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°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°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°C, and that this provides the driving force for the enhanced Mo dispersion observed.