铈铝复合载体对钼基催化剂耐硫甲烷化催化性能的研究

采用共沉淀法、浸渍法和沉积沉淀法制备了CeO₂-Al₂O₃复合载体,比较了不同复合载体浸渍钴钼后的耐硫甲烷化催化性能,并优化了复合载体中CeO₂的含量。结合N₂物理吸附、XRD、H₂-TPR等表征手段对复合载体及其负载的钴钼催化剂进行物相和结构分析发现,在Al₂O₃中添加CeO₂可以明显提高合成气的耐硫甲烷化活性,其中,沉积沉淀法制备的25% CeO₂-Al₂O₃复合载体负载钴钼后具有最佳催化活性。     

制备条件对MoS2/Al2O3耐硫甲烷化催化剂性能的影响

本文研究了前驱体MoO_3的负载量、浸渍温度和焙烧温度等制备条件对Mo S2/Al_2O_3耐硫甲烷化催化剂性能的影响,并通过XRD和H2-TPR表征了催化剂的物相和还原性能。结果表明,随着负载量增加,MoO_3与Al_2O_3间的相互作用增强,Al2(Mo O4)3相增多,导致催化剂更难被还原硫化,MoO_3还原温度升高。浸渍温度对CO转化率和CH4选择性有一定的影响,浸渍温度为70℃时,MoO_3的生成增多,且还原温度最低,CO转化率较高,而CH4选择性和CO_2选择性变化不大。随着焙烧温度升高,CO转化率先升高后降低,对CH4和CO_2选择性影响不大,其中以450℃焙烧的CO转化率最高,600℃焙烧的CO转化率最低。当焙烧温度在400~450℃时,Al2(Mo O4)3和Mo4O11的特征峰基本上消失,能够完全生成MoO_3,且结晶度较好。因此,合适的焙烧温度为400~450℃。     

ZrO2和Al2O3载体对Mo基催化剂上甲烷化反应性能的影响

通过共沉淀法制备了ZrO₂和Al₂O₃载体,采用等体积浸渍法制备了MoO₃质量分数为5%的Mo/ZrO₂和Mo/Al₂O₃催化剂,并用于甲烷化反应。在三种反应气氛下对两种预硫化的Mo基催化剂进行评价,发现ZrO₂载体均可显著促进甲烷化反应,同时能够促进水汽变换（WGS）反应。通过XRD、H₂-TPR、XPS和TEM等表征发现,两种载体上Mo物种的硫化程度以及暴露的活性位数量不同,从而导致两种催化剂上催化性能差异显著。与Mo/Al₂O₃相比,Mo/ZrO₂催化剂上的MoO₃更易被还原,硫化程度也更高,并且Mo⁴⁺的含量更高,Mo⁶⁺的含量更低。虽然ZrO₂载体上MoS₂尺寸较大,边位置的Mo比例有所降低,但是由于MoS₂沿ZrO₂颗粒表面弯曲生长,使得MoS₂基面成为反应的活性位;因此,Mo/ZrO₂催化剂在甲烷化与WGS反应中表现出更优异的催化性能。     

Catalytic behaviour of Mo-based catalysts in liquid phase epoxidation of propylene by hydroperoxides

The activity of different Mo-based catalysts in propylene epoxidation by t-BuO₂H was investigated. MoO₂(C₁₃H₁₀O₂N)₂ and MoO₂ (oxine)₂ gave quantitative yields in propylene oxide; other compounds were inactive and MoO₂ (acac)₂ was less active and selective.The different catalytic behaviour of these catalysts is attributed to the different strength of Mo-ligand bonds.

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t-BuO₂H. MoO₂ (C₁₃H₁₀O₂N)₂ MoO₂ ()₂ ; , MoO₂ (acac)₂ . Mo-.

