Low-temperature synthesis of supported hydrodesulfurization catalysts based on chevrel phases

A new method has been developed for the synthesis of finely dispersed, highly active, supported hydrodesulfurization catalysts based on Chevrel phases. It is hypothesized that the modification of MoS₂ with cobalt or nickel, which enhances the catalytic activity, and the same modification of Chevrel-type systems are of the same nature. The modifiers act through electron density donation into the conduction band of the active component. The increase in catalytic activity is due to the decrease of the effective charge of the molybdenum ion. The catalysts undergo partial restructuring during the reaction.     

Cobalt salts of decamolybdodicobaltic acid as precursors of the highly reactive type II CoMoS phase in hydrorefining catalysts

Catalysts have been synthesized using the Anderson polyoxometalates (POMs) (NH₄)₄[Ni(OH)₆Mo₆O₁₈] (NiMo₆POM), (NH₄)₆[Co₂Mo₁₀O₃₈H₄] · 7H₂O (Co₂Mo₁₀POM), and H₆[Co₂Mo₁₀O₃₈H₄] (Co₂Mo₁₀HPA) as the precursors and hydrogen peroxide as the solvent. The catalysts have been characterized by low-temperature nitrogen adsorption, XPS, and HRTEM. Their catalytic properties have been tested in thiophene hydrodesulfurization and in the hydrodesulfurization and hydrogenation of components of diesel oil. The active phase of the catalysts synthesized using the POMs is the type II CoMoS phase in which the mean plate length is 3.6–3.9 nm and the mean number of MoS₂ plate per plate packet is 1.8–2.0. Use of hydrogen peroxide provides an efficient means to reduce the proportion of Co²⁺ promoter atoms surrounded by oxygen in the case of an impregnating solution containing both an ammonium salt of a heteropoly acid and a Co²⁺ salt. In the catalysts synthesized using cobalt salts of Co₂Mo₁₀HPA, the support surface contains the multilayer type II CoMoS phase and cobalt sulfides. These catalyst show high catalytic properties in thiophene hydrogenolysis and diesel oil hydrorefining. Models are suggested for the catalysts synthesized using Anderson POMs.     

Hydrodesulfurization catalysts P-Mo-W/γ-Al2O3: Characterization and catalytic activity

P-Mo-W/γ-Al₂O₃ catalysts with various Mo and W contents have been synthesized. The parameters of the porous structure of their sulfide and oxide forms have been determined. The geometric parameters of the active phase of the sulfide catalysts have been calculated using high-resolution transmission electron microscopy data. The catalytic activity has been estimated in dibenzothiophene (DBT) hydrodesulfurization (HDS). The reaction under the conditions examined proceeds mainly as direct hydrodesulfurization. The catalytic activity has been correlated with the Mo/W molar ratio and with the proportions of edge and corner sites.     

Study structure of first and second row transition metal sulfides using SCF-SW-Xα cluster calculations

Energy levels and charge distributions for MS_{$\text{6}\text{?}$^?} clusters M = TiNi and ZrPd) have been calculated using the SCF-SW-Xα method. Calculated binding energies for the clusters are compared with corresponding features in the XPS spectra of the metal sulfides. Trends in the energy levels and charge distributions indicate that the bonding in the second row transition metal sulfides is more covalent than in the first row sulfides. This results largely from the increased metal-sulfur d-pπ interactions which occur for the second row transition metals. Trends in the bonding in the metal sulfides are discussed in light of the activity of these materials as hydrodesulfurization catalysts.     

Influence of the composition and morphology of nanosized transition metal sulfides prepared using the Anderson-type heteropoly compounds [X(OH)6Mo6O18]n? (X = Co, Ni, Mn, Zn) and [Co2Mo10O38H4]6? on their catalytic properties

