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Synthesis, characterization and catalytic properties of mesoporous MCM-48 containing zeolite secondary building units
LI Qiang, ZHANG Ying, DOU Tao, LI Yuping, WANG Shan, SUN Famin
Front. Chem. Sci. Eng.. 2007, 1 (1): 1-5.
https://doi.org/10.1007/s11705-007-0001-0
Mesoporous aluminosilicate MCM-48 containing zeolite secondary building units in the pore wall has been synthesized in alkaline media with a two-step procedure. The aluminosilicate precursors comprising zeolite secondary building units were first synthesized by carefully controlling reaction conditions and then were assembled using cotemplates of gemini surfactant [C18H37N(CH3)2(CH2)3N(CH3)2C18H37]2+ (18-3-18) and triethanolamine (TEA). X-ray Diffraction (XRD) patterns of the as-made samples indicated that highly ordered mesostructured MCM-48 was formed. Transmission Electron Microscopy (TEM) images further verified the formation of MCM-48 with uniform cubic pore channel system having the pore opening diameter of about 25 Å. Compared with the conventionally synthesized MCM-48, the as-synthesized MCM-48 sample showed an adsorption band at 520 600 cm-1 in its FT-IR spectrum, which was assigned to five-membered ring vibration from zeolite structure. This suggested the presence of zeolite building units in the pore wall. N2 adsorption data showed that the material had a much higher specific surface area (1 200 m2/g) than the conventional MCM-48(1 100 m2/g). Finally, the catalytic performance of the as-made MCM-48 was evaluated by hydrogenation dealkylation reaction of heavy aromatic hydrocarbons. Catalytic results showed that the as-made MCM-48 catalyst exhibited higher conversion than the conventional MCM-48 catalyst. The as-made mesostructured MCM-48 may have a potential catalytic application in the conversion of bulky molecules.
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Properties of La1-xCexCoO3 system perovskite-type catalysts for diesel engine exhaust removal
GONG Cairong, FAN Guoliang, HOU Yanfeng, ZHANG Zhongrong, SONG Chonglin, HUANG Qifei
Front. Chem. Sci. Eng.. 2007, 1 (1): 6-10.
https://doi.org/10.1007/s11705-007-0002-z
A series of complex oxide La1-xCexCoO3 catalysts was synthesized at a low temperature through a combustion process, in which x is among 0, 0.1, 0.2, 0.4 and 0.6 corresponding to the quantity of La3+ partial substitution by Ce4+. The catalysts were characterized for phase composition using chemical analysis and X-ray diffraction. The catalytic activity of the catalysts in removal of NOx, total hydrocarbon (THC) and particulate matter (PM) from diesel exhaust gases were examined in detail using temperature-programmed reaction technique. The results show that after partial substitution of La3+ with Ce4+, the oxygen vacancy concentration increases significantly and a Co3+-Co2+ system is formed. Consequently, the catalytic activity in the removal of THC and NOx is significantly improved. But for the PM, the effect is not so obvious. The possible catalytic mechanism for this was presented. It is also worth noting that the doped catalysts showed good stability.
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Effect of glow discharge plasma on rhodium-based catalyst for oxygenates synthesis
HUANG Lihong, CHU Wei, XU Junqiang, HONG Jingping, YI Min
Front. Chem. Sci. Eng.. 2007, 1 (1): 16-19.
https://doi.org/10.1007/s11705-007-0004-x
Rhodium-based catalysts were prepared by impregnation, treated with glow discharge plasma, characterized by X-ray diffraction, X-ray photoelectron spectroscopy, H2 temperature-programmed reduction, H2 temperature-programmed desorption and CO temperature-programmed desorption, and investigated for oxygenate synthesis from CO hydrogenation. Based on the characterization results, plasma treatment endowed the samples with smaller particle size, higher dispersion of active components, and an enrichment of active components on the surface as well. As a result, the reducibility and adsorption properties were modified. In catalytic tests, the catalytic activity for CO hydrogenation over the samples treated by plasma was improved remarkably: the conversion of CO and the yield of oxygenates increased at most by a factor of 78.62% and 51.96%, respectively, while the selectivity of ethanol and methanol in the oxygenates was enhanced as well.
