Hydrogenation active sites of unsupported molybdenum sulfide catalysts for hydroprocessing heavy oils

The purpose of the present study was to elucidate the nature of the hydrogenation active sites on unsupported molybdenum sulfide catalysts, aimed at the improvement of the catalysts for the slurry processes. The number of hydrogenation active sites was found to relate to the “inflection” on the basal plane of the catalyst particles. The comparison of the catalytic activity to that of an oil-soluble catalyst in the hydroprocessing of heavy oils suggests that the performance of the oil-soluble catalyst was near the maximum, unless another component such as Ni or Co was incorporated.     

Aromatic reduction properties of molybdenum sulfide clusters in HY zeolite

Molybdenum sulfide catalysts supported on an HY zeolite at various Mo contents were studied. Catalysts were prepared by incipient wetness impregnation with ammonium heptamolybdate solution and calcined without drying. Their reactivity has been evaluated in toluene hydrogenation under typical hydrotreating conditions. Compared to alumina supported catalysts, zeolite supported Mo catalysts are extremely active for aromatics hydrogenation. At low molybdenum loading, molybdenum sulfide phases inside the zeolite show a particularly high intrinsic activity. This activity can be attributed to molybdenum sulfide clusters differing from MoS₂ slabs.     

Effect of fluorine on hydrogenation of cyclohexene on sulfided Ni (or Co)Mo/Al2O3 catalysts

The effect of fluorine incorporation on alumina support on the surface structure of unpromoted molybdenum, promoted cobalt—molybdenum and nickel—molybdenum catalysts, and their activity for hydrogenation of cyclohexene has been studied. The incorporation of 0.2 and 0.8 wt.-% fluorine on the alumina was carried out by impregnation with NH₄F solutions. The catalysts in the oxidic state were characterized by X-ray diffraction and ammonia adsorption and in the sulfide state by X-ray photoelectron spectroscopy (XPS) and infra-red spectroscopy (IR) of adsorbed NO. The absence of significant changes in the binding energy values of Mo3d and Ni2p (or Co2p) levels in the XPS spectra of the fluorine-containing catalysts as compared to the fluorine-free counterpart does not support the existence of an electronic effect of fluorine. The quantitative XPS results showed, however, that fluorine clearly increases the dispersion of molybdenum and promoter, this being linearly correlated to surface fluorine content. The IR results of adsorbed NO also indicate that fluorine incorporation leads generally to minor sizes of MoS₂ slabs, and more exposed promoter atoms, except for the cobalt in the CoMo/F(0.2)A catalyst. It is suggested that the increase in the dispersion of the supported active phase is a secondary effect of fluorine incorporation, which may result from the observed textural changes of the alumina and its small partial solubilization provoked by NH₄F solution. It was found that the incorporation of fluorine enhances appreciably, moderately and considerably the hydrogenation activity of molybdenum, cobalt—molybdenum an nickel—molybdenum catalysts, respectively. Such increase in hydrogenation activity is not directly correlated to the exposed atoms probed by NO adsorption, and is only loosely related to molybdenum dispersion for the molybdenum and cobalt—molybdenum catalysts. The lack of similar reliable correlations for the nickel—molybdenum catalysts suggests that other structural parameters such as extent of reduction-sulfidation and certain configurations of molybdenum ions and sulfur vacancies may govern hydrogenation activity.     

Characteristics of bimetallic cobalt and molybdenum catalysts supported on activated carbon or alumina in hydrodesulfurization

A series of bimetallic cobalt (Co) and molybdenum (Mo) catalysts supported on activated carbon or alumina were prepared, and their activities in thiophene hydrodesulfurization and ethylene hydrogenation were compared. The nitric oxide (NO) chemisorption and temperature programmed desorption (TPD) were used to characterize the nature of the synergistic active sites. Carbon supported catalysts also demonstrated the synergism in activity, which is well known for alumina supported catalysts. The specific activity and the adsorption stoichiometry of each site were interpreted from NO chemisorption. The possibility of NO as a probe molecule for sulfide catalysts was provided by the present work.     

Rhenium,tungsten and molybdenum as substitutes for plantinum in aromatics hydrogenation catalysts

Three metal substitutes for platinum on alumina-supported catalysts have been investigated. These metals are rhenium, tungsten and molybdenum. In the absence of platinum, these metals are catalytically inactive. At high hydrogenation temperatures (≥100°C) rhenium, tungsten and molybdenum appear to substitute platinum up to at least 66.7, 50 and 33.3% of the platinum atoms, respectively, providing almost the same conversion as platinum. At low hydrogenation temperatures (～50°C), the catalyst containing 0.6 wt% Pt is more active than those containing metallic combinations. At low reaction temperatures, in particular for high platinum substitution ratios, tungsten appears functionless whereas molybdenum may act as an inhibitor for platinum.     

