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2013, Vol. 22, No. 6　Online: 2013-11-20


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Prof. Li and his coworkers in their Article on pages 819–825 reported the inspection on the morphology evolution of clustershaped silicon nanomaterials, which were prepared by following the procedure of FFC-Cambridge Process-molten salt electrochemical reduction. Using SiO₂ (quartz glass) as raw material, the structure of the silicon nanomaterial can be tuned easily. The purity of the prepared product is about 99.95% and further improvement can be expected.

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Nano Si preparation by constant cell voltage electrolysis of FFC-Cambridge Process in molten CaCl2 Ji Zhao, Shengmei Lu, Linyan Hu, Can Li 2013, 22(6): 819-825.  摘要 ( 5866 )   PDF(1KB) ( 1 )   Using FFC-Cambridge Process to prepare Si from SiO2 is a promising method to prepare nanostructured and highly pure silicon for solar cells. However, the method still has many problems unsolved and the controlling effect of the cell voltage on silicon product is not clear. Here we report in this article that nano cluster-like silicon product with purity of 99.95% has been prepared by complete conversion of raw material SiO2, quartz glass plate, using constant cell voltage electrolysis FFC-Cambridge Process. By analysis of XRD, EDS, TEM, HRTEM and ICP-AES as well as the discussion from the thermodynamics calculation, the morphology and components of the product based on the change of cell voltage are clarified. It is clear that pure silicon could be prepared at the cell voltage of 1.7-2.1 V in this reaction system. The silicon material have cluster-like structure which are made of silicon nanoparticles in 20-100 nm size. Interestingly, the cluster-like nano structure of the silicon can be tuned by the used cell voltage. The purity, yield and the energy cost of silicon product prepared at the optimized cell voltage are discussed. The purity of the silicon product could be further improved, hence this method is promising for the preparation of solar grade silicon in future.

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Dehydration of xylose to furfural over niobium phosphate catalyst in biphasic solvent system Boonrat Pholjaroen, Ning Li, Zhiqiang Wang, Aiqin Wang, Tao Zhang 2013, 22(6): 826-832.  摘要 ( 6348 )   Phosphoric acid treated niobic acid (NbP) was used for the dehydration of xylose to furfural in biphasic solvent system, which was found to exhibit the best performance among the tested catalysts. The excellent performance of NbP could be explained by the better synergistic cooperation between Brönsted and Lewis acid sites. Moreover, NbP showed good stability and no obvious deactivation or leaching of Nb could be observed after six continuous recycles.

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Mechanism of chain propagation for the synthesis of polyoxymethylene dimethyl ethers Yupei Zhao, Zheng Xu, Hui Chen, Yuchuan Fu, Jianyi Shen 2013, 22(6): 833-836.  摘要 ( 5605 )   Polyoxymethylene dimethyl ethers (PODE) were synthesized from the reaction of paraformaldehyde with dimethoxymethane (DMM) over different acid catalysts at different conditions. Products were found to follow the Schulz-Flory distribution law. The chain propagation proceeds through the insertion of an individual segment of CH2O one by one, while the simultaneous insertion of a few CH2O segments or their assembly is unlikely. Due to the restriction of this law, it is difficult to increase the selectivity to the desired products (e.g., PODE3-4).

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Polyvinyl acetate/poly(amide-12-b-ethylene oxide) blend membranes for carbon dioxide separation Shichao Feng, Jizhong Ren, Hui Li, Kaisheng Hua, Xinxue Li, Maicun Deng 2013, 22(6): 837-844.  摘要 ( 6740 )   In this paper, blend membranes from polyvinyl acetate (PVAc) and block copolymer poly(amide-12-b-ethylene oxide) (Pebax1074) are prepared by solution casting and solvent evaporation method. Although they are homogeneous on a macro-scale, the observations from DSC and SEM indicate micro-phase separation for PVAc/Pebax1074 blend membranes. With the increase of Pebax1074 content, gas permeabilities of CO2, H2, N2 and CH4 all increase greatly. PVAc/Pebax1074 blend membranes with high PVAc content are appropriate for CO2/CH4 separation. The temperature dependence of gas permeability is divided into rubbery region and glassy region. The activation energies of permeation in rubbery region are smaller than those in glassy region, and they all decrease with increasing Pebax1074 content. For N2, H2 and CH4, their gas permeation properties are mainly influenced by the dual-mode sorption and hydrostatic pressure effect. But for CO2, its permeability increases with the increase of pressure due to CO2-induced plasticization effect, which is more obvious for PVAc/Pebax1074 blend membranes with high PVAc content.

