The role of nickel in pyridine hydrodenitrogenation over NiMo/Al2O3

Al₂O₃ supported Mo, Ni, and NiMo/Al₂O₃ catalysts with various Ni contents were prepared to investigate the role of Ni as a promoter in a NiMo bimetallic catalyst system. The hydrodenitrogenation (HDN) reaction of pyridine as a catalytic probe was conducted over these catalysts under the same reaction conditions and the catalysts were characterized using BET surface area measurement, infrared spectroscopy, temperature programmed reduction, DRS and ESR. According to the results of reaction experiments, the NiMo/Al₂O₃ catalyst showed higher activity than Mo/Al₂O₃ catalyst in the HDN reaction and particularly the one with atomic ratio [Ni/(Ni+Mo)]=0.3 showed the best activity for the HDN of pyridine. The findings of this study lead us to suggest that the enhancement in the HDN activity with nickel addition could be attributed to the improvement in the reducibility of molybdenum and the formation of Ni-Mo-O phase.     

Mechanism of the hydrodenitrogenation of neopentylamine and adamantylamine on sulfided NiMo/Al2O3

Neopentanethiol, 1-adamantanethiol, and 2-adamantanethiol were primary products and neopentane and adamantane were secondary products in the hydrodenitrogenation of neopentylamine, 1-adamantylamine, and 2-adamantylamine, respectively, over sulfided NiMo/Al₂O₃. Dialkylamines and dialkylimines were formed as primary products in the reactions of 2-adamantylamine and neopentylamine as well. None of the three amines can react by ammonia elimination and a classic S_N2 substitution of the NH₂ group by H₂S is not possible for the adamantylamines either. The formation of di(2-adamantyl)imine and di(neopentyl)imine indicates that dehydrogenation and hydrogenation reactions occur and that imine or iminium-cation intermediates play an important role. NH₂-SH substitution takes place by dehydrogenation of the amine to an imine or iminium cation, which adds H₂S and eliminates NH₃. The secondary character of adamantane and neopentane demonstrates that hydrogenolysis of the aliphatic C–N bond does not take place over sulfided NiMo/Al₂O₃ below 340 °C. Even though 1-adamantylamine can neither react by classic S_N2, E1, and E2 reactions, nor via an imine or iminium cation, it formed 1-adamanethiol at 300 °C. This reaction might take place by an S_N1 reaction or by adsorption of the amine at a surface vacancy, followed by a shift of the adamantyl group to a neighboring sulfur atom.     

CoMo/Al2O3-TiO2催化剂上加氢深度脱硫反应及其宏观动力学

采用气液固三相滴流床反应器,在反应温度(493~558) K,氢压(1.5~3.0) MPa和氢油体积比为200~800条件下,研究了苯并噻吩和二苯并噻吩模型化合物在钴钼基催化剂上加氢脱硫反应及其宏观动力学。根据幂函数型动力学方程,以全局通用算法结合马夸特算法对动力学参数进行估值,建立了与实验数据相吻合的柴油中含硫模型化合物的深度加氢脱硫反应动力学模型。其中,苯并噻吩的一级方程活化能为3.985×104 J·mol^-1,二苯并噻吩的二级方程的活化能为3.130×104 J·mol^-1。残差检验和统计学考察表明,模型计算结果和实验数据吻合良好。     

Effect of supercritical deposition synthesis on dibenzothiophene hydrodesulfurization over NiMo/Al2O3 nanocatalyst

The synthesis of two NiMo/Al₂O₃ catalysts by the supercritical carbon dioxide/methanol deposition (NiMo‐SCF) and the conventional method of wet coimpregnation (NiMo‐IMP) were conducted. The results of the physical and chemical characterization techniques (adsorption–desorption of nitrogen, oxygen chemisorption, XRD, TPR, TEM, and EDAX) for the NiMo‐SCF and NiMo‐IMP demonstrated high and uniform dispersed deposition of Ni and Mo on the Al₂O₃ support for the newly developed catalyst. The hydrodesulfurization (HDS) of fuel model compound, dibenzothiophene, was used in the evaluation of the NiMo‐SCF catalyst vs. the commercial catalyst (NiMo‐COM). Higher conversion for the NiMo‐SCF catalyst was obtained. The kinetic analysis of the reaction data was carried out to calculate the reaction rate constant of the synthesized and commercial catalysts in the temperature rang of 543–603 K. Analysis of the experimental data using Arrhenius' law resulted in the calculation of frequency factor and activation energy of the HDS for the two catalysts. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Effect of restrictive diffusion on hydrodesulfurization of heavy residue oils over CoMo/Al2O3

