Observations of novel carbon nanotubes with multiple hollow cores

Usually carbon nanotubes (CNTs) containing only one hollow core are obtained from the catalytic decomposition of hydrocarbons when hydrocarbon gases flow straight into the reaction tube. However, unusual carbon nanotubes with multiple hollow cores were observed when the gas-feed method was changed in an attempt to increase CNT production yield using a floating catalyst method. The fraction of multicored carbon nanotubes can be as high as 60%. The formation of such an unusual structure is ascribed to the introduction of pentagon and heptagon defects to the CNTs in the growth process, owing to the change of gas-feed method. This finding enriches the family of CNTs and could be helpful in understanding the CNT formation mechanism.     

钾改性铁钼碳化物催化剂及其CO加氢性能

制备了碳化铁和钾掺杂碳化钼催化剂并对其CO加氢合成低碳混合醇性能进行了考察.结果表明当只有β-碳化钼存在时,产物主要是烃类以及微量的醇.经过钾改性后,β-碳化钼催化剂上产物低碳醇含鼍增加;而同时被碳化铁和钾改性后,低碳醇的含量进一步增加,并且高级醇(C_(2+)OH)收率町达到0.14 g/(mL·h).β-碳化钼催化剂上醇烃产物均符合线性Anderson-Schuhz-Mory(A-S-F)分布曲线,而钾改性β-碳化钼以及钾和碳化铁改性的催化剂上醇产物为独特的甲醇负偏离A-SF分布.这表明钾和碳化铁的加入有效促进了C_1OH到C_2OH的链增长步骤.从而有利于C_(2+)OH高级醇的生成.     

Facile synthesis of high surface area molybdenum carbide nanoparticles

Molybdenum carbide has immense potential as an active catalyst for reaction systems such as synthesis of important chemicals like ammonia. However, the carbide is not used as a commercial catalyst or support as the current synthesis processes produce low surface area material or have contaminants such as excess carbon and surface and chemisorbed oxygen. Moreover, attempts to refine the synthesis pathways are usually not supported by any thermochemical modeling. In this study, a facile and reproducible method to synthesize high surface area molybdenum carbide was developed with the help of thermochemical modeling to better understand molybdenum-carbon phase behavior. We have synthesized 2-5 nm particles of Mo_xC with surface areas of up to 360 m²/g as characterized using a variety of techniques including X-ray diffraction and electron microscopy.     

钛和沥青机械合金化合成纳米级碳化钛

Abstract TiC powder was synthesized by mechanical alloying of titanium and asphalt in this paper. Deoiled asphalt as a carbon source not only provided element C in the fabrication of TiC but also cracked itself by the mechanical alloying process. The results of X-ray diffraction demonstrated the synthesis of cubic TiC. Gas phase chromatography showed that the discharged gas was composed of low molecular weight hydrocarbons, including H2, CH4 and C2H6. The formation mechanism of titanium carbide by mechanical alloying, and the thermodynamic and kinetics were discussed. These results showed that mechanical alloying is a promising method to prepare TiC and to crack asphalt with some light fraction byproducts.     

The role of the hydrocarbon source on the growth of carbon materials

In recent years extensive studies on carbon nanotubes has led to the synthesis and characterization of other carbons with a wide range of morphologies. Current understanding is that the carbon reagents decompose in the presence of a catalyst to give C atoms that then combine or extrude into carbon nanotubes, fibers (or spheres). This mechanism does not indicate how the structure of the carbon source can impact on a material’s growth, in particular at low temperatures. In this paper we show that evidence exists to indicate that the structure of hydrocarbons (and other carbon reagents) has the ability to influence the carbon growth process. This can be achieved by catalyst–reactant effects (and subsequent catalyst reconstruction) that are influenced by both the production of carbon fragments and radicals produced in the gas phase or by direct reaction of the carbon source with the metal particle. A modification of the current Baker carbon growth model, to show the metal–catalyst interactions, that takes this information into account (particularly at temperatures lower than 500 °C) is proposed.     

Catalyst‐Assisted Growth of Single‐Crystalline Hafnium Carbide Nanotubes by Chemical Vapor Deposition

Single‐crystalline hafnium carbide (HfC) nanotubes were synthesized by a one‐step catalyst‐assisted chemical vapor deposition (CVD) method. The typical nanotubes had uniform diameters of ~60 nm and wall thicknesses of ~15 nm and preferentially grew along [201]. From HRTEM/EELS analysis, the growth mechanism based on carbon nanotubes (CNT) tip growth and CNT‐templated reaction was proposed for explaining the formation of HfC nanotubes. According to the mechanism, CNTs were first formed by diffusion of C atoms on the surface of solid Ni catalyst particles. Then, gaseous Hf species reacted with C atoms from CNTs to form HfC nanotubes. During the entire growth process, Hf atoms did not participate in the catalytic reaction. Thus, this process was distinguished from the conventional vapor–liquid–solid process.     

