Mo(CO)6 Adsorption on a Chromia-Silica Catalyst: Formation of Hetero-Adduct Metal Complexes

Molybdenum hexacarbonyl was admitted onto chromia-silica catalysts prepared both by reduction in CO, which produces Cr(II)-rich samples, and by reduction in hydrogen, which produces Cr(III)-rich samples. Cr(II)⋯OC-Mo(CO)₅ and Cr(III)⋯OC-Mo(CO)₅ adducts are formed whose infrared spectral features, particularly the stretching mode of the O-bonded CO entity, depend on the charge of the cation and on its coordination. Mo(CO)₆ species physisorbed on the support are also observed. These results are compared with previous results relative to molybdenum/silica catalysts.