Fischer-Tropsch reaction over cobalt catalysts supported on zirconia-modified activated carbon

An attractive Fischer-Tropsch catalyst was prepared using an activated carbon as carrier to support cobalt based catalysts. Zr promoted Co/AC catalysts remarkably enhanced the activity and the selectivity toward diesel distillates and lower the methane selectivity. This modification may be attributed to specific behavior of activated carbon with high surface area and the weak interaction between metallic cobalt active sites and activated carbon. It was emphasized that the pore size of activated carbon played a very important role in restricting the growth of carbon chain to wax.

Preparation of Mn substituted La-hexaaluminate catalysts by using supercritical drying

LaMnxAl12-xO19 catalysts were prepared from NH4OH and metal nitrates solutions. Supercritical drying (SCD) and conventional oven drying (CD) methods were used to extract the water in the hydrogel. The effects of drying methods on properties of the catalysts were investigated by means of TEM, N-2-adsorption, thermogravimetry (TG)-differential thermal analysis (DTA) and X-ray diffraction. SCD method is beneficial to maintain high surface area and improving catalytic activity for methane combustion of the catalyst. The specific surface area and pore volume of LaMn1Al11O19 catalyst prepared by SCD method are 28 m(2)/g and 0.23 cm(3)/g, respectively, and the ignition of methane could be carried out at 450degreesC. However, those of the CD catalyst prepared from the same precursor are 15 m(2)/g, 0.11 cm(3)/g and 530 degreesC, respectively. Suitable Mn content (0 less than or equal to x less than or equal to 2) could promote the formation of LaMnAl11O19 hexaaluminate, while further addition of Mn (2 less than or equal to x less than or equal to 6) cause the formation of LaMnO3. (C) 2003 Elsevier B.V All rights reserved.

Formation of a novel type of reverse microemulsion system and its application in synthesis of the nanostructured La0.95Ba0.05MnAl11O19 catalyst

In the study, a novel microemulsion system, consisting of water, iso-propanol and n-butanol, was developed to synthesize the nanostructured La0.95Ba0.05MnAl11O19 catalyst with high surface area and catalytic activity for methane combustion.

Difference of ZSM-5 zeolites synthesized with various templates

ZSM-5 zeolites with similar SUM ratio were synthesized successfully using various templates (n-butylamine (BTA), ethylamine (ETA), isopropylamine (IPA), ethylenediamine (EDA), ethanol (ETL), ethanol-ammonium (ETL-AM) and no template (NT)) under hydrothermal conditions. The samples were characterized by XRD, SEM, XRF, NH3-TPD and BET surface area measurements in order to understand the template effects and the differences of the ZSM-5 samples. The synthesis of ZSM-5 with organic templates was relatively easier than those with inorganic templates and without template. SEM results revealed that ZSM-5 synthesized with different templates had different morphology and particle size. The Si/Al ratio and BET specific surface area of the sample with ethanol as template was the lowest. NH3-TPD results showed that the sample synthesized without template had fewer strong acid sites than others. n-Hexane cracking reaction was carried out over the samples to evaluate the catalytic properties. All ZSM-5 zeolites were effective in n-hexane cracking reaction, especially for the sample synthesized without template. (C) 2004 Elsevier B.V. All rights reserved.

Activated carbon supported bimetallic CoMo carbides synthesized by carbothermal hydrogen reduction

A carbothermal hydrogen reduction method was employed for the preparation of activated carbon supported bimetallic carbide. The resultant samples were characterized by BET surface area measurement, X-ray diffraction, and temperature-programmed reduction-mass spectroscopy. The results showed that nanostructured beta-Mo2C can be formed on the activated carbon by carbothermal hydrogen reduction above 700 degreesC. The particle sizes of beta-Mo2C increase with increasing reaction temperatures and Mo loading. The bimetallic CoMo carbide can be synthesized by the carbothermal hydrogen reduction even around 600 degreesC. The bimetallic CoMo carbide is from carbothermal hydrogen reduction of CoMoO4 precursor and is easily formed when the Co/Mo molar ratio is 1.0. Separation of the bimetallic CoMo carbide phase into Mo carbide and Co metal occurs when the temperature of the reduction is above 700 degreesC. The addition of a second metal such as Co and Ni, decreases the formation temperature of carbide because the second metal promotes formation of CHx species from reactive carbon atoms or groups on carbon material and hydrogen, which further carburizes oxide precursors. (C) 2003 Elsevier Science Ltd. All rights reserved.