Using the Anderson-type heteropoly compounds (HPCs) [X(OH)₆Mo₆O₁₈] _n− (X = Co, Ni, Mn, Zn) and [Co₂Mo₁₀O₃₈H₄]₆₋ and cobalt (or nickel) nitrate, XMo/Al₂O₃ and Co(Ni)-XMo/Al₂O₃ catalysts were prepared. The catalysts were studied by low-temperature nitrogen adsorption, X-ray diffraction, and high-resolution transmission electron microscopy. The average length of the active-phase particles of the catalysts was 3.5 to 3.9 nm, and the average number of MoS₂ layers in a packet was 1.4 to 2.1. The catalytic properties of the samples, which were estimated in dibenzothiophene (DBT) hydrodesulfurization and in the hydrotreating of the diesel fraction, are considerably dependent upon both the type and composition of the HPC, and the nature of the applied promoter (Ni or Co). As compared to the Ni-promoted catalysts, the Co-promoted samples exhibit a higher desulfurization activity, whereas the hydrogenation ability of the Ni-XMo/Al₂O₃ catalysts surpasses that of the Co-XMo/Al₂O₃ ones. The catalytic properties depend on the morphology of the nanostructured active phase. With a growing number of MoS₂ layers in the packet of the catalysts’ active phase, the DBT hydrodesulfurization rate constants for both the direct desulfurization route and the preliminary hydrogenation rote rise linearly and the selectivity falls linearly for the hydrogenation route. The selectivity of Ni-XMo/Al₂O₃ decreases to a greater extent than that of Co-XMo/Al₂O₃. The dependences of the catalytic properties on the morphology of the catalysts’ active phase are consistent with the “dynamic” model of the functioning of the active sites of transition metal sulfides.     

Tungsten/Alumina Catalysts: Effect of H3PW12O40 Countercation on Surface Properties and Hydrodesulfurization Activity

H₃PW₁₂O₄₀ heteropoly acid (HPW₁₂) and its Co, Fe, Ni salts supported on alumina have been used to model hydrodesulfurization catalysts of different activity. All catalysts revealed a promoting effect of the countercation in thiophene hydrodesulfurization, that of the nickel cation being the highest. The catalysts were characterized by measurements of surface area, HDS activity, TPR, FTIR, and DR spectra. IR spectra confirmed an effect of the countercation on the phase composition of the supported heteropoly compounds. 12-Tungstoaluminate heteropoly anions and coordinately unsaturated anions of HPW₁₂ were detected in the IR spectra of the catalysts. The hydrotreating activity of the catalysts was proportional to the amount of hydrogen consumed in the range 20–500°C during TPR.     

Hollow Chevrel‐Phase NiMo3S4 for Hydrogen Evolution in Alkaline Electrolytes

Electrochemical water splitting to generate molecular hydrogen requires catalysts that are cheap, active, and stable, particularly for alkaline electrolyzers, where the cathodic hydrogen evolution reaction is slower in base than in acid even on platinum. Herein, we describe the synthesis of new hollow Chevrel‐phase NiMo₃S₄ and its alkaline hydrogen evolution reaction (HER) performance: onset potential of ?59 mV, Tafel slope of 98 mV per decade, and exchange current density of 3.9×10^?2 mA cm^?2. This Chevrel‐phase chalcogenide also demonstrates outstanding long‐term stability under harsh HER cycling conditions. Chevrel‐phase nanomaterials show promise as efficient, low‐cost catalysts for alkaline electrolyzers.     

过渡金属硫化物催化剂催化加氢作用机理

负载型过渡金属(Co、Mo、Ni、W)硫化物催化剂广泛应用于石油炼制催化加氢过程。为了开发高性能的加氢催化剂,过渡金属硫化物催化剂催化活性相的结构与加氢脱硫性能的关系一直以来是催化研究的热点之一。本文从过渡金属硫化物催化剂的活性相结构和反应物在催化剂表面活性位上的吸附-催化反应机理两个方面阐述了过渡金属硫化物催化剂的催化作用研究进展,并对过渡金属硫化物催化剂催化机理研究存在的争议和未来的研究方向进行了分析。     

Elucidation of hydrodesulfurization mechanism on molybdenum‐based catalysts using 35S radioisotope pulse tracer methods

Elucidation of the hydrodesulfurization (HDS) mechanism on molybdenum‐based catalysts using radioisotope tracer methods and reaction kinetics is reviewed. Firstly, to investigate the sulfidation state in Mo/Al₂O₃ and Co–Mo/Al₂O₃ catalysts, presulfiding of these catalysts has been performed using a ³⁵S pulse tracer method. Secondly, HDS of radioactive ³⁵S‐labeled dibenzothiophene was carried out over a series of sulfided molybdena–alumina catalysts and cobalt‐promoted molybdena–alumina catalysts in a pressurized flow reactor to estimate the behavior of sulfur on the working catalysts. Finally, sulfur exchange of a ³⁵S‐labeled catalyst with hydrogen sulfide was performed to estimate the relationship between the amount of labile sulfur and catalytically active sites.     