Deep oxidation of aqueous organics over a silicon carbide-activated carbon supported platinum–ruthenium bimetallic catalyst

In previous work, we developed a highly active bimetallic platinum–ruthenium catalyst supported on a very high surface area activated carbon substrate. In fixed bed reactors, this catalyst proved capable of the continuous long-term deep oxidation of a variety of aqueous organic contaminants associated with spacecraft wastewater streams at 121 °C. This work was extended to the mineralization of more typical environmental contaminants, including halocarbons and aromatics. The primary weakness of this catalyst was the tendency toward relatively high rates of chemical decomposition. To overcome this limitation, methods were developed for the production of a silicon carbide coating over the surface of the activated carbon, yielding a reasonable trade-off between increasing resilience and decreasing surface area. Here we report the catalytic decomposition of dissolved organic contaminants at 130 °C using this silicon carbide/activated carbon supported bimetallic catalyst.     

Processing of organochlorine waste components on bulk metal catalysts

A method for destroying chloroorganic waste components on catalysts, particularly bulk metal nickel (99.99%), nichrome (80% Ni and 20% Cr), and chromel (90% Ni and 10% Cr) is proposed. The process is accompanied by the formation of carbon nanofibers (CNFs) with feathery morphology. Catalytic destruction of 1,2-dichloroethane on bulk nickel catalysts is characterized by a long induction period (～3 h) with spontaneous activation of the alloy’s surface. Preactivation of the catalyst with acids or by alternative treatment in oxidizing and reducing environments shortens the induction period by one order of magnitude. The state of the surface before and after activation is studied by SEM, TEM, and EDX. The activity of catalysts is determined for the decomposition of 1,2-dichloroethane at temperatures of 500 to 700°C. Nichrome exhibited the greatest activity (yield of CNFs, 400 g/g of catalyst); the yield of CNFs on catalysts prepared by coprecipitation and mechanical activation was considerably lower. The proposed approach combines organochlorine waste disposal with the production of a useful product (CNFs). The use of bulk metal catalysts is promising since it simplifies the technology for their preparation, and the absence of carriers makes it easy to cleanse CNFs of impurities of catalyst fragments.     

我国聚氯乙烯行业未来发展布局的思考

电石法PVC工艺作为我国主流PVC生产工艺适宜我国国情需要,符合国家能源战略安全需求,近年来我国电石法PVC企业在加速产业转型升级、推动无汞催化剂绿色化技术研发等方面的有力举措为电石法工艺的未来发展奠定了坚实基础.作者认为电石法PVC在我国PVC行业未来5～10年,甚至更长时期,其路线重要,不可轻易替代.     

A continuous process for recovery of sulfur from natural gas containing low concentrations of hydrogen sulfide

A continuous catalytic process was developed to remove hydrogen sulfide from a natural gas stream using activated carbon as catalyst. The concentration range of hydrogen sulfide in the gas stream studied was 300–3000 ppmv (0.0126–0.126 moles/m³). Virtually 100 percent conversion of hydrogen sulfide was achieved by the combination of various parameters. The “field gas” employed in this study exhibited cracking of some heavier hydrocarbons and made the product sulfur slightly brown. These hydrocarbons should therefore be separated from the gas stream prior to the oxidation reaction. No carbon monoxide or carbon dioxide was produced during the oxidation of hydrogen sulfide. It is concluded that the process described herein has the potential for the removal of hydrogen sulfide as sulfur from a sour natural gas stream on a continuous basis and could therefore eliminate an environmental problem which now exists.     

Effect of crystallization temperature on the in situ valorization of physic nut (Jatropha curcus L.) wastes using synthetic HZSM-5 catalyst

