SELECTIVITY TO CYCLOHEXENE IN THE GAS-PHASE HYDROGENATION OF BENZENE OVER RUTHENIUM, AS INFLUENCED BY REACTION MODIFIERS .1. ADSORPTION OF THE REACTION MODIFIERS, WATER AND EPSILON-CAPROLACTAM, ON RUTHENIUM

Pre-adsorption of water and of ε{lunate}-caprolactam on the surface of ruthenium influences the selectivity to cyclohexene in the catalytic hydrogenation of benzene. In this article the behaviour of hydrogen-covered ruthenium samples with respect to water and lactam adsorption is studied. At room temperature and up to a water vapour pressure of 1.3 kPa, a clean ruthenium surface is hydrophobic. Due to the presence of chlorine on the surface of many ruthenium samples, hydro-phobicity changes into hydrophylicity. On a chlorine-free surface covered with a monolayer of hydrogen, ε{lunate}-caprolactam is strongly adsorbed (enthalpy of adsorption approx. -73.5 kJ/mol). Indications are found that ε{lunate}-caprolactam is hydrogenated over ruthenium to 6-aminohexanal. This compound may easily condense to substituted imines. © 1990.