【作者】 滕阳；

【导师】 胡永康； 王安杰；

【作者基本信息】 大连理工大学 ， 工业催化， 2010， 博士

【摘要】 过渡金属磷化物作为一类新型催化材料以其在加氢精制反应中的高活性和稳定性是目前催化领域研究的热点。本论文以磷化镍(Ni2P),磷化钼(MoP)和磷化钨(WP)为研究对象,考察了它们的制备方法以及对于含硫模型化合物二苯并噻吩(DBT)和4,6二甲基二苯并噻吩(4,6-DMDBT)的HDS反应性能。采用XRD、CO化学吸附、TPR、HRTEM、XPS等表征技术对制备的催化剂的结构进行了表征,并对得到的催化剂反应性能结果进行了原理的探讨。论文以全硅MCM-41作为载体制备了负载型的Ni2P, MoP和WP催化剂,考察了程序升温还原法制备磷化物过程中原子比,担载量和还原终温对催化剂的制备和反应性能的影响。对于Ni2P/MCM-41,最佳制备条件是Ni/P=1.25, NiO担载量12%以及还原终温500℃; MoP/MCM-41和WP/MCM-41的最佳制备条件均为Mo(W)/P=1, Mo(W)O3担载量40%以及还原终温650℃。比较了Ni2P/MCM-41, MoP/MCM-41和WP/MCM-41催化剂对DBT的反应性能以及H2S对反应性能的影响。其中Ni2P/MCM-41对于DBT的活性最高但其耐硫性能最差。对反应前后的各磷化物催化剂进行XRD和XRF分析结果表明,在反应后催化剂的体相保持了磷化物结构但表面有大量的硫进入。对新鲜磷化物进行硫化处理以及交替的HDS和加氢脱氮(HDN)实验证实了硫对磷化物HDS反应的促进作用。采用硫化后还原法制备的MoP/MCM-41催化剂相比于直接程序升温还原法得到的样品具有更高的HDS活性,对4,6-DMDBT的脱除效果尤为显著。通过MoP/MCM-41与MoS2/MCM-41混合催化剂活性的考察排除了MoP和MoS2混合晶相的协同作用使活性提高的可能性。通过XRD和HRTEM分析了样品的晶体结构,硫插入MoP晶格导致晶体结构发生畸变而使样品中MoP晶体的晶面间距略微增加。XPS结果表明硫的插入使钼原子上的电子转移到硫原子上造成钼原子上的电荷密度减小。实验考察了不同反应温度和不同重量时间下催化剂的HDS转化率和选择性的变化,并对MoP/MCM-41催化剂对DBT和4,6-DMDBT的HDS反应路径进行了分析,结果表明硫化后还原法得到的MoP/MCM-41催化剂加氢路径的活性得到了提高。论文还尝试采用硫化后还原法制备了WP/MCM-41和Ni2P/MCM-41催化剂。XRD,XPS和TPR结果表明WP的制备过程与MoP相似,但钨的还原较钼更难。硫化后还原法得到的WP/MCM-41催化剂其加氢性能更强,因此对于4,6-DMDBT的反应活性更高。硫化后还原法并不能提高Ni2P/MCM-41催化剂的活性,通过XRD、TPR和XPS手段对制备过程中Ni2P前体的变化状态进行了分析,Ni2P前体经过硫化得到了Ni3S2结构,再还原后生成了活性很低的Ni-P结构而不能形成Ni2P晶相。将分别制备出的两种磷化物机械混合得到了二组分磷化物催化剂,并以DBT和4,6-DMDBT的混合原料评价了催化剂的HDS活性。结果表明Ni2P与WP的组合对于DBT和4,6-DMDBT的同时脱硫表现出了最佳活性。实验还考察了二组分的装填方式和二组分比例对反应性能的影响,以石英砂的二组分均匀混合并当Ni2P与WP重量比为2时催化剂活性最高。这种二组分磷化物催化剂的反应性能更适应于深度脱硫的要求。更多还原

【Abstract】 Transition metal phosphide as a novel class of catalysts has attracted much attention in recent years due to their high activities and stabilities in hydrotreating reactions. In the present study, the preparation and HDS activities of Ni2P, MoP, and WP were investigated using DBT and 4,6-DMDBT as the model sulfur containing compounds. XRD, CO chemisorption, TPR, HRTEM, and XPS techniques were used to characterize the structures of metal phosphides, which provide some insights into the enhanced HDS activities.Siliceous MCM-41 supported-Ni2P, MoP and WP catalysts were prepared by temperature-programed reduction procedure. The effect of metal/P ratio, metal loading, and final reduction temperature on the phosphide structure and HDS activities were investigated. The results showed that the optimum preparation conditions for Ni2P/MCM-41 were Ni/P=1.25, NiO loading 12% and final reduction temperature of 500℃. The optimum preparation conditions for MoP/MCM-41 and WP/MCM-41 were Mo(W)/P=1, Mo(W)O3 loading of 40% and final reduction temperature of 650℃.The HDS performances of Ni2P/MCM-41, MoP/MCM-41, and WP/MCM-41 in the HDS of DBT were compared in the presence and absence of H2S. The results indicated that Ni2P was the most active among the three metal phosphides, but its tolerance to H2S was poor. XRD and XRF measurements of the catalysts before and after HDS reaction indicated that the bulk structure of phosphides did not change in the reactions but sulfur exists on the surface. The sulfidation of fresh phosphides and sequential HDS-HDN experiments revealed that sulfur played a positive role in the HDS reactions over metal phosphides.MoP/MCM-41 with enhanced activities especially in the HDS of 4,6-DMDBT was obtained via a sulfidation-reduction procedure. The much lower HDS activity over mixtures of MoP/MCM-41 and MoS2/MCM-41 excluded the synergetic effect of separate MoS2 and MoP phases. XRD and HRTEM characterization on crystal structure indicated that d-spacing values increased slightly via sulfidation-reduction, which was probably caused by the incorporation of sulfur in phosphide structure. A shift of the Mo 3d5/2 binding energy was observed in the XPS spectra, which might be related with the incorporation of sulfur in phosphide structure. The HDS performances of DBT and 4,6-MDBT over MoP/MCM-41 prepared via different procedures as a function of temperature and weight time were studied to analyze the reaction pathway. The results indicated that the reaction rate of hydrogenation route was accelerated over MoP/MCM-41 prepared by the sulfidation-reduction procedure.The preparation of WP/MCM-41 and Ni2P/MCM-41 was also attempted by the sulfidation-reduction procedure. The formation of WP was found to be more difficult than that of MoP. The resulting WP/MCM-41 catalyst via sulfidation-reduction showed higher activities than MoP/MCM-41 in the HDS of 4,6-DMDBT. Nevertheless, Ni2P could not be synthesized by this procedure. XRD, TPR, and XPS characterization results indicated that a Ni3S2 phase was formed during sulfidation, thus Ni-P alloy with poor activity instead of Ni2P was formed in the subsequent reduction.Ni2P-WP was prepared by a physical-mixing method, which exhibited much higher performance in the simultaneous HDS of DBT and 4,6-DMDBT than Ni2P and WP. The packing configurations of two phosphides in the bed were investigated, and the highest HDS activity was observed in homogeneous mixing together with quartz-sand particles at a Ni2P/WP mass ratio of 2.更多还原