Physic nut waste is selected as the biomass feedstock for fast pyrolysis as it is available in large amounts from biodiesel production in Thailand. The volatile matter and fixed carbon contents are 73.8% and 13.6% while ash contents are 5.8%. Carbon is the main element with 49.03 wt%. The oxygen content of 39.0 wt% is considerably high which could directly convert to the oxygenated pyrolysis liquid products. To decrease oxygenated compounds, HZSM-5 was used as a catalyst to upgrade pyrolytic products from fast pyrolysis using analytical pyrolysis–GC/MS method. The HZSM-5 catalyst was successfully synthesized by hydrothermal method at 160–180 °C for 24 h. The particle size, surface area, and pore diameter were 11.25–15.52 μm, 567–582 m²/g, and 21.78–26.11 Å, respectively. The pyrolysis was performed at 500 °C with the Jatropha wastes to catalyst ratio of 1:1–1:10. The presence of HZSM-5 contributed to eliminate the undesirable oxygenated compounds such as acids and ketones which could alleviate problem regarding acidity and instability in bio-oil. In addition, it enhanced significantly the yields of desirable hydrocarbon compounds. The increase in catalyst contents had an effect on the enhancement of hydrocarbons yields, and tended to promote deoxygenation and denitrogenation. At moderate biomass to catalyst ratio (1:5), HZSM-5 synthesized at 170 °C contributed to improve the hydrocarbon yields of 95%, including mainly toluene and xylene, which are valuable products because of their high heating value properties.     

典型碳氢化合物水蒸气重整制氢研究进展

  烃水蒸气重整是目前获取氢能源的重要方法之一,而甲烷、汽油和柴油作为典型烃类原料可满足于不同规模氢能源的需求。本文重点从催化剂、反应工艺和反应机理及动力学三个方面对甲烷、汽油和柴油蒸汽重整制氢进行介绍和评述。指出甲烷重整制氢镍基催化剂的改性和反应器设计以及反应条件的优化是其必然的发展趋势,汽油和柴油重整制氢催化剂未来设计必须具备高抗硫性和抗积炭性。此外,需加强甲烷、汽油和柴油蒸气重整制氢的机理和动力学研究。     

电石法聚氯乙烯生产中的汞污染治理

电石法生产聚氯乙烯所必需的氯化汞-活性炭触媒造成严重的汞污染,采用合适的治理措施不仅可以消除汞污染,还可实现汞资源的再利用,保障氯化汞触媒的稳定来源。通过采取低汞触媒的使用和废触媒的回收,可消除电石法聚氯乙烯生产过程中的汞污染,几乎全部的汞都能得到回用。     

Effect of hydrocarbons precursors on the formation of carbon nanotubes in chemical vapor deposition

High-temperature decomposition of hydrocarbons may lead to the formation of carbon deposits. However in our present studies, we found that the morphology of carbon deposits over MgO supported Fe catalyst during chemical vapor deposition (CVD) process was closely related to the thermodynamic properties and chemical structures of hydrocarbon precursors. Six kinds of hydrocarbons (methane, hexane, cyclohexane, benzene, naphthalene and anthracene) were used as carbon precursors in this study. Methane which has a pretty simple composition and is more chemically stable was favorable for the formation of high-purity single walled carbon nanotubes (SWNTs). For high-molecular weight hydrocarbons, it was found that the chemical structures rather than thermodynamic properties of carbon precursors would play an important role in nanotube formation. Specifically, the CVD processes of aromatic molecules such as benzene, naphthalene and anthracene inclined to the growth of SWNTs. While the cases of aliphatic and cyclic hydrocarbon molecules seemed a little more complicated. Based on different pyrolytic behaviors of carbon precursors and formation mechanism of SWNTs and multi-walled carbon nanotubes (MWNTs), a possible explanation of the difference in CVD products was also proposed.     

Continuous preparation of activated carbon supported zinc acetate catalyst and industrial synthesis of vinyl acetate from acetylene

A continuous manufacturing method of an activated carbon supported zinc acetate catalyst has been established. Based on the dipping of a crushed activated palm carbon into a zinc acetate aqueous solution, the catalyst is prepared for the synthesis of vinyl acetate from acetylene in an industrial fluidized reaction vessel. The relationship between the supported amount of zinc acetate and various factors has been studied. Based on these results, an empirical formula was developed. Using this formula, the continuous manufacturing apparatus was designed and constructed for the purpose of preparing the optimum supported fluidized catalyst. To minimize the activated carbon loss due to crushing and wearing, a vibrating conveyor system was employed. This continuous manufacturing process produced a uniform catalyst with an activated carbon feed rate of 0.25 m³ h^?1. Using this catalyst, a series of operational tests of the vinyl acetate synthesis was performed for investigating the optimum reaction conditions. These operational tests were carried out using an industrial fluidized reaction vessel of 3.28 m diameter and 50 tons day^?1 vinyl acetate production capacity. Based on these test results, the reaction rate constant and the deterioration rate constant were newly introduced, and the optimum operation conditions were then determined.     