Influence of the heat treatment conditions on the activity of the CoMo/Al2O3 catalyst for deep hydrodesulfurization of diesel fractions

The effect of the heat treatment temperature on the sulfidation and activity of CoMo/Al₂O₃ catalysts designed for deep hydrodesulfurization of diesel fuel was studied. The catalysts were prepared using citric acid as a chelating ligand. The organic ligands present in the samples heat-treated at 110 and 220°C retard the decomposition of dimethyl disulfide and the formation of the sulfide phase but make the catalyst more active than the samples calcined at higher temperatures.     

Unsupported Molybdenum and Cobalt-Molybdenum Nitrides for Thiophene Hydrodesulfurization

The catalytic activity and the structure of unsupported Mo and CoMo nitrided catalysts were investigated. It was found that the structure and catalytic activity of the nitrided catalysts are influenced by the conditions of nitridation. Molybdenum oxynitrides are more active in hydrodesulfurization (HDS) of thiophene than MoS₂. The addition of cobalt to nitrided Mo improves its HDS activity, however, sulfided CoMo catalyst is still more active than the nitrided one. Synergy between Co and Mo for the nitrided unsupported CoMo catalyst exists at lower degree than for the sulfided form of CoMo.     

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.     

Deep Oxidation of Methane over Nano-Sized Ferrites with Spinel Structures

Ferrites with spinel structures as catalysts for the deep oxidation of methane have been studied by X-ray phase analysis and temperature programmed reduction. The most active catalysts are the nano-sized ferrites of cobalt and nickel, prepared by the decomposition of polynuclear complexes, with Al₂O₃ as carrier and with addition of a surface active agent to increase the thermal stability of the catalysts. At low temperatures (up to 450 °C), the effect of the size factor appears with the increase in specific catalytic activity of cobalt and nickel ferrites with decreasing of their particles. A correlation of the catalytic activity with the quantity and mobility (reactivity) of oxygen in the ferrites has been established.     

Structure and Thiophene Hydrodesulfurization Activity of MoS2/Al2O3 Catalysts

It was found that, in MoS₂/Al₂O₃ catalysts prepared by exfoliation, the structure of MoS₂ is strongly distorted. The catalytic activities of these catalysts and traditionally prepared catalysts toward the hydrodesulfurization of thiophene were compared. It was established that the stacking dimension of MoS₂ in the catalysts prepared by exfoliation was 200 Å, whereas it was 20 Å in a standard catalyst. It was demonstrated that, although the number of molybdenum atoms in the edge plane per gram of MoS₂ in the catalysts prepared by exfoliation was 10 times smaller than that in the standard catalyst, the activity of these catalysts was close to the activity of the standard catalyst. On this basis, it was suggested that the hydrodesulfurization of thiophene can occur on the basal plane of MoS₂ that has a defect-free structure with a distorted environment of molybdenum.     

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.     

MgF2 as a non-conventional catalyst support

This review reports progress in the study of the surface structure of MgF₂ and its use as a support of catalytically active phases. Magnesium fluoride was applied first as a support in catalysis for systems containing individual oxides of transition metals (Mo, V, W, Cu, Cr) and then two different oxide phases (Cu-Cr, Cu-Mn), a metal phase (Ru, Pd) or heteropolyacids. Its use as a support enabled determination of the structure and surface properties of these catalysts. The MgF₂-supported catalysts are characterized by high activity and selectivity in such processes as: hydrodechlorination of chlorofluorocarbons (CFCs), hydrodesulfurization of organic compounds and purification of fuel combustion products from nitrogen oxides. Magnesium fluoride has been also used in MgF₂-doped chromium or aluminum fluoride catalysts for Cl/F exchange on hydrochlorocarbons.     

