SELECTIVITY TO CYCLOHEXENE IN THE GAS-PHASE HYDROGENATION OF BENZENE OVER RUTHENIUM, AS INFLUENCED BY REACTION MODIFIERS .2. CATALYTIC-HYDROGENATION OF BENZENE TO CYCLOHEXENE AND CYCLOHEXANE

A study has been made of the heterogeneous gas phase hydrogenation of benzene to cyclohexene and cyclohexane in a continuous-flow apparatus over a number of non-supported ruthenium samples and over an α-alumina-supported catalyst, at 0.11 MPa total pressure and in the range of temperatures from 293 to 313 K. When working with highly purified reactants, no formation of cyclohexene is detected. On adding water vapour to the feed a selectivity to cyclohexene is built up over a period of 10 h, provided the ruthenium surface is hydrophilic due to the presence of a certain coverage with chlorine. If the surface is pre-covered with water, the selectivity towards cyclohexene is effected immediately. Other useful reaction modifiers giving rise to the formation of cyclohexene are glycol and ε{lunate}-caprolactam; cyclohexene selectivities of 40 and 27%, respectively, are measured. Pre-adsorption of n-decane on ruthenium stabilizes the catalyst but does not give rise to the formation of cyclohexene. © 1990.