     

Solid acid catalysts for synthesis of biodiesel fuel from pyrolyzed natural and synthetic polymeric materials

New heterogeneous catalysts for synthesis of a biodiesel fuel, modified with strongly acidic groups, were developed. The catalysts are produced by pyrolysis and subsequent sulfation of fruit kernels and granulated porous copolymers and resins. The structural-sorption and catalytic properties of the materials obtained were studied in the reaction of catalytic re-esterification of rapeseed oil by methanol and ethanol. The conditions in which carbon materials with high content of surface acid groups are obtained were optimized.     

Aerobic reduction of olefins by in situ generation of diimide with synthetic flavin catalysts

A versatile reducing agent, diimide, can be generated efficiently by the aerobic oxidation of hydrazine with neutral and cationic synthetic flavin catalysts 1 and 2. This technique provides a convenient and safe method for the aerobic reduction of olefins, which proceeds with 1 equiv of hydrazine under an atmosphere of O(2) or air. The synthetic advantage over the conventional gas-based method has been illustrated through high hydrazine efficiency, easy and safe handling, and characteristic chemoselectivity. Vitamin B(2) derivative 6 acts as a highly practical, robust catalyst for this purpose because of its high availability and recyclability. Association complexes of 1b with dendritic 2,5-bis(acylamino)pyridine 15 exhibit unprecedented catalytic activities, with the reduction of aromatic and hydroxy olefins proceeding significantly faster when a higher-generation dendrimer is used as a host pair for the association catalysts. Contrasting retardation is observed upon similar treatment of non-aromatic or non-hydroxy olefins with the dendrimer catalysts. Control experiments and kinetic studies revealed that these catalytic reactions include two independent, anaerobic and aerobic, processes for the generation of diimide from hydrazine. Positive and negative dendrimer effects on the catalytic reactions have been ascribed to the specific inclusion of hydrazine and olefinic substrates into the enzyme-like reaction cavities of the association complex catalysts.     

Quinolines synthesis by reacting 1,3-butanediol with anilines in the presence of iron catalysts

2-, 4-, 6-, 7-, and 8-substituted quinolines were synthesized in 78–95% yield by the reaction of 1,3- butanediol with anilines in the presence of iron catalysts in carbon tetrachloride.     

Hydrocracking of vacuum gas oil in the presence of supported nickel-tungsten catalysts

The supports containing 70% Al₂O₃ and 30% β zeolite (AZ-1 and AZ-2), which differed in mixing procedures, and the Ni-W/AZ-1 and Ni-W/AZ-2 catalysts were characterized using an adsorption technique, high-resolution electron microscopy, IR spectroscopy, and X-ray photoelectron spectroscopy and tested in the hydrocracking reaction of vacuum gas oil (VGO). It was found that the supports differed in texture characteristics and surface Lewis acidity at the same composition and similar concentrations of Brønsted acid sites. The formation of Ni-W-S sulfide species on the surfaces of both of the supports occurred in different manners: multilayer Ni-W-S sulfide species were formed on AZ-1 (S _sp = 220 m²/g), whereas single-layer species were mainly formed on AZ-2 (S _sp = 380 m²/g). It was found that catalysts containing multilayer Ni-W-S sulfide species, which were characterized by a higher degree of sulfidation, provided a higher yield of diesel fuel upon the hydrocracking of VGO, whereas catalysts containing single-layer Ni-W-S sulfide species were more active in the reactions of VGO hydrodesulfurization and hydrodenitration.     

Specific action of nickel-zeolite catalysts in the methanation of carbon monoxide

The effect of nickel distribution in zeolites on their activity in CO methanation, determined by the state of nickel on the outer zeolite surface, indicates that nickel inside the zeolite cavities is inactive. Under the effect of the reaction medium, an increase in the average size of nickel particles does not change the catalyst activity.

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CO, . , . , .

