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2011, Vol. 20, No. 5　Online: 2011-09-20

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Communication

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Effective modification of MgO with surface transition metal oxides for NF3 decomposition Yanan Wang, Xiufeng Xu*, Pei Sheng, Hongguang Li, Tingting Wang, Youfen Huang, Fangshu Liu 2011, 20(5): 457-459.  DOI: 10.1016/S1003-9953(10)60223-X 摘要 ( 8758 )   NF3 decomposition over transition metal oxides coated MgO reagents in the absence of water is investigated. The results show that NF3 can be decomposed completely over pure MgO but the time of NF3 steady full conversion kept as short as 80 min, while the reactivities of coated MgO reagents were remarkably enhanced by transition metal oxides, for example the time of NF3 complete conversion over 12%Fe/MgO extended to 380 min. It is suggested that not only an increase in surface area but also a significant enhancement in the fluorination of MgO substrate caused by the surface transition metal oxides result in an improved reactivity of coated MgO reagents for NF3 decomposition.

Articles

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Preparation of activated carbons and their adsorption properties for greenhouse gases: CH4 and CO2 Hao Yang, Maochu Gong, Yaoqiang Chen* 2011, 20(5): 460-464.  DOI: 10.1016/S1003-9953(10)60232-0 摘要 ( 9939 )   Three kinds of activated carbons were prepared using coconut-shells as carbon precursors and characterized by XRD, FT-IR and texture property test. The results indicate that the prepared activated carbons were mainly amorphous and only a few impurity groups were adsorbed on their surfaces. The texture property test reveals that the activated carbons displayed different texture properties, especially the micropore size distribution. The adsorption capacities of the activated carbons were investigated by adsorbing CH4, CO2, N2 and O2 at 25 ℃ in the pressure range of 0-200 kPa. The results reveal that all the activated carbons had high CO2 adsorption capacity, one of which had the highest CO2 adsorption value of 2.55 mmol/g at 200 kPa. And the highest adsorption capacity for CH4 of the activated carbons can reach 1.93 mmol/g at 200 kPa. In the pressure range of 0-200 kPa, the adsorption capacities for N2 and O2 were increased linearly with the change of pressure and K-AC is an excellent adsorbent towards the adsorption separation of greenhouse gases.

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Carbon dioxide reforming of methane over Ni/Mo/SBA-15-La2O3 catalyst: Its characterization and catalytic performance Jian Huang, Renxiong Ma*, Tao Huang, Anrong Zhang, Wei Huang 2011, 20(5): 465-470.  DOI: 10.1016/S1003-9953(10)60226-5 摘要 ( 10936 )   The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 sorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.

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Comparison of three methods for natural gas dehydration Michal Netusil*, Pavel Ditl 2011, 20(5): 471-476.  DOI: 10.1016/S1003-9953(10)60218-6 摘要 ( 14080 )   This paper compares three methods for natural gas dehydration that are widely applied in industry: (1) absorption by triethylene glycol, (2) adsorption on solid desiccants and (3) condensation. A comparison is made according to their energy demand and suitability for use. The energy calculations are performed on a model where 105 Nm3/h water saturated natural gas is processed at 30 ℃. The pressure of the gas varies from 7 to 20 MPa. The required outlet concentration of water in natural gas is equivalent to the dew point temperature of -10 ℃ at gas pressure of 4 MPa.

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Effect of iridium loading on HZSM-5 for isomerization of n-heptane Herma Dina Setiabudi, Sugeng Triwahyono*, Aishah Abdul Jalil, Nur Hidayatul Nazirah Kamarudin, Muhammad Arif Ab Aziz 2011, 20(5): 477-482.  DOI: 10.1016/S1003-9953(10)60227-7 摘要 ( 10059 )   The effect of iridium loading on the properties and catalytic isomerization of n-heptane over Ir-HZSM-5 is studied. Ir-HZSM-5 was prepared by impregnation method and subjected to isomerization process in the presence of flowing hydrogen gas. XRD and BET studies show that the presence of iridium stabilizes the crystalline structure of HZSM-5, leading to more ordered framework structure and larger surface area. TGA and FTIR results substantiate that iridium species interacts with OH group on the surface of HZSM-5. Pyridine FT-IR study verifies the interaction between iridium and surface OH group slightly increased the Brönsted and Lewis acid sites without changing the lattice structure of HZSM-5. The presence of iridium and the increase of strong Lewis acid sites on HZSM-5 were found to bring an increase about 4.1%, 33.2% and 11.8% in conversion, selectivity and yield of n-heptane isomerization, respectively.

