Abstract
The temperature-programmed decomposition of Mo(CO)<sub>6</sub> entrapped in the faujasite-type zeolites Na<sub>85</sub>X, Na<sub>56</sub>Y, and Y* has been investigated with the use of <i>in situ</i> Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) as a function of the Si/Al ratio of the zeolites and the Mo(CO)<sub>6</sub> 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)<sub>6</sub> to Mo(CO)<sub>3</sub> and then a one-step irreversible decomposition of Mo(CO)<sub>3</sub> to Mo-metal aggregates. The Mo(CO)<sub>5</sub> and Mo(CO)<sub>4</sub> transient species appeared the most clearly under reduced CO pressure. The Na<sub>85</sub>X zeolite with high aluminum content (Si/Al = 1.26) promotes an easy decomposition of Mo(CO)<sub>6</sub> to Mo(CO)<sub>3</sub> 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 Na<sub>56</sub>Y increases the decomposition temperature of Mo(CO)<sub>6</sub> and decreases the stability of the Mo(CO)<sub>3</sub> species. The thermal behavior of Mo(CO)<sub>6</sub> entrapped in dealuminated zeolite Y* (Si/Al = 75) was found to be analogous to that of Mo(CO)<sub>6</sub> in the gas and solid phases.
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