     

Effect of cobalt oxide on performance of Pd catalysts for lean-burn natural gas vehicles in the presence and absence of water vapor

Pd-based catalysts modified by cobalt were prepared by co-impregnation and sequential impregnation methods, and characterized by X-ray powder diffraction (XRD), N_2 adsorption/desorption (Brunauer-Emmet-Teller method), CO-chemisorption and X-ray photoelectron spec-troscopy (XPS). The activity of Pd catalysts was tested in the simulated exhaust gas from lean-burn natural gas vehicles. The effect of Co on the performance of water poisoning resistance for Pd catalysts was estimated in the simulated exhaust gas with and without the presence of water vapor. It was found that the effect of Co significantly depended on the preparation process. PdCo/La-Al_2O_3 catalyst prepared by co-impregnation exhibited better water-resistant performance. The results of XPS indicated that both CoAl_2O_4 and Co_3O_4 were present in the Pd catalysts modified by Co. For the catalyst prepared by sequential impregnation method, the ratio of CoAl_2O_4/Co_3O_4 was higher than that of the catalyst prepared by co-impregnation method. It could be concluded that Co_3O_4 played an important role in improving water-resistant performance.     

One-step synthesis of 3-dichloromethylpyridine from pyridine in the presence of iron-containing catalysts

3-Dichloromethylpyridine was synthesized by reaction of pyridine with the system MeOH-CCl₄-iron catalyst [FeBr₂, Fe₃(CO)₁₂, or iron(III) naphthenate]. Iron(II) bromide at a FeBr₂-pyridine-CCl₄-MeOH ratio of 1:100:200:200 showed the highest catalytic activity.     

Catalytic synthesis of 1-arylethylphosphonates by the hydrogenation of unsaturated precursors in the presence of chitosan-based palladium catalysts

Three-component silica-supported palladium-containing systems based on chitosan were synthesized and studied by scanning electron microscopy. These systems showed catalytic activity in the hydrogenation (including chemoselective hydrogenation) of α,β-unsaturated phosphonic acids and their esters. Modification of chitosan on the silica surface with glutaraldehyde considerably enhances the stability and activity of the catalyst.     

The role of the acquisition methods in the analysis of natural and synthetic steroids and cholic acids by gas chromatography-mass spectrometry

An exhaustive GC-MS acquisition study was performed, for the simultaneous analysis of natural and synthetic steroids and cholic acids (in order to insert them into the last tierce of our multiresidue analysis system), such as androsterone, β-estradiol, transdehydroandro-sterone, transdehyroandrosterone, mestranol, dihydrotestosterone, ethinylestradiol, testosterone, norethisterone, estriol, 4-androstene-3,17-dione, gestodene, levonorgestrel, etonogestrel, coprostanol, progesterone, cholesterol, medroxyprogesterone-acetate, lithocholic acid, stigmasterol, cholic acid, chenodeoxycholic acid, β-sitosterol, ursodeoxycholic acid, 3-hydroxy-7-ketocholic acid and dehydrocholic acid, in total 26 compounds. As novelties to the field, for the trimethylsilyl (TMS) oxime ether/ester derivatives of steroids and cholic acids, at first, a tandem mass spectrometric (MS/MS), multiple reaction monitoring (MRM) type acquisition method has been developed in a single run; also for the first time, the three acquisition techniques, the full scan (FS), the selective ion monitoring (SIM), in our case the multiple ion monitoring (MIM) and the currently optimized MRM methods, have been compared; all three, in parallel, under strictly the same derivatization/instrumental conditions, both in matrix free solutions and municipal wastewater from two Hungarian wastewater treatment plants (WWTPs). Critical evaluation of the three acquisition protocols was collated on their analytical performances and validated under the same conditions. The data of six point calibration curves for FS, MIM and MRM methods, showed that both R2 (0.9995, 0.9858, 0.9975) and RSD (5.3, 5.8, 5.0), for two parallel derivatizations, each injected three times, proved to be independent of the acquisition processes. Whereas, for the method limit of quantification (LOQ) and the instrument limit of quantification (ILQ) values showed considerable differences. LOQ data, were decreasing in the FS, MIM, MRM line (expressed in ng/L), for all steroids and cholic acids. The same trend was determined in terms of the ILQ values. The practical utility of the optimized acquisition techniques was confirmed by the quantitation of the steroids and cholic acids contents of wastewater samples. Results confirmed the importance of the MRM acquisition method, even in comparison to the MIM one: with particular interest in selected cases: avoiding the extreme overestimation of the β-estradiol (156-1325%) and that of the ethinylestradiol (582-831%) concentrations in the wastewater samples.     

