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采用预置晶种法合成了含铁的微孔EU-1/ZSM-5复合分子筛,并采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、热重-微分热重(TG-DTG)、N2吸附-脱附、紫外-可见吸收光谱(UV-vis DRS)、X射线吸收精细结构(XAFS)等手段进行了表征。结果表明,复合分子筛具有EU-1和ZSM-5的特征衍射峰,是两种晶相相互作用的分子分散晶相材料,微孔孔径较Fe-EU-1分子筛有所增大。随原始溶胶中铁的质量分数增加,复合分子筛具有的23.09°和23.94°处的特征衍射峰逐渐向低角度方向偏移;紫外-可见漫反射谱图中在220~245 nm出现了宽的吸收谱带;XAFS表征表明,1s→3d电子跃迁的弱吸收峰逐渐增强,同时在吸收边顶部出现的1s→4p吸收峰逐渐由宽变窄。合成工艺的最佳条件为,原始溶胶中铁的质量分数为0.075%~0.15%,晶种添加比例为15.0%~21.0%,晶种SiO2/Al2O3物质的量比为50~60。 相似文献
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采用廉价的四丙基溴化铵(TPABr)的模板剂合成了TS-1分子筛,在晶化过程中,运用XRD,ICP,IR,^29SiMASNMR和UV-Vis光谱等表征手段,系统地研究了钛原子引入分子筛骨架的机制,观察到钛原子随分子筛的形成同步进入骨架的规律,另外,尽管在晶化初期固相中没有TiO2结晶出现,但存在分散态的TiOx物种,随晶化时间的延长,液相中钛物种之间聚合的几率增加,使固相中TiO2晶体不断形成。 相似文献
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综述了具有 MWW 结构钛硅分子筛的制备方法、孔道和晶体结构的调变和修饰以及催化应用三个方面的研究进展. 与 TS-1 相比, 具有 MWW 结构钛硅分子筛的制备方法多种多样; 其孔道结构可塑性强, 通过采用层间剥离、柱撑以及分子水平硅烷化插硅扩孔技术, 可以增大和暴露孔道和外表面, 满足不同选择氧化反应的要求. 由于 MWW 结构钛硅分子筛拥有复杂而独特的孔道结构, 所以在小分子 (如直链烯烃等) 的环氧化反应, 和大分子 (环状烯烃, 二苯并噻吩等) 氧化反应中都表现出优异的催化性能. 此外, 该钛硅分子筛表现出与 TS-1 完全不同的溶剂效应, 用于烯丙基氯液相环氧化与酮类氨氧化反应主产物选择性更高. 相似文献
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采用晶种法在极浓体系中,快速合成了L/EU-1复合分子筛,通过XRD、SEM、NH_3-TPD、TG-DTG等多种手段对其进行了表征.结果表明:随原始溶胶中添加硼和铁的质量分数的增加,复合分子筛中L分子筛的特征衍射峰分别向高角度和低角度方向发生偏移,L分子筛的晶胞参数和晶胞体积分别有所减小和增加;含硼和铁的L/EU-1复合分子筛尺寸大小长约为0.5~3μm,宽0.2~1μm,形貌为小颗粒聚集L分子筛附着生长管状镶嵌结构复合分子筛;镶嵌结构改变了复合分子筛的酸性、稳定性和孔道性质.影响因素分析表明,碱硅比低时,K~+对促进钙霞石笼的形成起主导作用,碱硅比高时,K~+对溶胶的聚沉起主导作用. 相似文献
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The structure of manganese(Ⅱ)-substituted aluminophosphate MnAPO-14 with AFN zeotype has been investigated by computational simulation in Cerius2 package. Starting from reported structure of MnAPO-14, total 28 theoretical models of Mn-substituted AFN have been built and optimized to obtain their stable conformation. In terms of the host-guest non-bonding interaction and the framework energies, the Mn(Ⅱ)-substituted sites and the bonded sites of two H2O molecules can be well predicted for MnAPO-14. The simulated structure is in good agreement with that of experimental MnAPO-14. Calculation results suggest that the replacement site of Al by Mn(Ⅱ) atom in AFN is dramatically effected by the guest molecules of organic templating resided in the channels, which is corresponding to the host-guest charge-density matching principle. This work will be helpful for the better understanding the structures of metal-substituted microporous materials. 相似文献
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利用量子力学中的密度泛函理论(DFT),对EU-1分子筛中与T1、T2、T3、T6、T7、T8位相邻的骨架铝原子的落位稳定性及酸强度进行理论计算.通过计算得知,双Al原子在EU-1分子筛骨架中优先落位于Al7(Si6-Si7)Al8、Al1(Si2-Si2)Al1、Al2(Si1-Si2)Al2、Al1(Si2-Si2)Al3、Al1(Si2)Al3;根据(Al/Si,H)取代能确定了质子的落位,质子氢较易落位于(O12-H)Al1-(O12-H)Al1、(O12-H)Al1-Al1(O13-H)、(O12-H)Al1-Al1(O12-H)、(O14-H)Al2-(O14-H)Al2、Al2(O12-H)-(O14-H)Al2、Al1(O12-H)-(O15-H)Al3、(O26-H)Al7-Al8(O28-H);且根据质子亲和势分析知,EU-1分子筛骨架中质子氢落位于NNN位的Brnsted酸强度小于NNNN位.借助1H MAS NMR分析合成的不同硅铝比的样品,可知硅铝比低的EU-1分子筛Brnsted酸吸收峰的面积增加;由NH3-TPD可知硅铝比低的EU-1分子筛的强酸脱附峰温度降低,酸强度减小.硅铝比低的EU-1分子筛的强酸表现出酸量高、酸强度低的性质. 相似文献
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SiCS分子结构及其稳定性的理论研究 总被引:5,自引:1,他引:4
采用DFT,QCISD及CCSD(T)方法对单重态、三重态SiCS的分子体系势能面进行理论计算,在QCISD/6-311G(d)水平上得到由3个过渡态连接的5个稳定构型.经动力学及热力学分析均是稳定的三重态线型分子SiCS(31)、单重态线型分子SiCS(11)以及单重态的环状分子cSiCS(12). 相似文献
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苯乙烯基吡啶类化合物几何结构与光谱的理论研究 总被引:5,自引:0,他引:5
