共查询到20条相似文献,搜索用时 15 毫秒
1.
Abdolraouf Samadi-Maybodi Robin K. Harris S. Naser Azizi Alan M. Kenwright 《Magnetic resonance in chemistry : MRC》2001,39(8):443-446
Silicon-29 NMR spectra were obtained for more than 20 aqueous alkaline silicate solutions containing methanol. A signal assigned to CH3OSi(OH)3 or one of its deprotonated congeners was studied in detail for the first time for the solution conditions involved. Its appearance was monitored as a function of the solution compositions. The pseudo-equilibrium constant for its formation is of the order of 0.65. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
2.
The chemical environments of europium-exchanged NaX (Si/Al =1.16) and NaY (Si/Al = 2.29) zeolites have been investigated by means of 129Xe NMR and isotherm measurements of adsorbed xenon. EuNaX and EuNaY samples with varied concentrations of Eu cations were subjected to diverse chemical and thermal treatments, namely dehydration, reduction, oxidation, and re-reduction. Thermal analyses of hydrated EuNaX and EuNaY samples indicate that both the structural stability and the saturation concentration of water increase with increasing Eu content. For dehydrated EuNaY zeolites, the Eu3+ cations tend to replace Na+ ions at S2 sites and tend to be located in framework supercages; similar behavior is found for Eu2+ ions after reduction. After subsequent oxidation, Eu3+ ions migrate from supercages into small sodalite and/or D6R cages; similar results were deduced for samples after re-reduction. In contrast to the behavior observed in EuNaY, Eu3+ ions tend to exchange for Na+ ions in the sodalite and/or D6R cages in dehydrated EuNaX zeolites, regardless of the thermal treatment; this behavior is ascribed to the existence of unlocalized S3 Na+ in EuNaX samples. 相似文献
3.
以含氟的二胺5,5’-(六氟异丙基)-二-(2-氨基苯酚)(6FHP)及二酐4, 4’-(六氟异丙基)-苯二酸酐(6FDA)或均苯四甲酸酐(PMDA)为单体,以分散红 1(DR1)为活性生色分子合成具有非线性光学特性的含氟聚酰亚胺,并采用溶胶-凝胶(Sol-Gel)法合成相应的聚酰亚胺/SiO2杂化材料.采用固态29 Si MAS NMR谱研究了含氟聚酰亚胺/SiO2杂化材料的交联结构,结果表明杂化材料中是以T3、Q3、Q4结构为主,说明在杂化材料中形成了交联网状结构.采用衰减全反射(ATR)测定了聚酰亚胺和杂化材料在832 nm处的电光系数,其值分别为 32、28、34和29 pm/V,结果表明具有较高的电光系数. 相似文献
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用~(29)Si(~(27)Al)MAS NMR和辅加乙酰丙酮(acac)处理样品的静态~(27)Al NMR研究了镧离子对脱铝Y型沸石(DAIY)骨架硅、铝和非骨架铝(EFAL)的影响.结果表明,~(29)Si MAS谱的化学位移及其形状不仅取决于连接[SiO_4]四面体的[AlO]-四面体数目,而且还与引入镧离子的量有关.镧离子的引入导致~(27)Al MAS谱的明显宽化和不对称形变.另外,还讨论了镧离子对非骨架铝的影响. 相似文献
6.
Blechta V Sýkora J Hetflejs J Sabata S Schraml J 《Magnetic resonance in chemistry : MRC》2006,44(1):7-10
It is demonstrated using a practical example that indirect detection of (29)Si NMR signals is sufficiently sensitive in LC-NMR stop-flow arrangement to analyze mixtures of siloxane polymers. New cryogenic probes with better signal-to-noise ratio will turn this version of LC-NMR into a routine method for analysis of siloxane polymers. 相似文献
7.
Madison L. Nelson Joelle E. Romo Stephanie G. Wettstein Joseph D. Seymour 《Molecules (Basel, Switzerland)》2021,26(18)
Zeolites are known to be effective catalysts in biomass converting processes. Understanding the mesoporous structure and dynamics within it during such reactions is important in effectively utilizing them. Nuclear magnetic resonance (NMR) T2 relaxation and diffusion measurements, using a high-power radio frequency probe, are shown to characterize the dynamics of water in mesoporous commercially made 5A zeolite beads before and after the introduction of xylose. Xylose is the starting point in the dehydration into furfural. The results indicate xylose slightly enhances rotational mobility while it decreases translational motion through altering the permeability, K, throughout the porous structure. The measurements show xylose inhibits pure water from relocating into larger pores within the zeolite beads where it eventually is expelled from the bead itself. 相似文献
8.
