Transformations of Cyclohexene over Silica-Supported Copper in the Presence of Deuterium

The transformations of cyclohexene were investigated over a silica-supported copper catalyst in a static circulation reactor in the presence of varying amount of D2at 443 K and in a flow system in the 323–573 K temperature range under D2flow. In the static system D2pressure significantly influenced the types of reactions taking place (distinct regions for dehydrogenation, dehydrogenation plus hydrogenation, and hydrogenation were observed). In the flow reactor benzene and cyclohexane were always formed together, due to the partial reactivation of the catalytic surface. The temperature of the reaction significantly influenced product distribution. During transformations, the deuterium content and the deuterium distribution were also monitored in both reactor types. The half-hydrogenated state, i.e., the adsorbed d1-cyclohexyl species, was found to be the key intermediate; nevertheless, π-allyl adsorption was also significant at higher D2pressure and in the flow system.