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Tuning surface active oxygen of lanthanum oxide via partial dissolution and regrowth of crystallites Zhiming Gao*, Huili Li 2011, 20(5): 483-486.  DOI: 10.1016/S1003-9953(10)60222-8 摘要 ( 9011 )   A commercial lanthanum oxide was modified into X%-La2O3 samples via partial dissolution and regrowth of crystallites, wherein the X value denotes the weight percent of the initial metal oxide powder dissolved by nitric acid. BET measurements and TEM observations indicate that the 20%-La2O3 sample has an increased specific surface area, relatively thin and small crystallites in size. TPD/TPR profiles also show that the 20%-La2O3 sample has more surface active oxygen than the 0%-La2O3 sample. Among the four X%-La2O3 samples, the highest activity for methane oxidation was obtained over the 20%-La2O3 sample. Therefore, the present work proves that the method of partial dissolution and regrowth of crystallites are effective to modify surface property of lanthanum oxide.

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Ni/MgO catalysts prepared using atmospheric high-frequency discharge plasma for CO2 reforming of methane Pan Qin, Huiyuan Xu, Huali Long, Yi Ran, Shuyong Shang, Yongxiang Yin*, Xiaoyan Dai 2011, 20(5): 487-492.  DOI: 10.1016/S1003-9953(10)60228-9 摘要 ( 11319 )   A new type of Ni/MgO catalyst was prepared by using atmospheric high-frequency discharge cold plasma. The influences of conventional method, plasma method, and plasma plus calcination method on the catalytic activity were studied and the CO2 reforming of methane was chosen as the probe reaction. The catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), X-ray photoelectron spectroscopy, and CO2 temperature-programmed surface reaction techniques. The results suggested that the nickel-based catalyst prepared by plasma plus calcination method possessed a smaller particle size and a higher dispersion of active component, better low-temperature activity and enhanced anti-coking ability. The conversion of CO2 and CH4 was 90.70% and 89.37% respectively, and the reaction lasted for 36 h without obvious deactivation under 101.325 kPa and 750 ℃ with CO2/CH4 = 1/1.

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Efficient oxidative degradation of 2-chlorophenol and 4-chlorophenol over supported CuO-based catalysts Jingjing Li, Yang Hu, Wenhui Lü, Lei Shi*, Qi Sun, Yonggang Zhou, Jianfeng Xu, Jian Wang, Bizhong Shen 2011, 20(5): 493-497.  DOI: 10.1016/S1003-9953(10)60217-4 摘要 ( 9139 )    A series of metal oxide catalysts for catalytic oxidative degradation of 2-chlorophenol (2-CP) and 4-chlorophenol (4-CP) were prepared, and the supported CuO catalysts were studied particularly. The supported CuO catalysts were characterized by XRD and NH3-TPD techniques, in which CuO/γ-Al2O3 exhibited high degradation activity. The addition of Na2O or K2O into CuO/γ-Al2O3 improved the oxidative degradation of CPs remarkably, in which Na2O was more efficient than K2O. Over CuO/γ-Al2O3-Na2O, CPs were completely converted and the liberation of the inorganic chloride from 2-CP or 4-CP reached 97% or 100% respectively at 30 ℃ for 2 h. The supported CuO catalysts with good dispersion of CuO particles and less acid sites were favorable for the efficient oxidative degradation of CPs. In addition, the initial pH of the reaction solution was found to be an important factor which influenced the catalytic oxidative degradation of CPs and the initial pH of 11.2 and 9.8 was preferred for the oxidative degradation of 2-CP and 4-CP respectively over CuO/γ-Al2O3 catalyst.

