ROLE OF MOLYBDENUM AT THE IRON-OXIDE SURFACE

The structure of Mo at the surface of Fe2O3/SO4 and ferrihydrite catal ysts was investigated using extended X-ray absorption fine structure ( EXAFS) spectroscopy. Molybdenum is found to be surrounded by 3-4 oxyge ns at 1.73-1.75 angstrom with no extended coordination shells beyond t he nearest oxygen shell. X-ray diffraction results for the Mo/ferrihyd rite catalysts after high temperature annealing demonstrate that the i ncorporation of Mo at the ferrihydrite surface effectively prohibits c rystal growth and allows the catalyst to maintain its dispersion to hi gher temperatures. (C) 1994 Academic Press. Inc.