The effect of the ratio of reactant molecular diameter to catalyst pore diameter (λ) on the restrictive diffusion under hydrodesulfurization (HDS) reactions of heavy residue oils over CoMo/Al₂O₃ catalysts was investigated. A series of Al₂O₃ with various pore structures were used as supports of CoMo sulfide. The HDS reaction was carried out in a semi-batch Carberry type reactor at 648 K and 10.3 MPa. Two empirical correlations for restrictive diffusion under HDS reaction conditions were developed depending on the value of λ. The results showed that the restrictive diffusion effect under HDS reaction conditions is severe for the lower values of λ. However, this effect seems not prominent for higher values of λ. The order of the magnitude of the effective diffusivity was in the range of 10^?6-10^?7 cm²/s for the sulfur-containing compounds of residue oil in CoMo/Al₂O₃ catalysts at 648 K.     

Mechanisms of hydrodesulfurization and hydrodenitrogenation

To study the problems inherent in deep hydrodesulfurization (HDS), the separate and simultaneous HDS of 4,6-dimethyldibenzothiophene and hydrodenitrogenation (HDN) of pyridine were investigated over a Ni-MoS₂/γ-Al₂O₃ and a Pd/γ-Al₂O₃ catalyst. The HDS of 4,6-dimethyldibenzothiophene and its three intermediates, 4,6-dimethyl-tetrahydro-dibenzothiophene, 4,6-dimethyl-hexahydro-dibenzothiophene and 4,6-dimethyl-dodecahydro-dibenzothiophene, demonstrated that, over the Pd catalyst, the (de)hydrogenation reactions were relatively fast compared to the C–S bond breaking reactions, whereas the reverse was true over the metal sulfide catalyst. The methyl groups of 4,6-dimethyldibenzothiophene strongly hinder the direct desulfurization HDS pathway over both catalysts. On the Pd catalyst the hydrogenation pathway is strongly promoted by the methyl groups, so that the total HDS rate does not decrease. Pyridine and piperidine were strong poisons for the hydrogenation pathway and H₂S was a strong poison for the direct desulfurization pathway.HDN of nitrogen-containing aromatic molecules occurs by hydrogenation of the aromatic heterocycle followed by C–N bond breaking. The C–N bond breaks by substitution of the alkylamine by H₂S to form an alkanethiol, followed by the loss of H₂S by elimination or hydrogenolysis. The NH₂-SH substitution does not occur by a classic organic substitution reaction but through a multi-step reaction pathway via an alkylimine. DFT calculations showed that the hydrogenolysis of ethanethiol to ethane and the elimination of ethane are relatively easy reactions.     

Si改性对NiMo/Al2O3催化剂加氢脱硫性能的影响

以中和法合成的不同SiO₂含量的改性氧化铝为载体,本文制备系列Si改性的NiMo/Al₂O₃催化剂,采用X射线衍射（XRD）、N₂物理吸附（BET）、程序升温脱附（NH₃-TPD）、吡啶吸附红外光谱（Py-IR）、程序升温还原（H₂-TPR）、高分辨透射电镜（HRTEM）和X射线光电子能谱（XPS）等分析手段进行详细表征。表征结果显示,引入Si减弱了活性金属与载体之间的相互作用,改善了催化剂的孔结构与表面酸性分布,提高了活性相分散度和金属硫化度,促使形成更多的II类NiMoS活性相。以二苯并噻吩（DBT）为模型化合物,在固定床加氢装置上考察了系列催化剂的加氢脱硫（HDS）性能,结果表明,引入Si可降低DBT的加氢反应活化能,提高反应速率常数,进而提高催化剂的加氢脱硫活性。对比DBT转化率在50%时的脱硫产物分布表明引入Si可影响催化剂的反应路径选择性,直接脱硫路径（DDS）选择性从83.69%增加至92.89%,证实了催化剂的表征规律。     

