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Wu Y Wang J Liu P Zhang W Gu J Wang X 《Journal of the American Chemical Society》2010,132(51):17989-17991
Incorporation of Ce and La into the framework of MCM-22 zeolite has been achieved by cohydrolysis and condensation of tetraethylorthosilicate and lanthanide salts in moderate/weak acidic media followed by a switch of synthesis gels to basic conditions for hydrothermal crystallization. The promotion effect of the framework Ce (La) when Ce(La)-MCM-22 serves as the catalyst support for hydroisomerization of n-heptane is demonstrated. Framework substitutions of lanthanides are evidenced by a set of mutually complementary characterizations, catalytic tests, and item-by-item comparisons with the impregnated and ion-exchanged counterparts. The novel synthesis strategy may give further outlines for the production of other types of heteroatomic zeolites. 相似文献
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Denayer JF Ocakoglu RA Thybaut J Marin G Jacobs P Martens J Baron GV 《The journal of physical chemistry. B》2006,110(17):8551-8558
Low-coverage adsorption properties (Henry constants, adsorption enthalpy, and entropy) of linear and branched alkanes (C3-C8) on zeolite MCM-22 were determined using the chromatographic technique at temperatures between 420 and 540 K. It was found that adsorption enthalpy and entropy of linear alkanes vary in a nonmonotonic way with carbon number. The adsorption behavior of alkanes was rationalized on the basis of the pore geometry. Short molecules prefer to reside in the pockets of the MCM-22 supercage, where they maximize energetic interaction with the zeolite. Longer molecules reside in the larger central part of the supercage. For carbon numbers up to six, singly branched alkanes are selectively adsorbed over their linear counterparts. This preference originates from the entropic advantage of singly branched molecules inside MCM-22 supercages, where these species have high rotational freedom because of their small length. 相似文献
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Magdolna R. Mihályi Ilian Kolev Vesselina Mavrodinova Christo Minchev Márton Kollár József Valyon 《Reaction Kinetics and Catalysis Letters》2007,92(2):345-354
Zeolite precursor MCM-22 samples were prepared by hydrothermal synthesis. The H-zeolites, obtained from the precursors, were
characterized by scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, and by their activity
in the title reaction. Despite of the lower Br?nsted acid site concentration of the zeolite having smaller crystallites, showed
higher activity, while the zeolite, having larger crystals were more selective for p-xylene formation. 相似文献
5.
Application of zeolite MCM-22 for basic dye removal from wastewater 总被引:13,自引:0,他引:13
MCM-22 was employed as an effective adsorbent for removal of basic dyes including methylene blue, crystal violet, and rhodamine B from aqueous solution. The adsorption kinetics and isotherms were investigated. The adsorption capacity of MCM-22 for three dyes follows an order of MB > CV approximately RB. Kinetic studies indicate that the adsorption follows the pseudo second-order kinetics and the adsorption is a two-step diffusion process with film diffusion dominating the process. The adsorption isotherm can be well fitted by both the Langmuir and the Freundlich models. Thermodynamic calculations suggest that the adsorption of basic dyes on MCM-22 is an endothermic reaction. 相似文献
6.