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Investigation of CO and formaldehyde oxidation over mesoporous Ag/Co3O4 catalysts Fangli Yu, Zhenping Qu, Xiaodong Zhang, Qiang Fu, Yi Wang 2013, 22(6): 845-852.  摘要 ( 5991 )   CO and formaldehyde (HCHO) oxidation reactions were investigated over mesoporous Ag/Co3O4 catalysts prepared by one-pot (OP) and impregnation (IM) methods. It was found that the one-pot method was superior to the impregnation method for synthesizing Ag/Co3O4 catalysts with high activity for both reactions. It was also found that the catalytic behavior of mesoporous Co3O4 and Ag/Co3O4 catalysts for the both reactions was different. And the addition of silver on mesoporous Co3O4 did not always enhance the catalytic activity of final catalyst for CO oxidation at room temperature (20 ℃), but could significantly improve the catalytic activity of final catalyst for HCHO oxidation at low temperature (90 ℃). The high surface area, uniform pore structure and the pretty good dispersion degree of the silver particle should be responsible for the excellent low-temperature CO oxidation activity. However, for HCHO oxidation, the addition of silver played an important role in the activity enhancement. And the silver particle size and the reducibility of Co3O4 should be indispensable for the high activity of HCHO oxidation at low temperature.

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Characteristics of La-modified Ni-Al2O3 and Ni-SiO2 catalysts for COx-free hydrogen production by catalytic decomposition of methane Chatla Anjaneyulu, Velisoju Vijay Kumar, Suresh K. Bhargava, Akula Venugopal 2013, 22(6): 853-860.  摘要 ( 6188 )   Hydrotalcite precursors of La modified Ni-Al2O3 and Ni-SiO2 catalysts prepared by co-precipitation method and the catalytic activities were examined for the production of COx-free H2 by CH4 decomposition. Physico-chemical characteristics of fresh, reduced and used catalysts were evaluated by XRD, TPR and O2 pulse chemisorptions, TEM and BET-SA techniques. XRD studies showed phases due to hydrotalcite-like precursors in oven dried form produced dispersed NiO species upon calcination in static air above 450 ℃. Raman spectra of deactivated samples revealed the presence of both ordered and disordered forms of carbon. Ni-La-Al2O3 catalyst with a mole ratio of Ni:La:Al = 2:0.1:0.9 exhibited tremendously high longevity with a hydrogen production rate of 1300 molH2·molNi-1. A direct relationship between Ni metal surface area and hydrogen yields was established.

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Low CO content hydrogen production from oxidative steam reforming of ethanol over CuO-CeO2 catalysts at low-temperature Xue Han, Yunbo Yu, Hong He, Jiaojiao Zhao 2013, 22(6): 861-868.  摘要 ( 6013 )   CuO-CeO2 catalysts were prepared by a urea precipitation method for the oxidative steam reforming of ethanol at low-temperature. The catalytic performance was evaluated and the catalysts were characterized by inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, temperature-programmed reduction, field emission scanning electron microscopy and thermo-gravimetric analysis. Over CuO-CeO2 catalysts, H2 with low CO content was produced in the whole tested temperature range of 250-450 ℃. The non-noble metal catalyst 20CuCe showed higher H2 production rate than 1%Rh/CeO2 catalyst at 300-400 ℃ and the advantage was more obvious after 20 h testing at 400 ℃. These results further confirmed that CuO-CeO2 catalysts may be suitable candidates for low temperature hydrogen production from ethanol.

