【作者】 吴平易；

【导师】 季生福；

【作者基本信息】 北京化工大学 ， 化学工程， 2009， 博士

【摘要】 目前,各国制定越来越严厉的法规来限制燃油中的硫含量,这导致石油炼制行业必须在石油加工过程中采用深度加氢脱硫技术脱除大部分的硫,而传统的Mo（W）CO（Ni）/Al2_O3加氢脱硫催化剂不能达到深度加氢脱硫的要求。研究表明碳化钼和磷化镍在加氢脱硫反应中显示了优异的催化性能,被认为是新一代的加氢脱硫催化剂;在以往的研究中负载型碳化钼或者磷化镍催化剂多以Al₂O₃或SiO₂为载体,它们比表面积较低不利于活性组分的分散,进而会影响催化剂的活性和稳定性。而介孔分子筛具有较高的比表面积和孔容积以及均一的孔径分布,被认为是优良的催化剂载体。因此,本文的研究思路是采用不同的组装方法把碳化钼和磷化镍引入到介孔分子筛中,以期利用介孔分子筛的特点获得高分散性的新型催化剂,再通过XRD、N₂吸脱附等温线、TEM和FTIR等分析手段对所得催化剂进行结构表征,最后采用噻吩和二苯并噻吩的加氢脱硫模型反应评价了催化剂的性能。首先,以介孔分子筛SBA-15为载体,采用浸渍法制备了不同Mo含量的MoO₃/SBA-15样品,再通过程序升温碳化法得到了M02C/SBA-15催化剂,所有氧化钼和碳化钼样品都具有良好的介孔结构,Si/Mo≥15时,纳米级碳化钼颗粒均一地分散在SBA-15的介孔结构中;M02C/SBA-15催化剂在常压下具有优良的噻吩HDS催化活性。然后,以硅酸钠为硅源、硫酸为酸源、钼酸钠为钼源、P123和CTAB为共模板剂,采用水热合成法在强酸性条件下成功合成了含钼SBA-15介孔分子筛Mo-SBA-15,再通过程序升温碳化法得到了MoxC-SBA-15,所有样品均具有高度有序的介孔结构,并且在合成过程中会有一部分Mo进入介孔分子筛SBA-15的骨架;与浸渍法相比,水热合成法得到的产物具有更高的比表面积和孔容积以及更好的活性组分分散性;二苯并噻吩的加氢脱硫反应中,Mo_xC-SBA-15（Si/Mo=7.5）的催化活性最好,在380℃时DBT的转化率为97.6%;Mo_xC-SBA-15催化剂上的二苯并噻吩加氢脱硫反应主要以直接脱硫（DDS）机理为主;并且除Si/Mo=30的样品以外,在噻吩以及二苯并噻吩的加氢脱硫反应中,水热合成法得到的碳化钼催化剂活性均远高于浸渍法得到的碳化钼催化剂。基于SBA-15组装碳化钼催化剂的制备经验,分别采用浸渍法和水热合成法制备了MoO₃/SBA-16和Mo-SBA-16,进而得到Mo₂C/SBA-16和Mo_xC-SBA-16,所有样品都具有立方介孔结构;同样,水热合成法得到的样品的活性组分分散性要明显高于浸渍法得到的样品,并且它们具有更高的比表面积和孔容积,这使得Mo_xC-SBA-16催化剂在噻吩和二苯并噻吩的加氢脱硫反应中显示了优于Mo₂C/SBA-16催化剂的催化性能。采用浸渍法将磷化镍前驱体引入到SBA-15介孔分子筛孔中,再通过程序升温还原法制备了一系列不同P/Ni（P/Ni=0.25,0.5,0.75,1.O,1.25,1.5和2）的Ni_xP/SBA-15介孔分子筛催化剂,所得样品均保留有介孔结构;当P/Ni=0.5时,活性相为Ni₂P和Ni₁₂P₅的混合相;当P/Ni≥0.75时,活性相为Ni₂P;在消除内外扩散的影响下研究了不同P/Ni的Ni_xP/SBA-15催化剂的加氢脱硫本征活性,反应条件为反应压力3.0 MPa,氢油比600,WHSV=26.7 h^-1,催化剂的颗粒尺寸为40-60目;可以发现P/Ni过高或者过低都会影响催化剂的加氢脱硫活性,Ni₂P的活性要高于Ni₁₂P₅,Ni_xP/SBA-15（P/Ni=0.75）具有最好的DBT加氢脱硫本征活性,在340℃时DBT的转化率就已达95.8%。对Ni_xP/SBA-15（P/Ni=0.75）催化剂进行稳定性实验,300h后DBT的转化率仍高于95%,而BP的选择性稳定在70%,CHB的选择性为30%,说明DBT的加氢脱硫反应主要以直接脱硫（DDS）机理为主;稳定性实验后样品的比表面积、孔容积和孔径基本没有发生变化,介孔结构及其有序性也没有被破坏,这些结果表明Ni_XP/SBA-15（P/Ni=0.75）催化剂具有很好的加氢脱硫活性和稳定性。最后,以无水乙醇为蒸发溶剂、氯化镍为镍源、TEOS为硅源、磷酸为磷源、P123为模板剂,采用蒸发诱导自组装法（EISA）把磷酸镍前驱体引入到介孔分子筛的孔中,再通过程序升温还原法得到相应的磷化镍催化剂。所得样品具有有序的立方介孔结构,并且具有较高的比表面积;其活性组分是纯的Ni₂P,Ni_xP/MMS（Si/Ni=2.5）,Ni_xP/MMS（Si/Ni=5）和Ni_xP/MMS-0.5K三个催化剂在340℃时DBT的转化率可以达到98%以上。更多还原

