以全硅MCM-41作载体制备W系深度加氢脱硫催化剂

【作者】 李翔；

【导师】 胡永康； 王安杰；

【作者基本信息】 大连理工大学 ， 工业催化， 2003， 博士

【摘要】 MCM-41分子筛具有比表面积大（＞1000 m²／g）、孔径分布均匀、表面酸强度适中、热稳定性好以及孔径可以在2～10nm范围内调节等特点。W系催化剂也因其优异的加氢活性和耐硫性能在深度加氢脱硫过程中展现出良好的应用前景。再者，我国有丰富的W资源。因此，本论文以石油馏分中最难脱除的含硫化合物之一——二苯并噻吩（DBT）为模型化合物，系统考察了以全硅MCM-41担载的W系催化剂加氢脱硫（HDS）性能。主要内容如下： 首先，用正交实验优化了全硅MCM-41（Si-MCM-41）的合成条件，并用0.5 M稀HNO₃在室温下通过离子交换改性制备了氢型Si-MCM-41（H-MCM-41）。研究结果表明，Si-MCM-41经稀HNO₃改性后孔道保持良好且孔径略有扩大，结构得到改善。最佳交换时间为6 h。Hammett指示剂、NH₃-TPD和探针反应结果表明，Si-MCM-41表面只有一些弱酸中心（酸强度+3.3＞H₀＞-3.0），而交换后会在表面产生酸度较强的新的酸中心，酸强度-5.6＞H₀＞-8.2。 在优化合成条件的基础上，用Si-MCM-41担载Ni-W和Co-W制备了深度HDS催化剂，并在高压固定床反应器上考察了它们对DBT和高硫直馏柴油的HDS性能。结果表明，Si-MCM-41是优良的HDS催化剂载体，由其担载制备的Ni-W催化剂表现出很高的HDS活性，且其活性远高于Co-W／Si-MCM-41。两类催化剂的最佳Ni（Co）／W摩尔比均为0.75。DBT在以Si-MCM-41作载体的W系催化剂上主要通过氢解反应路径脱硫，且Ni-W催化剂的加氢活性明显高于相应的Co-W催化剂。 Ni-W催化剂对DBT的HDS反应动力学研究结果表明，当Ni／W摩尔比等于0.75时，HDS反应的表观活化能E_HDS最低，说明催化剂的HDS活性与HDS反应的活化能有一定相关性。Ni对加氢反应路径和氢解反应路径活化能有不同的影响，说明在Ni-W催化剂中存在加氢和氢解两类不同的活性中心。通过UV-Vis和TPR表征结果可以推断，以全硅MCM一41作载体制备W系深度加氢脱硫催化剂加氢活性中心可能与催化剂表面八面体配位的Ni物种有关，氢解活性则与Nio一W03物种的还原性能有一定对应关系。 最后，本文还考察了以H一MCM一41作载体制备的Ni一W、Ni一MO、Co一Mo和Pt催化剂对DBT的HDS性能，并用UV-Vis和TPR对所制备的催化剂进行了表征。结果表明，在H一MCM一41担载的双金属硫化物催化剂中，Ni一W催化剂因其较高的HDS活性、最高的加氢活性以及最低的裂化活性而表现出最佳的综合性能。H一MCM一41担载的催化剂裂化反应活性均高于以Si一MCM一41作载体的催化剂，而且在P灯H一MCM一41上有环己烷基环戊烷（CHCP）和联环戊烷（BCP）的生成，进一步证明H一MCM一41有较强酸性。载体经稀HNO3交换后能够显著提高Ni一W和Ni一MoDBT在Co一Mo催化剂加氢活性、HDS活性和还原性能，的Ni一Mo、但对Co一Mo催化剂影响不大。催化剂以及Si一MCM一41Ni一W和Pt催化剂上，主要通过氢解反应进行脱硫，而在H一MCM一41担载担载Ni一W、Ni一M。和Pt制成的催化剂上，预加氢对脱硫过程有显著贡献。这说明催化剂加氢活性与H一MCM一41表面新的酸中心和活性组分活化氢的活性都有关。由此推断，在H一MCM一41表面新的酸中心和金属活性组分间可能存在以溢流氢为纽带的协同作用，这种协同作用能够促进催化剂的加氢活性，但对催化剂氢解脱硫活性影响不大。可能的机理是:DBT首先通过芳环吸附在这些酸中心上，并与溢流氢发生加氢反应，生成四氢二苯并曝吩（TH一DBT）。TH一DBT进一步转移到金属活性中心上发生氢解脱硫，生成环己烷基苯（CHB）。更多还原

【Abstract】 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 (YG) 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更多还原