Preparation Of Ni-based Catalyst And Its Application In Hydrodeoxygenation Of Dibenzofuran To Phenylcyclohexane

Coal-based liquids（including coal tar and coal liquefied oil）are rich in aromatic compounds,which are ideal sources for the production of chemicals.It contains a large number of oxygenated compounds,which are not the suitable component of the fuel because of the low calorific value.Dibenzofuran is one of the oxygen-containing compounds,which can be converted into high value-added chemicals by selective hydrogenation.In this thesis,MO_x-modified Ni/Si O₂ catalysts were designed and prepared through co-impregnation.Cyclohexylbenzene was prepared by controlling selective hydrogenation and C-O bond breaking of dibenzofuran.（1）The Ni-Ti O_2-x catalysts were prepared by the modification Ni/Si O₂ with Ti O_2-x and a feasible route for the preparation of cyclohexylbenzene from dibenzofuran was proposed.At the same time,the reaction temperature,pressure and the amount of Ti O₂ added were optimised.（2）The reaction mechanism of dibenzofuran hydrodeoxygenation over Ni-Ti O_2-x catalyst was investigated in detail by combining the characterization and activity evaluation experiments.（3）The effect of Ni/Si O₂ catalysts modified with different metal oxides on the catalytic hydrogenation of dibenzofuran was investigated.The main results are as follows:1.Within the thermodynamic interval of the reaction,lower the reaction temperature was favorable for hydrogenation,increasing the temperature was favorable for the cleavage of C-O bond.The optimal reaction temperature for the formation of cyclohexylbenzene was 280^oC.Reducing hydrogen pressure slowed down the hydrogenation rate and thus promoting the the selectivity of ring-opening product.The optimal hydrogen pressure was 2 MPa.The involvenment of Ti O₂ not only improved the conversion of dibenzofuran but also promoted the breakage of C-O bond as well as improved the selectivity of cyclohexylbenzene.The Ni-0.5Ti O_2-x catalyst at 2 MPa and 280 ^oC exhibited high conversion（97.8%）of dibenzofuran and yield（71.0%）of cyclohexylbenzene.2.A moderate amounts of Ti O₂ addition promotes the dispersion of and reduces the particle size of metallic Ni.A unique Ni-V?-Ti³⁺（V?stands for oxygen vacancy）interfacial structure was formed via the coupling of Ni and adiacent Ti O_2-x.This interface site improves the catalyst’s ability to activate the C-O bond.The addition of excess Ti O₂ causes agglomeration of itself and covers the metallic Ni surface,resulting in a reduction of interfacial sites and decrease in reactivity.3.Ni-W/Si O₂,Ni-Zr/Si O₂,Ni-Mo/Si O₂,Ni-Nb/Si O₂ and Ni-Cr/Si O₂ were prepared by the co-impregnation method and the catalytic hydrogenation performance was evaluated.Under the same reaction conditions,the order of dibenzofuran conversion activities of catalysts were:Ni-Cr/Si O₂（100%）>Ni-Zr/Si O₂（71.8%）>Ni-Mo/Si O₂（68.0%）>Ni/Si O₂（58.7%）>Ni-Nb/Si O₂（21.3%）>Ni-W/Si O₂（3.3%）.The best performance of Ni-Cr/Si O₂ on the hydrogenation of dibenzofuran could be attributed to the addition of Cr can promote the dispersion of metallic Ni.The average particle size of Ni in Ni-Cr/Si O₂is only 3.1 nm.This enables the Ni-Cr/Si O₂ catalysts to provide more active metal sites at the same loading amount,thus increasing the reaction rate.