磷添加方式对NiMo/Al2O3催化剂加氢脱硫性能的影响

采用分步浸渍法制备了不同磷添加方式改性的NiMo/Al₂O₃催化剂,在固定床微反装置上考察了该系列催化剂对焦炉煤气中噻吩加氢脱硫（HDS）性能的影响,采用BET、X射线衍射（XRD）、H₂程序升温还原（H₂-TPR）、NH₃程序升温脱附（NH₃-TPD）、C₄H₄S(H₂)程序升温脱附[C₄H₄S(H₂)-TPD]、X射线光电子能谱（XPS）、高清透射电镜（HRTEM）和拉曼（Raman）等分析手段对催化剂进行表征。结果表明,不同磷添加方式制备NiMo/Al₂O₃催化剂的HDS性能存在较大差异。其中,催化剂PNi-Mo/Al和PMo-Ni/Al表面弱吸附解离活性位增强,对焦炉煤气中噻吩有较好的低温加氢脱硫活性,以含292.5mg/m³噻吩的模拟焦炉煤气为原料时,PNi-Mo/Al在250℃下对噻吩的脱硫率达61%。对于PNi-Mo/Al和PMo-Ni/Al催化剂,先浸渍P、Ni或者P、Mo时,P优先和载体Al₂O₃作用,减弱了活性金属组分Ni、Mo与载体间的相互作用,而又防止Ni或者Mo与载体间相互作用过低而聚集,提高了Ni、Mo在载体表面的均匀分散,生成能够促进硫化形成Ⅱ型活性相Ni-Mo-S的NiMoO₄物种。NiMoO₄和MoO₃之间的协同作用提高了催化剂的硫化度,使HDS活性得以提高。     

Mechanism of carbon-nitrogen bond cleavage during amylamine hydrodenitrogenation over a sulphided NiMo/Al2O3 catalyst

By comparison of the hydrodenitrogenation rate of amylamine with those of neopentylamine and tert-amylamine over a conventional catalyst, it was evidenced that the hydrogen atoms of the carbon in the position with respect to the nitrogen atom participate in the C-N bond cleavage. A detailed mechanism including the interaction with the catalyst is proposed for this reaction.     

Highly active Mo/Al2O3 hydrodesulfurization catalyst presulfided with ammonium thiosulfate

Ammonium thiosulfate ((NH₄)₂S₂O₃) was used as an ex situ sulfiding agent to pretreat Mo/Al₂O₃ catalyst through impregnation. After H₂ activation, Mo/Al₂O₃ presulfided with (NH₄)₂S₂O₃ exhibits much higher catalytic activity in thiophene hydrodesulfurization (HDS) than Mo/Al₂O₃ in situ sulfided by dimethyl disulfide. Through (NH₄)₂S₂O₃ presulfidation, Al₂O₃ support is modified by sulfate groups, leading to a decrease of interaction between Mo and support; this promotes the formation of multi-layer type II MoS₂ that contributes to the high HDS activity of the ex situ presulfided Mo/Al₂O₃ catalyst.     

MgO-supported Mo, CoMo and NiMo sulfide hydrotreating catalysts

The most common preparation of high surface area MgO (100–500 m² g⁻¹) is calcination of Mg(OH)₂ obtained either by precipitation or MgO hydration or sol–gel method. Preparation of MoO₃/MgO catalyst is complicated by the high reactivity of MgO to H₂O and MoO₃. During conventional aqueous impregnation, MgO is transformed to Mg(OH)₂, and well soluble MgMoO₄ is easily formed. Alternative methods, that do not impair the starting MgO so strongly, are non-aqueous slurry impregnation and thermal spreading of MoO₃. Mo species of MoO₃/MgO catalyst are dissolved as MgMoO₄ during deposition of Co(Ni) by conventional aqueous impregnation. This can be avoided by using non-aqueous impregnation. Co(Ni)Mo/MgO catalysts must be calcined only at low temperature because Co(Ni)O and MgO easily form a solid solution. Literature data on hydrodesulfurization (HDS) activity of MgO-supported catalysts are often contradictory and do not reproduced well. However, some results suggest that very highly active HDS sites can be obtained using this support. Co(Ni)Mo/MgO catalysts prepared by non-aqueous impregnation and calcined at low temperature exhibited strong synergism in HDS activity. Co(Ni)Mo/MgO catalysts are much less deactivated by coking than their Al₂O₃-supported counterparts. Hydrodenitrogenation (HDN) activity of Mo/MgO catalyst is similar to the activity of Mo/Al₂O₃. However, the promotion effect of Co(Ni) in HDN on Co(Ni)Mo/MgO is lower than that on Co(Ni)Mo/Al₂O₃.     