硫化型NiMoS/CNTs加氢催化剂的制备与性能研究

以碳纳米管为载体,以含硫前驱物四硫代钼酸铵为钼源,采用等体积浸渍法制备了以Mo-Ni为主要活性组分的硫化型NiMoS/CNTs加氢催化剂。在固定床高压微反装置上考察了NiMoS/CNTs催化剂上二苯并噻吩（DBT）加氢脱硫（HDS）性能,并与NiMoS/γ-Al2O3催化剂进行了对比。评价结果表明,NiMoS/CNTs催化剂的HDS活性和选择性明显高于NiMoS/γ-Al2O3催化剂。碳纳米管负载的NiMoS/CNTs催化剂起始还原温度较低,具有更高的二硫化钼堆积层数、Mo4+原子占比和适宜的二硫化钼晶片长度,活性位密度大,这是催化剂加氢性能高的主要原因。     

Migration and diffusion of molybdenum catalyst during CO/steam coal hydrogenation

CO/steam hydrogenation of an Australian high volatile bituminous coal was carried out at 350–400 °C with molybdenum as catalyst. In most experiments, molybdenum trioxide was mechanically mixed with coal, although impregnation of the coal with a solution of ammonium paramolybdate was also investigated. Naphthalene was used as a vehicle. Microscopic examination of the hydrogenation residues indicated that the molybdenum had migrated towards the coal surface at the early stages of CO/steam hydrogenation. It is thought that molybdenum carbonyl formation is the most likely pathway for molybdenum migration and diffusion. The physical distribution and quantity of catalyst had little influence on conversion yields, as would be expected if only a small proportion of the molybdenum is in highly mobile catalytic form. By itself, molybdenum hexacarbonyl was found to be an excellent CO/steam hydrogenation catalyst.     

Activity of carbided molybdena–alumina for CO2 hydrogenation

The relationship between the catalytic activity of carbided molybdena–alumina and the methane desorption from carbidic carbon through temperature-programmed surface reaction (TPSR) were studied. The effects of passivation and hydrogen treatment on the catalytic activities of molybdenum carbides for CO₂ hydrogenation were determined. When the 973 K-carbided catalyst was reduced at 773 K with hydrogen, the catalyst exhibited the highest activity for the reaction, the activity decreasing with increasing H₂ pretreatment temperature. Passivation of this catalyst decreased the reaction rate by 20%. TPSR results were correlated with the activity to reveal that molybdenum carbide with slightly deficient carbidic carbon (Mo₂C_0.962C_1.0) serves as an active site for CO₂ hydrogenation.     

The impact of surface science on the commercialization of chemical processes

Surface science developed instruments for atomic- and molecular-scale studies of catalyst surfaces, their composition and structure, both in a vacuum and at high pressures, under reaction conditions (bridging the pressure gap). Surfaces ranging from single crystals, nanoparticles and thin films to porous high surface area catalytic materials have been studied. Classes of surface structure sensitive and insensitive reactions have been identified by surface science studies, including ammonia synthesis, hydrodesulfurization, reforming, combustion and hydrogenation. Rates of reactions often vary by orders of magnitude between using the right and the wrong surface structures. The roles of many promoters that modify the catalyst surface structures and bonding of adsorbates have been verified. Surface reaction intermediates could be identified and the mobility of adsorbates and the adsorbate induced reconstruction of the catalysts attest to the dynamic nature of the catalytic systems during the reaction turnover. The important active sites for catalysis include the low coordination surface step, kink, oxygen and chloride ion vacancies sites and sites at oxide-metal interfaces. Uncovering the molecular ingredients of heterogeneous catalysts will have a major impact on the understanding of reaction selectivity to help the evolution of green chemistry and selective reaction of many types.     