用~(29)Si MAS NMR、~(27)Al MAS NMR、XRD及IR等方法对4种不同脱铝方法处理的USY、SSY、US-SSY和DAY的微观结构进行了研究,结合脱铝方法讨论了骨架硅铝的分布以及非骨架硅铝和羟基空穴等的形成和含量不同的原因.发现不同脱铝方法可导致骨架上不同Si(nAl)单元的脱除.XRD结果表明,SSY经进一步高温水蒸汽处理得到的US-SSY的相对结晶度可高达97%.脱铝后,微孔保留愈多,二次孔越少,相对结晶度愈高.最后对~(29)Si MAS NMR、XRD和IR3种测定骨架单胞铝(N_(Al))_F的结果进行了比较. 相似文献
9.
Jan Schraml Peter Sandor Stefan Korec Martin Krump Bronislav Foller 《Magnetic resonance in chemistry : MRC》2013,51(7):403-406
It is shown by experiments that replacing one‐pulse sequence by RIDE (ring down elimination) pulse sequence may dramatically improve the baseline of 29Si NMR spectra and eliminate the signal from the probe. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
10.
分子筛材料具有酸性可调节和择形选择性的优势, 因而在多相催化反应中表现出优异的性能. 本文综述了利用固体核磁共振(ssNMR)光谱对分子筛的酸性和择形选择性进行研究的最新进展. 通过采用或不采用探针分子的ssNMR技术, 探测了分子筛中酸性位的数量、 酸强、 酸类型及酸位之间的协同作用. 此外, 通过直接观察多相催化反应中关键中间体的存在, ssNMR光谱提供了分子筛择形选择性的证据. 酸性和择形选择性的协同作用有助于更好地设计分子筛材料, 以实现更好的多相催化. 相似文献
11.
高硅ZSM-5分子筛和二次合成Ti-ZSM-5分子筛的结构 总被引:1,自引:0,他引:1
运用度角旋转(MAS)和交叉极化(CP)等核磁共振波谱和红外光谱技术,分别对采用不同模板剂制备的高硅ZSM-5分子筛和以此为母体,经气固同晶取代法得到Ti-ZSM-5分子筛的结构特性进行了研究.结果表明:在水热法合成高硅ZSM-5分子筛过程中,模板剂明显制约着所制得的分子筛的结构特性.通过选用合适的模板剂,可直接获得具有正交晶系结构的高硅ZSM-5分子筛.在随后的气固相同晶取代过程中,钛原子通过占据分子筛骨架中的缺陷位进入骨架,形成具有一定Ti/Si比例的钛硅分子筛(Ti-ZSM-5)。骨架结构中缺陷位的含量直接影响分子筛的载钛量。 相似文献
12.
Sam Smet Pieter Verlooy Fadila Saïdi Francis Taulelle Johan A. Martens Charlotte Martineau-Corcos 《Magnetic resonance in chemistry : MRC》2019,57(5):224-229
The 1H–29Si multiple-contact cross polarization (MC-CP) MAS NMR experiment is evaluated for the class of silicate-siloxane copolymers called POSiSils, that is, polyoligosiloxysilicones. It proves a reasonably good solution to tackle the challenge of recording quantitative 29Si NMR data in experimental time much reduced compared with single pulse acquisition. In a second time, we report 29Si–29Si MC-CP double-quantum single-quantum (MC-CP-DQ-SQ) NMR experiment, which provides information about the through-space proximities between all silicon species despite the high degree of heterogeneity of this material. This work furthers the NMR tools for NMR crystallography for inorganic polymers, as it covers flexible polymers with different dimensionalities and long or heterogeneous relaxation characteristics at low 29Si natural abundance. 相似文献
13.
The utility of 29Si NMR spectroscopy has been demonstrated on sediment-like materials in the quantitative and qualitative determination of polyorganosiloxanes (silicones) in selected environmental samples. This technique is highly selective for polydimethylsiloxanes (PDMS) and is non-destructive to the sample. Also, specific identification of polyorganosiloxanes in sediment is possible, in contrast to previous methods which provided only quantitative information while consuming the sample. The detection limit for a 9 h experiment is approximately 45 ppm. 相似文献
14.
