Studies On Selective Hydrogenation Of Benzene To Cyclohexene Over Nano-supported Ru Catalysts

Because of its double-bond and active a-H atoms, cyclohexene is an important intermediate for the production of organic chemicals, which have found significant applications in organic chemical industry. Mainly three approaches for the production of cyclohexene, including the oxidative dehydration of cyclohexane, the dehydration of cyclohexanol and the selective hydrogenation of benzene, were reported in the literatures, and among others, the latter route has attracted much more attentions, due to its shorter technological process, simple operation, low cost and high atomic economy.The supported catalysts with high activity and high selectivity enjoy more special advantages than unsupported ruthenium catalysts. The ruthenium-based catalyst supported on ZrO2showed the highest efficiency due to its excellent hydrophilicity. However, the content of ruthenium in catalysts supported on ZrO2is very high and the stability of the catalysts is not satisfying in the industrial application. Zinc sulphate (ZnSO4·7H2O) has been reported to be the best additive among various inorganic salts which increased cyclohexene selectivity have been reported in literatures. One drawback is the possible corrosion of the reactor due to acidic PH of the aqueous phase and the gradual deactivation of the catalyst. The addition of organic substances has been investigated to be the best substitution.Therefore, a series of novel heterogeneous catalysts with Ru supported on Nano-Al2O3and Nano-ZSM-5were investigated in detail in this work due to their excellent properties as supports. Ba and Co were used as modifiers in the preparation process of the catalysts, and experiments have been carried out aiming to maximizing the yield of cyclohexene. PEG-400was found to be effective to improve the selectivity of cyclohexene, and the mechanism of the interaction between the catalyst and PEG-400in the catalytic system was discussed in detail. The main achievements are illustrated as follow:1. The impregnation method was employed to obtain supported ruthenium catalysts and the optimization technologic conditions over Ru/Nano-Al2O3catalysts were:the addition amount of PEG-400is 0.5mL, the reaction temperature is423K, the reaction pressure is3MPa and the stirring rate is900rpm. The highest yield of cyclohexene has been obtained as8.11%with Ru/Ba mol ratio was10:30with Ba as modifier. The optimal reaction conditions for the best yield9.33%of catalyst Ru:Ba=10:30(Ru/Nano-Al2O3=1.83wt.%) are:the addition amount of PEG-400is0.5mL, the reaction temperature is443K, the reaction pressure is3MPa and the stirring rate is900rpm.2. It has been found that the isoelectric point of nano-Al2O3increase with the addition amount of Li, which can increase the density of the electron cloud and the number and intensity of active sites on catalyst surface. Based on the characterization of H2-TPR and analysis of the spectrogram, it can be conclude that it is beneficial for the increase of the activity of the catalysts for the reason that the reduction temperature of the catalysts can be greatly reduced.3. Uniform crystalline Nano-ZSM-5with different SiO2/Al2O3mol ratio were synthesized successfully by hydrothermal process. The highest yield of cyclohexene was gained as8.69%with the SiO2/Al2O3mol ratio reached120. With Co as modifier,when the mol ratio of Ru/Co was10:0.6, The optimal reaction conditions for the catalyst Ru:Co=10:0.6(Ru/Nano-ZSM-5-120=1.83wt.%) were found as follow: the addition amount of PEG-400is0.2mL, the reaction temperature is423K, the reaction pressure is3MPa and the stirring rate is900rpm.4. The basic physicochemical properties, favorable hydrophily, solubilization to benzene of PEG-400were introduced in detail. FT-IR technique was employed to analyze catalysts before and after the reaction, and the result showed that PEG-400absorbed tightly onto the surface of the nano-support via not only physical interaction but also chemical interaction in these catalytic systems. The mechanism of the interaction between PEG-400and the catalyst was studied in depth.