Inhibition and deactivation in staged hydrodenitrogenation and hydrodesulfurization of medium cycle oil over NiMoS/Al2O3 catalyst

Hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) of a commercial medium cycle oil (MCO) were performed over a commercial NiMoS/Al₂O₃ catalyst through both single- and two-stage hydrotreatments at 340°C. The reaction atmosphere was replaced with fresh hydrogen, with or without additional dose of catalyst, for the second-stage treatment to determine the mechanism of reduced activity. Sulfur and nitrogen molecular species in MCO were identified by gas chromatography with an atomic emission detector (GC-AED) to quantify their respective reactivities and susceptibilities to inhibition. Under single-stage (30 min) conditions, the reactivity orders in HDS and HDN were BT>DBT>4-MDBT>4,6-DMDBT and In>alkylIn>Cz>1-Cz>1,8-Cz, respectively. Additional reaction time beyond the initial 30 min, without atmosphere or catalyst replacement, gave little additional conversion. Replacement of the first-stage gas with fresh hydrogen strongly improved second-stage conversions, particularly those of the more refractory species. An additional dose of catalyst for the second stage with hydrogen renewal facilitated additional HDS of dibenzothiophene (DBT), 4-monomethylated DBT (4-MDBT), and 4,6-dimethylated DBT (4,6-DMDBT) which was independent of their initial reactivity, while HDN of carbazole (Cz), 1-Cz, and 1,8-Cz was improved, the least reactive species being most denitrogenated. Such results suggest the strong inhibition of the gaseous products H₂S and NH₃. The catalyst deactivation was most marked with HDN of 1,8-Cz, suggesting that acidity is essential to the reaction. H₂S is suspected to inhibit both S elimination and hydrogenation of S and N species at the level of concentration obtained during desulfurization. The inhibition by remaining substrates may still influence the HDS and HDN of refractory species in the second stage, even if their contents were reduced by the first stage. It appears very important to clarify the inhibition factor of all species on the refractory sulfur species, and to determine the inhibition susceptibility of these species at their lowered concentration to enable the effective achievement of 50 ppm sulfur level in distillate products. The conversions of inhibitors must be accounted for during reactions. Catalyst and reaction configuration to reduce the inhibition by the gaseous products are the keys for deep refining.     

胜利煤液化中油在NiMo/Al_2O_3、NiMo/MCM-48和NiMo/Betonite上加氢性能研究

在400℃、5MPa H2下对实验室获得的胜利煤液化中油在硫化的NiMo/Al_2O_3、NiMo/MCM-48和NiMo/Betonite催化剂上的脱硫和脱氮性能进行研究.结果表明胜利煤液化中油在不同催化剂上脱硫和脱氮性能差异显著,所有催化剂的脱氮性能均远大于脱硫性能,催化剂的载体性质对脱硫和脱氮活性有显著影响且影响规律不同;脱氧性能NiMo/Betonite＞NiMo/Al_2O_3＞NiMo/MCM-48;降芳烃能力NiMo/Al_2O_3＞NiMo/MCM-48＞NiMo/Betonite.     

