制备条件对碳化钼催化剂加氢脱硫性能的影响

以MoO3为前驱体,在CH4/H2气氛中程序升温还原碳化反应制备了Mo2C催化剂,用XRD和BET进行了表征. 以二苯并噻吩/环己烷溶液为模型反应物,评价了制备条件对碳化钼催化剂加氢脱硫性能的影响. 结果表明,在还原碳化温度为675 ℃,恒温保持150 min的合成条件下可制得高纯度的a-Mo2C催化剂,该催化剂表现出了较高的加氢脱硫活性,用质量分数为0.6%的二苯并噻吩/环己烷溶液为反应物,反应压力3.0 MPa,反应空速8 h-1,反应温度330 ℃实验条件下的二苯并噻吩加氢脱硫转化率达到了73.29%. 随还原碳化温度的升高和恒温保持时间的延长,制备的碳化钼催化剂的比表面积下降,表面积炭增多,引起其二苯并噻吩加氢脱硫活性的下降. 适当增大制备过程中还原碳化气体空速,有利于还原碳化反应过程中C、 O之间局部规整反应的进行,并对其二苯并噻吩加氢脱硫活性有明显的促进作用. 实验确定的还原碳化气体空速以1.8×104h-1为宜.     

一种新型高活性加氢脱硫催化剂:二氧化硅担载的磷化镍

 以硝酸镍和磷酸氢二铵为原料,采用程序升温还原方法在823 K和氢气气氛中制备了纯相和 二氧化硅担载的磷化镍催化剂,并采用类似的方法制备了纯相和二氧化硅担载的磷化钼和 镍钼磷新型磷化物. 对这些磷化物及其相应硫化物的加氢脱硫活性进行了考察. 结果表明,Ni2P/SiO2催化剂具有相对较高的二苯并噻吩转化率和联苯选择性, Ni2P/SiO2对二苯并噻吩加氢脱硫的催化活性甚至高于硫化态的Ni-Mo催化剂.     

钴掺杂对碳化钼催化噻吩加氢脱硫性能的影响

以MoO3和CoMo混合氧化物为前驱体, 制备了碳化钼和碳化钼-钴催化剂, 采用XRD, BET, SEM和XPS等技术对其进行了表征, 研究了Co掺杂对碳化钼催化剂噻吩加氢脱硫性能的影响. 结果表明, 掺入适量的Co后制得的CoMo双金属混合氧化物为MoO3和CoMoO4的两相混合体, 经CH4/H2气氛程序升温还原碳化反应生成共生共存的Co-Mo2C, Co以金属细颗粒的形态均匀地分散在生成的Mo2C组分之间. 在共生过程中含Co物种的掺入可降低制备碳化钼所需要的还原碳化温度, 使制备的碳化钼颗粒变小, 比表面积增大, 表面Mo2+含量增多, 从而对碳化钼的噻吩加氢脱硫活性有较好的促进作用, Co的添加量以Co/Mo摩尔比为0.2左右较为适宜. 用化学共沉淀法制得的Co-Mo2C共生共存体系的噻吩加氢脱硫反应活性, 好于由金属Co与Mo2C机械混合法制得的Co+Mo2C二相共存体系. 这表明当两个活性相共存时, 只有经过相互共生过程才能发挥其最佳的协同效应.     

Mo助剂含量对Mo-Ni2P/SBA-15/堇青石整体式催化剂加氢脱硫性能的影响

 采用共浸渍法制备了 P/Ni 摩尔比为 2 的 Ni2P/SBA-15, 再通过二次浸渍引入助剂 Mo 制得 Mo-Ni2P/SBA-15, 将它调制成活性胶后均匀涂敷于预处理后的载体表面, 干燥焙烧后在氢气流中采用程序升温还原法, 制备了一系列 Mo-Ni2P/SBA-15/堇青石整体式催化剂. 采用 X 射线衍射、N2 吸附-脱附和 X 射线光电子能谱对催化剂结构进行了表征, 以二苯并噻吩为模型含硫化合物, 考察了催化剂的加氢脱硫性能. 结果表明, Mo 的加入增大了催化剂的比表面积, 在催化剂表面形成了 MoNiP2, 且 Ni2P 为主要活性物相. Mo 在催化剂表面主要以 Mo6+和 Moδ+形式存在; 当 w(Mo) = 4.2% 时, n(Mo)/n(Ni+Mo) = 0.18 的整体式催化剂上二苯并噻吩的转化率最高, 且在较低反应温度时以直接脱硫机理为主, 而较高反应温度时以加氢脱硫机理为主.     

碳化钼催化剂加氢脱氮性能研究

MoO3在CH4/H2气氛中程序升温还原碳化反应制备了Mo2C催化剂,用XRD、BET、SEM、XPS进行了表征。以吡啶/环己烷溶液为模型化合物,在高压微反装置上评价了碳化钼催化剂的吡啶加氢脱氮性能。结果表明,MoO3在CH4/H2气氛中程序升温至675℃可制得高纯度的β-Mo2C,SEM表征其形貌为板块状颗粒,平均粒径约3.9μm,比表面积达到了10.7m2/g,高于其前驱体MoO3 的2.7倍。在反应压力3.0MPa,空速为8h－1,H2/原料液体积比为500∶1,体积分数为5%的吡啶/环己烷溶液中,碳化钼催化剂在340℃下的吡啶加氢脱氮转化率达到了86.30%,高于相应MoS2约8%。随还原碳化温度的升高,碳化钼催化剂的比表面积降低,表面积炭增多,导致其吡啶加氢脱氮活性下降。确定的碳化钼催化剂的合成条件以还原碳化温度675℃、还原碳化气体空速1.8×104h－1左右较为适宜。     

氮、磷、碳化物比较研究初探

环保法规的日益严格使得研究者越来越重视新型加氢脱硫、脱氮催化剂的开发。国内外学者在对负载型Mo—Co、Mo—Ni和W—Ni等传统硫化物催化剂进行不断改进的同时，新型催化材料尤其是具有贵金属性质的过渡金属间充化合物一氮化物、碳化物和磷化物的研究也受到很大的关注。人们在探索不同的载体或者是不同的助剂对单金属间充化合物-氮化物、碳化物或磷化物催化剂活性组分的表面状态和结构以及其深度加氢脱硫脱氮性能的影响，而对同一载体负载的氮、磷、碳化物催化剂缺乏横向的比较。本研究制备了以γ-Al2O3为载体的负载型氮化钼、磷化钼和碳化钼催化剂，比较了它们的孔结构、比表面积，并初步分析了钼的质量分数为19％，氮化、磷化和碳化温度均为650℃时三类催化剂的二苯并噻吩加氢脱硫性能。     

氧化钼在CH4/H2气氛中还原碳化机理研究

采用TG-DTA技术研究了MoO3在CH4/H2气氛中的还原碳化行为,考察了程序升温速率和还原碳化终点温度对氧化钼还原碳化行为的影响,并探索适宜的还原碳化条件。结果表明,在1℃/min的程序升温条件下,MoO3在CH4/H2气氛中经三段失重过程被还原碳化为Mo2C,相应的反应历程为MoO3→MoO2→MoOxCy→Mo2C,适宜的还原碳化终点温度为675℃;程序升温速率升至2℃/min以上时,MoO3在CH4/H2气氛中的反应历程为MoO3→MoO2→Mo＋MoOxCy→Mo2C,且随程序升温速率的增大,第二段失重过程中金属Mo的生成量增大,还原碳化反应的始、终点温度升高。提高还原碳化终点温度,MoO3在CH4/H2气氛中的还原碳化反应规律相同,但过高的还原碳化温度会引起有机烃类分解生炭反应的发生,沉积在催化剂的表面,导致制备的碳化钼催化剂表面积炭增多,比表面积降低,从而引起催化活性的下降。     

MCM-41担载的镍钼硫化物上二苯并噻吩的加氢脱硫反应动力学

 采用高压滴流床反应器研究了在WHSV＝30~90 h-1,p＝5.0 MPa和θ＝280~340 ℃的条件下,二苯并噻吩(DBT)在不同Ni含量的Ni-Mo/MCM-41催化剂样品上的加氢脱硫(HDS)反应动力学. 应用拟1级活塞流模型计算了该系列催化剂上的HDS反应的表观反应速率常数以及加氢反应路径和氢解反应路径的反应速率常数. 结果表明,加氢反应路径的速率常数和氢解反应路径的速率常数在同一个数量级上,说明在Ni-Mo/MCM-41上进行DBT的HDS反应时, 这两个平行的反应路径是并重的. 随着催化剂中Ni/Mo原子比的增大,两个反应路径的速率常数均增大,并在Ni/Mo原子比为0.75时达到最大值. 当Ni/Mo原子比增大到1.0时,两个反应路径的速率常数均大幅下降. 根据Arrhenius方程求得了DBT在Ni-Mo/MCM-41上进行HDS反应的表观活化能. 结果表明,催化剂的活性与表观活化能存在明显的相关关系,活化能越低,活性越高.     

Ni2P/SBA-15催化剂的结构及加氢脱硫性能

以硝酸镍为镍源, 磷酸氢二铵为磷源, 介孔分子筛SBA-15为载体, 用共浸渍法制备了含磷化镍前驱体的样品, 然后在氢气流中采用程序升温还原法, 制备了Ni2P质量分数为5%-40%的Ni2P/SBA-15催化剂. 用X射线衍射(XRD)、N2吸附脱附、透射电子显微镜(TEM)、傅立叶变换红外光谱(FTIR)等分析测试技术对催化剂的结构进行了表征, 以噻吩和二苯并噻吩(DBT)为模型化合物, 在微型固定床反应器上对催化剂的加氢脱硫(HDS)性能进行了评价. 结果表明, Ni2P/SBA-15催化剂中SBA-15 的介孔结构依然存在, 活性组分Ni2P具有良好的分散性, 但随Ni2P含量的增加, 催化剂的比表面积、孔容和孔径均有明显减小. 当反应温度为320 ℃时, Ni2P含量为15%-25%(w)的催化剂就具有很好的加氢脱硫催化性能; 反应温度在360 ℃以上时, 所有催化剂都具有优异的深度脱硫催化性能. Ni2P/SBA-15催化剂对二苯并噻吩的加氢脱硫(HDS)主要以直接脱硫机理(DDS)进行.     

溶胶-凝胶法制备MoP/SiO2催化剂加氢脱硫催化活性的研究

以正硅酸乙酯为硅源,以钼酸铵和磷酸二氢铵为钼源和磷源,采用溶胶-凝胶法,经干燥、焙烧,程序升温还原制备得到二氧化硅负载磷化钼(MoP)催化剂。以噻吩、二苯并噻吩为模型化合物,对负载催化剂的加氢脱硫活性进行评价,考察了负载量、反应压力、反应温度等因素对催化活性的影响。实验结果表明,MoP/SiO₂催化剂Mo的最佳负载量为20%,升高反应压力和温度均有利于提高二苯并噻吩的转化率,但降低了产物中联苯的含量。     

络合物分解法制备碳氮夹杂钼基催化剂及其催化性能

通过调变六次甲基四胺与金属钼盐的摩尔比例,以络合物分解法制备了碳氮夹杂钼基催化剂,并将其负载于氧化铝载体上．采用X射线衍射（XRD）、X射线光电子能谱（XPS）、低温氮吸附、元素分析等方法对催化剂进行了表征,发现碳氮夹杂钼基催化剂实为碳化钼（β-Mo2C）与碳氮化钼（M02CxNy）的混合物．以二苯并噻吩（DBT）的加氢脱硫反应（HDS）为探针,比较了负载型碳化钼、氮化钼及碳氮夹钼基催化剂的催化活性,发现由于夹杂催化剂中含有新的活性相Mo2CxNy。而表现出高于碳化钼和氮化钼催化剂的催化活性．     

Mo-Ni2P/SBA-15催化剂的制备、表征及加氢脱硫催化性能

以介孔分子筛SBA-15 为载体, 通过分步浸渍硝酸镍、磷酸氢二铵、钼酸铵, 然后在H₂气流下程序升温还原(H₂-TPR), 制备了一系列不同Mo 含量的Mo-Ni₂P/SBA-15 催化剂. 采用X 射线衍射(XRD)、氮气吸脱附(BET)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)对催化剂的结构进行了表征, 评价了催化剂对二苯并噻吩(DBT)的加氢脱硫(HDS)活性. 结果表明, Mo-Ni₂P/SBA-15 催化剂仍然保留有介孔结构, 催化剂的物相主要是Ni₂P. 催化剂表面的Ni 以Ni^δ+和Ni²⁺形式存在; P以P^δ-和P⁵⁺形式存在; Mo以Mo^δ+和Mo⁶⁺形式存在. Mo能促进催化性能的提高, 其中Mo含量为1% (w, 质量分数)的Mo-Ni₂P/SBA-15 催化剂具有最好的二苯并噻吩加氢脱硫催化活性, 在反应温度为380 ℃, 反应压力为3.0 MPa的条件下, 二苯并噻吩的转化率可达99.03%, 所有考察的Mo-Ni₂P/SBA-15都以直接加氢脱硫(DDS)途径为主.     

Intermediate molybdenum oxides involved in binary and ternary induced electrodeposition

The first stages of Co–Ni and Co–Ni–Mo deposition in sulphate–citrate medium at pH 4.0 were analysed. In both cases, the formation of non-hydrogenated nickel on the electrode before alloy deposition was detected by linear sweep voltammetry and inductively coupled plasma mass spectrometry. Co–Ni electrodeposition was anomalous since the Co/Ni ratio in the alloy was higher than the corresponding [Co(II)]/[Ni(II)] ratio in solution. The adsorption of Co(II) over the initial nickel could explain the anomalous codeposition, which persisted with the addition of molybdate to the Co–Ni bath. However, the formation of intermediate molybdenum oxides also took place. A mechanism has been proposed to describe the sequence of steps for Co–Ni–Mo electrodeposition. Under our conditions, the alloy is formed mainly from free Co²⁺ and Ni²⁺ cations, whereas molybdate is reduced firstly to molybdenum oxide from MoO₄(H₃Cit)²⁻ and, secondly, NiCit⁻ catalyses the subsequent reduction to molybdenum metal of the intermediate [MoO₂–NiCit⁻]_ads species.     

The efficient synthesis of a molybdenum carbide catalyst via H2-thermal treatment of a Mo(VI)-hexamethylenetetramine complex

An efficient method for preparation of Mo(2)C catalyst is described, where Mo(2)C is obtained by the heat treatment of a single solid precursor containing (NH(4))(6)Mo(7)O(24) and hexamethylenetetramine (HMT) at 923 K in H(2) flow without conventional prolonged carbonization. The catalysts are characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), BET surface area measurement, and transmission electron microscopy (TEM). Furthermore, these catalysts are evaluated in the dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction, and proved to be superior to those prepared by a temperature-programmed reduction (TPRe) method. The better catalytic performance is ascribed to higher dispersion of Mo(2)C on the support and a lower surface polymeric carbon content. This hydrogen thermal treatment (HTT) method provided a new strategy for the preparation of a highly active molybdenum carbide catalyst.     

NiMoW/P-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Hydrotreating Catalysts: Influence of the Mo/W Ratio on the Hydrodesulfurization and Hydrogenation Activity

A series of NiMoW/P-Al₂O₃ catalysts with different Mo/W ratios (sample containing Mo only, Mo/W = 2: 1, Mo/W = 1: 1, Mo/W = 1: 2, and sample containing W only; P₂O₅ content of the support 2.0 wt %) were synthesized. The precursors of the active phase were the heteropoly acids H₃PMo₁₂O₄₀?nH₂O and H₃PW₁₂O₄₀?nH₂O, and also nickel citrate. The sulfide phase in the samples was studied by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy; the catalytic activity of the samples in dibenzothiophene hydrodesulfurization and naphthalene hydrogenation was determined. For the dibenzothiophene hydrogenolysis in the presence of quinoline and naphthalene (content in the model mixture, wt %: dibenzothiophene 0.3, naphthalene 1.5, and quinoline 0.5), k_HDS for different samples is in the range 17.6–42.5 h^–1 at 275°C and 24.6–45.9 h^–1 at 300°C. For the naphthalene hydrogenation, k_HYD varies from 0.79 to 1.89 h^–1 at 275°C and from 0.91 to 3.78 h^–1 at 300°C. The sample based on molybdenum showed the highest activity in hydrogenation and hydrodesulfurization.     

Preparation,characterization and hydrodesulfurization performances of Co-Ni_2P/SBA-15 catalysts

A series of Co-Ni2P/SBA-15 catalysts with various Co contents, Ni2P contents and P/Ni molar ratios were prepared by impregnating nickel nitrate, diammonium hydrogen phosphate, and then cobalt nitrate into SBA-15 support followed by temperature-programmed reduction in a H2 flow. The catalyst structure was characterized by X-ray diffraction(XRD), high resolution-transmission electron microscopy(HR-TEM)and N2adsorption-desorption techniques and their catalytic performance of the hydrodesulfurization(HDS) of dibenzothiophene(DBT) was evaluated. The effects of Co contents, Ni2 P contents and P/Ni molar ratios on the catalyst structure and HDS of DBT over the Co-Ni2P/SBA-15 catalyst were investigated. The results indicated that the mesoporous structure was mainly maintained and the nickel phosphides were well dispersed in all of the characterized catalysts. The 4Co-25Ni2P/SBA-15(P/Ni = 0.8) catalyst with the Co and Ni2 P contents of 4 wt% and25 wt%, respectively, and the P/Ni molar ratio of 0.8 showed the highest catalytic performance for HDS of DBT. Under the reaction conditions of 380?C and 3.0 MPa, the DBT conversion can reach 99.62%. The HDS of DBT proceeded mainly via the direct desulfurization(DDS)pathway with biphenyl(BP) as the dominant product on all of the catalysts and the BP selectivity was slightly enhanced after the introduction of Co promoters.     

Sulfur‐33 Isotope Tracing of the Hydrodesulfurization Process: Insights into the Reaction Mechanism,Catalyst Characterization and Improvement

The novel approach based on ³³S isotope tracing is proposed for the elucidation of hydrodesulfurization (HDS) mechanisms and characterization of molybdenum sulfide catalysts. The technique involves sulfidation of the catalyst with ³³S‐isotope‐labeled dihydrogen sulfide, followed by monitoring the fate of the ³³S isotope in the course of the hydrodesulfurization reaction by online mass spectrometry and characterization of the catalyst after the reaction by temperature‐programmed oxidation with mass spectrometry (TPO‐MS). The results point to different pathways of thiophene transformation over Co or Ni‐promoted and unpromoted molybdenum sulfide catalysts, provide information on the role of promoter and give a key for the design of new efficient HDS catalysts.     

Sulfur‐33 Isotope Tracing of the Hydrodesulfurization Process: Insights into the Reaction Mechanism,Catalyst Characterization and Improvement

The novel approach based on ³³S isotope tracing is proposed for the elucidation of hydrodesulfurization (HDS) mechanisms and characterization of molybdenum sulfide catalysts. The technique involves sulfidation of the catalyst with ³³S‐isotope‐labeled dihydrogen sulfide, followed by monitoring the fate of the ³³S isotope in the course of the hydrodesulfurization reaction by online mass spectrometry and characterization of the catalyst after the reaction by temperature‐programmed oxidation with mass spectrometry (TPO‐MS). The results point to different pathways of thiophene transformation over Co or Ni‐promoted and unpromoted molybdenum sulfide catalysts, provide information on the role of promoter and give a key for the design of new efficient HDS catalysts.     

Molybdenum HDS catalysts supported on niobia-silica

The effect of the amount of Nb₂O₅on the dispersion and reductive properties of Mo/Nb₂O₅-SiO₂ catalysts has been studied. Addition of niobium leads to an increase of the dispersion, and the reducibility of molybdenum. A synergetic effect of niobium on the catalytic activity in hydrodesulfurization of thiophene was observed at 5.4 wt.% of Nb₂O₅. This revised version was published online in June 2006 with corrections to the Cover Date.     

Catalysis for One‐step Synthesis of Dimethyl Ether from Hydrogenation of CO

In this paper, a new catalyst system Cu‐Mn‐(M)/γ‐Al₂O₃ was developed for the directly synthesis dimethyl ether (DME) from synthesis gas in a fixed‐bed reactor. The catalysts with different n (Cu) : n (Mn) ratios, several promoter M (M is one of Zn, Cr, W, Mo, Fe, Co or Ni) were prepared and tested. The results showed the catalysts have a high conversion of CO and a high DME selectivity. The DME yield in tail gas reached 46.0% (at 63.27% conversion of CO) at 2.0 MPa, 275°C, 1500 h^?1 with the Cu₂Mn₄Zn/γ‐Al₂O₃ catalyst.