【Abstract】 Today,many countries enact severe regulations to limit the sulfur contents in fuel.It has been recognized that the current commercial hydrodesulfurization（HDS） catalysts are not adequate to meet the regulation requirements.This urges the worldwide research efforts to find new HDS catalysts,in which molybdenum carbide and nickel phosphide are believed to be the next-generation HDS catalysts for their excellent performance in HDS. In previous studies,supported molybdenum carbide and nickel phosphide catalysts often used Al₂O₃ or SiO₂ as support.The Al₂O₃ or SiO₂ supported catalysts has poor dispersion of active components as their low specific surface area resulting in the low catalytic activity in the reaction.Mesoporous molecular sieves（MMSs） have been recognized as the good catalytic supports for their high specific area and pore volume as well as the uniform pore size distribution.Thus,in this paper,molybdenum carbide and nickel phosphide were introduced into the MMSs by different assembly methods.It expects that the new-type catalysts can be obtained by utilizing the advantages of MMSs. Then,the prepared catalysts were characterized by XRD,N₂ adsorption-desorption isotherms,TEM and FTIR.Finally,the catalytic performances of the catalysts were evaluated by HDS of thiophene and dibenzothiophene（DBT）,respectively.Firstly,the MoO₃/SBA-15 samples with different Mo contents were prepared by impregnation method by using SBA-15 as support.Then,the corresponding Mo₂C/SBA-15 catalysts were obtained by temperature-programmed carburization（TPC） method.All obtained samples had well mesoporous structure.When Si/Mo≥15（molar ratio）,nano-sized particles of molybdenum carbide were homogeneously dispersed into the mesoporous structure of SBA-15.Mo₂C/SBA-15 catalysts have excellent HDS activity of thiophene in atmospheric pressure.Secondly,the Mo-SBA-15 samples were hydrothermally synthesized in strong acidic condition by using sodium silicate as silicon source,H₂SO₄ as acid source,sodium molybdate as molybdenum source,P123 and CTAB as co-template agents.Then,the corresponding Mo_xC-SBA-15 catalysts were prepared by TPC method.All obtained samples had highly ordered mesoporous structure.Some Mo ions may be located in the pore walls of SBA-15 in synthesis.Compared with the samples prepared by impregnation, the samples prepared by hydrothermal synthesis had higher specific surface area and pore volume,as well as the better dispersion of active components.In the HDS of DBT,MO_xC-SBA-15（Si/Mo=7.5） had the best catalytic activity with the DBT conversion of 97.6%at 380℃.The HDS of DBT over the SBA-15-containing molybdenum carbide catalyts mainly followed the direct desulfurization（DDS） mechanism.Except for the catalyt with the Si/Mo molar ratio of 30,the catalytic activities of carbide catalysts prepared by hydrothermal synthesis were much higher than those of catalysts prepared by impregnation method. Based on the experimental experiences of SBA-15-containing molybdenum carbide catalysts,the MoO₃/SBA-16 and Mo-SBA-16 samples were prepared by impregnation method and hydrothermal synthesis, respectively.Then,the Mo₂C/SBA-16 and Mo_xC-SBA-16 catalysts were prepared by TPC method.All obtained samples have cubic mesoporous structure.Also,the samples prepared by hydrothermal synthesis had higher specific surface area and pore volume,as well as the better dispersion of active components,resulting in the higher catalytic activity in the HDS of thiophene and DBT,respectively.Then,a series of Ni_xP/SBA-15 catalysts with different P/Ni molar ratios （P/Ni=0.25,0.50,0.75,1.0,1.25,1.5 and 2.0） were prepared by temperature-programmed reduction（TPR） method,respectively.All obtained samples had mesoporous structure.The active phase is the mixture phase of Ni₂P and Ni₁₂P₅ for Ni_xP/SBA-15（P/Ni=0.5）,whereas the active phase is Ni₂P for the catalysts with P/Ni≥0.75.The intrinsic activities of DBT HDS for the Ni_xP/SBA-15 catalysts with different P/Ni molar ratios were investigated by ruling out the existence of diffusional limitations under 3.0 MPa of total pressure,H₂/oil ratio of 600 and with weight hourly space velocities（WHSV） of 26.7 h^-1.It was found that the HDS activity can be affected by P/Ni,and Ni₂P had better acitivity than Ni₁₂P₅.Ni_xP/SBA-15（P/Ni=0.75） had the best intrinsic HDS activity of DBT with the DBT conversion of 95.8%at 340℃.The stability test was performed for Ni_xP/SBA-15（P/Ni=0.75）.The DBT conversion was higher than 95%after 300 h on stream,and the selectivity of BP was stabilized to 70%.It indicated that the DBT HDS over Ni_xP/SBA-15 （P/Ni=0.75） mainly followed the DDS mechanism.After the stability test,the specific surface area,pore volume and pore diameter remained unchanged. The ordering of mesoporous structure was also not destroyed.It indicated that Ni_xP/SBA-15（P/Ni=0.75） has the excellent activity and stability in the HDS of DBT.Finally,the nickel phosphate precursors were introduced into the MMS by Evaporation-Induced Self-Assembly（EISA） method using ethanol as solvent,nickel chloride as nickel source,TEOS as silicon source,H₃PO4 as phosphor source and P123 as template agent.Then,the corresponding nickel phosphide catalysts were prepared by TPR method.The obtained samples had ordered SBA-16-like cubic mesoporous structure with high specific surface area.The active phase of catalysts was Ni₂P The DBT conversion can reach 98%at 340℃over Ni_xP/MMS（Si/Ni=2.5）,Ni_xP/MMS（Si/Ni=5） and Ni_xP/MMS-0.5K.更多还原