Preparation And Performance Of Ru-based Catalysts For Partial Hydrogenation Of Benzene To Cyclohexene

Cyclohexene with an active C=C double bond is an important organic intermediate to synthesize valuable cyclohexanol,caprolactam and acetic acid,etc..Compared with cyclohexanol dehydration,dehydrohalogenation of halogen cyclohexane and cyclohexane dehydrogenation routes for cyclohexene synthesis,the partial hydrogenation of benzene to cyclohexene method has advantages of abundant raw materials,economical,and simple route.However,from a view of thermodynamics,due to the ?rGm???for complete hydrogenation of benzene to cyclohexane?-98 kJ·mol-1?is lower than that of partial hydrogenation of benzene to cyclohexene?-23 kJ·mol-1?,the cyclohexene is hard to be obtained by hydrogenation of benzene.Therefore,to overcome this disadvantage,a suitable catalyst is expected to introduction in the hydrogenation reaction,thus improving the selectivity of cyclohexene.In this thesis,a series of zirconia nanosheets?ZrO₂-NS?were prepared by hydrothermal method,which are used as dispersants or supports for Ru-based catalyst for the partial hydrogenation of benzene to cyclohexene.H2-TPR,SEM,XRD,TEM,XPS,Raman,N2-Physical adsorption-desorption and FTIR techniques were used to characterize the ZrO₂ and Ru-based catalyst.Concretely,the structures and physical-chemical properties of ZrO₂ calcinated at different temperature,ZrO₂-supported Ru-based catalysts prepared by different methods and Ru-based catalysts with Zn and/or Fe promoters,which are carefully investigated.The main contents are as follows:?1?A series of precursors of ZrO₂ were synthesized by hydrothermal method,followed by calcinated at different temperature to obtained ZrO₂.It can be concluded that the BET surface and the content of surface hydroxyl of ZrO₂ were affected by the calcinated temperature;when correlating to the catalytic performance as dispersant in the partial hydrogenation of benzene to cyclohexene reaction,it is found that the larger the BET surface area of ZrO₂,the higher conversion of benzene is,and the more hydroxyl on the surface of ZrO₂,the higher selectivity of cyclohexene is.The Zr02 calcinated at 350 ? possesses the moderate BET surface area and appropriate amount of surface hydroxyl,thus showing excellent performance in the partial hydrogenation of benzene to cyclohexene reaction as dispersant.?2?Two types of RuZn/ZrO₂ were prepared by deposition-precipitation and hydrothermal-precipitation method using ZrO₂ as support.It is found that the ZrO₂-supported Ru-based catalyst is ideal to obtain metallic Ru with high dispersion and small particle size.For the partial hydrogenation of benzene to cyclohexene,high conversion of benzene and yield of cyclohexene can be achieved when small amount of Ru was loaded on ZrO₂.Furthermore,the as-prepared Ru catalyst reduced in gas is prone to show high benzene conversion,while the one reduced in liquid is easy to obtain catalyst with high cyclohexene selectivity.The catalyst that is prepared by deposition-precipitation method and reduced in liquid displays high selectivity and yield of cyclohexene.?3?The influence of Zn and/or Fe additives on the structures and catalytic performance for the partial hydrogenation of benzene to cyclohexene were investigated.It can be noted that the interaction between Ru and additive results in the spillover of H,thus reducing the Zn²⁺ and Fe²⁺and forming Ru-Zn or Ru-Fe alloy.Compared to the RuZn catalyst,the RuFe catalyst possesses a smaller grain size and higher dispersion of Ru nanoparticles,leading to higher benzene conversion.The RuZnxFey shows high benzene conversion and good cyclohexene selectivity,because of the combined effect of Zn and Fe additives.When the Zn and Fe additives with a ratio of 5:1?wt.?were introduced to the Ru catalyst,the as-obtained catalyst is high in benzene conversion,cyclohexene selectivity and cyclohexene yield,which is thought to be prospective for commercial application.