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Adsorptive removal of nitrogen-containing compounds from fuel by metal-organic frameworks Zhaoyang Wang, Zhiguo Sun, Linghao Kong, Gang Li 2013, 22(6): 869-875.  摘要 ( 6411 )   The adsorptive denitrogenation from fuels over three metal-organic frameworks (MIL-96(Al), MIL-53(Al) and MIL-101(Cr)) was studied by batch adsorption experiments. Four nitrogen-containing compounds (NCCs) pyridine, pyrrole, quinoline and indole were used as model NCCs in fuels to study the adsorption mechanism. The physicochemical properties of the adsorbents were characterized by XRD, N2 physical adsorption, FT-IR spectrum and Hammett indicator method. The metal-organic frameworks (MOFs), especially the MIL-101(Cr) containing Lewis acid sites as well as high specific surface area, can adsorb large quantities of NCCs from fuels. In addition, the adsorptive capacity over MIL-101(Cr) will be different for NCCs with different basicity. The stronger basicity of the NCC is, the more it can be absorbed over MIL-101(Cr). Furthermore, pore size and shape also affect the adsorption capacity for a given adsorbate, which can be proved by the adsorption over MIL-53(Al) and MIL-96(Al). The pseudo-second-order kinetic model and Langmuir equation can be used to describe kinetics and thermodynamics of the adsorption process, respectively. Finally, the regeneration of the used adsorbent has been conducted successfully by just washing it with ethanol.

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Methane conversion into higher hydrocarbons with dielectric barrier discharge micro-plasma reactor Baowei Wang, Wenjuan Yan, Wenjie Ge, Xiaofei Duan 2013, 22(6): 876-882.  摘要 ( 6209 )   We reported a coaxial, micro-dielectric barrier discharge (micro-DBD) reactor and a conventional DBD reactor for the direct conversion of methane into higher hydrocarbons at atmospheric pressure. The effects of input power, residence time, discharge gap and external electrode length were investigated for methane conversion and product selectivity. We found the conversion of methane in a micro-DBD reactor was higher than that in a conventional DBD reactor. And at an input power of 25.0 W, the conversion of methane and the total C2+C3 selectivity reached 25.10% and 80.27%, respectively, with a micro-DBD reactor of 0.4 mm discharge gap. Finally, a nonlinear multiple regression model was used to study the correlations between both methane conversion and product selectivity and various system variables. The calculated data were obtained using SPSS 12.0 software. The regression analysis illustrated the correlations between system variables and both methane conversion and product selectivity.

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Required catalytic properties for alkane production from carboxylic acids：Hydrodeoxygenation of acetic acid Zhong He, Xianqin Wang 2013, 22(6): 883-894.  摘要 ( 6577 )   The supported Pt catalysts (1 wt%) were prepared by the incipient impregnation method and analyzed using synchrotron-based X-ray diffraction, BET surface area, oxygen adsorption, CO pulse chemisorption, temperature-programmed desorption (TPD) of acetic acid, H2-TPD, NH3-TPD, O2-TPD, and H2-TPR. The reactivity of Pt-based catalysts was studied using a fixed bed reactor at 300 ℃ and 4 MPa for hydrodeoxygenation of acetic acid, where Pt/TiO2 was very selective for ethane production. TPD experiments revealed that several conditions must be satisfied to achieve this high selectivity to ethane from acetic acid, such as Pt sites, moderate acidity, and medium metal-oxygen bond strength in the oxide support. This work provides insights in developing novel catalytic materials for hydrocarbon productions from various organics including bio-fuels.

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Synthesis, isolation and characterization of methyl levulinate from cellulose catalyzed by extremely low concentration acid Hui Li, Lincai Peng, Lu Lin, Keli Chen, Heng Zhang 2013, 22(6): 895-901.  摘要 ( 6237 )   A direct synthesis of methyl levulinate from cellulose alcoholysis in methanol medium under mild condition (180-210 ℃) catalyzed by extremely low concentration sulfuric acid (≤0.01 mol/L) and the product isolation were developed in this study. Effects of different process variables towards the catalytic performance were performed as a function of reaction time. The results indicated that sulfuric acid concentration, temperature and initial cellulose concentration had significant effects on the synthesis of methyl levulinate. An optimized yield of around 50% was achieved at 210 ℃ for 120 min with sulfuric acid concentration of 0.01 mol/L and initial cellulose concentration below 100 g/L. The resulting product mixture was isolated by a distillation technique that combines an atmospheric distillation with a vacuum distillation where n-dodecane was added to help distill the heavy fraction. The light fraction including mainly methanol could be reused as the reaction medium without any substantial change in the yield of methyl levulinate. The chemical composition and structural of lower heavy fraction were characterized by GC/MS, FTIR, 1H-NMR and 13C-NMR techniques. Methyl levulinate was found to be a major ingredient of lower heavy fraction with the content over 96%. This pathway is efficient, environmentally benign and economical for the production of pure levulinate esters from cellulose.

