Hydrodesulfurization of 4,6-dimethyldibenzothiophene over promoted (Ni,P) alumina-supported molybdenum carbide catalysts:activity and characterization of active sites

摘要

The effect of phosphorus and nickel on alumina-supported molybdenum oxycarbides has been studied.Catalysts were characterized by elemental analysis,X-ray diffraction,CO chemisorption,transmission electron microscopy,energy-dispersive spectroscopy,X-ray photoelectron spectroscopy,and infrared spectroscopy.Propene and tetralin hydrogenation was to probe the activity of the doped materials.Hydrodesulfurization of 4,6-dimethyldibenzothiophene (613K and 4 MPa total pressure) was investigated as a probe for the deep HDS of diesel fuel.For contact times ranging from 0 to 0.4 s (conversion<45%),the HDS of 4,6-DMDBT is zero order with respect to the reactant and proceeds via two parallel routes,direct desulfurization and hydrogenation pathways,the former being preponderant.Phosphorus modifies catalytic behavior in several ways:increase in the Mo~(4+) abundance,increase in the number of Lewis acid sites,and consequent enhancement of the DDS rate.Nickel induces the highest HDS activity;a nickel-molybdenum interaction observed by FTIR spectroscopy of adsorbed CO could be responsible for this behavior.