The Study Of Hydrodesulfurization Performances Of CeO₂-modified MoP Catalysts

MoP and CeO2-modified MoP catalyst was prepared by co-precipitation of molybdenum phosphate followed by in situ temperature-programmed reduction with H2. The hydrodesulfurization of dibenzothiophene and its hydrogenated intermediates1,2,3,4-tetrahydro-dibenzothiophene and1,2,3,4,4a,9b-hexahydro-dibenzothiophene was studied at340℃and4MPa. The effects of CeO2on the MoP was studied with different preparation conditions, then XRD and XPS techniques were used to characterize the structures of the catalysts. According to the results, the HDS reaction mechanisms and kinetics of sulfur-containing molecules was discussed over bulk MoP and Ce02-modified MoP catalyst.Terminal reductive temperature had a significant impact on activity of hydrodesulfurization of MoP modified by CeO2. Below600℃, The activity of hydrodesulfurization of MoP was inhibited via addition of CeO2but substantially be improved at650℃. Besides that, the introduction of CeO2also promoted the hydrogenation activity of the catalyst but had little impact on direct desulfurization activity. The optimal molar ratio of Ce to Mo was0.05, desulfurization activity decreased with the increasing of CeO2. The XRD results suggested that CeO2and MoP existed separately in CeO2-modified MoP catalyst, but not in the form of a solid solution. The XPS results showed Ce existed in the form of tetravalence and trivalence on the surface of catalyst.The hydrogenation of TH-DBT and dehydrogenation of HH-DBT were both fast over bulk MoP and CeO2-modified MoP catalyst and these two molecules tended to equilibrium at high weight time. The desulfurization of TH-DBT to CHB was faster than that of DBT to BP, which illustrated the higher degree of unsaturation of sulfur compounds, the more difficult to desulfurize from it. The hydrogenation capacity of MoP towards single benzene ring was low and CeO2-modified MoP catalyst had no significant impact on it either. MoP and CeO2-modified MoP catalysts might have mildly acidic property and resulted in migration of double bond of alkene but had no effect on transalkylation process.