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.     

Characterization of the active phase of NiMo/Al2O3 hydrodesulfurization catalysts

The active phase of the NiMo/Al₂O₃ catalyst for hydrodesulfurization reactions has been investigated in this work. Special attention has been focused on the effect of the order of metal impregnation on the formation of the active phase in the reaction. The Mo and Ni oxides and their sulfides on the alumina were investigated by XPS and DRS analyses. The Ni-Mo oxides or precursor of the active phase which are chemically bonded between Mo and Ni were also confirmed from the binding energy shifts of the XPS peaks. The amount of Ni-Mo oxides was determined after the formation of metal oxides during calcination. The Ni-Mo sulfide (active phase) was then induced through sulfidation. It was important that Mo should be located at the tetrahedral sites on the alumina with a high Mo dispersion. These results indicated that there are two important factors in preparing highly efficient Ni-Mo catalysts; one is that Mo should be located at the tetrahedral coordination on Al₂O₃ in high dispersion (Mo/Al₂O₃) and the other is that the Ni species should be supported on MoAl₂O₄ to form Ni-Mo oxides which change into the Ni-Mo sulfide active sites by sulfidation.     

Hydrodeoxygenation of Anisole over Ni/α-Al2O3 Catalyst

Ni-based catalysts supported on di erent supports (α-Al₂O₃,γ-Al₂O₃, SiO2, TiO₂, and ZrO₂) were prepared by impregnation. Effects of supports on catalytic performance were tested using hydrodeoxygenation reaction (HDO) of anisole as model reaction. Ni/α-Al₂O₃ was found to be the highest active catalyst for HDO of anisole. Under the optimal conditions, the anisole conversion is 93.25% and the hydrocarbon yield is 90.47%. Catalyst characteriza-tion using H₂-TPD method demonstrates that Ni/α-Al₂O₃ catalyst possesses more amount of active metal Ni than those of other investigated catalysts, which can enhance the cat-alytic activity for hydrogenation. Furthermore, it is found that the Ni/α-Al₂O₃ catalyst has excellent repeatability, and the carbon deposited on the surface of catalyst is negligible.     

Ni/HZSM-5的结构及催化木糖醇水相加氢合成液体烷烃的性能研究

采用浸渍法制备了Ni/HZSM-5双功能催化剂,采用BET、XRD、NH3-TPD、H2-TPR、FTIR和TG等方法表征了催化剂比表面、孔结构、酸性、还原能力及骨架结构等信息,研究了其催化木糖醇水相加氢合成液体烷烃的性能及催化剂失活的原因。结果表明,在优化的金属中心/酸中心的协同作用下,木糖醇可通过水相加氢高选择性地合成C5-C6烷烃;过高的金属中心或酸中心均会导致C-C键断裂形成轻质烷烃,以2%Ni/HZSM-5催化剂上木糖醇水相加氢活性最高,木糖醇C转化率为94%液体烷烃总收率可达90%,这与其具有较大的比表面积、合适的孔径分布、较多的金属活性中心、适中的酸量和强酸量有关。催化剂6次重复使用后活性明显降低,其骨架部分脱铝和表面积碳是其失活的主要原因。     

In Situ Radioisotopic Study of the Active Sites of Sulfide CoMo Catalysts and the Mechanism of Thiophene Hydrodesulfurization

The mechanism of thiophene hydrodesulfurization over sulfide catalysts for hydrotreating and the effect of the catalyst composition and feed on the number, distribution, and performance of active sites were studied using ³⁵S and ³H isotopes. Based on the results of radioisotopic study, a method for systematic testing–monitoring of sulfide Co(Ni)Mo catalysts for hydrotreating is developed. The method involves the evaluation of the fraction of the active phase surface occupied by SH groups and the ratio between the concentrations of the surface SH groups and coordinatively unsaturated sites including functioning vacancies. General conditions for the formation and functioning of active sites are formulated on the basis of the monitoring data. Criteria for evaluation of the catalyst performance under conditions of hydrodesulfurization of various kinds of crude are proposed. The results of the pilot tests of commercial catalysts suggest that the criteria proposed are suitable.     