Nature and population of Li+ cationic sites in MCM-22 zeolite and its pillared form (MCM-36) were investigated by means of adsorption of CO as a probe molecule. CO stretching frequency and adsorption heat were measured by FTIR spectroscopy and adsorption microcalorimetry. Intrazeolitic carbonyl complexes on Li+ cations in MCM-22 and MCM-36 are characterized by two main vibrational bands at 2,195 and 2,188 cm?1. Band at higher wavenumbers is ascribed to carbonyls on Li+ ions coordinated only to two oxygen atoms at the intersection of 10-ring channels and interacting with CO molecule by energy around 45 kJ mol?1. Band at 2,188 cm?1 was assigned to the carbonyls on Li+ cations located on top of 5 or 6-rings on the channel walls and coordinated to three or four oxygen atoms, interacting with CO molecule by energy 33–36 kJ mol?1. Effect of pillaring and layered form of zeolite on nature and population of Li+ cationic sites is also discussed, as well as the formation of dicarbonyl complexes. 相似文献
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在动态水热条件下,研究了硅溶胶、白炭黑、硅酸及硅胶为硅源时对MCM-22分子筛合成及物化性质的影响。以硅溶胶、白炭黑、硅酸三种硅源均可合成出高结晶度且无杂晶的片状MCM-22分子筛,其平均粒径分别为190、220和750 nm。硅源影响分子筛的聚集形态,三种硅源分别形成晶粒分散、晶粒半分散及晶粒聚集形态。三组样品的酸强度分布基本一致,都具有较多的中强酸分布,由硅溶胶和硅酸所得MCM-22分子筛在中强酸范围具有更高的B/L酸比值,以白炭黑合成的分子筛总酸量最高。NMR结果表明,样品中的铝以骨架铝为主,不存在明显的非骨架铝。由于硅胶对合成体系中游离水的吸附作用,水热反应难以发生,不能得到MCM-22分子筛,硅胶作为分子筛合成硅源时需要选择合适的反应条件。 相似文献
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MCM-22型分子筛中苯分子吸附行为的蒙特卡罗模 拟研究 总被引:3,自引:0,他引:3
用巨正则统计系综蒙特卡罗模拟方法研究了纯硅MCM-22型分子筛(ITQ-1)中苯分子的吸附行为。结果表明苯分子在ITQ-1型分子筛中主要存在4个吸附位点。从苯分子粒子分布云图上可以看到苯分子的扩散和吸附主要在12元环超笼内发生。在苯分子的扩散过程中,S2位置附近的苯分子分布较为集中,而S3和S4附近的苯分子分布则较为离散。苯分子通过10元环窗口的运动路径势能面的计算结果表明,苯分子在12元环超笼内可以较为自由迁移,而通过10元环窗口从一个超笼扩散到附近的超笼时则需要较高的激发能量,这个能量大约为100kJ/mol。 相似文献
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采用十六烷基三甲基溴化铵(CTAB)和六亚甲基亚胺(HMI)组成双模板体系, 以气相二氧化硅为硅源, 在 150℃下动态原位合成了薄层的 MWW型 MCM-22分子筛纳米片, 并考察了 CTAB添加量对分子筛产物的影响。采用粉末 X射线衍射(PXRD)、扫描电子显微镜(SEM)、N2吸附-脱附、氨气程序升温脱附(NH3-TPD)、高倍透射电子显微镜(HRTEM)、吡啶红外(Py-IR)和 2, 6-二叔丁基吡啶红外(DTBPy-IR)测试方法对合成的分子筛样品进行表征。结果表明:采用双模板体系可以制备出 5~10 nm的薄层MWW型纳米片。同时, 通过偏三甲苯异构化反应对样品的催化性能进行了表征, 催化结果显示样品 d-MWW-4 %CTAB具有较好的催化性能, 其中偏三甲苯的质量转化率、均三甲苯质量收率及均三甲苯选择性分别为 34.97 %、22.42 %和 64.09 %, 这主要归因于薄层纳米片 MCM-22具有的较大外表面积和片层间形成的晶间介孔结构。 相似文献
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Yongchen Shang Wenxiang Zhang Mingjun Jia Piaoping Yang Dazhen Jiang Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2005,85(2):245-251
Summary Modification of HMCM-22 zeolite with tetraethoxysilane (TEOS) can considerably improve the catalytic performances, especially the selectivity to isobutene, for the reaction of n-butene skeletal isomerization. 相似文献
