Siliceous Mcm-41 Carrier Was Prepared. W Line Of Deep Hydrodesulfurization Catalysts

Mesoporous MCM-41 has been the focus of much research interest since its discovery because it offers a uniform pore of 2 to 10 nm, very high surface area (1000 m2/g) and mild acidity. W-based catalysts are known for their hydrodesulfurization (HDS) activity as well as higher hydrogenation activity and sulfur tolerance. Moreover, tungsten minerals are abundant in China. Accordingly, this dissertation was addressed on the research of the HDS properties of siliceous MCM-41-supported W-based catalysts by using dibenzothiophene (DBT) as model compound, and the following results have been obtained.Firstly, the synthesis conditions of Si-MCM-41 were optimized by means of orthogonal experiment method. And H-MCM-41 was prepared by ion exchange of Si-MCM-41 with dilute HNO3 solution. The results of XRD and N2 adsorption indicate that the structural properties of Si-MCM-41 were improved by HNO3 ion exchange, and the optimal ion exchange time is 6 h. The acidity of the mesoporous materials was characterized by means of NH3-TPD, Hammett indicators and a probe reaction. It is revealed that Si-MCM-41 only possesses some weak acid sites (5.6> Ho>8.2), whereas new strong acid sites (5.6 Ho>8.2) are generated after HNO3 ion exchange.W-based deep HDS catalysts were prepared by depositing Ni-W and Co-W species over Si-MCM-41. The HDS activity of prepared catalysts was evaluated in a trickle bed reactor by using a model fuel containing 0.5 % DBT in decalin and a high sulfur diesel (283wt% S). It is indicated that the optimal molar ratio for either Ni-W or Co-W is 0.75. The supported Ni-W catalysts exhibited much higher HDS activity than the supported Co-W catalysts. The analysis of HDS product distribution suggests that the HDS of DBT predominately takes the route of hydrogenolysis over Si-MCM-41 supported W catalyst. And it is indicated that Ni-W/Si-MCM-41 exhibited higher hydrogenation activity than Co-W/Si-MCM-41. Ni-W catalysts showed excellent performance in the HDS of both DBT and a high sulfur-containing diesel, suggesting that Si-MCM-41 is a promising support for deep HDS catalysts.The kinetic study indicates that the HDS of DBT over Si-MCM-41 -supported Ni-W(0.75) exhibited the lowest apparent activation energy , suggesting that there may exist some correlation between HDS activity and the apparent activation energy. The different effects of Ni on the hydrogenation activation energy and the hydrogenolysis activation energy (î–ŽYG) suggest that the two reactions take place on different types of catalytic sites. It isfurther confirmed by the results of UVVis and TPR that the active sites of hydrogenation is correlated with the octahedral coordinated Ni species, while the hydrogenolysis activity of Ni-W is related with the reducibility of NiO-WO3 species.H-MCM-41 supported Ni-W Ni-Mo, Co-Mo, and Pt catalysts were also prepared. The catalysts were evaluated by means of HDS of DBT and characterized by TPR and UV-Vis. It is indicated that among the supported sulfides, Ni-W sulfide supported over H-MCM-41 exhibits the best overall properties due to its higher HDS activity, the highest hydrogenation activity and the least cracking activity. The strong acidity of H-MCM-41 can also be confirmed by the increase in the hydrocracking activity of H-MCM-41 supported bimetallic sulfides and the presence of BCP and CHCP during the HDS of DBT over Pt/H-MCM-41.It is also indicate that the hydrogenation activity, HDS activity and reducibility of Ni-Mo and Ni-W catalysts can be significantly influenced by the ion exchange of the support with HNOs. Nevertheless, a little difference is observed for Co-Mo/Si-MCM-41 and Co-Mo/H-MCM-41The HDS of DBT over Co-Mo catalysts or Si-MCM-41 supported Ni-Mo, Ni-W or Pt catalysts occurs mainly through the hydrogenolysis route, whereas both hydrogenolysis and hydrogenation play important roles for H-MCM-41-supported Ni-Mo, Ni-W and Pt catalysts. These results suggest that a synergy between the new acid sites and the active sites, which involves the spillover hydrogen migration, may exist on the surf...