采用量子化学密度泛函理论(DFT)方法分别在B3LYP/6-31G*, 6-31G**, 6-31+G*水平上对苯乙烯基吡啶类化合物进行计算研究. 通过在相同水平下的振动频率分析发现苯乙烯基吡啶类化合物具有C1对称性, 酯基的碳氧原子与苯环形成不同的离域大π键, 空间位阻和共轭效应使得两苯环处于两个不同平面, 二面角在60°与62°之间. 使用含时密度泛函理论(TD-DFT)方法计算第一激发态的电子垂直跃迁能, 得到最大吸收波长λmax. 计算结果表明末端烷基链的长度对该类化合物的几何结构与振动光谱、电子光谱无影响. 相似文献
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双环-HMX结构和性质的理论研究 总被引:5,自引:2,他引:5
在DFT-B3LYP/6-311G*水平上, 计算研究了高能化合物四硝基四氮杂双环辛烷(双环-HMX) α和β两种异构体的结构和性质. 比较分子对称性、分子内氢键和环张力等几何参数以及分子总能量和前线轨道能级等电子结构参数, 发现α比β稳定. 分子中N—N键较长, N—N键集居数较小, 预示该键为热解和起爆的引发键. 基于简谐振动分析求得IR谱频率和强度. 运用统计热力学方法求得200~1000 K温度的热力学性质. 以非限制性半经验PM3方法探讨其热解机理, 求得各反应通道的过渡态和活化能, 发现热解始于侧链N—NO2键的均裂. 还从理论上预测了该化合物的密度、爆速和爆压, 有助于寻求高能量密度材料(HEDM). 相似文献
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Density functional theory was used to optimize structures of different methylaluminoxane nanotubes with general formula [(AlOMe)2]n, [(AlOMe)3]n and [(AlOMe)4]n cycle unit, where n ranges from 1 to 10. To explore the stability of nanotubes, the binding energies and total energies are calculated. The results indicate that [(AlOMe)3]n and [(AlOMe)4]n have the stable structure of nanotubes. When n is 3, they have the most stable structure in all systems. Moreover, [(Al5O5)]n and [(Al7O7)]n are also considered, but their dimers have irregular and distorted structures. So [(Al5O5)]n and [(Al7O7)]n nanotubes are impossible to exist. 相似文献
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The structures and stability of triplet HFSiS system were investigated by density functional theory(DFT)in detail. The optimized geometrical parameters and vibrational frequencies of all species were obtained at the level of B3LYP/6-311G** and the assignments of them were performed. At the same theoretical level, IRC calculations were carried. In addition, the singlet-point energies and relative energies were calculated by high level electron-correlation CCSD(T)/6-311G**. The isomerized and dissociated processes were explained by vibrational mode analysis method. The triplet PES is compared to the singlet one. The results are as the following: there are six isomers on the triplet PES. Moreover, 3HFSiS is found to be the most thermodynamically and kinetically stable and is able to be observed in experiments. Structures 2 are the more stable ones between the two group bond cycled isomers and are predicted to be detected. 3SiSHF is the most unstable isomer in thermodynamics and kinetics. 相似文献
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A seeded approach was developed to synthesize high-silica EU-1 zeolite via inhibiting the co-crystallization of ZSM-48 in the presence of hexamethonium (HM) ions. A systematic study was carried out to determine factors such as seed content and SiO(2)/Al(2)O(3) ratio, which influenced the crystallization of high-silica EU-1 and transformation of EU-1 into ZSM-48. Using EU-1 seeds, not only well-crystallized pure EU-1 zeolites with SiO(2)/Al(2)O(3) ratios more than 500 were synthesized, but also the co-crystalline of ZSM-48/EU-1 or pure ZSM-48 was obtained in control from silica-rich mixture gels. Furthermore, the kinetic features of the seeded synthesis of EU-1 zeolites with SiO(2)/Al(2)O(3) ratios of 55, 190, and 500 were examined. It was found that seeds played crucial roles in the decrease of apparent activation energy of EU-1 nucleation and inhibiting the transformation of EU-1 into ZSM-48. The HM and Al species performed synergistic roles to inhibit the formation ZSM-48 during high-silica EU-1 nucleation and crystal growth. 相似文献