Synthesis and spectroscopic study of mesoporous aluminum methylphosphonate foam templated by dibutyl methylphosphonate

New types of templates and novel interactive mechanisms between template and framework are very important for creating porous materials. In this work, by using neutral dibutyl methylphosphonate as a template, an inorganic-organic hybrid mesoporous material, aluminum methylphosphonate, was prepared. The as-synthesized material was studied by P-31 magnetic angle spinning nuclear magnetic resonance (MAS NMR), Al-27 MAS NMR, C-13 CP/MAS, FT-IR spectroscopy, thermogravimetry (TG), differential thermal analysis (DTA), and transmission electron microscopy. After thermal treatment at 673 K and 10 mmHg for 2 h, hybrid mesoporous foam was obtained. The transformation process was investigated by FT-IR. TG-DTA results indicate that the methyl group bonded to the framework keeps intact up to 792 K under air and 823 K under nitrogen. The characterization results from nitrogen gas adsorption-desorption measurements show that the BET surface area and the Barrett-Joyner-Halenda desorption cumulative pore volume of the foam are 90 m(2) g(-1) and 0.32 cm(3) g(-1) respectively. (C) 2003 Elsevier Inc. All rights reserved.

Shape selectivity in methane dehydroaromatization over Mo/MCM-22 catalysts during a lifetime experiment

Dehydroaromatization of CH4 with 2% CO2 on 6Mo/MCM-22 in a 100-h lifetime test was carried out at 993 K, atmospheric pressure and 1500 mL/gh. The duration of the lifetime test can be divided into an induction stage, stable stage and deactivation stage on the basis of the selectivities of hydrocarbons and coke. The characteristics of deposited coke with different time onstream were studied using TPO and TG techniques. There were two peaks corresponding to two kinds of coke recorded in TPO profiles, and the oxidation temperature of coke shifted to higher values with less hydrogen content with the increase of coke deposits. BET and Benzene-TPD techniques were employed to study the variation of specific surface area of the external and micropore surface versus time onstream. With the accumulation of coke deposits, although the pores became partially blocked and the internal surface decreased, methane could still enter the channel and was converted to benzene with shape selectivity until a critical value of coke deposition was reached.

Effects of inoculated Microcoleus vaginatus on the structure and function of biological soil crusts of desert

Microcoleus vaginatus Gom., the dominant species in biological soil crusts (BSCs) in desert regions, plays a significant role in maintaining the BSC structure and function. The BSC quality is commonly assessed by the chlorophyll a content, thickness, and compressive strength. Here, we have studied the effect of different proportions of M. vaginatus, collected from the Gurbantunggut Desert in northwestern China, on the BSC structure and function under laboratory conditions. We found that when M. vaginatus was absent in the BSC, the BSC coverage, quantified by the percentage of BSC area to total land surface area, was low with a chlorophyll a content of 4.77 x 10(-2) mg g(-1) dry soil, a thickness of 0.86 mm, and a compressive strength of 12.21 Pa. By increasing the percentage of M. vaginatus in the BSC, the BSC coverage, chlorophyll a content, crust thickness, and compressive strength all significantly increased (P < 0.01). The maximum chlorophyll a content (13.12 mg g(-1)dry soil), the highest crust thickness, and the compressive strength (1.48 mm and 36.60 Pa, respectively) occurred when the percentage of inoculated M. vaginatus reached 80% with a complex network of filaments under scanning electron microscope. The BSC quality indicated by the above variables, however, declined when the BSC was composed of pure M. vaginatus (monoculture). In addition, we found that secretion of filaments and polymer, which stick sands together in the BSC, increased remarkably with the increase of the dominant species until the percentage of M. vaginatus reached 80%. Our results suggest that not only the dominant species but also the accompanying taxa are critical for maintaining the structure and functions of the BSC and thus the stability of the BSC ecosystems.