油溶性纳米MoS2加氢催化剂的合成、表征和应用

传统MoS₂加氢催化剂粒径大、油溶性差而催化效率相对较低。纳米粒子合成方法很多，其中液相化学合成技术尤其水(溶剂)热、微乳液、单层二硫化钼重堆积和微波液相介电加热法等更为便捷、高效。在油溶性纳米MoS₂的合成中，表面修饰剂的选择最为关键。综述了油溶性纳米MoS₂的合成、表征和应用研究进展，提出了高稳定性、高活性和油溶性纳米MoS₂加氢催化剂高效合成优化参数，为实现工业应用提供了参考。     

Molybdate catalysts prepared by a novel impregnation method: Effect of citric acid as a ligand on the catalytic activities

Molybdate, nickel-molybdate and cobalt-molybdate/γ-alumina catalysts were prepared by an impregnation method using citric acid as well as ammonia as ligands. Molybdenum structures in the impregnating solutions and on the sulfided catalysts were characterized by EXAFS and XPS. Agglomerated molybdenum octahedra existed in the impregnating solutions containing citric acid, in contrast to the monomeric molybdenum tetrahedra obtained when using ammonia. The nickel-molybdenum catalyst prepared by using citric acid was inferior to the one prepared by using ammonia in terms of both hydrogenation and HDN activities, which might be due to a decrease in the amount of active Ni-Mo-S phase. On the other hand, the cobalt-molybdenum catalyst prepared using citric acid was superior to the one prepared using ammonia in terms of HDS activity. A decrease in the lateral size of MoS₂-like crystallites might attribute to an increase in the HDS activity.     

浆态床油溶性加氢催化剂前体的研究进展

浆态床渣油加氢工艺是加工劣质油品的有效方法,由于原料具有高沥青质、高金属含量的特点,工艺的核心在于提供稳定高效的加氢裂化催化剂。油溶性催化剂前体能够原位转化为纳米级尺寸的催化剂活性相,其分散度高、加氢活性高,因而成为浆态床渣油加氢工艺的首选。本文主要介绍了4类常见的油溶性有机钼化合物,即二烷基(芳基)二硫代氨基甲酸钼(Mo-DTC)和二烷基二硫代磷酸钼（Mo-DTP）、环烷酸钼（MoNaph）、异辛酸钼、六羰基钼,比较它们在氢气和硫作用下的转化过程以及对重质原料的加氢性能,找出各自在应用过程中的优缺点,为深入研究和设计开发油溶性催化剂前体提供思路和借鉴。     

Dynamics of active sites transformation in HDS-HDA catalyst

Benzene hydrogenation in steady-state and unsteady-state regimes over sulfide Ni-W/γ-Al₂O₃ catalyst is studied. The mechanism and dynamic model of hydrogenation and hydrogenolysis active sites transformation are proposed. The reactions were shown to be quasi steady-state ones with slow poisoning of both hydrogenation and hydrogenolysis active sites by the formation of intermediate surface compounds of sulfur. The dynamic behavior was described by the proposed model with sufficient accuracy.     

雷尼镍活性本质的探讨

本文认为雷尼镍（Raney nickel）催化剂产生活性的原因是因为表面缺陷部位存在活性中心,原始合金相组成和制备方法影响缺陷的类型,从而可形成不同类型的活性中心。对于普通加氢反应，相对应的活性中心将氢分子活化为弱吸附的线性Ni-H表面物种，使其参与加氢反应；对于不对称加氢反应，前手性底物吸附在手性活性中心之上，使其构型稳定，从而生成单一对映体。     

Kinetics-assisted identification and regulation of active sites for Pd-catalyzed propyne selective hydrogenation

Identification and regulation of active sites are significant for guiding the design and optimization of hydrogenation catalysts toward the target product but remain a great challenge. Herein, we demonstrate a kinetics-assisted identification method combined with theoretical calculations for identifying and further regulating the dominant active sites of Pd catalysts for propyne hydrogenation. Kinetics analysis and model calculations based on the cuboctahedron shape of Pd nanoparticles in the catalysts indicate the Pd(111) sites as the dominant active sites for the propyne conversion and propylene formation while the Pd(100) sites as those for the propane formation, which are further rationalized by theoretical calculations. Moreover, the Pd catalyst with electron-rich properties exhibits relatively higher activity and selectivity, guided by which the SiO₂ support with abundant electron-donating hydroxyl groups is employed to increase the Pd electron density. Such electronic regulation for the Pd catalyst clearly enhances the selective hydrogenation of propyne.     

