Dependence of reactivity on pretreatment in molybdena-alumina catalysts for propene metathesis

The MoO3/Al2O3 catalytic systems were studied. The catalysts, were highly s elective and moderately active in propene metathesis at a low temperature ( 303 K). It was shown by XPS that preliminary thermal treatment of the catal ysts affects their final reactivity towards propene. The surface of the mol ybdena-alumina catalyst, which was evacuated at 523 K and then activated at 873 K in argon, underwent partial reduction to Mo-V phase under the influe nce of propene at 303 K. This effect was not observed in the case of the mo lybdena-alumina catalyst, which was calcinated at 823 K and then analogousl y activated. It was concluded that the reducibility of the surface molybden um was connected with the activity of the catalyst in propene metathesis. I t was proposed that the difference of the reactivity towards propene of bot h catalysts was caused by the difference in the homogeneity of the surface molybdenum. It was stated that the activation of the catalysts in argon at 873 K increased the homogeneity of the surface molybdenum. (C) 2000 Elsevie r Science B.V. All rights reserved.