TIME-OF-FLIGHT SIMS STUDY OF BI-MO SELECTIVE OXIDATION CATALYSTS

The potential applicability of time-of-flight secondary ion mass spect rometry (TOF SIMS) to control the various stages of preparation of sil ica-supported Bi-Mo selective oxidation catalysts has been studied. Th ese catalysts were prepared from coordination compounds (bismuth(III) and molybdenum(II) acetates or benzoates) as precursors. It has been s hown that: (1) through the observation of the molecular ions and most characteristic fragments of the coordination compounds, TOF SIMS can p rovide direct information about the preservation of these precursors o n the silica surface before calcination, (2) as the three pure bismuth molybdate phases (alpha-Bi2Mo3O12, beta-Bi2Mo2O9 and gamma-Bi2MoO6) s how the same fragmentation patterns in TOF SIMS, they can only be dist inguished in a indirect way, namely by comparing some SIMS intensity r atios from their positive spectra. These SIMS intensity ratios have be en successfully used to determine the nature of bismuth molybdate phas es formed on silica surface. And (3) TOF SIMS imaging provides valuabl e information about the dispersion of bismuth molybdate phase on silic a surface.