Benzene Selective Hydrogenation To Cyclohexene New Ru-zn Catalysts

The preparation and characterization of a novel Ru-Zn catalyst for selective hydrogenation of benzene to cyclohexene have been carried out in this paper. The selective hydrogenation of benzene is of great synthetic and industrial line owing to its atomic economy and clean production; therefore it is very significant to study on these catalysts no matter in industrial application or in theory field.1 .The preparation conditions of Ru-Zn and Ru-Fe catalyst are as following: The suitable mass ratio of Zn/Ru is 8:92, and the concentration of RuCl₃· xH₂O is about 0.18 mol·L^-1. At 70⁸0℃, the mixture of RuCl₃· xH₂O and ZnSO₄ was added drop by drop to a solution of sodium hydroxide (20 wt.% NaOH), leading to a black ruthenium-zinc hydroxide precipitate. Then the precipitate together with the mother liquid was reduced in an autoclave under the conditions of 140℃, hydrogen pressure keeps 5.0 MPa and stirring rate of 1000 r/min for 2h. After reduction, the precipitate was washed thoroughly to pH=8±0.5 .The optimal operation conditions of the Ru-Zn catalyst are that the reaction temperature is about 140℃, the hydrogen pressure is 5.0 MPa and the stirring rate is 1000 r/min, pretreatment time is 1 h. The suitable composition of the slurry is 50mL H₂O, 29mL C₆H₆, 0.25 g Ru-Zn or Ru-Fe catalyst, 8.79g ZnSO₄-7H₂O and 1.25g ZrO₂.The Ru-Zn catalyst was used for hydrogenation of benzene under above conditions, at 15 min, the yield of cyclohexene achieve 49.1% at benzene conversion of 77.3%.2. XRD results show crystal and solid solution character of the catalysts. Zinc exists in its metal state in the catalyst with lower content of zinc, while the content of zinc increasing further, a new phase of zinc is found. Meanwhile it was found that Ru crystallite size decreases from 5.6 nm to 4.6 nm with increase of the content of zinc in the catalyst.BET results show that activities of the catalysts are relative to their specific surface areas. The larger the specific surface area is, the higher the activity and...