Computational study of the factors controlling enantioselectivity in ruthenium(II) hydrogenation catalysts

The reduction of prochiral ketones catalyzed by Ru(diphosphine)(diamine) complexes has been studied at the DFT-PBE level of theory. Calculations have been conducted on real size systems [trans-Ru(H)2(S, S-dpen)(S-xylbinap) + acetophenone], [trans-Ru(H)2(S, S-dpen)(S-tolbinap) + acetophenone] and [trans-Ru(H)2(S, S-dpen)(S-xylbinap) + cyclohexyl methyl ketone] with the aim of identifying the factors controlling the enantioselectivity in Ru(diphosphine)(diamine) catalysts. The high enantiomeric excess (99%) in the hydrogenation of acetophenone catalyzed by trans-Ru(H)2(S, S-dpen)(S-xylbinap) has been explained in terms of the existence of a stable intermediate along the reaction pathway associated with the (R)-alcohol. The formation of this intermediate is hindered with the competitive pathways, which consequently increases the activation energy for the hydrogen transfer acetophenone/(S)-phenylethanol reaction. For the [trans-Ru(H)2(S, S-dpen)(S-tolbinap) + acetophenone] system, the lower enantioselectivity (i.e. 80%) is rationalized by the smaller differences in the activation energy between the competitive pathways which differentiate between the two diastereomeric approaches of the prochiral ketone. The DFT-PBE results suggest that this reaction is driven to the (R)-product only by the process of binding the acetophenone to the active site of the trans-Ru(H) 2(S, S-dpen)(S-tolbinap) catalyst. For the hydrogenation of cyclohexyl methyl ketone catalyzed by trans-Ru(H)2(S, S-dpen)(S-xylbinap), the low performance in the enantioselective hydrogenation of the dialkyl ketone (i.e. 37%) is again explained by the small differences in the activation and binding energies which are the factors which could effectively differentiate between the two alkyl groups.     

Selective methanation of CO in the presence of CO<Subscript>2</Subscript> in hydrogen-containing mixtures on nickel catalysts

The screening of commercial nickel catalysts for methanation and a series of nickel catalysts supported on CeO₂, γ-Al₂O₃, and ZrO₂ in the reaction of selective CO methanation in the presence of CO₂ in hydrogen-containing mixtures (1.5 vol % CO, 20 vol % CO₂, 10 vol % H₂O, and the balance H₂) was performed at the flow rate WHSV = 26000 cm³ (g Cat)⁻¹ h⁻¹. It was found that commercial catalytic systems like NKM-2A and NKM-4A (NIAP-07-02) were insufficiently effective for the selective removal of CO to a level of <100 ppm. The most promising catalyst is 2 wt % Ni/CeO₂. This catalyst decreased the concentration of CO from 1.5 vol % to 100 ppm in the presence of 20 vol % CO₂ in the temperature range of 280–360°C at a selectivity of >40%, and it retained its activity even after contact with air. The minimum outlet CO concentration of 10 ppm at 80% selectivity on a 2 wt % Ni/CeO₂ catalyst was reached at a temperature of 300°C.     

Determination of natural and synthetic estrogens in water by gas chromatography with mass spectrometric detection

A procedure for the determination of six natural and synthetic estrogens (diethylstilbestrol, estrone, 17beta-estradiol, mestranol, 17alpha-ethinylestradiol and estriol) in water samples is described. Samples, up to 2000 ml, were concentrated using Oasis HLB solid-phase extraction cartridges. Analytes were derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide and determined by GC-MS or GC-MS-MS. The reactivity of several silylation reagents versus aliphatic and aromatic hydroxyl groups contained in the structure of the selected analytes was evaluated. Influence of parameters such as sample pH, nature of the water samples and derivatization conditions on the performance of the whole analytical procedure was systematically studied. Under optimal conditions, quantification limits between 1 and 3 ng/l were achieved for the determination of the considered estrogens in sewage water.     