Highly selective synthesis of diphenyl methane via liquid phase benzylation of benzene over cobalt doped zinc nanoferrite catalysts at mild conditions

Liquid phase benzylation of benzene with benzyl chloride was investigated over different compositions of cobalt zinc ferrite (Co_xZn_1-xFe₂O_4, x-0.0, 0.25, 0.5, 0.75, 1.0) nano composites, synthesized by sol–gel method. The un-substituted cobalt ferrite catalyst exhibited excellent activity among the series effecting complete conversion of benzyl chloride in 60?min at 90?°C with 100% selectivity for diphenyl methane. The effect of various reaction parameters on the reaction was studied. Higher benzylation activity of cobalt ferrite nanocomposite is attributed to the presence of higher quantities of moderately acidic sites and a good correlation was observed between surface acidity and benzylation activity of catalysts. The catalysts are reusable without any significant structural change as indicated by X-ray Diffraction (XRD) and Atomic Absorption Spectrophotometer (AAS).     

Sulfide Catalysts Supported on Al2O3: VI. Synthesis of Catalysts with the Use of Binuclear Molybdenum(V) Complexes with Sulfur-Containing Ligands

A new method was developed for the preparation of sulfide catalysts supported on aluminum oxide. The surface assembling of a direct precursor of the active component was used in this method. The method consists in the sequential immobilization of binuclear molybdenum complexes with S-containing ligands on the support surface followed by the immobilization of nickel (cobalt) compounds at the surface molybdenum complexes. The complexation and structure of the resulting complexes in solution and the structure of surface complexes were studied by ⁹⁵Mo and ¹⁷O NMR, IR, and EXAFS spectroscopy. The surface assembling of a direct precursor of the active component of sulfide hydrodesulfurization catalysts was demonstrated using IR and EXAFS spectroscopy. The activity of the resulting catalysts in a model reaction of thiophene hydrogenolysis was comparable to the activity of sulfide catalysts of the metal complex origin and was much higher than the activity of commercial catalysts and catalysts prepared by impregnation.     

Selective Hydrogenation of Diethyl Disulfide to Ethanethiol in the Presence of Sulfide Catalysts

The gas-phase reaction of diethyl disulfide hydrogenation at atmospheric pressure in the presence of supported transition metal sulfides was studied. The reaction of diethyl disulfide with hydrogen at T = 200°C resulted in ethanethiol, and the selectivity to ethanethiol was no lower than 94%. The selectivity decreased at a higher temperature because of diethyl disulfide decomposition to ethylene and hydrogen sulfide. The reaction of diethyl disulfide in the presence of hydrogen occurred at a higher rate and selectivity than that in an atmosphere of helium. The activity of metal sulfides supported on aluminum oxide was higher than on the other studied supports—aluminosilicate, silica gel, and a carbon support. Metal sulfides supported on Al₂O₃ were arranged in the following order according to their activity: Rh > Ru > Mo Pd > Ni > W. Bimetallic catalysts were less active than monometallic catalysts. The activity of catalysts increased with the sulfide sulfur content; the partial reduction of metal sulfides also increased the catalytic activity.     

NiMo催化剂载体中纳米HY分子筛和氧化铝混合方式对柴油加氢脱硫性能的影响

以纳米HY分子筛-氧化铝混合物为载体,根据两者混合方式的不同（溶胶凝胶法和机械混合法）制备了两种NiMo加氢脱硫催化剂,并对其进行了XRD、BET、TPD、H₂-TPR、HRTEM和FT-IR等表征。与溶胶凝胶法催化剂相比,机械混合法催化剂表现出了较好的纹理结构和更高酸量,其金属相更易还原,边角位Mo原子的分散度更高,表现出了更高的加氢脱硫性能。但溶胶凝胶法催化剂的type-Ⅱ Ni-Mo-S活性相前驱物比例更高,MoS₂晶片长度更大,堆垛程度更高,活性组分分散度较差。虽然溶胶凝胶法有利于提高type-Ⅱ Ni-Mo-S活性相前驱物比例,但是该方法导致的较差孔结构抑制了这种优势,并且降低了活性组分分散度,减弱了催化活性。