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2005, Vol. 14, No. 2　Online: 2005-06-30

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Advances in Synthesis of Mesostructured Aluminophosphates Benjing Xu;Chenxi Zhao;Zifeng Yan 2005, 14 (2): 65-76.  摘要 ( 7273 )   PDF(1765KB) ( 2575 )   More and more attention has been paid to the synthesis of mesostructured aluminophosphates for many years. A lot of valuable research results, including various synthetic approaches and structural materials, have been obtained. This paper reviews the progress in the synthesis of mesostructured aluminophosphates over the past few years, with the hope of revealing opportunities for future work.

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On the Role of Vanadia Species for VOx/SiO2 in the Selective Oxidation of Methane Shaojun Miao;Ding Ma;Qingjun Zhu;Heng Zheng;Guoqing Jia;Shutian Zhou;Xinhe Bao 2005, 14 (2): 77-87.  摘要 ( 10621 )   PDF(2387KB) ( 2039 )   Various VOx/SiO2 catalysts were prepared by the methods of physical mixing, conventional wetness impregnation and ultrasonication-assistant impregnation. The catalysts were characterized by XRD, UV-Vis DRS, Raman, TPR, ESR and TPSR techniques and the nature of the vanadium species were correlated to their catalytic performance in the reaction of direct conversion of methane to formaldehyde. It is concluded that highly dispersed monomeric and low oligomeric vanadia species are formed on the sample prepared with both traditional wetness impregnation method and ultrasonication-assistant impregnation, whereas in the latter case, the amount of oligomeric vanadia species is much smaller. The V2O5 microcrystallines are the dominant species on the material prepared by physical mixing method. During the selective oxidation of methane, VV species are reduced to VIV paramagnetic species and both microcrystalline V2O5 species and oligomeric vanadia species are found to further disperse and transform into tetrahedral vanadia species. Based on the results of UV Raman spectroscopy and TPSR, CO2 is suggested to be formed via two different routes, in which one is from the sequence reaction of CH4 → HCHO →CO → CO2 over monomeric vanadia species, and the other is from the direct oxidation of methane to CO2 over oligomeric vanadia species. Oligomeric vanadia species is more active than monomeric vanadia species for methane activation.

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Selective Oxidation of Propane by Lattice Oxygen of Vanadium-Phosphorous Oxide in a Pulse Reactor Rusong Zhao;Jian Wang;Qun Dong;Jianhong Liu 2005, 14 (2): 88-94.  摘要 ( 9841 )   PDF(359KB) ( 2653 )   Selective oxidation of propane by lattice oxygen of vanadium-phosphorus oxide (VPO) catalysts was investigated with a pulse reactor in which the oxidation of propane and the re-oxidation of catalyst were implemented alternately in the presence of water vapor. The principal products are acrylic acid (AA), acetic acid (HAc), and carbon oxides. In addition, small amounts of C1 and C2 hydrocarbons were also found, molar ratio of AA to HAc is 1.4–2.2. The active oxygen species are those adsorbed on catalyst surface firmly and/or bound to catalyst lattice, i.e. lattice oxygen; the selective oxidation of propane on VPO catalysts can be carried out in a circulating fluidized bed (CFB) riser reactor. For propane oxidation over VPO catalysts, the effects of reaction temperature in a pulse reactor were found almost the same as in a steady-state flow reactor. That is, as the reaction temperature increases, propane conversion and the amount of C1+C2 hydrocarbons in the product increase steadily, while selectivity to acrylic acid and to acetic acid increase prior to 350oC . then begin to drop at temperatures higher than 350 oC, and yields of acrylic acid and of acetic acid attained maximum at about 400 oC. The maximum yields of acrylic acid and of acetic acid for a single-pass are 7.50% and 4.59% respectively, with 38.2% propane conversion. When the amount of propane pulsed decreases or the amount of catalyst loaded increases, the conversion increases but the selectivity decreases. Increasing the flow rate of carrier gases causes the conversion pass through a minimum but selectivity and yields pass through a maximum. In a fixed bed reactor, it is hard to obtain high selectivity at a high reaction conversion due to the further degradation of acrylic acid and acetic acid even though propane was oxidized by the lattice oxygen. The catalytic performance can be improved in the presence of excess propane. Propylene can be oxidized by lattice oxygen of VPO catalyst at 250 oC, nevertheless, selectivity to AA and to HAc are even lower, much more acetic acid was produced (molar ratio of AA to HAc is 0.19:1–0.83:1) though the oxidation products are the same as from propane.

