SUBCARBONYL SPECIES OF MOLYBDENUM HEXACARBONYL SUPPORTED ON SILICA - A DRIFT STUDY

Subspecies of partially decarbonylated molybdenum hexacarbonyl support ed on silica were studied by diffuse reflectance IR spectroscopy. Mo(C O)(6)/SiO2 was prepared in a fluidized bed reactor by vapor-phase adso rption of molybdenum hexacarbonyl under nitrogen flow. Decarbonylation begins when Mo(CO)(6) has adsorbed onto the silica. Dehydroxylation o f the support during calcination facilitates the formation of subspeci es of Mo(CO)(6). The activation energy needed for bond formation betwe en a transition metal and silica and for decarbonylation is lower than the desorption energy of physisorbed Mo(CO)(6), and this was seen in the IR spectra as a disappearance of bands due to subspecies. When the supported Mo(CO)(6) was reheated the physisorption bands were the las t to disappear from the IR spectra.