Influence Of Piperidine And Alkali Metal Ions On Hydrodesulfurization (HDS) Performance Over Pt And Pd Catalysts

Increasingly stringent environmental legislation and intensification of crude oil inferior and heavy degree make deep desulfurization of distillate oil become one of the important topics of producing extremely clean fuel. Dibenzothiophene (DBT) and its alkylated derivatives are the most refractory sulfur-containing molecules to desulfurize due to steric hindrance. So the DBT hydrodesulfurization (HDS) activity and selectivity were studied over different catalysts using a model fuel containing0.8%DBT in decalin at different weight time.Synthesis of the materials was started from the H-type MCM-41(HM) mesoporous materials on the basis of the preliminary work. ZSM-5/MCM-41mesoporous aluminosilicate molecular sieve (ZM) was hydrothermally synthesized by assembling zeolite subunits, which were generated by the hydrolysis of ZSM-5in a Na2SiO3aqueous solution, in the presence of cetyltrimethylammonium bromide as the template. The strong Acidic mesoporous aluminosilicate molecular sieve was also hydrothermally synthesized using aluminum isopropoxide as the aluminum source. Na-MCM-41(NaM) or K-MCM-41(KM) was prepared by the ion exchange of H-Form MCM-41(HM) with an aqueous solution of Na2C2O4or K2C2O4. The supported Pd and Pt catalysts were prepared by an incipient wetness impregnation method.The influence of the nitrogen-containing compound on the hydrodesulfurization performance of acid mesoporous materials supported Pt and Pd was studied using dibenzothiophene (DBT) and piperidine (PI) as the model molecules in chapter2. The results indicated that both the direct desulfurization (DDS) and the hydrogenation (HYD) pathways were important over Pd/HM catalyst. The HYD passway is primary over Pd/ZM and Pd/AIM catalysts. However DBT HDS over three Pt catalysts predominately took the route of direct desulfurization (DDS). The addition of PI strongly inhibited the HDS of DBT. Compared with the direct desulfurization pathway (DDS), PI showed stronger inhibition effect on the hydrogenation pathway (HYD). And the desulfurization of the sulfur-containing intermediates of the HYD pathway was almost completely suppressed by PI over Pt catalysts. The kinetic study revealed that the HDS of DBT and the DDS pathway were first order while the HYD pathway was zero order under the conditions studied, suggesting that the DDS and HYD reactions take place on different active sites of these catalysts. The influence of Na+and K+on the hydrodesulfurization (HDS) performances of the Pd and Pt catalysts was studied in chapter3. The results indicated that the introduction of Na+and K+strongly inhibited the HDS activity of these Pd and Pt catalysts. Compared with the DDS pathway, the HYD pathway was more inhibited by Na+and K+. The COFT-IR results suggested that the introduction of Na+and K+led to an increase in the electron density of Pd and Pt atoms, and these particles were in an electron-rich state, which may have negative influence on the absorption of DBT via the π mode, and thus strongly inhibited the HYD pathway.