A SURFACE SPECTROSCOPIC STUDY OF CALCINATED MOLYBDENUM-ALUMINUM OXIDEMODEL CATALYSTS

Supported molybdena model catalysts, prepared by wet deposition of amm onium molybdate on oxide-coated planar samples of aluminum, were studi ed especially as a function of calcination temperature (200, 350 and 4 50 degrees C). Characterizations by X-ray photoelectron spectroscopy ( XPS), secondary ion mass spectrometry (SIMS) and secondary electron mi croscopy (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 a fter calcination at this temperature. It is hypothesized that direct M o-O-Al surface linkages are formed at 450 degrees C, and that this pro vides the driving force for the enhanced Mo dispersion observed. (C) 1 998 Elsevier Science B.V.