Formation of a supported cobalt catalyst for the synthesis of carbon nanofibers on aluminum oxide

Comparative studies of the effect of the physicochemical characteristics of a support (aluminum oxide) on the formation of a supported Co catalyst and its activity in the pyrolysis of alkanes (propane-butane) were performed. The effect of the crystalline modification of alumina on the yield of catalytic filamentous carbon (CFC) ((g CFC)/(g Co)) was studied. The surface morphologies of Co-containing catalysts and synthesized carbon deposits were studied by scanning electron microscopy. It was found that carbon deposits with a well-defined nanofiber structure were synthesized by the pyrolysis of a propane-butane mixture in the presence of hydrogen at 600°C on supported Co catalysts prepared by homogeneous precipitation on macroporous corundum (α-Al₂O₃). The yield of CFC was no higher than 4 (g CFC)/(g Co). On the Co catalyst prepared by homogeneous precipitation on mesoporous Al₂O₃, the intense carbonization of the initial support; the formation of cobalt aluminates; and, as a consequence, the deactivation of Co⁰ as a catalyst of FC synthesis occurred. The dependence of the yield of CFC on the preheating temperature (from 200 to 800°C) of Co catalysts before pyrolysis was studied. It was found that, as the preheating temperature of supported Co/Al₂O₃ catalysts was increased, the amount of synthesized carbon, including CFC, decreased because of Co⁰ deactivation due to the interaction with the support and coke formation.     

Synthesis of hydrocarbons from Co and H2 in the presence of supported Co catalysts modified by palladium

A study has been made of the effect of Pd on the activity and selectivity of Co catalysts prepared by impregnating various supports (SiO₂, SiO₂-Al₂O₃, Al₂O₃) with cobalt carbonyl or nitrate in the synthesis of hydrocarbons from CO and H₂. It is shown that the addition of Pd leads to an increase in the yield of liquid hydrocarbons and to a change in their composition. It has been established by IR spectroscopy that the introduction of Pd into the composition of carbonyl catalysts affects the formation of their surface.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 521–524, March, 1990.     

Formation of Co-Ru/MgO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the Fischer-Tropsch synthesis: A magnetic method for the estimation of cobalt particle size

The physicochemical properties of Co-supported catalysts were studied, and the particle size of Co in Co/MgO/Al₂O₃ and Co-0.2% Ru/MgO/Al₂O₃ catalysts for the Fischer-Tropsch synthesis (FTS) was estimated using a magnetic method. It was found that a considerable fraction of superparamagnetic Co particles, which increase selectivity for C₅₊ hydrocarbons and decrease the yield of methane in the FTS, was present in a ruthenium-containing catalyst along with single-domain ferromagnetic particles. In this case, the catalyst activity increased by a factor of 10.     

Catalytic Performance and Characterization of Pt‐Co/Al2O3 Catalysts for CO2 Reforming of CH4 to Synthesis Gas

Pt‐Co/Al₂O₂ catalyst has been studied for CO₂ reforming of CH₄ to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al₂O₃ was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al₂O₃ and Pt/Al₂O₃ catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al₂O₃ > Pt/Al₂O₃ > Co/Al₂O₃. With 9% Co, the Co/Al₂O₃ calcined at 923 K was also active for CO₂ reforming of CH₄, however, its carbon formation was much more fast man that of the Pt‐Co/Al₂O₃ catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl₂O₄, formed during calcining of Co/Al₂O₃ at high temperature before Pt addition. Promoted by Pt, Co/Al₂O₄ in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al₂O₄ reduction are responsible for high activity of the Pt‐Co/Al₂O₃ catalyst, and the remain Co/Al₂O₄ is beneficial to suppression of carbon deposition over the catalyst.     

One pot synthesis using supported reagents system KSCN/SiO2-RNH3OAc/Al2O3: synthesis of 2-aminothiazoles and N-allylthioureas

A simple and efficient method has been developed for the synthesis of 2-aminothiazoles and N-allylthioureas from commercially available materials in one pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which α-halo ketone reacts first KSCN/SiO₂ and the product, α-thiocyanatoketone, reacts with RNH₃OAc/Al₂O₃ to give the final product, 2-aminothiazoles, in good yield and allyl bromide reacts with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give N-allylthiourea.     

