Morphology And Structure Control Of Alumina Supports And Construction Of MoS₂ Active Phase

In the pressures of crude oil poor-qualitilization and increasing stringent environmental regulations,the requirment of hydrotreating catalyst performance improves.Preparing a new kind of catalyst with higher activity and selectivity is the best way to deal with this problem.Currently,the study for hydrotreating catalyst has focused on the nature of supports,the preparation of new support,and the invention of new preparative technique.In the beginning,the aim of the dissertation focuses on the synthesis of?-alumina with different morphologies and sizes.On this basis,the relationship between the morphology of?-alumina and the catalytic performance of CoMo hydrodesulfurization?HDS?catalyst was studied.Then,a new impregnation-precipitation method was applied to the preparation of sulfided Mo-based catalyst.After that,cobalt was added in this catalyst to study the effect of assistant introduction on the HDS activity of the catalysts.At last,the impregnation-precipitation method was used to prepare pre-sulfided Co Mo catalysts,the influence of preparation process on the Co-Mo-S active phase was also investigated.The above researches provide theoretical guidance for the development of HDS catalyst with better catalytic properties.During the preparation of ammonium aluminum carbonate hydroxide?AACH?and?-alumina,the effect of synthesis temperature,pH value,reaction time,and the addition of template on the morphology,size and pore structures of?-alumina was studied.Then,the formation mechanism of AACH was illustrated.Characterization results show that the morphology of the?-alumina inherits from the AACH precursor,and the formation of AACH follows an self-assembly mechanism,pH value plays a key role in the self-assembling process.With the growth of pH values,the length-diameter ratio of AACH particles become smaller,the morphology changes from rod-like to particle-like.Besides,the excess of NH₄⁺inhibits the growth of crystallites by absorbing on the surfaces.AACH thermal decomposition method was used to prepare?-alumina with different morphologies and sizes.Their textural,structural,and surface properties were also characterized.The relationship between the morphology and the surface property was studied.Then,the?-alumina with different morphologies were used as the support in CoMo HDS catalyst.The crystal structure,reductivity,the morphology of active phase and the HDS activity were characterized.Characterization results show that the rod-like?-alumina support possesses less hydroxyl and exhibits lower surface acidity.Hence,more?-CoMoO₄ generated in the CoMo catalyst.The sulfidity of the active component is improved,the stacking number of MoS₂ particles becomes higher,and 4,6-DMDBT is easier removed from the hydrogenation routes.A new impregnation-precipitation method was applied to prepare the MoS₂/Al₂O₃catalyst with excellent HDS performance.The loading capacity was confirmed.The catalyst prepared by the impregnation method was used to discuss the effect of impregnation-precipitation method on the pore structure,the morphology and the dispersion of active phase.It is found that the impregnation-precipitation method improves the surface area of the as-synthesized catalyst.Moreover,this method not only enhances the reducibility and dispersity of MoS₂ particles,but improves the stacking number of MoS₂ particles appropriately.Due to the easier removal of sulphur atoms,the impregnation-precipitation method creates more active sites.Therefore,the catalyst exhibits a higher HDS activity.Two kinds of Co were introduced to the MoS₂/Al₂O₃ catalysts which made by the impregnation-precipitation method by refluxing and impregnation method.The best preparation technology was selected,and the effect of Co adding method on the structure and morphology of active phases was also investigated.It is shown that,due to the mild reaction condition,cobalt acetylacetonate added by the refluxing method can not change the pore structure of the MoS₂/Al₂O₃ catalyst,the as-formed CoMo catalyst will maintain a high specific surface area,and the morphology of MoS₂ particles does not changed either.Although the adding of cobalt nitrate makes the MoS₂ particles become shorter,it can not change the morphology of MoS₂ active phase totally,the key factor should still be the preparation method of MoS₂/Al₂O₃.The adding of cobalt acetylacetonate by the refluxing method endows the catalyst with better HDS activity.The Co atoms locate in the edge of MoS₂ particles,and more type II Co-Mo-S active phase are generated.Hence,the catalyst has a better HDS activity.Cobalt nitrate was used as the assistant to synthesize the presulfided CoMo/Al₂O₃ HDS catalyst by the impregnation-precipitation method.The catalyst prepared by the impregnation method was also used to discuss the effect of impregnation-precipitation method on the pore structure,the morphology and the dispersion of active phase.Because the impregnation-precipitation process makes the contact of Co and Mo more complete,the utilization of Co is improved,more Co-Mo-S active phase are generated accordingly.Hence,the activity of the catalyst is improved finally.