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Removal of carbonyl sulfide from CO2 stream using AgNO3-modified NaZSM-5 Yanjun Wang, Shaoyun Chen, Heng Chen, Xingzhou Yuan, Yongchun Zhang 2013, 22(6): 902-906.  摘要 ( 5956 )   Removal of carbonyl sulfide (COS) from CO2 stream is significant for the production and utilization of food grade CO2. This study investigates the adsorption performance of Ag/NaZSM-5 as adsorbent prepared by incipient wetness impregnation for the removal of COS from a CO2 stream in a fixed-bed adsorption apparatus. Effects of various conditions on the preparation of adsorbent, adsorption and desorption were intensively examined. The results revealed that COS can be removed to below 1×10-9 from a CO2 stream (1000 ppm COS/CO2) using Ag/NaZSM-5 (10 wt% AgNO3) with an adsorption capacity of 12.86 mg·g-1. The adsorbent can be fully regenerated using hot air at 450 ℃. The adsorption ability remained stable even after eight cycles of regeneration.

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Controllable synthesis of high loading LiFePO4/C nanocomposites using bimodal mesoporous carbon as support for high power Li-ion battery cathodes Fei Cheng, Duo Li, Anhui Lu, Wencui Li 2013, 22(6): 907-913.  摘要 ( 6100 )   Mesoporous LiFePO4/C composites containing 80 wt% of highly dispersed LiFePO4 nanoparticles (4-6 nm) were fabricated using bimodal mesoporous carbon (BMC) as continuous conductive networks. The unique pore structure of BMC not only promises good particle connectivity for LiFePO4, but also acts as a rigid nano-confinement support that controls the particle size. Furthermore, the capacities were investigated respectively based on the weight of LiFePO4 and the whole composite. When calculated based on the weight of the whole composite, it is 120 mAh·g-1 at 0.1 C of the high loading electrode and 42 mAh·g-1 at 10 C of the low loading electrode. The electrochemical performance shows that high LiFePO4 loading benefits large tap density and contributes to the energy storage at low rates, while the electrode with low content of LiFePO4 displays superior high rate performance, which can mainly be due to the small particle size, good dispersion and high utilization of the active material, thus leading to a fast ion and electron diffusion.

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Insight into the topology effect on the diffusion of ethene and propene in zeolites：A molecular dynamics simulation study Chuanming Wang, Bowei Li, Yangdong Wang, Zaiku Xie 2013, 22(6): 914-918.  摘要 ( 6461 )   Selectivity control is a difficult scientific and industrial challenge in methanol-to-olefins (MTO) conversion. It has been experimentally established that the topology of zeolite catalysts influenced the distribution of products. Besides the topology effect on reaction kinetics, the topology influences the diffusion of reactants and products in catalysts as well. In this work, by using COMPASS force-field molecular dynamics method, we investigated the intracrystalline diffusion of ethene and propene in four different zeolites, CHA, MFI, BEA and FAU, at different temperatures. The self-diffusion coefficients and diffusion activation barriers were calculated. A strong restriction on the diffusion of propene in CHA was observed because the self-diffusion coefficient ratio of ethene to propene is larger than 18 and the diffusion activation barrier of propene is more than 20 kJ/mol in CHA. This ratio decreases with the increase of temperature in the four investigated zeolites. The shape selectivity on products from diffusion perspective can provide some implications on the understanding of the selectivity difference between HSAPO-34 and HZSM-5 catalysts for the MTO conversion.