One-pot synthesis of N-allylthioureas using supported reagents

A simple and efficient method has been developed for the synthesis of N-allylthioureas from allylic bromides in one-pot by using a supported reagents system, KSCN/SiO₂-RNH₃OAc/Al₂O₃, in which allyl bromide reacts first with KSCN/SiO₂ and the product, allyl isothiocyanate, reacts with RNH₃OAc/Al₂O₃ to give the final product, N-allylthiourea, in good yield.     

Stoichiography in the study of spatial heterogeneity of the chemical composition and structure of thin films and nanostructured systems

We present the principles of stoichiography and a reference-free stoichiographic differential (separating) dissolution method used to study the composition and structure of thin films and nanostructured systems: HTS films with 123 different compositions, Al–Au–Sn–Co–Mn, Si/SiO₂/Ni(Cr)–Cu–Cu2S, Cr–Cu–S, and Cu–S multilayer films, Bi–Ti–O films on Ru/SiO₂/Si, Mn_1–xZn _x S, and ZnS–EuS supports, and also nanostructured manganese ferrite in borate glass matrices, nanodisperse composite sorbents and the Co–Si–Pt–O/Al₂O₃ catalyst modified by Pt nanoparticles, and oxide catalyst precursor Fe₂Co/Al₂O₃ for the synthesis of carbon nanotubes.     

Size Distribution of Cobalt Particles in Catalysts for the Fischer-Tropsch Synthesis

The effect of the size distribution of metal particles on the process kinetics was studied for the oxidation and reduction of cobalt nanoparticles (6–10 nm) in the Co/SiO₂, Co/Al₂O₃, and Co/ZrO₂ systems in both isothermic and temperature-programmed regimes in the temperature range from 280 to 500 K. The average size of the cobalt particles was estimated by measurements of the coercive force and residual magnetization using a vibration magnetometer. It was found that the average particle size increases upon cobalt oxidation and decreases upon cobalt reduction due to changes in the fraction of nonsuperparamagnetic particles with sizes of at least 6.5 nm.     

Synthesis of hydrocarbons from CO and H2 in the presence of Co-Ru and Co-Pd catalysts containing aluminum oxide

The influence of additions of 0.1–0.5% Pd or Ru in a 10% Co/Al₂O₃ catalyst on its activity and selectivity in the synthesis of liquid hydrocarbons from CO and H₂ has been studied. It has been shown that the bimetallic systems make it possible to carry out the synthesis of hydrocarbons with a higher extent of conversion of CO and a higher yield of C ₅ ⁺ carbons in comparison with the original Co catalyst. Co-Ru catalysts exhibit exceptionally high selectivity (up to 80%) with respect to the formation of liquid products. It has been demonstrated by temperature-programmed reduction (TPR) that the introduction of Pd an dRu promotes the reduction of Co at lower temperatures and the formation of cobalt aluminates.N. D. Zelinskii Institute of Organic Chemistry, Russian Academy of Sciences, 117913 Moscow. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 60–64, January, 1992.     

Untersuchungen an Nickeloxid-Mischkatalysatoren. XVI. Reduktionsverhalten amorpher NiO?Al2O3/SiO2-Katalysatoren

Studies on Nickel Oxide Mixed Catalysts. XVI. Reduction Behaviour of Amorphous NiO? Al₂O₃/SiO₂ Catalysts The reduction behaviour of NiO? Al₂O₃/SiO₂ catalysts prepared by precipitationdeposition is influenced by the phase composition (amorphous nickel layersilicates and nickel alumino layersilicates, nickel spinels, nickel oxide) and the differences of the composition between surface and bulk. TPR measurements, determinations of the reduction degree, and the nickel particle sizes by static magnetic measurements showed that the reducibility of the NiO? Al₂O₃/SiO₂ catalysts is enhanced and the nickel dispersity is decreased at low Al₂O₃ contents. The decrease of the reducibility at Al₂O₃ contents >5 mole% is caused by the formation of nickel spinels and the decrease of the Ni^II ion surface concentration.     