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Influence of MgO contents on silica supported nano-size gold catalyst for carbon monoxide total oxidation Huiyuan Xu*, Weiyi Li, Shuyong Shang, Chunrong Yan 2011, 20(5): 498-502.  DOI: 10.1016/S1003-9953(10)60219-8 摘要 ( 9610 )   A series of nano-size gold catalysts were prepared by deposition-precipitation method using silica material promoted with different amounts of MgO as the carrier. The influences of MgO addition on the structure and property of the nano-size gold catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), O2 temperature-programmed desorption (O2-TPD), and inductively coupled with plasma atomic emission spectroscopy (ICP-AES) techniques. The total oxidation of CO was chosen as the probe reaction. The results suggest that for the gold catalysts supported on the silica material after MgO modification, the size of the gold particles is pronouncedly reduced, the oxygen mobility is enhanced, and the catalytic activity for low-temperature CO oxidation is greatly improved. The gold catalyst modified by 6 wt% MgO (Mg/SiO2 weight ratio) shows higher CO oxidation activity, over which the temperature of CO total oxidation is lower about 150 K than that over the silica directly supported gold catalyst.

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Effect of heat transfer on the oscillatory behavior in partial oxidation of methane over nickel catalyst Xiubin Ren, Xiangyun Guo* 2011, 20(5): 503-506.  DOI: 10.1016/S1003-9953(10)60216-2 摘要 ( 10091 )   Monte Carlo method was applied to simulate the oscillatory behavior during partial oxidation of methane under non-isothermal condition. The simulation was performed to examine the influences of heat transfer constant and particle size on the kinetic oscillation. The oscillatory period and amplitude were observed to increase with the increase of heat transfer constant. The increase of catalyst particle size was found to result in short oscillatory period and more or less regular oscillations combined with the formation of oxide down to L = 100.

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Quantitative interpretation to the chain mechanism of free radical reactions in cyclohexane pyrolysis Yingxian Zhao*, Bo Shen, Feng Wei 2011, 20(5): 507-514.  DOI: 10.1016/S1003-9953(10)60233-2 摘要 ( 16142 )   Pyrolysis of cyclohexane was conducted with a plug flow tube reactor in the temperature range of 873-973 K. Based on the experimental data, the mechanism and kinetic model of cyclohexane pyrolysis reaction were proposed. The kinetic analysis shows that overall conversion of cyclohexane is a first order reaction, of which the rate constant increased from 0.0086 to 0.0225 to 0.0623 s-1 with the increase of temperature from 873 to 923 to 973 K, and the apparent activation energy was determined to be 155.0±1.0 kJ·mol-1. The mechanism suggests that the cyclohexane is consumed by four processes: the homolysis of C-C bond (Path I), the homolysis of C-H bond (Path II) in reaction chain initiation, the H-abstraction of various radicals from the feed molecules in reaction chain propagation (Path III), and the process associated with coke formation (Path IV). The reaction path probability (RPP) ratio of XPath I : XPath II : XPath III : XPath IV was 0.5420 : 0.0045 : 0.3897 : 0.0638 at 873 K, and 0.4336 : 0.0061 : 0.4885 : 0.0718 at 973 K.

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Gas sensing performance of polyaniline/ZnO organic-inorganic hybrids for detecting VOCs at low temperature Jing Huang, Taili Yang, Yanfei Kang, Yao Wang, Shurong Wang* 2011, 20(5): 515-519.  DOI: 10.1016/S1003-9953(10)60230-7 摘要 ( 10397 )   Polyaniline (PANI) was prepared by the chemical oxidative polymerization of aniline, and ZnO, with the mean particle size of 28 nm, was synthesized by a non-aqueous solvent method. The organic-inorganic PANI/ZnO hybrids with different mass fractions of PANI were obtained by mechanically mixing the prepared PANI and ZnO. The gas sensing properties of PANI/ZnO hybrids to different volatile organic compounds (VOCs) including methanol, ethanol and acetone were investigated at a low operating temperature of 90 ℃. Compared with the pure PANI and ZnO, the PANI/ZnO hybrids presented much higher response to VOCs. Meanwhile, the PANI/ZnO hybrid exhibited a good reversibility and a short response-recovery time, implying its potential application for gas sensors. The sensing mechanism was suggested to be related to the existence of p-n heterojunctions in the PANI/ZnO hybrids.