Direct electrochemistry of horseradish peroxidase immobilized in calcium carbonate microsphere doped with phospholipids

Protein electrochemistry affords a direct method to study the biological electron transfer processes. However, supplying a biocompatible environment to maintain the native state of protein is all-important and challengeable. Here, we chose vaterite, one of the crystalline polymorphs of calcium carbonate, with highly porous nature and large specific surface area, which was doped with phospholipids, as the matrix to immobilize horseradish peroxidase (HRP). The integrity of HRP was kept during the simple immobilization procedure. By virtue of this organic/inorganic complex matrix, the direct electrochemistry of HRP was realized, and the activity of HRP for catalyzing reduction of O-2 and H2O2 was preserved.

Preparation of Pd/C catalyst for formic acid oxidation using a novel colloid method

A novel colloid method using (WO3)(n)center dot xH(2)O as colloidal source was developed to prepare Pd/C catalyst for formic acid oxidation. Transmission electron microscopy image shows that the Pd/C nanoparticles have an average size of 3.3 nm and a narrow size distribution. Electrochemical measurements indicate that the Pd/C catalyst exhibits significantly high electrochemical active surface area and high catalytic activity with good stability for formic acid oxidation compared with that prepared by common method.

Synthesis, characterization and optical property of flower-like indium tin sulfide nanostructures

We report a simple method for novel flower-like In4SnS8 nanostructure synthesis. A flower-like In4SnS8 nanostructure was synthesized via a one-pot hydrothermal route using the biomolecule L-cysteine as a sulfur source. The structure was characterized using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption analysis and photoluminescence spectra. This flower-like structure consists of crosslinked nanoflakes and possesses good thermostability and a high BET surface area.

Hydrothermal Synthesis, Structures, and Luminescent Properties of Seven d(10) Metal-Organic Frameworks Based on 9,9-Dipropylfluorene-2,7-Dicarboxylic Acid (H(2)DFDA)

A series of Zn(II) and Cd(II) metal-organic frameworks, namely, [Zn(DFDA)] (1), [Cd(DFDA)(C2H5OH)] (2), [Zn-2(DFDA)(2)(L-1)(2)](2) center dot 3H(2)O (3), [Cd-2(DFDA)(2)(L-1)(2)] (4), [Zn(DFDA)(L-2)] (5), [Cd(DFDA)(L-2)(DMF)] (6), and [Zn(DFDA)(L-3)] (7) (where DFDA = 9,9-dipropylfluorene-2,7-dicarboxylate anion, L-1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L-2 = 1,1'-(1,4-butanediyl) bis(imidazole), L-3 = 2,2'-bipyridine) have been synthesized under hydrothermal conditions and structurally characterized. Compound 1 exhibits a three-dimensional (3D framework containing one-dimensional (1D) Zn(II)-O clusters, with (4(8).6(7)) topology. Compound 2 contains hydrophobic channels built from infinite 1D Cd(II)-O clusters, with (4(8).5(4).6(3)) topology.

Single-walled carbon nanohorn as new solid-phase extraction adsorbent for determination of 4-nitrophenol in water sample

Single-walled carbon nanohorn (SWCNH) was developed as new adsorbent for solid-phase extraction using 4-nitrophenol as representative. The unique exoteric structures and high surface area of SWCNH allow extracting a large amount of 4-nitrophenol over a short time. Highly sensitive determination of 4-nitrophenol was achieved by linear sweep voltammetry after only 120 s extraction. The calibration plot for 4-nitrophenol determination is linear in the range of 5.0 x 10(-8) M-1.0 x 10(-5) M under optimum conditions. The detection limit is 1.1 x 10(-8) M. The proposed method was successfully employed to determine 4-nitrophenol in lake water samples, and the recoveries of the spiked 4-nitrophenol were excellent (92-106%).

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH4)(2)PtCl6 and Ru(OH)(3)) on the carbon support before metal reduction: the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method. even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst.

The size-controlled synthesis of Pd/C catalysts by different solvents for formic acid electrooxidation

The size-controlled synthesis of Pd/C catalyst for formic acid electrooxidation is reported in this study. By using alcohol solvents with different chain length in the impregnation method, the sizes of Pd nanoparticles can be facilely tuned; this is attributed to the different viscosities of the solvents. The results show that a desired Pd/C catalyst with an average size of about 3 nm and a narrow size distribution is obtained when the solvent is n-butanol. The catalyst exhibits large electrochemically active surface area and high catalytic activity for formic acid electrooxidation.