不同硅铝比Al-ITQ-13分子筛的甲醇制丙烯反应催化性能

采用晶种法直接合成了硅铝比(SiO_2/Al_2O_3物质的量比)为137、224和309的三种Al-ITQ-13分子筛,并采用粉末X射线衍射(XRD)、扫描电镜(SEM)、N_2吸附-脱附、固体核磁共振(MAS NMR)和NH_3-程序升温脱附(NH_3-TPD)等分析方法对不同硅铝比分子筛进行了表征,并在固定床微型反应评价装置上,考察了硅铝比对甲醇转化制丙烯反应性能的影响。结果表明,不同硅铝比Al-ITQ-13分子筛呈现出相似的织构性质,酸量及酸强度随着硅铝比的升高逐渐下降。硅铝比对甲醇转化反应的产物分布存在较大的影响;随着硅铝比的升高,氢转移反应和芳构化反应活性降低,使得乙烯选择性下降,而丙烯和丁烯的选择性升高。硅铝比由137提高到309,丙烯的选择性(质量分数)由46.04%增加到55.52%,而丙烯/乙烯比由3.39提高到6.57。     

系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

Influence of preliminary treatment on activity and selectivity of Co-alumosilicate catalyst in hydrocarbon synthesis from CO and H2

The temperature and medium of preliminary treatment of 10% Co/SiO ₂·Al₂O₃ influence the activity and selectivity in hydrocarbon synthesis from CO and H₂. Treatment with NH₃ reduces the yield. Increasing the treatment temperature leads to a loss of activity and a change in the composition of hydrocarbons formed. The reason for deactivation is a change in the catalyst surface texture, its adsorptive properties, and the ability to be reduced.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1709–1713, August, 1990.     

Effect of preliminaey heating on the physicochemical properties of 10% Co/Al2O3 catalyst and its behavior in hydrocarbon synthesis from CO and H2

The effect of preliminary heating of 10% Co/Al₂O₃ in air at 20–600°C on its surface composition, reducibility, and adsorption properties has been studied by programmed thermal reduction (PTR), IR spectroscopy, and DTA. It has been shown that increasing the pretreatment temperature strengthens the interaction between cobalt and the carrier, resulting in an increase in the fraction of weakly bound adsorbed CO on the surface of the reduced catalyst. The activity of Co/Al₂O₃ has been studied in the Fischer-Tropsch synthesis and it has been proposed that the centers of weakly bound linear forms of CO adsorption are involved in the formation of C₂ ⁺ hydrocarbons from CO and H₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2444–2450, November, 1991.     

Deactivation behaviors of hybrid Fischer–Tropsch catalysts in the production of middle distillate from synthesis gas in a dual-bed reactor

Production of middle distillate (C₁₀–C₂₀) from synthesis gas (CO + H₂) through hydrocracking of wax (>C₂₁₊) was carried out in a dual-bed reactor. Fischer–Tropsch catalyst (Co/TiO₂) was used in the first-bed reactor to produce wax from synthesis gas, and a mesoporous Pd–alumina composite catalyst (Pd–Al₂O₃) was used in the second-bed reactor to produce middle distillate through hydrocracking of wax. Both Fischer–Tropsch synthesis function of Co/TiO₂ catalyst and hydrocracking function of Pd–Al₂O₃ catalyst were deactivated during 100 h-hybrid Fischer–Tropsch synthesis reaction. It was revealed that deactivation behaviors of Co/TiO₂ and Pd–Al₂O₃ catalysts were governed by different factors. Wax accumulation and Co sintering were responsible for deactivation of Co/TiO₂ catalyst in the Fischer–Tropsch synthesis reaction. Loss of Pd dispersion and Pd surface area of Pd–Al₂O₃ catalyst was responsible for its decreased catalytic performance in the production of middle distillate through hydrocracking of wax.     

