Time-of-flight SIMS study of Bi-Mo selective oxidation catalysts

The potential applicability of time-of-flight secondary ion mass spectrometry (TOF SIMS) to control the various stages of preparation of silica-supported Bi-Mo selective oxidation catalysts has been studied. These catalysts were prepared from coordination compounds (bismuth(III) and molybdenum(II) acetates or benzoates) as precursors. It has been shown that: (1) through the observation of the molecular ions and most characteristic fragments of the coordination compounds, TOF SIMS can provide direct information about the preservation of these precursors on the silica surface before calcination, (2) as the three pure bismuth molybdate phases (alpha-Bi2Mo3O12, beta-Bi2Mo2O9 and gamma-Bi2MoO6) show the same fragmentation patterns in TOF SIMS, they can only be distinguished in a indirect way, namely by comparing some SIMS intensity ratios from their positive spectra. These SIMS intensity ratios have been successfully used to determine the nature of bismuth molybdate phases formed on silica surface. And (3) TOF SIMS imaging provides valuable information about the dispersion of bismuth molybdate phase on silica surface.