xenon spectra. This indicates that the chemical reaction is occurring in regions of the zeolite that are inaccessible to xenon. On the basis of the NMR spectra and adsorption data, we propose that Mo is able to migrate into the sodalite cages and/or the hexagonal prisms of the Na-Y structure.