共查询到17条相似文献,搜索用时 140 毫秒
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Y型沸石脱铝机制和铝状态的NMR研究 总被引:2,自引:2,他引:0
对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,29Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,27Al MAS NMR谱、二维章动NMR及1H-27Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合29Si和27Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。 相似文献
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用MAS NMR方法研究了SAPO-34分子筛的晶化过程.发现硅进入骨架有两种方式,在晶核形成过程中,硅直接参与反应,与磷和铝同时进入骨架;在晶化过程的后期,部分硅原子取代了骨架中的磷原子或磷铝原子对进入骨架,从而形成了SAPO-34分子筛的多种硅铝结构. 相似文献
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研究了因焙烧过程升温速率对β沸石模板剂的热分解过程的影响 ,不同升温速率下Naβ沸石焙烧的尾气组成 ;还测定了Naβ沸石的TG -DTG谱 ,40 0℃下Naβ沸石的FTIR谱图 ,以及在不同温度下焙烧 4h后的XRD谱图及2 9Si、2 7Al的NMR结果 .根据这些结果 ,提出了分段焙烧脱胺方法 ,使有机胺在 2 6 0~ 42 0℃间的两个恒温段充分发生Hofmann降解反应 ,从而使分解产生的乙烯和水蒸气能够随空气流自然排出焙烧体系 ,可使焙烧过程中产生的热能得到分阶段逐步地释放 ,同时可避免高温下沸石骨架水热脱铝的负作用 ,得到骨架脱铝少、结晶度高的脱胺 β沸石 . 相似文献
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研究四乙基氢氧化铵(TEA-OH)模板剂用量对合成的β沸石的结构及脱胺行为的影响。合成β沸石的模板剂的较佳用量(TEA+/Al)为2.10~1.68,合成的β沸石的相对结晶度均大于84%;β沸石中的铝含量(Al/Al+Si)及骨架铝含量(TdAl/TdAl+OhAl)随晶化混合液的TEA+/Al而变,存在最佳TEA+/Al点为1.9,此时合成的β沸石非骨架铝量最少,结构硅铝比最高;含TEA的β沸石脱胺过程为Hofmann降解反应,TGA测定的失重量、DSC测定的吸热量与β沸石中TEA含量密切相关. 相似文献
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八面沸石中的骨架铝可按其环境次邻位上出现的铝数分为4类。环境无次邻铝的铝离子形成分子筛的强酸中心;周围有1至3个次邻铝的铝离子形成的酸中心酸性较弱,与前者相比易于从骨架上解脱。基于一级动力学近似,用Monte-Carlo方法模拟八面沸石脱铝过程,得到4种类型铝离子的数目随硅铝比改变而演化的规律。预计硅铝比在6.68附近,脱铝八面沸石中的强酸中心数目达到极大值;如果强、弱酸中心铝离子的解脱速率差别较大,则脱铝八面沸石中强酸中心浓度较高。
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稀土掺杂P2O5-Al2O3-BaO玻璃的制备及其结构研究 总被引:1,自引:0,他引:1
稀土掺杂磷酸盐玻璃具有优异的光学和光谱特性,在激光介质、有色滤光材料等领域中有着重要的应用。在P2O5_Al2O3_BaO_Sm2O3(PABS)玻璃形成能力研究的基础上,借助MAS NMR、红外光谱等分析手段,研究了玻璃的结构、玻璃组成与热处理等对玻璃结构的影响。结果表明:不同组成PAB(S)玻璃的31P MAS NMR谱在-20ppm~-25ppm范围内均存在单一的特征信号峰,对应于磷氧多面体[PO4]的Q2型结构;在18ppm、-12ppm和-36ppm处27Al的MAS NMR谱的三个特征信号峰分别对应于27Al的[AlO5][、AlO6]、[AlO6]配位结构,稀土离子的掺入以及热处理均使得[AlO6]向[AlO5]转变;玻璃的网络结构主要由Q2型[PO4]、[AlO5]和[AlO6]构成,并P_O_P、P_O_Al的形式相连接。玻璃在1383 cm-1处出现的吸收峰可能是玻璃结构中形成了P_O_Sm键所致。 相似文献
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High silica zeolite SSZ-13 with Si/Al ratios varying from 11 to 17 was characterized by aluminum-27 and silicon-29 NMR spectroscopy. Aluminum-27 MAS and MQMAS NMR data indicated that in addition to tetrahedral aluminum sites, a fraction of aluminum sites are present in distorted tetrahedral environments. Although in samples of SSZ-13 having high Si/Al ratios all aluminum atoms are expected to be isolated, silicon-29 NMR spectra revealed that in addition to isolated aluminum atoms (Si(1Al)), non-isolated aluminum atoms (Si(2Al)) exist in the crystals. To model these contributions of the various aluminum atoms, a mixed-domain distribution was developed, using double-six membered rings (D6R) as the basic building units of SSZ-13. A combination of different ideal domains, one containing isolated and the other with non-isolated aluminum sites, has been found to describe the experimental silicon-29 NMR data. 相似文献
