Skeletal isomerization of hydrocarbons on molybdenum catalysts: III. Catalytic study of alumina-supported catalysts

Abstract Catalytic results obtained at a reaction temperature of 350 °C with an alumina-supported molybdenum catalyst (6% MoO 3 Al 2 O 3 ) are presented. Before all catalytic experiments the catalyst was treated under hydrogen flow at temperatures ranging from 550 to 950 °C. The effect of reduction temperature has been studied. Up to and including 750 °C, the reaction mechanisms are essentially acidic. After reduction at 950 °C, the reaction mechanisms change and become metallic. This supported catalyst reduced at 950 °C behaves exactly like the unsupported metallic molybdenum powder reported on in Part II [ J. Catal. 104 , 211–224 (1987)]. Isomerization occurs on metallic sites via a metallacycle intermediate evolving to a carbene-olefln intermediate giving exclusively bond shift migration. This mechanism accounts for the relative migration rates of the alkyl groups which have been studied by 13 C labeling experiments.