Hydrogenolysis of dimethyl disulfide in the presence of bimetallic sulfide catalysts

The hydrogenolysis of dimethyl disulfide in the presence of Ni,Mo and Co,Mo bimetallic sulfide catalysts was studied at atmospheric pressure and T = 160–400°C. At T ≤ 200°C, dimethyl disulfide undergoes hydrogenolysis at the S-S bond, yielding methanethiol in 95–100% yield. The selectivity of the reaction decreases with increasing residence time and temperature due to methanethiol undergoing condensation to dimethyl disulfide and hydrogenolysis at the C-S bond to yield methane and hydrogen sulfide. The specific activity of the Co,Mo/Al₂O₃ catalyst in hydrogenolysis at the S-S and C-S bonds is equal to or lower than the total activity of the monometallic catalysts. The Ni,Mo/Al₂O₃ catalyst is twice as active as the Ni/Al₂O₃ + Mo/Al₂O₃ or the cobalt-molybdenum bimetallic catalyst.     

In Situ Confined Growth Based on a Self‐Templating Reduction Strategy of Highly Dispersed Ni Nanoparticles in Hierarchical Yolk–Shell Fe@SiO2 Structures as Efficient Catalysts

Ni‐based magnetic catalysts exhibit moderate activity, low cost, and magnetic reusability in hydrogenation reactions. However, Ni nanoparticles anchored on magnetic supports commonly suffer from undesirable agglomeration during catalytic reactions due to the relatively weak affinity of the magnetic support for the Ni nanoparticles. A hierarchical yolk–shell Fe@SiO₂/Ni catalyst, with an inner movable Fe core and an ultrathin SiO₂/Ni shell composed of nanosheets, was synthesized in a self‐templating reduction strategy with a hierarchical yolk–shell Fe₃O₄@nickel silicate nanocomposite as the precursor. The spatial confinement of highly dispersed Ni nanoparticles with a mean size of 4 nm within ultrathin SiO₂ nanosheets with a thickness of 2.6 nm not only prevented their agglomeration during catalytic transformations but also exposed the abundant active Ni sites to reactants. Moreover, the large inner cavities and interlayer spaces between the assembled ultrathin SiO₂/Ni nanosheets provided suitable mesoporous channels for diffusion of the reactants towards the active sites. As expected, the Fe@SiO₂/Ni catalyst displayed high activity, high stability, and magnetic recoverability for the reduction of nitroaromatic compounds. In particular, the Ni‐based catalyst in the conversion of 4‐nitroamine maintained a rate of over 98 % and preserved the initial yolk–shell structure without any obvious aggregation of Ni nanoparticles after ten catalytic cycles, which confirmed the high structural stability of the Ni‐based catalyst.     

Rational Design and Controlled Synthesis of V-Doped Ni3S2/NixPy Heterostructured Nanosheets for the Hydrogen Evolution Reaction

Rational construction of high-efficiency and low-cost catalysts is one of the most promising ways to produce hydrogen but remains a huge challenge. Herein, interface engineering and heteroatom doping were used to synthesize V-doped sulfide/phosphide heterostructures on nickel foam (V-Ni₃S₂/Ni_xP_y/NF) by phosphating treatment at low temperature. The incorporation of V can adjust the electronic structure of Ni₃S₂, expose more active sites, and protect the 3D structure of Ni foam from damage. Meanwhile, the heterogeneous interface formed between Ni₃S₂ and Ni_xP_y can provide abundant active sites and accelerate electron transfer. As a result, the V-Ni₃S₂/Ni_xP_y/NF nanosheet catalyst exhibits outstanding activity in the hydrogen evolution reaction (HER) with an extremely low overpotential of 90 mV at a current density of 10 mA cm⁻² and stable durability in alkaline solution, which exceeds those most of the previously reported Ni-based materials. This work shows that rational design by interfacial engineering and metal-atom incorporation has a significant influence for efficient hydrogen evolution.     

Selective hydrogenation of 1,3-pentadiene over mono- and bimetallic sulfidized Ni(Cu)—S/SiO<Subscript>2</Subscript> catalysts

The activity and selectivity of the Ni/SiO₂ catalyst, as well as the mono- and bimetallic Ni(Cu)—S/SiO₂ systems were investigated in the selective hydrogenation of 1,3-pentadiene to pentenes. The presulfiding of the catalysts in a hydrogen sulfide flow substantially increases the selectivity to olefins in gas mixtures with a range of H₂/diene molar ratio of 2.5–10. The samples activated in hydrogen at elevated temperatures turned out to be more active. The effect of modification of the nickel—sulfide catalysts with copper, resulting in an increase in the activity and selectivity to olefins, was found. The weight ratio Ni/Cu = 4 was shown to be optimum for achieving the maximum conversion and selectivity on the surface.     