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采用十六烷基三甲基溴化铵(CTAB)和六亚甲基亚胺(HMI)组成双模板体系,以气相二氧化硅为硅源,在150 ℃下动态原位合成了薄层的MWW型MCM-22分子筛纳米片,并考察了CTAB添加量对分子筛产物的影响。采用粉末X射线衍射(PXRD)、扫描电子显微镜(SEM)、N2吸附-脱附、氨气程序升温脱附(NH3-TPD)、高倍透射电子显微镜(HRTEM)、吡啶红外(Py-IR)和2,6-二叔丁基吡啶红外(DTBPy-IR)测试方法对合成的分子筛样品进行表征。结果表明:采用双模板体系可以制备出5~10 nm的薄层MWW型纳米片。同时,通过偏三甲苯异构化反应对样品的催化性能进行了表征,催化结果显示样品d-MWW-4%CTAB具有较好的催化性能,其中偏三甲苯的质量转化率、均三甲苯质量收率及均三甲苯选择性分别为34.97%、22.42%和64.09%,这主要归因于薄层纳米片MCM-22具有的较大外表面积和片层间形成的晶间介孔结构。 相似文献
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凝胶制备对气相合成MCM-22沸石的影响 总被引:2,自引:0,他引:2
以硅酸钠为硅源、硫酸铝为铝源制备硅铝干凝胶,六亚甲基亚胺(HMI)为模板剂,采用气相法合成MCM-22沸石。对硅铝干凝胶进行了29 Si MAS NMR、27 Al MAS NMR、红外以及透射电镜表征,讨论了pH值对硅铝干凝胶及合成MCM 22沸石的影响。结果表明,pH值的改变影响硅铝聚集态、干凝胶的结构及其粒径等物理性质,合成时硅铝干凝胶解聚、气固间传质及固相溶解速度不一致,影响产物MCM-22的结晶度。当制备干凝胶的pH值为8.7~10.7时,得到结晶度高的MCM-22沸石;当pH值增大到11.1时,产物出现杂晶丝光沸石;pH为11.6时只能得到丝光沸石。 相似文献
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Peng He Hui Liu Yanfeng Li Jiqin Zhu Shiping Huang Zhigang Lei Peng Wang Huiping Tian 《Adsorption》2012,18(1):31-42
The GCMC (grand canonical Monte Carlo) simulation technique was used to predict the competition adsorption characteristics
of benzene and propene in different pore systems of MCM-22. The nine-site model of benzene was used, which proved to be effective
and efficient. The zeolite was divided into three adsorption sites following a simulated annealing method. It is found that
benzene and propene have the same preferential adsorption site and a similar adsorption order in different sites. Moreover,
the pure and mixture isotherms of the three sites are drawn. From the isotherms, we obtained a selectivity reversal of the
mixture isotherms of benzene and propene in different sites. It is also noted that the competition adsorption in the three
adsorption sites for the two adsorbates can fall into three successive steps and the adsorption order of propene in mixture
in these three sites is S3→S1→S2. A new model is presented to predict the benzene and propene adsorption equilibrium in MCM-22.
This approach yields better multicomponent equilibrium predictions than ideal adsorbed solution theory (IAST). Isotherms at
different mole fraction of benzene in gas phase indicate an advantage to increase the feed radio of benzene and propene. Thus,
this work is helpful for a better understanding of the adsorption mechanism of benzene and propene in MCM-22 and hence the
relation of the catalytic properties of the zeolite to its structure. 相似文献
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S. Sivasanker S. G. Hegde S. V. Awate S. R. Padalkar S. B. Kulkarni 《Reaction Kinetics and Catalysis Letters》1988,36(1):173-176
The creation of strong acid sites in alkaline K-L-zeolites on ion-exchanging with La-ions is reported. Acidity measurements have been carried out by temperature programmed desorption of adsorbed ammonia. Reaction data which confirm the creation of acid sites are also reported.