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Synthesis and Characterization of ZSM-5/β Co-Crystalline Zeolite Tianbo Zhao;Huiying Zhang;Fengyan Li;Chao Yang;Baoning Zong 2005, 14 (2): 95-100.  摘要 ( 8921 )   PDF(1947KB) ( 2597 )   ZSM-5/β co-crystalline zeolites with different content of ZSM-5 have been synthesized by adding different amount of ZSM-5 to the synthetic system of β zeolite with NaAlO2, silica sol as the source of aluminum and silica, respectively, and TEA+ as the template under controlled condition of the synthesis. The ZSM-5/β co-crystalline zeolite was studied by XRD, SEM, BET and NH3-TPD. The reaction activity of toluene alkylation was investigated with a mixture of toluene-methanol as the feedstock in a pulse micro-reactor over the ZSM-5/β co-crystalline zeolite. It is found that ZSM-5/β co-crystalline zeolite has two kinds of zeolite structure including ZSM-5 and β zeolite, not in the form of a physical mixture. The pore structure of ZSM-5/β co-crystalline zeolites is different from that for β zeolite, ZSM-5 and their physical mixture. In addition, the peaks of both high and low temperature desorption of ammonia over the ZSM-5/β co-crystalline zeolite shift 23 oC to lower temperatures and the acid amount of its strong acid is 3% more than the physical mixture. So the ZSM-5/β co-crystalline zeolite produces the highest content of xylene, which is 10.4% higher than the physical mixture. And the ZSM-5/β co-crystalline zeolite has better selectivity for toluene alkylation and weaker de-methylation than β zeolite, ZSM-5 and their physical mixture.

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Methane Decomposition in to Carbon Fibers over Coprecipitated Nickel-Based Catalysts Yan Ju;Fengyi Li;Renzhong Wei 2005, 14 (2): 101-106.  摘要 ( 8217 )   PDF(582KB) ( 2249 )   Decomposition of methane in the presence of coprecipitated nickel-based catalysts to produce carbon fibers was investigated. The reaction was studied in the temperature range of 773 K to 1073 K. At 1023 K, the catalytic activities of three catalysts kept high at the initial period and then decreased with the reaction time. The lifetimes of Ni-Cu-Al and Ni-La-Al catalysts are longer than that of Ni-Al catalyst. With three catalysts, the yield of carbon fibers was very low at 773 K. The yield of carbon fibers for Ni-La-Al catalyst was more than those for Ni-Al and Ni-Cu-Al catalysts. For Ni-La-Al catalyst, the elevation of temperature from 873 K up to 1073 K led gradually to an increase in the yield of carbon fibers. XRD studies on the Ni-La-Al catalyst indicate that La2NiO4 was formed. The formation of La2NiO4 is responsible for the increase in the catalytic lifetime and the yield of carbon fibers synthesized on Ni-La-Al at 773–1073 K. Carbon fibers synthesized on Ni-Al catalyst are thin, long carbon nanotubes. There are bamboo-shaped carbon fibers synthesized on Ni-Cu-Al catalyst. Carbon fibers synthesized on Ni-La-Al catalyst have large hollow core, thin wall and good graphitization.