Modern concepts on catalysis of hydroprocessing and synthesis of alcohols from syngas by transition metal sulfides

A concept on the dynamic nature of active centers (AC) of the catalysts based on transition metal sulfides is described. The concept formed the basis of a “dynamic” model, according to which AC formed and functioning under the reaction conditions can oscillate between layers of promoted molybdenum sulfide. The model assumes the existence of “rapid” and “slow” AC and the possibility of their intertransformation due to the reversible migration of sulfur and promoter between the crystallite layers in a hydrogen atmosphere. The frequency of these migrations (oscillations) determines the catalyst activity. An assumption is substantiated that the hydrogenation sites are localized at the rims of Co(Ni)MoS₂ crystallites and desulfurization (hydrodesulfurization) sites are localized on the edges. The proposed model makes it possible to develop criteria for the evaluation of the efficiency of catalytic performance for hydrodesulfurization of hydrocarbon raw materials of various types and for synthesis of higher alcohols from syngas.     

Dry Reforming of Methane on a Highly‐Active Ni‐CeO2 Catalyst: Effects of Metal‐Support Interactions on C−H Bond Breaking

Ni‐CeO₂ is a highly efficient, stable and non‐expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO₂ at temperatures as low as 300 K, generating CH_x and CO_x species on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density‐functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO_2?x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CH_x or C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way.     

Dehydrogenation of isopropanol on a cerium-nickel catalyst

The effect of a cerium additive on the catalytic activity of a 2 wt % Ni/SiO₂ catalyst is studied. It found that under both flow and static conditions the activity of (2 wt % Ni + 0.2 wt % Ce)/SiO₂ catalyst is higher than that of the original sample; the increase in activity results from a sharp increase in the number of active sites. A change in the composition of the surface layer of the catalysts is analyzed by X-ray photoelectron spectroscopy. It was found that the fraction of nickel decreases and the fraction of carbon increases in cerium-containing catalyst. An explanation of the change in the elemental composition of the catalytic active sites of a nickel catalyst in the presence of cerium is proposed on the basis of XPS data and previous quantum chemical calculations.     

助剂对Ni-Al合金和Raney-Ni催化剂结构及1,4-丁烯二醇加氢性能的影响

采用等体积浸渍法将助剂(MgO、CuO、Co2O3)引入商品Ni-Al合金粉,经10%(w/w)NaOH溶液浸取制备Raney-Ni催化剂。通过能量色散X射线(EDX)、X射线衍射(XRD)、N2吸附-脱附测试、透射电镜(TEM)、NH3程序升温脱附(NH3-TPD)、X射线光电子能谱(XPS)等方法表征和评价实验,考察了金属助剂对Ni-Al合金粉及Raney-Ni催化剂元素组成、晶相结构、孔结构特征、表面形貌、表面酸碱性的影响。表征分析显示,不同助剂催化剂的元素含量、比表面积及表面形貌均表现出明显的差异。其中,添加助剂Cu的催化剂表面检测到较多的活性组分Ni,接近90%(w/w),该催化剂平均孔径最小(3.87 nm)、活性组分Ni颗粒分散性好。评价结果表明,该催化剂具有较佳的加氢性能,其1,4-丁烯二醇(BED)转化率为100%,1,4-丁二醇(BDO)选择性和收率分别为59.62%和59.62%,这与该催化剂较大的活性组分Ni负载量、酸强度和适中的酸量及存在的Cu对Ni分散性的提高进一步防止了Ni的严重烧结(即"限域效应")等有较大关联。     

HDM of the vanadyl octaethylporphyrin on MoS2-based catalysts: Nature and repartition of the vanadium deposit

Electron microprobe analyses are used for characterizing the repartition of vanadium deposited during the hydrodemetallation of vanadyl octaethyl porphyrin on a classical Ni–MoS₂--Al₂O₃ catalyst. It is found that a part of vanadium can displace Ni initially interacting with the MoS₂ platelets (Ni MoS phase) and another part is forming a crown as vanadium sulfide around the catalyst particle. The displaced nickel also formed large nickel sulfide crystallites.     