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Catalytic performance of Fe modified K/Mo2C catalyst for CO hydrogenation Minglin Xiang*, Dudu Wu, Juan Zou, Debao Li, Yuhan Sun, Xichun She 2011, 20(5): 520-524.  DOI: 10.1016/S1003-9953(10)60215-0 摘要 ( 11843 )   Fe modified and un-modified K/Mo2C were prepared and investigated as catalysts for CO hydrogenation reaction. Compared with K/Mo2C catalyst, the addition of Fe increased the production of alcohols, especially the C2+OH. Meanwhile, considerable amounts of C5+ hydrocarbons and C=2--C=4 were formed, whereas methane selectivity greatly decreased. Also, the activity and selectivity of the catalyst were readily affected by the reaction pressure and temperature employed. According to the XPS results, Mo4+ might be responsible for the production of alcohols, whereas the low valence state of Mo species such as Mo0 and/or Mo2+ might be account for the high activity and selectivity toward hydrocarbons.

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Correlation between hydrocarbon distribution and water-hydrocarbon ratio in Fischer-Tropsch synthesis Xiaofeng Zhou*, Qingling Chen, Yuewu Tao, Huixin Weng 2011, 20(5): 525-530.  DOI: 10.1016/S1003-9953(10)60225-3 摘要 ( 11006 )   In order to shorten the evaluation cycle of cobalt catalyst before the optimized catalyst is fixed on, a mathematical method is proposed to calculate weight percentage of C5+ hydrocarbons. Based on the carbide polymerization mechanism and the main hydrocarbons being linear alkanes and α-olefins, the correlation between hydrocarbon distribution and the molecular mass ratio of water to hydrocarbons is discussed. The result shows the ratio was within the range of 1.125-1.286 and the lower the ratio, the more gaseous hydrocarbons were obtained. Moreover, a linear equation between the weight percentage of C5+ hydrocarbons and the weight ratio of C5+ hydrocarbons to the total water is established. These results are validated by corresponding experiments. The weight percentage of C5+ hydrocarbons could be immediately calculated by this linear equation without detailed gas chromatography (GC) analysis of them.

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P-Tstability conditions of methane hydrate in sediment from South China Sea Shicai Sun*, Yuguang Ye, Changling Liu, Fengkui Xiang, Yan Ma 2011, 20(5): 531-536.  DOI: 10.1016/S1003-9953(10)60224-1 摘要 ( 10214 )   For reasonable assessment and safe exploitation of marine gas hydrate resource, it is important to determine the stability conditions of gas hydrates in marine sediment. In this paper, the seafloor water sample and sediment sample (saturated with pore water) from Shenhu Area of South China Sea were used to synthesize methane hydrates, and the stability conditions of methane hydrates were investigated by multi-step heating dissociation method. Preliminary experimental results show that the dissociation temperature of methane hydrate both in seafloor water and marine sediment, under any given pressure, is depressed by approximately -1.4 K relative to the pure water system. This phenomenon indicates that hydrate stability in marine sediment is mainly affected by pore water ions.

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Preparation, characterization and catalytic behavior of Pt-Cu nanoparticles in methane combustion Florica Papa, Catalin Negrila, Gianina Dobrescu, Akane Miyazaki, Ioan Balint* 2011, 20(5): 537-542.  DOI: 10.1016/S1003-9953(10)60221-6 摘要 ( 8956 )   Fine and well dispersed Pt-Cu bimetallic nanoparticles stabilized by polyvinyl pyrrolidone (PVP) were synthesized by alkaline polyol method. The molar ratio of Pt to Cu was 1 : 1. Further, the Pt-Cu bimetallic nanoparticles were supported on alumina and their catalytic behavior in methane combustion was investigated. The as-prepared as well as the supported Pt-Cu nanoparticles were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fractal analysis and X-ray diffraction (XRD). The dependence of methane combustion on the morphology and surface composition of Pt-Cu nanoparticles was analyzed based on the experimental results.