IR. MAS NMR法研究富硅超稳镨氢Y沸石 总被引:1,自引:0,他引:1
制备了NH_4Y、USY、PrHY、USPrHY、F8Y及FSPrHY催化剂, 测定其组成和物性. 于红外光谱装置上比较了上述催化剂羟基峰的异同, 通过对吡啶的吸脱附测定了诸催化剂的酸强度. B 酸强度顺序为: FSPrHY>FSY>USPrHY>USY>PrHY>NH_4Y. ~(29)Sit MAS NMR谱表明, 在USPrHY 及FSPrHY 的Si(0Al)%甚多于PrHY 和NH_4Y中的Si(0Al)%. IR、~(29)Si MAS NMR及活性测试等结果说明: 沸石中0NNN铝位的存在, 是达到强酸性的必要条件. 高价稀土阳离子形成(?)及Pr(OH)~(2+)抵消了方钠石笼中AlO_4~-上的电荷, 增强了剩余铝位上羟基酸强度; 且从骨架羟基上吸引电子, 因而使质子酸性更强, 从而提高了裂解、岐化、脱烷基活性. 相似文献
15.
以四丙基溴化铵为模板剂合成TS-1分子筛的研究 总被引:2,自引:0,他引:2
运用1H→13CCP/MASNMR、29SiMASNMR、IR、XRD和元素分析等表征方法,研究了以四丙基溴化铵(TPABr)为模板剂的合成体系中,Ti酯和模板剂用量以及不同碱源对TS-1分子筛的影响,考察了不同Ti含量固体样品催化丙烯环氧化反应.实验结果表明:随着凝胶中Ti酯用量的增加,制得的分子筛结构对称性由单斜晶系逐渐向正交晶系转变,其丙烯环氧化活性也相应增加.尽管凝胶中所加减源只调变凝胶碱度而不起模板剂作用,然而凝胶的强碱环境对骨架钛原子引入有利.当凝胶中TPABr/SiO2摩尔比值在0.05-0.25之间时,TPABr加入量的变化不影响TS-1分子筛中骨架钛含量. 相似文献
16.
Georgi N. Vayssilov Markus Staufer Thomas Belling Konstantin M. Neyman Helmut Knoezinger Notker Roesch 《ChemInform》1999,30(49):no-no
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option. 相似文献
17.
Schraml J Blechta V Sýkora J Soukupová L Curínová P Pronek D Lachman J 《Magnetic resonance in chemistry : MRC》2005,43(10):829-834
The lines in (29)Si NMR spectra of silylated polyphenols and some other compounds are difficult to assign owing to the absence of couplings with protons outside the silyl group. The assignment can be derived through small (n)J((29)Si, (13)C) couplings (n > 1). Using a previously described method for measurements of these couplings, the assignment procedure is demonstrated here on three examples of trimethylsilylated phenols: 7-hydroxyflavone, ferulic acid, and quercetin. In some cases the procedure can be used to identify carbon atoms to which the siloxy groups are attached. 相似文献
18.
A technique based on the29Si NMR spectra for analyzing the spatial structure of cyclolinear polymethylsiloxanes has been developed. The role of certain factors influencing the formation of the spatial structure of the chains during the preparation of these polymers has been studied.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1460–1466, August, 1993. 相似文献
19.
Dr. Erica Brendler Thomas Heine Wilhelm Seichter Jörg Wagler Raiker Witter 《无机化学与普通化学杂志》2012,638(6):935-944
29Si NMR shielding tensors of a series of triphenylsilanes Ph3SiR with R = Ph, Me, F, Cl, Br, OH, OMe, SH, NH2, SiPh3, C≡CPh were determined from 29Si CP/MAS spectra recorded at low spinning rates. In addition the principal components of the shielding tensor were calculated employing the DFT‐IGLO method. For most silanes experimental and calculated values are in good accordance. Larger differences were observed for systems with hydrogen bridge forming substituents and the halides bromide and chloride. In some of the spectra the shielding information interfered with residual dipolar couplings. The different contributions of the various substituents to the principal components of the shielding tensor and the orientation of the tensor within the molecules are discussed and compared for the compounds under investigation. 相似文献
20.
Dirk Mehlhorn Dr. Rustem Valiullin Prof. Dr. Jörg Kärger Kanghee Cho Prof. Dr. Ryong Ryoo 《Chemphyschem》2012,13(6):1495-1499
Specially synthesized extra‐large crystallites of zeolite LTA with intentionally added mesoporosity are used for an in‐depth study of guest diffusion in hierarchical nanoporous materials by the pulsed field gradient NMR technique. Using propane as a guest molecule, intracrystalline mass transfer is demonstrated to be adequately described by a single effective diffusivity resulting from the weighted average of the diffusivities in the two (micro‐ and meso‐) pore spaces. Gas‐kinetic order‐of‐magnitude estimates of the diffusivities are in satisfactory agreement with the experimental data and are thus shown to provide a straightforward means for predicting and quantifying the benefit of hierarchically structured nanoporous materials in comparison with their purely microporous equivalent. 相似文献