Comprehensive kinetic study for Fischer–Tropsch reaction over KMoFe/CNTs nano-structured catalyst

The kinetics of the Fischer–Tropsch (FT) reaction was evaluated through detailed experimentation with a KMo bimetallic promoted Fe catalyst supported on carbon nanotubes (CNTs). The kinetic tests were conducted in a fixed-bed reactor under operating conditions of P = 6.9–41.3 bar, T = 543–563 K, H₂/CO = 1, gas hourly specific velocity (GHSV) = 2000 h⁻¹. This study aimed to investigate the mechanism prevailing in CO activation and the rate equation for CO consumption during FT reactions over a 0.5K5Mo10Fe/CNTs catalyst. To evaluate the synergistic effects of Fe, Mo, and K phases on the catalyst activity, both fresh and spent catalysts were thoroughly characterized using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and energy-dispersive spectroscopy (SEM-EDS), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) to ascertain the different phases (active sites) present and relevant interactions. Based on the adsorption of carbon monoxide and hydrogen, 22 possible mechanisms for monomer formation were proposed for FT synthesis in accordance with the Langmuir–Hinshelwood–Hougen–Watson (LHHW) and Eley–Rideal (ER) adsorption theories. The best fit kinetic model was identified through a multi-variable non-linear regression analysis. The selected mechanistic model was based on carbide formation approach, where H₂-assisted adsorption of CO was considered for the derivation. Kinetic parameters such as activation energy, adsorption enthalpies of H₂, and CO were estimated to be 65.0, −13.0, and −54.0 kJ/mol, respectively. Considering the developed kinetic model, the effects of reaction temperature and pressure were assessed on Fischer–Tropsch synthesis (FTS) product distribution. Additionally, the kinetic model was compared with the typical Anderson–Schulz–Flory model, suggesting the effects of water-gas-shift and the existence of additional formation pathway such as secondary re-adsorption of olefins for heavier hydrocarbons.     

电石法聚氯乙烯生产中汞污染减排初探

根据电石法生产聚氯乙烯过程中汞流向的查定结果,制定了减少废水排放的措施.介绍了低汞触媒的使用和合成气中汞的回收情况.     

Production of Silicon Carbide from Rice Husks

This paper reports the formation of ß-silicon carbide by the process of pyrolyzing rice husks (RH). The sequence of transformations and the mechanism of formation of crystalline silica, carbon, and silicon carbide from RH were investigated in detail. The structural evolution of silicon carbide particulates during the conversion process was critically examined by various techniques. Studies using X-ray diffraction and infrared spectroscopic techniques revealed that a temperature of 1500°C is desirable for the completion of the reaction between RH silica and carbon, thereby leading to the formation of ß-silicon carbide. Except for the gradual change in the morphology leading to the formation of dense crystals of ß-SiC_p, formation of alpha-SiC_p was not evidenced in the present studies. The fine particle size of ß-SiC, formed at lower reaction temperatures, apparently precluded the transformation to alpha-SiC.     

Developing ash-free high-strength spherical carbon catalyst supports

The possibility of using furfurol for the production of ash-free high-strength active carbons with spheroidal particles as adsorbents and catalyst supports is substantiated. A single-stage process that incorporates the resinification of furfurol, the molding of a spherical product, and its hardening while allowing the process cycle time and the cost of equipment to be reduced is developed. Derivatographic, X-ray diffraction, mercury porometric, and adsorption studies of the carbonization of the molded spherical product are performed to characterize the development of the primary and porous structures of carbon residues. Ash-free active carbons with spheroidal particles, a full volume of sorbing micro- and mesopores (up to 1.50 cm³/g), and a uniquely high mechanical strength (its abrasion rate is three orders of magnitude lower than that of industrial active carbons) are obtained via the vapor-gas activation of a carbonized product. The obtained active carbons are superior to all known foreign and domestic analogues and are promising for the production of catalysts that operate under severe regimes, i.e., in moving and fluidized beds.     

Wet oxidation of wastewater containing hydrocarbons by novel supported Pd catalysts

Pd catalysts supported on TiO₂, ZrO₂, ZSM-5, MCM-41 and activated carbon were used in catalytic wet oxidation of hydrocarbons such as phenol, m-cresol and m-xylene. It was found that the Pd/TiO₂ catalyst was highly effective in the wet oxidation of hydrocarbon. The activities of catalysts with various hydrocarbon species, catalyst support, oxidation state of catalyst performed in a 3-phase slurry reactor show that reaction on Pd surface is more favorable than that in aqueous phase and that the active site is oxidized Pd in catalytic wet air oxidation of hydrocarbons. Based on the experimental results, a plausible reaction mechanism of wet oxidation of hydrocarbons catalyzed over Pd/TiO₂ catalyst was proposed. This catalyst is superior to other oxide catalysts because it suppressed the formation of hardly-degradable organic intermediates and polymer.