共查询到20条相似文献,搜索用时 31 毫秒
1.
Zhiping Huo Xiangyu Xu Zhi Lv Jiaqing Song Mingyuan He Zhaofei Li Qian Wang Lijun Yan Yang Li 《Journal of Thermal Analysis and Calorimetry》2013,111(1):365-369
NaP zeolites samples with different morphologies were successfully synthesized and their thermal behaviors were fully characterized by in situ HT-XRD, IR spectrum, and TG-DSC techniques. It was found that the cubic zeolite NaP phase underwent the same phase transitions, despite their different morphologies. During the whole heating process, they first underwent a minor phase transition into the tetragonal phase at 200 °C. Then they were gradually converted into the phillipsite phase between 400 and 700 °C. Finally, a very stable NaAlSiO4 nepheline phase formed when the calcination temperature reached 800 °C, which would be kept even after the sample was cooled to room temperature. Although samples with different morphologies had similar phase transitions, they did have different thermal stability as proved by the TG-DSC study. 相似文献
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N. E. Gordina V. Yu. Prokof’ev O. E. Hmylova Yu. N. Kul’pina 《Journal of Thermal Analysis and Calorimetry》2017,129(3):1415-1427
The effect of ultrasonic treatment on the thermal behavior of the mixtures from metakaolin, sodium hydroxide and alumina designed for LTA zeolites synthesis was studied. X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy and synchronous thermal analysis have been used. It was shown that after evaporation of the suspension, LTA zeolite (24 mass%) is contained in the samples. It was established that the new phase (sodium aluminum silicate) is formed at a calcination temperature of about 600 °C. It was demonstrated that at a calcination temperature over 800 °C, nepheline is synthesized. The reaction of nepheline formation has been described by the topochemical equation of four-dimensional nucleation/nucleus growth according to Avrami/Erofeev. Using the Ozawa–Flynn–Wall analysis for non-isothermal data, the values of the activation energy and the pre-exponential factor have been calculated. It is shown that after the ultrasonic treatment the activation energy of the nepheline synthesis reaction has smaller values than in the sample without pretreatment. These phenomena have been explained by differences between the structural parameters of the particles (dimension of the coherent scattering region, the value of microdeformations). 相似文献
3.
NaA zeolite was synthesized from mechanically activated granulated mixtures of metakaolin, sodium hydroxide, and aluminum oxide. The thermal treatment and hydrothermal crystallization processes were studied. It is shown that the optimal temperature of thermal treatment of grains based on a mechanically activated metakaolin is 600°C at a NaA zeolite content of about 65 wt %. Raising the calcination temperature leads to a decrease in the content of the zeolite and to formation of nepheline. It was found that the optimal concentration of the crystallization solution of NaOH is 2–4 M. Under these conditions, the content of the zeolite exceeds 90 wt %. Raising the alkali concentration leads to a decrease in the content of the zeolite and to its recrystallization into sodalite. 相似文献
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用红外光谱研究温度对沸石酸性的影响,结果表明,温度使沸石表面酸性(酸强度)增强,酸性增强的规律是大孔道或大孔腔中的酸性羟基>表面硅醇基(或缺陷羟基)>小笼中的酸性羟基,在所研究的温度范围内(290~510K)酸性随温度的变化呈线性关系。 相似文献
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Prof. Dr. Abdolraouf Samadi‐Maybodi Seyed Naser Azizi S. Masoomeh Pourali Salma Ehsani Tilami 《无机化学与普通化学杂志》2012,638(1):214-219
Bismuth‐modified zeolite‐P (Bi‐ZP) was synthesized by hydrothermal methods during the phase transformation of analcime to zeolite‐P. The evolution of phase transformation of pure analcime to Bi‐ZP was investigated. The results showed that bismuth atoms were incorporated into the framework of the microporous zeolite‐P. The effect of various Bi/Al (0–3) and Si/Bi (1–5) mole ratios on the synthesis of bismuth modified zeolite were studied by X‐ray diffraction (XRD) technique and FT‐IR spectroscopy. Evolution of the growth process of Bi‐ZP spheres was carried out at different time intervals with XRD patterns and FE‐SEM images. The energy dispersive X‐ray (EDX) spectrum indicated the existence of bismuth atoms in the synthesized Bi‐ZP. Framework substitutions of bismuth were evidenced by a set of complementary characterizations such as diffusive reflectance UV/Vis (DRS) and Raman spectroscopy on the synthesized Bi‐ZP (Si/Bi = 1). 相似文献
8.