Modulating the active phase structure of NiMo/Al2O3 by La modification for ultra-deep hydrodesulfurization of diesel

Herein, a series of mesoporous NiMo/LaAlO_x with various La contents were constructed through a solvent evaporation-induced self-assembly protocol, and their catalytic activities were investigated for hydrodesulfurization (HDS) of 4,6-DMDBT. It has been confirmed that the incorporation of La influences the electronic structure and morphology of NiMoS active phase. The lower amount of La (x ≤ 1.0 wt.%) could facilitate the formation of “Type II” NiMoS phase by weakening the interaction of Mo-O-Al leakage and promoting the sulfidation of both Mo and Ni species as well as increasing the ratio of “Type II” NiMoS phase, thereafter boosting the HDS performances. Further increasing La incorporation, however, leads to the generation of inactive NiS_x phase and decrease of NiMoS active phase proportion, the HDS activities of corresponding catalysts were suppressed. NiMo/LaAlO_x-1.0 exhibits the highest activity for 4,6-DMDBT HDS because of its moderate metal-support interaction, optimal morphology and the largest proportion of “Type II” NiMoS active phase.     

Iminium cations as intermediates in the hydrodenitrogenation of alkylamines over sulfided NiMo/γ-Al2O3

The mechanism of the hydrodenitrogenation of the mixed dialkyl- and trialkylamines C₁NHC₆ and C₁N(C₆)₂ was studied over sulfided NiMo/γ-Al₂O₃ at 280 °C and 3 MPa. C₁NHC₆ reacted by disproportionation to C₁N(C₆)₂ as well as C₆N(C₁)₂ and by substitution by H₂S to methylamine and hexanethiol as well as hexylamine and methanethiol. C₁N(C₆)₂ reacted by substitution with H₂S to C₁NHC₆ and C₆NHC₆ and methane- and hexanethiol. The probability of breaking the C₁N bond was only slightly smaller than of breaking the C₆N bond in C₁N(C₆)₂. In the reaction of an equimolar mixture of C₅NHC₅ and C₁N(C₆)₂ both C₁N(C₅)₂ and C₆N(C₅)₂ were formed. The transfer of the methyl group in these reactions cannot be explained by imine and enamine intermediates, only iminium cation intermediates can explain all the products in the hydrodenitrogenation of monoalkyl-, dialkyl- and trialkylamines.     

CoMo/Al_2O_3-SiO_2催化剂原位红外光谱研究

采用原位红外光谱技术,以CO作为探针分子研究了加氢脱硫CoMo/Al2O3-SiO2催化剂的活性吸附位的变化规律。原位硫化温度范围为300~550℃,获得了CoMo/Al2O3-SiO2催化剂的MoS(2110cm2-1)和CoMoS(2070cm-1)活性相在增加硫化温度过程中的转变规律。在CoMo/Al2O3-SiO2催化剂中,当载体中SiO2含量逐渐增加时,能够显著改变催化剂活性相的相对强度变化,表明载体中加入适量的SiO2能够显著改变加氢脱硫CoMo/Al2O3-SiO2催化剂的载体与活性金属(Co和Mo)的相互作用,从而提高金属在加氢催化剂载体上的分散性能,产生更多活性吸附位。     

CoMo/Al2O3催化木质素加氢液化工艺的研究

对木质素催化加氢液化进行了研究。实验表明,液化的最佳工艺条件为:反应温度240℃,氢压1 MPa,溶剂原料比100∶30(mL∶g),反应时间60 min。用气相-质谱联用仪对液化产物进行了分析。     

Preparation of alumina catalyst supports and NiMo/Al2O3 catalysts

Several alumina catalysts were prepared to investigate effects of catalyst preparation variables on pore structure, including sintering time and temperature, acid type, and fiber type and loading. Each catalyst was characterized with a porosimeter and sorptometer in terms of pore size distribution, average pore diameters, pore volumes, densities and surface area. Bimodal NiMo catalysts were effectively prepared without losing surface area by using a combined method of coextrusion and fiber incorporation.     

助剂B对含硅NiMo/Al2O3加氢处理催化剂性能的影响

考察了助剂B对含硅NiMo/Al₂O₃催化剂孔结构及表面酸性的影响，制备出一种孔容和比表面积大、孔分布集中、金属分布均匀和酸性适宜的加氢精制催化剂。分析结果表明，B的加入可以改善含硅氧化铝载体及催化剂的孔结构及表面酸性，有利于C—N键的断裂，从而提高催化剂的加氢脱氮性能。活性评价结果表明，采用适量B助剂改性的加氢处理催化剂具有高的加氢脱氮活性和稳定性。