Abstract
Abstract In order to determine the active center of ethylene polymerization over MoO3–Al2O3, the g-tensor and the amount of molybdenum(V) in each chemical state were determined by means of ESR measurement. The anisotropy of the g-tensor revealed the strength of the crystal field in the state; the decreasing order of the strengths was as follows: state(S)>state(M)>state(W)>MoO3–SiO2\fallingdotseqfree MoO3. In the state(S) molybdenum oxide is insoluble in aq.10M–NH3, in the state(M) it is soluble in aq. NH3 but insoluble in water, and in the state(W) it is soluble in water. The amount of molybdenum(V) in the state(W) was studied in connection with the activity, because only the state(W) was suitable for polymerization. The behavior of the activity was in fair agreement with that of the molybdenum(V) content in the state(W) and this content depedned on the amount of supported MoO3 and on the extent of reduction. The amount of molybdenum(V) in the state(W) corresponded to the amount of chemisorbed hydrogen, which was a polymerization initiator. The chemisorption of oxygen on the catalyst caused a complete disappearance of both the activity and the molybdenum(V) content in the state(W). Therefore, it was concluded that the active center of the polymerization was molybdenum(V) in the state(W).
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