The transformations of cyclohexene were investigated over a silica-supported copper catalyst in a static circulation reactor in the presence of varying amount of D-2 at 443 K and in a how system in the 323-573 K temperature range under D-2 how In the static system D-2 pressure significantly influenced the types of reactions taking place (distinct regions for dehydrogenation, dehydrogenation plus hydrogenation, and hydrogenation were observed). In the how 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 d(1)-cyclohexyl species, was found to be the key intermediate; nevertheless, pi-allyl adsorption was also significant at higher D-2 pressure and in the flow system.