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Influence of Aging Time on the Properties of Precursors of CuO/ZnO Catalysts for Methanol Synthesis Deren Fang;Zhongmin Liu;Shuanghe Meng;Ligang Wang;Lei Xu;Hua Wang 2005, 14 (2): 107-114.  摘要 ( 9320 )   PDF(381KB) ( 2161 )   The aging process of pure copper precursors and copper-zinc binary precursors were studied by XRD, TG-DTG and TPR techniques. The catalytic activity and stability of CuO/ZnO were tested using fixed-bed flow reactor, and the physical properties of the catalysts and Cu species were characterized with N2 adsorption and N2O passivation method, respectively. For the Cu-Zn binary system prepared at the precipitating condition of pH=8.0 and temperature=80 ‰, the initial phase was a mixture of copper nitrate hydroxide Cu2(NO3)(OH)3, georgeite and hydrozincite Zn5(CO3)2(OH)6. By increasing the duration of its aging time, the phase of Cu2(NO3)(OH)2 first transited to georgeite, and then interdiffused into Zn5(CO3)2(OH)6 and resulted in two new phases: rosasite (Cu,Zn)2CO3(OH)2 and aurichalcite (Zn,Cu)5(CO3)2(OH)6. The former phase was much easier to be formed than the latter one, while the latter phase was more responsible for the activity of methanol synthesis than the former one. It is found that the composition and structure of the precursors altered obviously after the colour transition point. The experimental results showed that methanol synthesis is a structure-sensitive catalytic reaction.

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A Novel Cu-Mo/ZSM-5Catalyst for NOx Catalytic Reduction with Ammonia Zhe Li;Dang Li;Wei Huang;Kechang Xie 2005, 14 (2): 115-118.  摘要 ( 9020 )   PDF(323KB) ( 2294 )   The Cu-Mo/ZSM-5 catalysts with different Cu/Mo ratios were prepared by wet impregnation method, and their catalytic performance for selective catalytic reduction of NOx was studied. The results showed that Cu-Mo/ZSM-5 is a very effective catalyst for NOx catalytic reduction with ammonia, especially when Cu/Mo molar ratio is about 1.5. It not only exhibited the extremely high catalytic activity, but also showed good stability for O2. The bulk phase structure of Cu-Mo/ZSM-5 catalysts was determined by XRD technique, and the results indicated that there is a maximum dispersion for Cu species when Cu/Mo molar ratio is 1.5, and an interaction between Cu and Mo along with HZSM-5 may be present in Cu-Mo/ZSM-5, which may possibly result in a special structure favorable for the catalytic reduction of NOx over Cu-Mo/ZSM-5 catalyst.

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Theoretical Study of Ethanethiol Adsorption on HZSM-5 Zeolite Renqing Lv;Guangmin Qiu;Chenguang Liu 2005, 14 (2): 119-124.  摘要 ( 9078 )   PDF(568KB) ( 2236 )   The density functional theory and the cluster model methods have been employed to investigate the interactions between ethanethiol and HZSM-5 zeolites. Molecular complexes formed by the adsorption of ethanethiol on silanol H3SiOH with two coordination forms, model Bronsted acid sites of zeolite cluster H3Si(OH)Al(OH)2SiH3 interaction with ethanethiol, aluminum species adsorbed ethanethiol have been comparatively studied. Full optimization and frequency analysis of all cluster models have been carried out using B3LYP hybrid method at 3-21G basis level for hydrogen atoms and 6-31G(d) basis set level for silicon, aluminum, oxygen, carbon, and sulfur atoms. The structures and energy changes of different coordination forms of H3Si(OH)Al(OH)2SiH3-ethanethiol, silanol-ethanethiol and Al(OH)3-ethanethiol have been studied. The calculated results showed the nature of interactions was van der Waals force as exhibited by not much change in geometric structures and properties. The preference order of ethanethiol adsorbed on HZSM-5 zeolite may be residual aluminum species, bridging hydroxyl groups and silanol OH groups from the adsorption heat. The adsorbed models of protonized ethanethiol on bridging hydroxyl OH groups and linear hydrogen bonded ethanethiol on bridging OH groups suggested in literature might not exist as revealed by this theoretical calculation. Possible adsorption models were obtained for the first time.