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

Author： Brémard C. Depecker C. Des Grousilliers H. Legrand P.

Publisher： Society for Applied Spectroscopy

ISSN： 0003-7028

Source： Applied Spectroscopy, Vol.45, Iss.8, 1991-09, pp. : 1278-1284

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Abstract

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.