CONVERSION OF CYCLOHEXANE ON NI-(SB, PB, CU)/AL2O3 BIMETALLIC CATALYSTS

Alumina-supported Ni catalysts, containing Sb, Pb, or Cu as a second metal (termed here the "bimetal"), were studied in the conversion of cyclohexane. Activity and selectivity strongly depend on the reaction conditions as well as on the composition and the pretreatment of the catalysts. Each of the three second metals caused very similar positive effects, namely suppressed hydrogenolysis, enhanced dehydrogenation, and prolonged lifetime, as far as the conversion at 500°C is concerned, but at 300°C only a negative, poisoning effect was observed. The conditions for a maximum positive "bimetal effect" are restricted to a Ni: second metal ratio of 9:1 and to calcination and reduction temperatures each of 500°C. TPR experiments displayed interactions of Cu and of Sb with Ni. The positive bimetal effect is explained by an ensemble effect due to a suggested dilution of Ni clusters by the second metals. © 1991.