- K-L La. - . , .相似文献
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Yu Zhang Haijun Xing Piaoping Yang Peng Wu Mingjun Jia Jiazhong Sun Tonghao Wu 《Reaction Kinetics and Catalysis Letters》2007,90(1):45-52
Pillared layered MCM-36 zeolite was prepared from MCM-22 precursor with polymeric silica as pillaring agent. Both MCM-36 and
MCM-22 zeolites are very active for the alkylation of benzene with propylene, and MCM-36 shows higher selectivity to cumene
compared with MCM-22 zeolite. 相似文献
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Synthesis of MCM-22 zeolite using rice husk as a silica source under varying-temperature conditions 总被引:1,自引:0,他引:1
Cheng Y Lu M Li J Su X Pan S Jiao C Feng M 《Journal of colloid and interface science》2012,369(1):388-394
In this study, rice husk, an abundant agricultural byproduct, was utilized as an alternative silica source for the synthesis of MCM-22. The zeolite with high crystalline was synthesized using a three-stage varying-temperature hydrothermal method. The prepared silica and MCM-22 were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results showed that the duration required for zeolite crystallization was significantly decreased under varying-temperature conditions. The MCM-22 was in the form of thin platelet-like crystals, and no amorphous material existed in the framework of the MCM-22 after calcination and ammonium exchange. Cationic brilliant red 5GN, a basic dye used in the wool and blanket factories for fiber dyeing, was selected as the adsorptive to study the adsorption performance of the MCM-22. Adsorption experiments indicated that the maximum extent of adsorption was obtained at pH of 10, contact time of 60 min, and MCM-22 dose of 1.0 g/L. The adsorption kinetic has been described by first-order and pseudo-second-order models. It was observed that the rate of dye adsorption followed pseudo-second-order model. 相似文献
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以碳黑为第二模板剂在氟离子体系中一步水热合成了多级结构MCM-22分子筛组装体(简称为MCM-22-FC)。考察了碳黑和氟离子对MCM-22分子筛形貌和催化性能的影响。MCM-22-FC分子筛是由大量片状晶体交错生长形成的组装体结构,其中MCM-22的片层结构更薄,在其固有的微孔中存在的晶间孔呈现大孔和介孔的特征。MCM-22-FC负载Mo后得到的Mo/MCM-22-FC催化剂在甲烷无氧芳构化反应(MDA)中提高了苯收率和芳烃选择性,并且提高了催化剂的寿命。通过氨气程序升温脱附(NH3-TPD)表征,吡啶红外(Py-IR)表征,结合热重(TG)分析,得出的结论是Mo/MCM-22-FC在MDA中优越的催化性能是由于氟离子进入到分子筛骨架当中,形成具有拉电子效应的结构单元,从而提高了分子筛的Brönsted酸量,较多的Brönsted酸性位将更多的Mo物种迁移至分子筛孔道内部,形成更多的MoCx或MoOxCy活性物种以及更有利于大分子产物扩散的MCM-22薄片层的结构。少量过剩的Brönsted酸性位在成型后保留在Mo/HMCM-22-FC催化剂活性中心抑制了积碳的形成,也有助于改善芳烃的选择性。 相似文献
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多级孔ZSM-5分子筛: 丰富的外表面酸中心和良好的二甲苯异构化催化性能 总被引:3,自引:0,他引:3
多级孔沸石分子筛的结构性质及其催化性能是近年来分子筛研究的热点.本文采用蒸汽辅助晶化的方法制备了多级孔ZSM-5沸石分子筛,采用NH3程序升温脱附和原位吸附红外光谱等方法研究了其表面酸性质,用邻二甲苯异构化反应考察了其催化性能.结果表明,多级孔结构分子筛的结晶度和总酸量有所下降,但Lewis酸中心却有所增加.进一步研究发现,多级孔结构分子筛的外表面酸中心数量远高于常规分子筛,从而证实了多级孔结构可以将更多的酸中心暴露到外表面;而外表面酸中心数量的增多和扩散传质的改善是多级孔ZSM-5分子筛在邻二甲苯异构化反应中具有更高催化活性和对二甲苯产率的重要原因. 相似文献