The catalytic hydrogenation of benzene over supported metal catalysts.: III. Gas-phase hydrogenation of benzene over silica-supported Ru-Cu catalysts

Abstract

A study has been made of the gas-phase hydrogenation of benzene over silica-supported Ru-Cu catalysts in the temperature range from 300 to 400 K and at a total pressure of 130 kPa. Special attention has been given to the catalytic stability and the activity of the catalysts as compared with monometallic supported ruthenium and copper catalysts, described in previous articles. Via a reductive deposition technique, copper was deposited on silica-supported ruthenium catalysts. Two bimetallic catalysts were prepared, one with about 10% of the ruthenium surface covered by copper and one with about 70% copper coverage. The texture of the catalysts was studied by means of mercury penetration, nitrogen physisorption, hydrogen chemisorption and transmission electron microscopy, whereas surface analysis was performed by XPS/AES. At 11% copper coverage a shift in the copper electron binding energy is observed, pointing to a small electron transfer from ruthenium to copper, but at 68% copper coverage this shift has disappeared. Copper deposition on ruthenium increases the lifetime of the catalysts considerably without seriously affecting the activity per ruthenium surface atom. At low copper coverage the reaction kinetics are very similar to the kinetics found with ruthenium, but at high copper coverage the small size of the ruthenium ensembles influences the kinetics considerably.