Electron microscopy of some molybdenum oxide phases after use as catalysts in oxidative ammonolysis and ammoxidation of toluene

• Five molybdenum oxide samples, subjected to conditions of oxidative ammonolysis and ammoxidation of toluene at 450 and 460°C, respectively, have been characterized using X-ray diffraction, scanning and transmission electron microscopy, and specific surface area measurements. In oxidative ammonolysis, the relatively large, freshly prepared MoO3 crystals are reduced to smaller MoO2 crystals with a crystallite size of 5–30 nm. This process gives a perfectly pseudomorphous product with pores less than 5 nm. The specific surface area increases from <0.1 m2/g to almost 40 m2/g. In subsequent ammoxidation, MoO2 transforms first into orthorhombic Mo4O11 and finally into MoO3. The crystals of Mo4O11 are about 1 μm in diameter, and their formation leads to a decrease of specific surface area. The original MoO3 morphology is retained even after the sequence of transformation as follows: MoO3 → MoO2 → Mo4O11 (→MoO3). In some cases, the new generation of MoO3 crystals grows parallel to the original MoO3 crystals.

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TEKNIK OCH TEKNOLOGIER  -- Kemiteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Chemical Engineering (hsv//eng)

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