α,β-不饱和醛/酮中双键选择性加氢催化剂的研究进展

α,β-不饱和醛/酮中双键选择性加氢制备相应的饱和醛/酮是一类重要的精细化工反应,高选择性催化剂的设计和制备是实现该类反应工业化的关键。从活性金属、助剂和载体材料等方面综述了国内外α,β-不饱和醛/酮中双键选择性加氢催化剂的研究进展,并且从反应物分子在金属活性位上的吸附模型和空间位阻效应等方面理论上阐释了活性金属种类、金属粒径等影响α,β-不饱和醛/酮中双键加氢选择性的本质原因。对近期α,β-不饱和醛/酮选择性加氢制备相应饱和醛/酮反应工艺方面的研究进展进行了评述。     

Structures of the distillates obtained from hydrogenation and pyrolysis of Liddell coal

The structures of the distillable fractions (oils, b.p. >200 °C and volatile fractions, b.p. <200 °C) of the products from hydrogenation and pyrolysis of an Australian bituminous coal (Liddell) were investigated by gas chromatography-mass spectrometry (g.c.-m.s.) and nuclear magnetic resonance spectroscopy (n.m.r.). The distillable oil generated from hydrogenation of Liddell coal at 400 °C, using nickel molybdenum ortin (II) chloride as catalyst and tetralin or recycle oil as vehicle, consisted of a wide range of compounds. Long straight-chain alkanes were important components together with alkyl-substituted benzenes and tetralins, phenols and polycyclic material. When yields were low, as in the case of catalytic experiments with nickel molybdenum catalysts and no vehicle, isoprenoids could be identified. When a substantial proportion of the coal was converted to oil, branched-chain alkanes were not important components of the product. The replacement of tetralin and nickel molybdenum catalyst with stannous chloride reduced the amounts of methyl tetralins in the product. When tetralin was replaced by recycle oil, alkanes were more important components of the liquid products. Although alkenes were absent in oils generated by hydrogenation, they were important components of oils generated by pyrolysis. The highly volatile fractions (b.p. <200 °C) produced during hydrogenation consisted of alkyl-substituted benzenes, decalins, methylindan and straight-chain alkanes. Straight-chain alkanes were more abundant in those volatile fractions generated by hydrogenation with recycle vehicle than with tetralin. The Brown-Ladner method of estimating the fraction of aromatic carbon in distillable oils was adequate for less volatile fractions but was inadequate for the highly volatile fractions because of the large amounts of α-CH₃ and β-CH₃ alkyl groups present.     

Nickel-containing catalysts for hydroprocessing of aromatic oils

A series of nickel-containing catalysts was prepared by a sequence of impregnation and calcining steps using a γ-alumina support. The calcined catalysts were reduced in a flow of hydrogen and mixtures of hydrogen with hydrogen sulfide. Both the calcining temperature and nickel loading strongly influenced the hydrogenation activity. The changes in surface species which resulted from some of the preparation steps were identified by spectroscopy. The catalysts containing nickel without molybdenum were quickly poisoned by sulfur, but a certa in sulfur tolerance was achieved by a two-step impregnation and calcining procedure. Improved hydrogenation activity and high hydrogenation vs. hydrocracking selectivity of nickel—molybdenum catalysts were obtained with relatively low loading of molybdenum and high loading of nickel. A three-step impregnation and calcining procedure appeared to produce the most effective catalysts.     

制备条件对碳化钼催化剂及正己烷异构化的影响

采用程序升温还原法制备B-Mo_2C/SAPO-11催化剂,研究制备条件对β-Mo_2C/SAPO-11催化剂上正己烷异构化的影响。XRD分析及实验结果表明,升温速率过快导致碳化程度较低,钼相多为单质钼,升温速率小于2℃·min~(-1),催化剂制备效果较好;碳化终温对碳化程度影响较大,终温过低使碳化后的样品含有较多的MoO_2。对正庚烷和正己烷作为碳源的碳化效果进行比较,结果表明,正己烷作为碳源较合适。催化剂中碳化钼负载质量分数为15%,催化剂上金属组分的加氢和脱氢活性与SAPO-11载体的异构化活性达到最佳平衡。     

Cold Lake Bitumen Upgrading Using Exfoliated MoS2

Exfoliated MoS₂ has been investigated as a dispersed catalyst for Cold Lake bitumen upgrading. The results are compared with MoS₂ prepared in situ by the decomposition of molybdenum naphthenate. Although liquid yield and coke suppression were similar among the catalysts, better hydrogenation activity, especially hydrodenitrogenation, and asphaltene and microcarbon residue (MCR) removal, were obtained with the exfoliated MoS₂. The improved hydrogenation is suggested to be a consequence of increased rim-edge sites associated with the exfoliated MoS₂. The potential for recycle of the exfoliated MoS₂ is also reported.