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Diffuse Reflectance Infrared Spectroscopy Investigations of the Thermal Decomposition of Hexacarbonyl Molybdenum (0) Entrapped in Faujasite-type Zeolites

Volume 45, Number 8 (Oct. 1991) Page 1278-1284

Brémard, C.; Depecker, C.; Des Grousilliers, H.; Legrand, P.

The temperature-programmed decomposition of Mo(CO)6 entrapped in the faujasite-type zeolites Na85X, Na56Y, and Y* has been investigated with the use of in situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) as a function of the Si/Al ratio of the zeolites and the Mo(CO)6 loading level. These investigations were undertaken either under dynamic vacuum or in an atmosphere of CO or He. Evidence is presented for a reversible, sequential decomposition of Mo(CO)6 to Mo(CO)3 and then a one-step irreversible decomposition of Mo(CO)3 to Mo-metal aggregates. The Mo(CO)5 and Mo(CO)4 transient species appeared the most clearly under reduced CO pressure. The Na85X zeolite with high aluminum content (Si/Al = 1.26) promotes an easy decomposition of Mo(CO)6 to Mo(CO)3 at room temperature and stabilizes this adsorbed subcarbonyl species at temperatures above 500 K. A decrease of the aluminum content (Si/Al = 2.5) in Na56Y increases the decomposition temperature of Mo(CO)6 and decreases the stability of the Mo(CO)3 species. The thermal behavior of Mo(CO)6 entrapped in dealuminated zeolite Y* (Si/Al = 75) was found to be analogous to that of Mo(CO)6 in the gas and solid phases.