The selective oxidation of 1-butene to maleic anhydride over cobalt molybdate catalysts containing excess molybdenum trioxide was studied using a fixed bed, integral reactor system. Pure catalysts, as well as those containing excess molybdenum trioxide, were prepared by precipitation and by solid state reactiontechniques. Cobalt molybdate samples containing excess molybdenum trioxide were found to have a high selectivity (∼48%) for maleic anhydride whereas pure cobalt molybdate was completely nonselective. The catalytic behavior of this system was very similar to that of nickel molybdate catalysts containing excess molybdenum trioxide. Phase transformations were investigated using X-ray diffraction and laser Raman spectroscopy. It was shown that a-phase modification determines the catalytic reaction since b-phase is not stable under reaction conditions as verified by post-reaction characterization.
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