Preparation Of H?-MCM-41 Supported Pt Catalysts

Because of the increasing restrictions on sulfur contents of gasoline and diesel,the more effective stable and cheaper catalysts are needed in the field of hydrodesulfurization.Noble metal have attracted more and more attention due to their excellent low temperature hydrogenation activity and thus are good candidates for deep HDS.Noble metal catalysts have been used in the second-stage of hydrodesulfurization and as three-way catalysts for the treatment of COX,NOX,CHX compounds in automobile exhaust.Noble metal have not been widely used in industry for their relatively high price and sensitive to sulfur and nitrogen compound.In this paper,hydrothermal crystallization method was used to synthesize the overgrowth type H?-MCM-41.H?-MCM-41 supported Pt catalysts were prepared by an incipient wetness impregnation method using chloroplationic acid at ambient temperature.In order to compare the difference between the mechanical mixture(H?+MCM-41)supported Pt catalyst and the overgrowth type H?-MCM-41 supported Pt catalyst,X ray diffraction(XRD),infra-red spectroscopy of pyridine adsorption(Py-IR),NH3-TPD,transmission electron microscopy(TEM)and N2 physical adsorption were used to characterize the catalysts and supports.The overgrowth type H?-MCM-41 was modified by alkali metal,alkaline earth metal and rare-earth metal ion.HDS reactivity of the catalysts was studied using dibenzothiophene(DBT)as model compound(Reaction temperature was 260 oC-320 oC,Reaction pressure was 5 MPa).XRD spectra showed that the composite contains MCM-41 and H? crystalline phases.The TEM spectra showed that H? was covered by a layer of MCM-41 and the MCM-41 pore channels are found to be oriented outward from the inner H? core.All the Pt catalysts mainly took the DDS pathway except Pt/H? in the HDS reaction.The conversion and selectivities of Pt/BM catalyst were remarkably better than the mechanical mixture Pt/B+M,which indicated that the pore structure of the composite was more favorable for the reaction of DBT.The introduction of conversion of alkali metal ions,alkali-earth ions and rare earth metal ions decreased the DBT conversion of the catalysts,but the selectivities of the products differed from one another.