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CF4 decomposition without water over a solid ternary mixture consisting of NaF, silicon and one metal oxide Xiufeng Xu*, Xianjun Niu, Jie Fan, Yanan Wang, Ming Feng 2011, 20(5): 543-546.  DOI: 10.1016/S1003-9953(10)60220-4 摘要 ( 9250 )   A solid ternary mixture consisting of NaF, silicon and one of the metal oxides such as Al2O3, MgO, CaO, SrO, BaO was prepared and used as a defluorinated reagent for CF4 decomposition. The results show that the initial conversion of CF4 reached 100% over NaF-Si-MgO and NaF-Si-CaO at 850 ℃, and the reagent with NaF/Si/MgO molar ratio of 33/34/33 exhibited a high reactivity with a full conversion of CF4 lasting for 57 min. The plausible paths of CF4 decomposition over NaF-Si-Al2O3, NaF-Si-MgO, NaF-Si-CaO, NaF-Si-SrO and NaF-Si-BaO are proposed.

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Methane dehydro-aromatization over Mo/HZSM-5 catalysts in the absence of oxygen: Effect of steam-treatment on catalyst stability Tingting Zhao, Hongxia Wang* 2011, 20(5): 547-552.  DOI: 10.1016/S1003-9953(10)60231-9 摘要 ( 11974 )   The effect of steam-treatment to HZSM-5 zeolite and Mo/HZSM-5 with a steaming time range of 0.5--1 h on the catalytic performance of methane dehydro-aromatization (MDA) over Mo/HZSM-5 catalyst prepared with impregnation has been studied in detail in combination with the characterization of 1H MAS NMR technique. Both the deactivation rate constant (kd) and the Brönsted acid sites per unit cell were calculated to quantitatively evaluate the stability of Mo/HZSM-5 catalysts treated with steam at 813 K before and after impregnation of molybdenum species, and the corresponding variation of their Brönsted acid sites. The results reveal that a V-shape relationship between kd) and the number of B1 acid sites per unit cell is presented on Mo/HZSM-5 catalyst under the tested steam-treatment and reaction conditions.

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Effects of preparation methods on the performance of Cu-Mo-Fe-Ox in the hydrogen production from water Si Chen, Wei Chu*, Xu Liu, Dongge Tong* 2011, 20(5): 553-557.  DOI: 10.1016/S1003-9953(10)60214-9 摘要 ( 10221 )   Two Cu-Mo-Fe-Ox samples, which can store and supply pure hydrogen through repeated redox reaction (Fe3O4+4H2↔3Fe+4H2O), were prepared by co-precipitation (FCM-C) and impregnation (FCM-I) methods, respectively, and the performance of hydrogen production from water were investigated. Compared with the impregnated sample, the co-precipitation sample presented better catalytic activity. The samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and temperature-programmed reduction (H2-TPR) techniques. XRD, FE-SEM and XPS results suggest that the FCM-C sample has smaller particle size and higher dispersion of iron oxide than that of FCM-I sample. In addition, FT-IR and H2-TPR analyses indicate that the weak interaction among metal oxides in FCM-C sample may induce facile reduction of active metal and superior property of hydrogen production by decomposing water in succession.

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Ti-Si composite oxide-supported cobalt catalysts for CO2 hydrogenation Jakrapan Janlamool, Piyasan Praserthdam, Bunjerd Jongsomjit* 2011, 20(5): 558-564.  DOI: 10.1016/S1003-9953(10)60213-7 摘要 ( 10638 )   In the present work, different silica-based supported cobalt (Co) catalysts were synthesized and used for CO2 hydrogenation for methanation. Different supports, such as SSP, MCM-41, TiSSP and TiMCM were used to prepare Co catalysts with 20 wt% Co loading. The supports and catalysts were characterized by means of N2 physisorption, XRD, SEM/EDX, XPS, TPR and CO chemisorption. It is found that after calcination of catalysts, Ti is present in the form of anatase. The introduction of Ti plays important roles in the properties of Co catalysts by: (i) facilitating the reduction of Co oxides species which are strongly interacted with support, (ii) preventing the formation of silicate compounds, and (iii) inhibiting the RWGS reaction. Based on CO2 hydrogenation, the CoTiMCM catalyst exhibites the highest activity and stability.