The Study Of Hydrodesulfurization Of Dibenzothiophene Over TiO₂-modified Ni2-P Catalysts

With the development of economy and the combustion of materials containing sulfur, the air pollution becomes worse, which affects the people’s health seriously. Therefore, the hydrodesulfurization has drawn much public attention. Ni2P and TiO2-modified M2P catalysts were prepared by co-precipitation of nickel phosphate followed by in situ temperature-programmed reduction with H2.XRD, XPS and NH3-TPD techniques were used to characterize the structure of the catalysts. The hydrodesulfurization (HDS) of dibenzothiophene (DBT) and its hydrogenated intermediates1,2,3,4-tetrahydro-dibenzothiophene (TH-DBT) and l,2,3,4,4a,9b-hexahydro-dibenzothiophene (HH-DBT) was studied over Ni2P and Ti02-modified Ni2P at340oC and4MPa both in the presence and absence of piperidine.The bulk Ni2P and TiO2-modified Ni2P precursors were prepared by co-precipitation with aqueous solutions of Ni(NO3)26H2O and (NH4)2HPO4. The XRD results indicate that addition of TiO2hinders the formation of impurities.The HDS activity of Ni2P was substantially improved by the introduction of TiO2. TiO>2had different promoting effects on the direct desulfurization pathway and the hydrogenation pathway activities of Ni2P, suggesting that TiO2and Ni2P existed separately in catalyst, but not in the form of a solid solution. XPS results show that the content of TiO2on the surface was higher. NH3-TPD results show that the number of acid centers decreased when introduced TiO2.The research of their HDS performance shows that the HDS activity of M2P was substantially improved by the introduction of TiO2. And the enrichment of Ti on the surface may be related with the increased activity. The activity of Ni2P increased with the content of TiO2initially, the activity reached its maximum at a Ti/Ni atomic ratio-0.05, and then decreased. TiO2has some co-catalysis effect on reaction, which may be mainly attributed to the higher electron density of Ni2P caused by the transference of the electrons produced in the reduction process of Ti4+to Ti3+under reduction atmosphere.TiO2had different promoting effects on the direct desulfurization pathway and the hydrogenation pathway activities of Ni2P. In addition, TiO2-doped bulk Mi2P had higher hydrogenation and hydrogenolysis capability, promoting C-N breaking. During the HDS of DBT over bulk Ni2P and Ti0.03Ni2P, biphenyl (BP) was the final product of the DDS pathway; TH-DBT, HH-DBT and three isomers (CHEBs) were the intermediates of the HYD pathway, and cyclohexylbenzene (CHB) was the final product of the HYD pathway; the final products the isomer(ISO1) and bicyclohexyl (BCH) of HDS of DBT over Ti0.03Ni2P didn’t exist over Ni2P.During the HDS of TH-DBT over bulk Ni2P and Ti0.03Ni2P,1-cyclohexen-1-yl-benzene (CHEB-1) was produced by hydrogenolysis of the C-S bond, and HH-DBT was produced by hydrogenation; BP is most likely formed by a disproportionation reaction. ISO1only existed in the products of HDS of TH-DBT over Ti0.03Ni2P.During the HDS of TH-DBT over bulk Ni2P and Tio.03Ni2P,2-cyclohexen-1-yl-benzene (CHEB-2) may be produced by β-elimination of the hydrogen atom attached to carbon atom C(4); CHEB-2may isomerize to CHEB-1and3-cyclohexen-1-yl-benzene(CHEB-3); HH-DBT reacted to TH-DBT by dehydrogenation, and also reacted to BCH by hydrogenation and desulfurization. ISO1only existed in the products of HDS of HH-DBT over Ti0.03Ni2P as well as TH-DBT.