A surface spectroscopic study of calcinated molybdenum-aluminum oxide model catalysts

Supported molybdena model catalysts, prepared by wet deposition of ammonium molybdate on oxide-coated planar samples of aluminum, were studied especially as a function of calcination temperature (200, 350 and 450 degrees C). Characterizations by X-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS) and secondary electron microscopy (SEM) indicate that the Mo disperses uniformly on the support at 450 degrees C. Observations of the Al(KLL) Auger peak, excited by bremsstrahlung radiation, and the corresponding Auger parameter, were taken to indicate the formation of a new surface bonding arrangement after calcination at this temperature. It is hypothesized that direct Mo-O-Al surface linkages are formed at 450 degrees C, and that this provides the driving force for the enhanced Mo dispersion observed. (C) 1998 Elsevier Science B.V.