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Ni/Al2O3 catalysts for CO methanation：Effect of Al2O3 supports calcined at different temperatures Jiajian Gao, Chunmiao Jia, Jing Li, Meiju Zhang, Fangna Gu, Guangwen Xu, Ziyi Zhong, Fabing Su 2013, 22(6): 919-927.  摘要 ( 9492 )   The correlation between phase structures and surface acidity of Al2O3 supports calcined at different temperatures and the catalytic performance of Ni/Al2O3 catalysts in the production of synthetic natural gas (SNG) via CO methanation was systematically investigated. A series of 10 wt% NiO/Al2O3 catalysts were prepared by the conventional impregnation method, and the phase structures and surface acidity of Al2O3 supports were adjusted by calcining the commercial γ-Al2O3 at different temperatures (600-1200 ℃). CO methanation reaction was carried out in the temperature range of 300-600 ℃ at different weight hourly space velocities (WHSV = 30000 and 120000 mL·g-1·h-1) and pressures (0.1 and 3.0 MPa). It was found that high calcination temperature not only led to the growth in Ni particle size, but also weakened the interaction between Ni nanoparticles and Al2O3 supports due to the rapid decrease of the specific surface area and acidity of Al2O3 supports. Interestingly, Ni catalysts supported on Al2O3 calcined at 1200 ℃ (Ni/Al2O3-1200) exhibited the best catalytic activity for CO methanation under different reaction conditions. Lifetime reaction tests also indicated that Ni/Al2O3-1200 was the most active and stable catalyst compared with the other three catalysts, whose supports were calcined at lower temperatures (600, 800 and 1000 ℃). These findings would therefore be helpful to develop Ni/Al2O3 methanation catalyst for SNG production.

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A bird nest-like manganese dioxide and its application as electrode in supercapacitors Fen Ran, Huili Fan, Lingren Wang, Lei Zhao, Yongtao Tan, Xuanxuan Zhang, Lingbin Kong, Long Kang 2013, 22(6): 928-934.  摘要 ( 6561 )   A novel bird nest-like nanostructured MnO2 (BNNS-MnO2) was prepared by a facile and cost-effective strategy. Their structures and morphologies were characterized by field emission scanning electron microscopy, transmission electron microscopy and powder X-ray diffraction. Capacitive behaviors were investigated by cyclic voltammetry and galvanostatic charge-discharge. The obtained nano-MnO2 possesses a well designed loose-assembled hierarchical nanoarchitecture with an appropriate crystallinity which gives rise to excellent performances as an electrode material for supercapacitors. A maximum specific capacitance of 917 F/g has been obtained at a current density of 5 mA/cm2 in 6 mol/L KOH aqueous solution, and a specific capacitance of 210 F/g has been maintained for 500 cycles. As the low cost of MnSO4 and KCr2O7 and the low reaction temperature, the present method avoids the requirements for complicated operations, time/energy-consuming and expensive reagents, and perhaps is ready for the industrialization of nano-MnO2 production.

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Effect of natural and synthetic antioxidants on oxidative stability of FAMEs obtained from hevea brasiliensis S. Nivetha, D. Vetha Roy 2013, 22(6): 935-941.  摘要 ( 5119 )   Biodiesel (fatty acid alkyl esters), an alternate to fossil fuel, has the tendency of autoxidation and hence requires antioxidants for long term storage. The influence of synthetic and natural antioxidants on the oxidative stability was analysed for fresh FAMEs (fatty acid methyl esters) obtained from hevea brasiliensis at 140 ℃. Higher activity was observed for synthetic antioxidants following the order of GA>BHT>DTBP>Q>GT-M>PH-M>GT-C, whereas the oxidative stability of stored FAMEs samples measured at 110 ℃ reveals a nearly inverse trend. Storage stability was tested for the FAMEs obtained from hevea brasiliensis stored at 30 ℃, after addition of synthetic and natural antioxidants-butylated hydroxytoluene (BHT), 2,6-di-tert-butylphenol (DTBP), quercetin (Q), gallic acid (GA), methanol extracts from green tea (GT-M), pomegranate hull (PH-M), and chloroform extract of green tea (GT-C). Antioxidant activities above 1500 ppm was in the order of DTBP>BHT>GA>GT-C>GT-M>Q>PH-M. Synthetic antioxidants have been found more efficient to improve the storage stability of FAMEs obtained from hevea brasiliensis. DTBP in particular has the highest protection factor.