D. V. Makarov A. T. Belyaevskii Yu. P. Men’shikov D. P. Nesterov M. F. Yusupova 《Russian Journal of Applied Chemistry》2007,80(2):175-180
Behavior of a skeleton silicate, nepheline, in the reaction of fluorination with ammonium hydrofluoride was studied by means of differential-thermal, X-ray phase, and chemical analyses, IR spectroscopy, and scanning electron microscopy. 相似文献
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在强碱性水溶液体系中,以水玻璃为硅源,以铝酸钠为铝源,在类质同晶高硅P沸石晶种导向作用下,反应物中自发生成的A型沸石可转晶为纯相高铝MAP沸石。升高反应温度有利于提高产物的结晶度。由不同温度下的晶化曲线计算出MAP沸石表观生长活化能为59.6kJ.mol^-^1。不用晶种时,同一反应物体系结晶产物为单一的A型沸石。在该反应物体系中,A型沸石的成核活化能与生长活化能分别为40.3和50.7kJ.mol^-^1。MAP高的生长活化能以及A型沸石相对低的成核与生长活化能揭示合成MAP沸石时使用晶种的原因。 相似文献
10.
Wakihara T Kohara S Sankar G Saito S Sanchez-Sanchez M Overweg AR Fan W Ogura M Okubo T 《Physical chemistry chemical physics : PCCP》2006,8(2):224-227
The structure of amorphous precursor species formed under hydrothermal conditions, prior to the onset of crystallization of microporous aluminosilicate zeolites, is determined employing high-energy X-ray diffraction (HEXRD). The investigation, combined with the use of reverse Monte Carlo modelling suggests that even numbered rings, especially 4R (R: ring) and 6R, which are the dominant aluminosilicate rings in zeolite A, have already been produced in the precursor. The model implies that the formation of double 4Rs occurs at the final step of the crystallization of zeolite A. 相似文献
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Synthesis of a Sulfate Enclathrated Zeolite with Intermediate Framework Structure between Sodalite and Cancrinite
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Josef‐Christian Buhl 《无机化学与普通化学杂志》2017,643(15):1030-1036
A sulfate enclathrated microporous zeolite of composition Na7.4[SiAlO4]6(SO4)0.7(H2O)4.8 with intermediate framework structure (INT) between the well known zeolites sodalite (SOD) and cancrinite (CAN) can be prepared by the autothermal synthesis, a method first demonstrated in reference 1 . The product (abbreviated as “SO4‐INT”) was characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray analysis (EDX‐analysis), Fourier transform infrared spectroscopy (FT‐IR) and thermogravimetry (TG). SO4‐INT was found to crystallize as spheres with 1–6 μm in diameter with a rough surface. Sometimes the spheres are agglutinated to each other by a few amount of amorphous material within the sample. The thermal behavior of the new phase was further studied. At elevated temperature (1000 °C) a transformation of SO4‐INT into a large amount of nosean was observed beside some parts of nepheline, formed by crystallization of the amorphous byproduct. The nosean phase was found to be stable up to 1250 °C, before the onset of a total destruction by melting during further heating. Finally a re‐crystallization of the melt during cooling yielded carnegieite as the final product (low form at room temperature). This unusual thermal behavior of SO4‐INT is discussed in terms of structural interactions of the sulfate guests inside the aluminosilicate host‐framework and in comparison with literature data of the intermediate phases CO3‐INT 2 , 3 as well as NO3‐INT. 4 相似文献
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Concellón JM Rivero IA Rodríguez-Solla H Concellón C España E García-Granda S Díaz MR 《The Journal of organic chemistry》2008,73(15):6048-6051
The transformation of enantiopure (2R,4R)- and (2S,4S)-N,N-dibenzyl-1,2:4,5-diepoxypentan-3-amine, 1 and 2, into the corresponding enantiopure (3S,5S)- and (3R,5R)-3,5-dihydroxy-3-aminopiperidines, 3 and 4 respectively, is described. The opening of the two epoxide rings with a range of amines takes place with total regioselectivity and high yields, in the presence of LiClO4. A mechanism to explain this transformation is proposed. 相似文献
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以硅藻土为硅源, 在Na2O-Al2O3-SiO2(硅藻土)-H2O体系中, 采用水浴加热搅拌的方法在较低温度下快速合成了LTA型硅铝分子筛NaA. 通过调节温度和反应物的活性, 优化了NaA分子筛的合成过程, 实现了其在较短时间、 较低温度下的快速合成. 所合成的NaA分子筛展现出良好的质子传导性能, 在室温和100%相对湿度条件下, 其质子传导率为1.72×10-3 S/cm, 且随着温度的升高其质子传导率逐渐增大, 在80 ℃和100%相对湿度条件下, 质子传导率可以达到5.96×10-3 S/cm. 相似文献
15.