Impact of the Oxygen Defects and the Hydrogen Concentration on the Surface of Tetragonal and Monoclinic ZrO2 on the Reduction Rates of Stearic Acid on Ni/ZrO2

The role of the specific physicochemical properties of ZrO₂ phases on Ni/ZrO₂ has been explored with respect to the reduction of stearic acid. Conversion on pure m‐ZrO₂ is 1.3 times more active than on t‐ZrO₂, whereas Ni/m‐ZrO₂ is three times more active than Ni/t‐ZrO₂. Although the hydrodeoxygenation of stearic acid can be catalyzed solely by Ni, the synergistic interaction between Ni and the ZrO₂ support causes the variations in the reaction rates. Adsorption of the carboxylic acid group on an oxygen vacancy of ZrO₂ and the abstraction of the α‐hydrogen atom with the elimination of the oxygen atom to produce a ketene is the key to enhance the overall rate. The hydrogenated intermediate 1‐octadecanol is in turn decarbonylated to heptadecane with identical rates on all catalysts. Decarbonylation of 1‐octadecanol is concluded to be limited by the competitive adsorption of reactants and intermediate. The substantially higher adsorption of propionic acid demonstrated by IR spectroscopy and the higher reactivity to O₂ exchange reactions with the more active catalyst indicate that the higher concentration of active oxygen defects on m‐ZrO₂ compared to t‐ZrO₂ causes the higher activity of Ni/m‐ZrO₂.     

Efficient Hydrogen Oxidation Catalyzed by Strain‐Engineered Nickel Nanoparticles

The hydroxide‐exchange membrane fuel cell (HEMFC) is a promising energy conversion device. However, the development of HEMFC is hampered by the lack of platinum‐group‐metal‐free (PGM‐free) electrocatalysts for the hydrogen oxidation reaction (HOR). Now, a Ni catalyst is reported that exhibits the highest mass activity in HOR for a PGM‐free catalyst as well as excellent activity in the hydrogen evolution reaction (HER). This catalyst, Ni‐H₂‐2 %, was optimized through pyrolysis of a Ni‐containing metal‐organic framework precursor under a mixed N₂/H₂ atmosphere, which yielded carbon‐supported Ni nanoparticles with different levels of strains. The Ni‐H₂‐2 % catalyst has an optimal level of strain, which leads to an optimal hydrogen binding energy and a high number of active sites.     

Effect of the calcination temperature on the properties of Fe2O3/SiO2 catalysts for oxidation of hydrogen sulfide

The effect of the calcination temperature on the properties of supported iron oxide catalysts for hydrogen sulfide oxidation prepared by impregnation of silica with iron(III) nitrate has been studied. An increase in the calcination temperature was found to diminish the catalytic activity of the Fe₂O₃/SiO₂ catalysts in hydrogen sulfide oxidation. This behavior can be explained by the agglomeration of iron oxide particles and by a decrease in the surface concentration of active sites. It has been shown that an increase in the calcination temperature makes the catalyst more stable towards the sulfidation of the active component (Fe₂O₃) to the iron disulfide phase.     

焙烧温度对Ni/CaO-Al2O3结构及其催化重整性能的影响

采用共沉淀法制备了一系列具有类水滑石结构前驱体的Ni/CaO-Al₂O₃复合催化剂，考察了制备过程中焙烧温度对复合催化剂结构及性能的影响。结果表明，焙烧温度可调控活性组分Ni与载体之间的相互作用力，进而调变复合催化剂的比表面积、活性组分Ni的颗粒粒径。当焙烧温度为700 ℃时，Ni与载体之间相互作用力适宜，复合催化剂具有最大的比表面积（21.42 m²/g）和最小的Ni颗粒粒径（19.51 nm）；该复合催化剂在CO₂吸附强化CH₄/H₂O重整制氢过程中可得到98.31%的H₂浓度和94.87%的CH₄转化率，循环10次后，H₂浓度仍能保持在97.35%以上。这是因为大的比表面积为反应提供了更多的活性位点，利于CO₂吸附过程的强化，而小的Ni颗粒粒径提高了复合催化剂的抗烧结能力。