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Ganapathy S Gore KU Kumar R Amoureux JP 《Solid state nuclear magnetic resonance》2003,24(2-3):184-195
Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra. 相似文献
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NMR探讨粉煤灰研磨过程中铝氧多面体的变化 总被引:4,自引:0,他引:4
采用27Al魔角旋转核磁共振和二维三量子魔角旋转(2D 3QMAS)核磁共振方法对研磨前后粉煤灰中铝氧多面体结构进行了探讨. 结果表明:粉煤灰中铝氧多面体主要以四面体和八面体形式存在. 分析认为铝氧四面体和八面体有多种结构环境形式,导致它们宽化峰的出现. 经过机械研磨后,处于玻璃体硅氧四面体网络中的四配位结构相对稳定,只有微小的变化;网络外作为调整离子的六配位多面体有一部分脱离网络向结构环境对称性状态转变. 从2D图谱中还可以辨别出原先少量的五配位不稳定结构在研磨后消失. 相似文献
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Bachmann S Hellriegel C Wegmann J Händel H Albert K 《Solid state nuclear magnetic resonance》2000,17(1-4):39-51
Pure organic polyalkylvinyl ether phases were synthesized by suspension polymerization using different ratios and compositions of n-butylvinyl ether (C4VE) and n-octadecylvinyl ether (C18VE) with triethylene glycol divinyl ether or divinylbenzene as crosslinkers, respectively. These phases were investigated by means of solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) spectroscopy and 1H high-resolution magic angle spinning (HR MAS) NMR spectroscopy in suspended-state. A comparison of these two methods showed the substantial advantages of 1H HR MAS NMR measurements. Structure elucidation was achieved using a 2D H,H-COSY NMR experiment performed under MAS conditions enabling full peak assignment of the 1H NMR spectra of these phases. The dynamic behavior of the polyalkylvinyl ether phases was determined by employing temperature-dependent measurements of spin–lattice relaxation times (T1) as well as accumulation of a 2D wide line separation NMR spectrum. 相似文献
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The question of the homogeneous broadening that occurs in 2D solid-state NMR experiments is examined. This homogeneous broadening is mathematically introduced in a simple way, versus the irreversible decay rates related to the coherences that are involved during t1 and t2. We give the pulse sequences and coherence transfer pathways that are used to measure these decay rates. On AlPO4 berlinite, we have measured the 27Al echo-type relaxation times of the central and satellite transitions on 1Q levels, so that of coherences that are situated on 2Q, 3Q, and 5Q levels. We compare the broadenings that can be deduced from these relaxation times to those directly observed on the isotropic projection of berlinite with multiple-quantum magic-angle spinning (MAS), or satellite-transition MAS. We show that the choice of the high-resolution method, should be done according to the spin value and the corresponding homogeneous broadening. 相似文献