W. Lutz W. Wieker D. Müller M. Schneider C. H. Rüscher J.‐Ch. Buhl 《无机化学与普通化学杂志》2000,626(6):1460-1467
The steaming of zeolite Y (here at 873 K for 7 hours) leads to the formation of an amorphous aluminium aluminosilicate in addition to the dealuminated zeolite (DAY). An alkaline treatment of DAY causes the transformation of the non‐framework phase into an alkali aluminosilicate and the partial desilication of the DAY framework. The alkali aluminosilicate is decomposed by a moderate acid leaching under the formation of silica gel. The 29Si MAS NMR and IR spectra of DAY and its chemically treated modifications are superimposed by the signals of the crystalline zeolite framework and the amorphous non‐framework materials whereas XRD measurements only characterize the current state of the framework. 相似文献
16.
Maoying SongXiqing Wang Weizheng ZhouHeyong He Yaojun SunTailiu Wu Yingcai Long 《Journal of solid state chemistry》2002,164(1):19-26
MTN-type zeolite with tetragonal symmetry was hydrothermally synthesized in a reactant system of Na2O-SiO2-NaF-H2O using N-ethyl-hexamethylenetetraammonium bromide as the template. A spontaneous phase transformation of the as-synthesized zeolite at ambient temperature from tetragonal to cubic symmetry was investigated with polarized light microscopy, X-ray powder diffraction, 29Si magic angle spinning nuclear magnetic resonance, and differential scanning calorimetry. The results of the investigations indicate that the as-synthesized tetragonal MTN zeolite is a metastable phase. 相似文献
17.
The synthesis and structural characterization of the sterically congested pyrophosphite 6-[(2,4,8,10-tetrakis(1,1-dimethylethyl)-dibenzo[d,f][1,3,2]dioxaphosphepin-6-yl)oxy]-2,4,8,10-tetrakis(1,1-dimethylethyl)-dibenzo[d,f][1,3,2]dioxaphosphepin, 3, is described. In solution at room temperature, a single species was observed that was consistent with a pyrophosphite structure without any evidence for the tautomeric diphosphine monoxide. Below the coalescence temperature (T(C)), 0 degrees C, three atropisomers were observed with relative absolute configurations of (R,R,R), (R,S,R), and (R,R,S). Ring inversion of the seven-membered rings below the T(C) is slow on the NMR time scale, which leads to observable diastereoisomerism because of the presence of two independent stereoaxes (sp2-sp2 C-C single bond connecting the two aryl rings). Additionally, a rotation about an exocyclic P-O single bond connecting the two seven-membered rings, which constitutes a third stereoaxis, is slowed on the NMR time scale. In the X-ray crystal structure of 3, the solid-state conformation was found to be the same as the major conformation in solution below the T(C), namely, the (R,R,S) atropisomer. The results of a conformational search, performed with a specifically parametrized AMBER force field, were in agreement with the 31P NMR assignment of the major (R,R,S) atropisomer, which was found to be an energy minimum. Additionally, we could independently assign the relative configuration of the minor isomers based on the calculated results. 相似文献
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UV-Raman and NMR spectroscopic studies on the crystallization of zeolite A and a new synthetic route
Ren L Li C Fan F Guo Q Liang D Feng Z Li C Li S Xiao FS 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(22):6162-6169
UV-Raman and NMR spectroscopy, combined with other techniques, have been used to characterize crystallization of zeolite A. In situ UV-Raman spectroscopy shows that the starting gel for crystallization of zeolite A contains a lot of four-ring (4R) building units and the appearance of six-ring (6R) building blocks is the signal for crystal formation. (29)Si NMR spectroscopy results suggest that the starting gel is double four-ring (D4R) rich and during crystallization of zeolite A both α and β cages appear. (27)Al NMR spectroscopy results indicate the absence of Al (2Si) species in the starting gel, suggesting the absence of single 4R building units in the starting gel. Furthermore, composition analysis of both solid and liquid samples shows that the solid rather than liquid phase predominates for the crystallization of zeolite A. