噻吩在γ-Mo2N(100)表面上加氢脱硫反应的密度泛函理论研究

利用密度泛函理论研究了γ-Mo₂N(100)表面上的噻吩加氢脱硫(HDS)过程. 噻吩在γ-Mo₂N(100)表面上不同作用形式的结构优化结果显示, η5-Mo₂N吸附构型最稳定, 具有最大的吸附能(-0.56 eV), 此时噻吩通过S原子与Mo2原子相连平行表面吸附在四重空位(hcp 位). H原子和噻吩在hcp位发生稳定共吸附, hcp位是噻吩HDS的活性位点. 噻吩在γ-Mo₂N(100)表面进行直接脱硫反应, HDS过程分为S原子脱除和C₄产物加氢饱和两部分. 过渡态搜索确定了HDS最可能的反应机理及中间产物, 首个H原子的反应需要最大的活化能(1.69 eV),是噻吩加氢脱硫的控速步骤. 伴随H原子的不断加入, 噻吩在γ-Mo₂N(100)表面上优先生成―SH和丁二烯, 随后―SH加氢生成H₂S, 丁二烯加氢饱和生成2-丁烯和丁烷. 由于较弱的吸附, H₂S、2-丁烯和丁烷很容易在γ-Mo₂N(100)表面脱附成为产物.     

Hydrodesulfurization of Selective Catalytic Cracked Gasoline

Hydrodesulfurization (HDS) reaction of catalytic cracked gasoline (CCG) on Co–Mo/γ-Al₂O₃ was investigated in detail to make clear the important factors for deep HDS of CCG. A CCG containing 229 ppm sulfur and 30.4 vol% olefins was used in this study. Eleven alkylthiophenes and 2 alkylbenzothiophenes, 3 alkylthiacyclopentanes, and 2 disulfides were identified in this CCG by means of GC-AED analyses. In the reaction at 220 °C and 1.6 MPa using a conventional flow reactor of bench pilot scale, these sulfur compounds were hydrodesulfurized, whereas thiols were produced from H₂S and olefins. The reactions of thiophene HDS, isoolefin and n-olefin hydrogenation (HG) were studied to clarify the active sites on the catalyst. First, the effect of H₂S on the reaction was examined. The HG of n-olefin as well as thiophene HDS was inhibited by H₂S, while the HG of isoolefin was promoted. The effects of Co on these three reactions were also examined over the catalysts with different Co/(Co + Mo) ratios. Thiophene HDS was promoted by Co, while isoolefin HG was little affected and n-olefin HG was largely retarded. From these examinations, three types of active sites for thiophene HDS, isoolefin HG and n-olefin HG were proposed. Oligomers of isoolefins were found in the isoolefin hydrotreated product. The possibility of improving the HDS selectivity by carbonaceous deposit was investigated for HDS reactions of CCG and model compounds. The coking pretreatment was carried out on the catalyst and each reaction was examined. HDS selectivity (higher activity for HDS and lower activity for olefin HG) on CCGHDS was improved. Relative deactivation was in the following order, isoolefin HG > thiophene HDS > n-olefin HG. Pyridine modification (i.e. pyridine injection at 150 °C and partial pyridine desorption at 300 °C) was investigated on thiophene and olefins reaction. Thiophene HDS was little affected. Olefin HG and thiol production reaction were strongly inhibited. Improvement of HDS selectivity was observed in the reactions of CCG after pyridine modification. Improvement of HDS selectivity by pyridine modification was considered to result from the selective deactivation of the active sites for olefin reactions (hydrogenation and thiol production).     

Improvement of the Mo/TiO2-Al2O3 Catalyst by the Control of the Sol-Gel Synthesis

Traditional hydrotreating catalysts are constituted by molybdenum deposited on Al₂O₃ promoted by nickel and phosphorous. Several studies have shown that TiO₂-Al₂O₃ mixed oxides are excellent supports for the active phases. Results concerning the preparation, characterization and testing of molybdenum catalyst supported on titania-alumina are presented. The support was prepared by sol-gel route using titanium and aluminum isopropoxides, the titanium one chelated with acetylacetone (acac) to promote similar hydrolysis ratio for both the alcoxides. The effect of nominal molar ratio [Ti]/[Ti+Al] on the microstructural features of nanometric particles was analyzed by X-Ray Diffraction, N₂ Adsorption Isotherms and Transmission Electron Microscopy. The catalytic activity of Mo impregnated supports was evaluated using the thiophene hydrodesulfurization at different temperatures and atmospheric pressure. The pores size distribution curve moves from the micropores to the mesopores by increasing the Ti contents, allowing the fine tuning of average size from 2.5 to 6 nm. Maximal (367 m²·g^?1) and minimal (127 m²·g^?1) surface area were found for support containing [Ti]/[Ti+Al] ratio equal to 0.1 and 1, respectively. The good mesopore texture of alumina-titania support with [Ti]/[Ti+Al] molar ratio between 0.3 and 0.5 was found particularly valuable for the preparation of well dispersed MoS₂ active phase, leading to HDS catalyst with somewhat higher activity than that prepared using a commercial alumina support.     

噻吩在γ-Mo_2N(100)表面上加氢脱硫反应的密度泛函理论研究

利用密度泛函理论研究了γ-Mo2N(100)表面上的噻吩加氢脱硫(HDS)过程.噻吩在γ-Mo2N(100)表面上不同作用形式的结构优化结果显示,η5-Mo2N吸附构型最稳定,具有最大的吸附能(-0.56 eV),此时噻吩通过S原子与Mo2原子相连平行表面吸附在四重空位(hcp位).H原子和噻吩在hcp位发生稳定共吸附,hcp位是噻吩HDS的活性位点.噻吩在γ-Mo2N(100)表面进行直接脱硫反应,HDS过程分为S原子脱除和C4产物加氢饱和两部分.过渡态搜索确定了HDS最可能的反应机理及中间产物,首个H原子的反应需要最大的活化能(1.69 eV),是噻吩加氢脱硫的控速步骤.伴随H原子的不断加入,噻吩在γ-Mo2N(100)表面上优先生成―SH和丁二烯,随后―SH加氢生成H2S,丁二烯加氢饱和生成2-丁烯和丁烷.由于较弱的吸附,H2S、2-丁烯和丁烷很容易在γ-Mo2N(100)表面脱附成为产物.     

Effect of support on the synergy in HDS of thiophene and HDN of pyridine over Mo sulfide catalysts promoted by Rh

The effect of support (SiO₂-Al₂O₃, Al₂O₃,MgO) of the Rh-Mo(S) sulfide catalysts on the synergy in hydrodesulfurization (HDS) of thiophene and hydrodenitrogenation (HDN) of pyridine was studied. The synergy in HDS was between 7–10 regardless of the kind of support used. The synergy in HDN varied from none over the MgO supported sample to about 3 over SiO₂-Al₂O₃ supported catalyst, in accord with the positive effect of increasing support acidities. This revised version was published online in June 2006 with corrections to the Cover Date.     

On the kinetics of the catalytic thiophene hydrodesulfurization in pulse system

Conversion of thiophene hydrodesulfurization has been measured on nine different, MoO_x - or WO_x-based, metal- (Co, Ni, Pd, Pt) -promoted, sulfided catalysts at different flow rates of thiophene. The kinetic equation of the process and an activity parameter for the catalysts was determined. The correlation observed previously between the number of exchangeable sulfur atoms in the catalysts and their HDS conversion was found to be valid by applying these activity parameter data. This revised version was published online in August 2006 with corrections to the Cover Date.     

Cobalt-promoted MoS2 nanosheets: A promising novel diesel hydrodesulfurization catalyst

MoS₂ has been commonly used as a catalyst in hydrodesulfurization (HDS) of petroleum cuts in crude oil refineries. In this study, the synthesis of unsupported MoS₂ and Co-promoted MoS₂ nanosheets produced from molybdenum oxide and thiourea is reported. The synthesized samples were characterized by using x-ray fluorescence, x-ray diffraction, Brunauer–Emmett–Teller (BET), temperature-programmed reduction, thermal gravimetric analysis, and transmission electron microscopy methods, and then they were utilized for HDS of diesel through a fixed-bed catalytic reactor. Results indicated that a cobalt promoter affected both the number and the performance of active sites of the molybdenum sulfides, and the activity of the promoted MoS₂ catalyst was consistently higher than that of the MoS₂ catalyst. More significantly, the activity of the promoted catalyst was slightly declined during 48 h continuous HDS reaction, which indicated the stability of this catalyst. Additionally, during 12 h of test run, the HDS activity of the promoted catalyst was about 60% higher than MoS₂ one.     

Decomposition of molybdate–hexamethylenetetramine complex: One single source route for different catalytic materials

Decomposition of ammonium heptamolybdate–hexamethylentetramine (HMTA) complex (HMTA)₂(NH₄)₄Mo₇O₂₄·2H₂O was studied as a function of treatment conditions in the range 300–1173 K. The evolution of solid products during decomposition was studied by thermal analysis and in situ EXAFS. Depending on the nature of the gas used for treatment, single phases of highly dispersed nitrides Mo₂N, carbide Mo₂C, or oxide MoO₂ can be obtained. The nature of the products obtained was explained by qualitative thermodynamical considerations. Morphology of the solids considerably depends on such preparation parameters as temperature and mass velocity of the gas flow. For the nitride-based materials, catalytic activity was evaluated in the model thiophene HDS reaction. It was demonstrated that NH₃-treated samples showed better catalytic activity than N₂-treated ones due to cleaner surface and better morphology. Transmission microscopy, XRD and XPS studies showed that MoS₂ is formed on the surface during HDS reaction or sulfidation with H₂S. Optimized nitride-derived catalysts showed mass activity several times higher than unsupported MoS₂ or MoS₂/Al₂O₃ reference catalyst.     

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.     

Improvement of HDS catalysts through the modification of the oxidic precursor with 1,5-pentanediol: Gas phase sulfidation and thiophene conversion

The performance, in thiophene HDS, of a CoMo/Al₂O₃ catalyst was successfully improved through chemical modification of its oxidic precursor by impregnation with 1,5-pentanediol solution. The gas phase activation with a H₂/H₂S mixture was followed by thermogravimetric analysis coupled with a rapid chromatograph; the catalysts were characterized at different steps of the activation using X-ray photoelectron spectroscopy (XPS). It appeared that the addition of the organic agent retards the sulfidation of the supported metals, leading to a simultaneous sulfidation of Co and Mo atoms. This induces the formation of smaller MoS₂ slabs and thus an increase in the number of active CoMoS sites, directly correlated with the better HDS performance of the modified solid. The role of 1,5-pentanediol is likely to inhibit, at low temperature, the adsorption of H₂S on the solid and thus the sulfidation of the supported metals.     

TiO2柱撑海泡石负载Ni2P的噻吩加氢脱硫性能

以氢氧化镍为镍源, 亚磷酸为磷源, TiO₂柱撑海泡石(Ti-Sep)为载体, 采用浸渍法制备了含磷化镍前驱体的样品, 然后采用程序升温还原法制备了Ni质量分数(w)为5%-25%的Ni₂P/Ti-Sep催化剂, 并考察了其噻吩加氢脱硫性能. 采用X射线衍射(XRD)、N₂吸附-脱附、热重分析(TGA)、透射电子显微镜(TEM)和傅里叶变换红外(FTIR)光谱对催化剂样品进行了表征. 结果表明, 海泡石经TiO₂柱撑之后层间距增大, 比表面积和孔容都明显变大, 热稳定性增强, 活性组分Ni₂P能很好地分散在海泡石层间及表面, 并且没有破坏海泡石的层状结构. 上述原因导致Ni₂P/Ti-Sep催化剂的噻吩加氢脱硫活性明显优于Ni₂P/Na-Sep(NaCl改性海泡石)和Ni₂P/HCl-Sep(HCl改性海泡石)催化剂. 当Ni负载量为15% (w)时, Ni₂P/Ti-Sep催化剂具有最好的噻吩加氢脱硫性能; 在反应温度为400℃时, 噻吩转化率达100%.     

Comparing the hydrodesulfurization reaction of thiophene on γ-Al2O3 supported CoMo, NiMo and NiW sulfide catalysts

The thiophene hydrodesulfurization (HDS) reaction on γ-Al₂O₃ supported CoMo, NiMo and NiW sulfide catalysts was compared in order to gain insight into the promoter effect on direct desulfurization (DDS) and hydrogenation (HYD) pathways. Ni-promoted Mo (or W) sulfide catalysts favor the hydrogen transfer reactions relative to CoMo sulfide catalyst, which facilitates the direct route instead. This different performance and also the dependence of the apparent Arrhenius parameters with the catalyst formulation were attributed to the major participation of Mo (or W) edge for the Ni-containing catalysts and S edge for CoMo sulfide catalyst upon the thiophene-HDS reaction.     

Kinetic behavior of benzene hydrogenation and thiophene hydrogenolysis on sulfide Ni-Mo/Al2O3 catalyst

Summary An unsteady-state kinetic model of both benzene hydrogenation (HDA) and thiophene hydrogenolysis (HDS) on a sulfide hydrotreating catalyst Ni-Mo/Al₂O₃ has been developed. The model adequately describes experimental data obtained at the pressure 2 MPa, temperature 573 K and at various contact times and ratios of benzene/thiophene. The model is based on the assumption that the catalyst surface contains only one type of active sites, i.e., Ni atoms in the sulfide bimetallic species, which are responsible for both hydrogenolysis and hydrogenation reactions.     

二苯并噻吩和吲哚在NiMoS/γ-Al2O3上加氢脱硫和加氢脱氮反应的相互影响

在固定床高压微反装置上考察了预硫化型NiMoS/γ-Al2O3催化剂上二苯并噻吩（DBT）加氢脱硫（HDS）反应和吲哚加氢脱氮（HDN）反应之间的相互影响。结果表明,吲哚对DBT的加氢脱硫反应具有抑制作用,其中对加氢路径（HYD）比对氢解路径（DDS）的抑制作用强,温度升高后,吲哚的抑制作用减弱。吲哚对DBT加氢脱硫反应的抑制作用源于吲哚及其HDN反应的中间产物在活性位上的竞争吸附。DBT和原位生成的H2S促进了催化剂表面硫阴离子空穴（CUS）向B酸位的转化,从而提高1,2-二氢吲哚（HIN）分子中C(sp3)—N键的断裂能力,使得吲哚的转化率和产物中邻乙基苯胺（OEA）的相对含量增大。HDN活性相的形成虽然需要硫原子的参与,但是活性相的保持并不需要大量的硫原子,较高含量硫化物存在时加氢活性位减少,不利于脱氮反应。     

The effect of nickel on the component state and HDS activity of alumina-supported heteropolytungstates

Hydrotreating Ni heteropolytungstate catalysts have been prepared by impregnation of γ-Al₂O₃-alumina with solutions of H₃PW₁₂O₄₀ acid and its Ni salt. The nickel content is varied by adding Ni(NO₃)₂ salt. The calcined samples are characterized by BET, IR, TPR, and XPS techniques. The catalytic activity is tested for HDS of thiophene. It is shown that the initial heteropolyanion, its lacunary analog, and nickel substituted heteropolyanion are present on the surface as a result of the interaction between the active component and the alumina support. The mixed NiWS phase formed after sulfidation determines the HDS activity of the catalysts. Published in Russian in Kinetika i Kataliz, 2007, Vol. 48, No. 6, pp. 905–911. This article was submitted by the authors in English.     

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。     

Titania-supported mixed HPMoV polyoxometallates as precursors of hydrodesulfurization catalysts

HDS catalysts were prepared by loading H₃PMo₁₂O₄₀ or H₄PMo₁₁V₁O₄₀ polyoxometallates on TiO₂ (0.5 and 1.0 mmol (Mo+V)). Activity of the catalysts was tested in the HDS of thiophene. The activity of catalysts of low concentration was 2–3 times higher than the activity of those of high concentration. Temperature programmed reduction (TPR) and IR spectroscopy were used to determine the properties of the catalyst. TPR measurements proved that vanadium promotes and stabilizes HDS activity due to an increase in the Mo⁵⁺/Mo⁴⁺ ratio.     

Ni_2P/TiO_2-Al_2O_3催化剂的制备及其加氢脱硫、脱氮性能

采用溶胶-凝胶法制备了TiO2-Al2O3复合载体,采用浸渍法制备了Ni2P/TiO2-Al2O3催化剂,并用X射线衍射(XRD)、N2吸附比表面积(BET)测定、热重-差热分析(TG-DTA)、X射线光电子能谱(XPS)等技术对催化剂的结构和性质进行了表征.催化剂加氢脱硫(HDS)和脱氮(HDN)活性评价在实验室固定床连续反应装置上,以噻吩和吡啶为模型反应物进行.考察了不同载体、Ni2P负载量、标称Ni/P摩尔比、催化剂焙烧温度对Ni2P/TiO2-Al2O3催化剂上同时进行的噻吩加氢脱硫和吡啶加氢脱氮性能的影响.结果表明,TiO2含量为80%(w)的TiO2-Al2O3复合氧化物为载体,Ni2P负载量为30.0%(w),标称Ni/P摩尔比为1/2,催化剂焙烧温度为500℃时,Ni2P/TiO2-Al2O3催化剂加氢脱硫脱氮活性最高.在360℃,3.0MPa,氢油比800(V/V),液时体积空速1.5h-1的条件下,噻吩HDS和吡啶HDN转化率分别为61.32%和64.43%.     

高表面积复合氧化物Co-O-Si的制备及其催化1-己烯骨架异构和噻吩加氢脱硫活性

通过硝酸钴与硅酸钠共沉淀、辅以正丁醇干燥技术制备了具有原子分散度的Co-O-Si复合氧化物（Co/Si原子比 ≈ 0.65）,该催化剂具有较大的比表面积（562 m²/g）和较强表面酸性. 在硫化处理后,能够形成高度分散的硫化物活性组分,在模型汽油加氢处理反应中显示了较高的催化活性,在573 K时,噻吩的加氢脱硫活性可达99.4%,同时,1-己烯的骨架异构收率达到了35%. 该催化剂虽然不含Mo,其加氢脱硫活性可与工业催化剂Co-Mo/γ-Al₂O₃相当. 而在汽油深度加氢脱硫过程中,直链烯烃往往被加氢饱和,造成辛烷值损失. 该催化剂则可使部分直链烯烃发生骨架异构而生成异构烷烃,可减少深度加氢脱硫过程中的辛烷值损失.