Hydrodesulfurization Performance Of Pt Or Pd Catalysts Supported On Mesoporous Molecule Sieves

Due to the stringent environmental legislations,as well as the inferiority and poor-quality of crude oils,hydrotreating processes have been focus on developing highly active deep hydrodesulfurization(HDS) catalysts.Dibenzothiophene(DBT) and 4,6-dimethyldibenzhothiophene(4,6-DMDBT) are representative as the most refractory bulky aromatic sulfur-containing compounds in diesel fraction.DBT can be desulfurized effectively by direct desulfurization(DDS) route over conventional CoMo/γ-Al₂O₃,but 4,6-DMDBT cannot,it can only be desulfurized via hydrogenation(HYD) route owing to the steric hindrance of the methyls at 4 and 6 position.Therefore,to improve the catalysts HYD ability is of key importance to develop deep HDS catalysts.Among the catalytic active species applied in HDS,noble metals have a better hydrogenation activity,especially in the hydrogenation of aromatics.While noble metal catalysts are still of limited use in deep HDS,because they are sensitive to the sulfur-containing feed and deactivated by sulfur poisoning.Thus,to enhance the thioresistance of noble metals is the key factor to develop noble metal based HDS catalysts. Among the methods to improve the noble metals sulfur tolerance,the support has an obvious effect that the interaction between noble metals and supports has a close relationship with the catalytic activity of the supported catalysts.Thereby,it is necessary to study the support effects in the HDS reaction catalyzed by supported noble metal catalysts.In Chapter 3,γ-Al₂O₃,SiO₂,siliceous Si-MCM-41 and Al-MCM-41 were chosen to be the supports for noble metal catalysts(Pd and Pt),and were used to investigate the effect of the support in the HDS of DBT and 4,6-DMDBT.From the HDS of DBT results,the nature of the carrier and the interaction between the noble metals and the support are close related to the HDS activity,and especially the selectivities to HYD pathway.Whenγ-Al₂O₃ and SiO₂ were as the supports for Pd and Pt,the HDS of DBT proceeded by DDS route.While as for the Si-MCM-41 and Al-MCM-41 counterparts,the HDS of DBT proceeded predominately via HYD route.Compared with Si-MCM-41,the surface acidity of Al-MCM-41 had a promotion effect to the HDS activity,the HYD selectivities and stability for the supported Pd and Pt catalysts.Pd/Al-MCM-41 and Pt/Al-MCM-41 showed the highest selectivities to HYD pathway in DBT HDS,which can explain their superior HDS activities of 4,6-DMDBT among the respective Pd and Pt counterparts. In Chapter 4,a series of ZM mesoporous molecule sieves were obtained by dissolution of HZSM-5 zeolite in Na₂SiO₃ aqueous solution,which have a similar regular mesopore structure of MCM-41-type materials.It can obtain a series of mesoporous materials with different surface acidities by dissolution of different amounts of HZSM-5 zeolites.On the premise that all the supports have a better mesoporous structure,it is to investigate the effect of the support's surface acidity on the HDS performances of DBT and 4,6-DMDBT catalyzed by supported Pd and Pt catalysts.From the HDS of DBT results,the HDS activities of the ZM-supported Pd and Pt catalysts were a function of the Si/Al atomic ratio of the support. The HDS activities have a "volcano-type" trend with decreasing the ratio.When the Si/Al ratio is 25,that is ZM(25).is supported Pd and Pt catalysts showed the highest HDS activity and stability in the HDS of DBT.Compared with theγ-Al₂O₃ and Al-MCM-41 counterparts, Pd/ZM(25) and Pt/ZM(25) showed the superior HDS activity in the HDS of 4,6-DMDBT among the respective Pd and Pt catalysts.