The conversion of natural gas to higher hydrocarbons using a microwave plasma and catalysts

Methane, the major constituent of natural gas, had been converted to higher hydrocarbons by a microwave plasma. The yield of C2+ products increased from 29.2% to 42.2% with increasing the plasma power and decreasing the flow rate of methane. When the catalysts were used in the plasma reactor, the selectivities of ethylene and acetylene increased while the yield of C2+ remained constant. Among the various catalysts used, the Fe catalyst showed the highest ethylene selectivity of 30%. When we introduced the actual natural gas, more C2+ products were obtained (46%). This is due to the ethane and propane in the natural gas. When an electric field inductance for evolving the high plasma was applied, a high yield in C2+ products of 63.7% was obtained for the Pd-Ni bimetal catalyst.     

Selective oxidation of hydrocarbons into synthesis gas at short contact times: Design of monolith catalysts and main process parameters

This review summarizes the main achievements of the Boreskov Institute of Catalysis (Siberian Division, Russian Academy of Sciences) in the development of efficient and stable monolith catalysts for selective oxidation of hydrocarbons into synthesis gas at short contact times. Research in this field has included (1) design of new types of active component based on metal oxides, (2) design of new types of monolith support and development of supporting procedures for active components, and (3) optimization of process parameters for different types of fuel (natural gas, isooctane, and gasoline) and oxidant (air oxygen, including its mixtures with water and carbon dioxide), including the start-up regime. Design of active components (platinum, nickel, or their combination) supported on fluorite-like solid solutions based on cerium dioxide and rare-earth (samarium, gadolinium, and praseodymium) or zirconium cations has been aimed at separating hydrocarbon activation (on metal sites) and oxidation (on the support) and conjugating the separated steps of hydrocarbon oxidation at the metal-oxide interface. Optimization of oxygen mobility in the support lattice by varying the nature and concentration of doping cation along with optimization of hydrocarbon activation on supported metal clusters allow hydrocarbons to be completely converted into synthesis gas by selective oxidation or dry or steam reforming at contact times of a few milliseconds, ruling out undesirable carbon build-up on the catalyst surface. The development of new types of monolith support has targeted the enhancement of thermal shock resistance, including testing of supports based on thermally stable metal foils and composites (cermets). The main steps of the production of these supports have been refined, including unique technologies of blast dusting and hydrothermal treatment. The electric conductivity of these systems allows a quick startup of selective oxidation to be performed by passing electric current, and their thermal conductivity minimizes the temperature gradient arising from heat transfer in the bed. Procedures for loading monolith supports with active components have been developed, including impregnation, washcoating, or encapsulation in cermet matrices. The catalysts produced show a high efficiency and an operational stability adequate to the above tasks in the selective oxidation and steam-air autothermal reforming of natural gas (including processes under pressure), isooctane, and gasoline into synthesis gas.__________Translated from Kinetika i Kataliz, Vol. 46, No. 2, 2005, pp. 243–268.Original Russian Text Copyright © 2005 by Sadykov, Pavlova, Bunina, Alikina, Tikhov, Kuznetsova, Frolova, Lukashevich, Snegurenko, Sazonova, Kazantseva, Dyatlova, Usoltsev, Zolotarskii, Bobrova, Kuzmin, Gogin, Vostrikov, Potapova, Muzykantov, Paukshtis, Burgina, Rogov, Sobyanin, Parmon.     

"Common synthetic scaffolds" in the synthesis of structurally diverse natural products

Selected natural products have long been considered as desirable targets for total synthesis due to their unique biological properties and their challenging structural complexity. Laboratory synthesis of natural compounds usually relies on target-oriented synthesis, involving the production, isolation and purification of successive intermediates, requiring multiple steps to arrive to the final product. A far more economical approach using common synthetic scaffolds that can be readily transformed through biomimetic-like pathways to a range of structurally diverse natural products has been evolved in the last decade, leading synthesis to new directions. This tutorial review critically presents the hallmarks in this field.