1969 Volume 42 Issue 4 Pages 871-874
The catalytic activity and the sintering property of iron oxide catalysts with and without potassium additives have been studied. The potassium oxide acts as a promoter and is effective under given conditions in increasing the activity of the catalyst from four to ten times. The effects of the promoter can be classified thus: (1) Structural promoter: The increase in the apparent bulk density and the shrinkage of the catalyst tablet upon calcination during the preparation of the catalyst are prevented by potassium additives. The differences in the specific surface area and in the pore volume of the catalyst between with and without potassium promoter are slight. These effects on iron oxide appear to be caused largely by the formation of K2Fe22O34. (2) Synergetic promoter: The potassium promoter changes the apparent energy of activation of the dehydrogenation reaction from 28 to 43 kcal/mol. The increase in the catalytic activity is due to the increase in the pre-exponential factor. The increase in the factor can be explained in terms of the higher concentration of the active center produced by the interaction of the potassium promoter with iron oxide. (3) Selectivity promoter: The formation of benzene by a side reaction is retarded by potassium additives.
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