Organic‐Free,ZnO‐Assisted Synthesis of Zeolite FAU with Tunable SiO2/Al2O3 Molar Ratio

Zeolite FAU with tunable SiO₂/Al₂O₃ molar ratio has been successfully synthesized in the absence of organic structure‐directing agents (OSDA). Specifically, the addition of zinc species contributes to the feasible and effective adjustment of the framework SiO₂/Al₂O₃ molar ratio between about 4 and 6 depending on the amount of zinc species added in the batch composition. In contrast, a typical OSDA such as tetramethylammonium hydroxide (TMAOH) has a limited effect on the SiO₂/Al₂O₃ molar ratio of the zeolite. The role of zinc species is essential for the crystallization of zeolite FAU with a higher SiO₂/Al₂O₃ molar ratio under the particular synthesis conditions. It is speculated that zinc species may suppress the incorporation of aluminum into the aluminosilicate framework, which is due to the Coulombic repulsive interaction. A higher SiO₂/Al₂O₃ molar ratio is also found to be accompanied by a lower CO₂ adsorption heat for CO₂/CH₄ separation.     

AES investigation of thermally sprayed Al2O3 coatings on steel

Summary The investigation of plasma sprayed steel/Al₂O₃ composites by means of Auger Electron Spectroscopy (AES) combined with depth profile analysis is described. Incomplete sprayed Al₂O₃ layers permit analysis of single sprayed particles and of surrounding uncovered steel substrate regions. More complete coatings are separated from the substrates, so that contact surfaces of substrates and Al₂O₃ layers can be analyzed. In order to determine the influence of preheating the substrates on the interface widths between steel substrate and Al₂O₃ coating and therefore on the adherence mechanism, both procedures are carried out for two preheating temperatures. It is shown that preheating hardly effects the interface widths beneath single sprayed particles but it causes laterally constant widths for complete layer fragments. Additionally, a comprehensive view about oxide layer thicknesses on the steel substrates before and after plasma spraying is offered.     

Preparation and characterization of supports with a synthesized layer of catalytic filamentous carbon: IV. Synthesis of carbon nanofibers on a Co/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst

A comparative study of the synthesis of carbon layers, including catalytic filamentous carbon, on the surface of various alumina modifications was made. The synthesis was performed by the pyrolysis of alkanes (a propane-butane mixture) on Co/Al₂O₃ supported catalysts. The texture characteristics (specific surface area and pore structure) of the starting supports and adsorbents with a synthesized carbon layer were studied. The surface morphology of Co/Al₂O₃ catalysts and the synthesized carbon deposits was studied by scanning electron microscopy. It was found that carbon nanofibers were formed only on the catalysts prepared by the homogeneous precipitation of Co compounds onto the surface of macroporous α-Al₂O₃, whereas carbon deposits on mesoporous aluminum oxides did not exhibit a pronounced fibrous structure. The applicability of C/Co/Al₂O₃ carbon-containing adsorbents to the immobilization of the nitrile hydratase enzyme and the preparation of a biocatalyst for acrylonitrile hydration to acrylamide was considered.     

Eco-friendly synthesis of high silica zeolite Y with choline as green and innocent structure-directing agent

Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure-directing agents (OSDAs), which are chronically hazardous to humans and the environment. It is a growing trend to develop an eco-friendly and nuisanceless OSDA for zeolite synthesis. Herein, choline is employed as a non-toxic and green OSDA to synthesize high silica Y zeolite with SiO₂/Al₂O₃ ratios of 6.5–6.8. The prepared Y zeolite samples exhibited outstanding (hydro)thermal stability at ultrahigh temperature owing to the higher SiO₂/Al₂O₃ ratio. The XRF, SEM, ²⁹Si-NMR and ¹³Na+ results suggested that choline plays a structure-directing role in the synthesis of Y zeolite, while the feed molar fraction of Na⁺ is a crucial determinant for the framework SiO₂/Al₂O₃ ratio and the crystal morphology.     

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.