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Preparation and influence of performance of anodic catalysts for direct methanol fuel cell
WANG Zhenbo, YIN Geping, SHI Pengfei
Front. Chem. Sci. Eng.. 2007, 1 (1): 20-25.
https://doi.org/10.1007/s11705-007-0005-9
This research aims at increasing the utilization of platinum-ruthenium alloy (Pt-Ru) catalysts and thus lowering the catalyst loading in anodes for methanol electrooxidation. The direct methanol fuel cell s (DMFC) anodic catalysts, Pt-Ru/C, were prepared by chemical reduction with a reducing agent added in two kinds of solutions under different circumstances. The reducing agent was added in hot solution with the protection of inert gases or just air, and in cold solution with inert gases. The catalysts were treated at different temperatures. Their performance was tested by cyclic voltammetry and potentiostatic polarization by utilizing their inherent powder microelectrode in 0.5 mol/L CH3OH and 0.5 mol/L H2SO4 solution. The structures and micro-surface images of the catalysts were determined and observed by X-ray diffraction and transmission electron microscopy, respectively. The catalyst prepared in inert gases showed a better catalytic performance for methanol electrooxidation than that prepared in air. It resulted in a more homogeneous distribution of the Pt-Ru alloy in carbon. Its size is small, only about 4.5 nm. The catalytic performance is affected by the order of the reducing agent added. The performance of the catalyst prepared by adding the reductant at constant temperature of the solution is better than that prepared by adding it in the solution at 0?C and then heating it up to the reducing temperature. The structure of the catalyst was modified, and there was an increase in the conversion of ruthenium into the alloyed state and an increase in particle size with the ascension of heat treatment temperature. In addition, the stability of the catalyst was improved after heat treatment.
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Effect of steady shear on multi-axial texture of symmetric diblock copolymers
XU Hui, LIU Honglai, HU Ying
Front. Chem. Sci. Eng.. 2007, 1 (1): 26-34.
https://doi.org/10.1007/s11705-007-0006-8
The effect of steady shear on multi-axial texture of symmetric diblock copolymer was investigated by using dynamic density functional theory. Through modifying the periodic boundary condition, the parallel-transverse biaxial texture and perpendicular-parallel-transverse triaxial texture have been observed. In the formation of the multi-axial texture, there are two critical velocities μ*per-par and µ*par-tra, at which the transition between the perpendicular and the parallel lamellar morphology, and the transition between the parallel and the transverse lamellar morphology occur, respectively. The two critical velocities increase as the interaction parameter increases, but they almost remain constant at different shear rates. Furthermore, the rotation from the transverse lamellae to the parallel lamellae induced by the shear strain, and the increase of lamellar spacings of the three lamellae after removing the shear, have also been observed by the time evolution of the morphologies. These phenomena are consistent with experimental work.
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Preparation and characterization of SO42-/TiO2 and S2O82-/TiO2 catalysts
MA Xuedan, GUO Daishi, JIANG Qizhong, MA Zifeng, MA Zhengfei, YE Weidong, LI Chunbo
Front. Chem. Sci. Eng.. 2007, 1 (1): 45-49.
https://doi.org/10.1007/s11705-007-0009-5
Nanosized solid superacids SO42-/TiO2 and S2O82-/TiO2, as well as MCM-41-supported SO42-/ZrO2, were prepared. Their structures, acidities, and catalytic activities were investigated and compared using XRD, N2 adsorption-desorption, and in situ FTIR-pyridine adsorption, as well as an evaluation reaction with pseudoionone cyclization. The results showed that SO42-/TiO2 and S2O82-/TiO2 possess not only nanosized particles with diameters <7.0 nm, a BET surface greater than 140 cm2/g and relatively regular mesostructures with pores around 4.0 nm, but also a pure anatase phase and strong acidity. Different from the Lewis acid nature of SO42-/ZrO2/MCM-41, SO42-/TiO2 and S2O82-/TiO2 exhibit mainly Br¢nsted acidities. The strongest Br¢nsted acid sites were produced on SO42-/TiO2 promoted with H2SO4, while Lewis acid sites on S2O82-/TiO2 even stronger than those on SO42-/ZrO2/MCM-41 were generated when persulfate solution was used as sulfating agent. Because of their distinct acid natures, SO42-/TiO2 and S2O82-/TiO2 exhibited catalytic activities for the cyclization of pseudoionone that were much higher than that of SO42-/ZrO2/MCM-41. It can be concluded that the existence of more Br¢nsted acid sites was favorable for proton participation in the cyclization reaction.
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Preparation and properties of nano SiO2 core-shell structured additives and their nanocomposite with polypropylene
KE Yangchuan, SUN Mingzhuo, SONG Yanxin, YANG GuangFu
Front. Chem. Sci. Eng.. 2007, 1 (1): 76-80.
https://doi.org/10.1007/s11705-007-0016-6
To improve the performance of traditional nucleation additives and their compatibility with other additives, as well as to solve complex problems in practical applications, SiO2 precursors were reactively grafted in situ with the symmetrical hydroxyl groups of the nucleation agents. With this approach, the dissymmetrical part of the nucleation agents plays an important role. As a result, the prepared composite additive the nanoparticle precursor (NPP0) produces excellent results. The NPP0-PP composite has a transparency of over 93%, haze lower than 15%, and a heat distortion temperature (HDT) of 142?C, which is more than the 110?C of the pure PP matrix. In addition, it maintains over 90% of the mechanical properties with a deformation coefficient less than 1%. This indicates a strong nanoeffect.
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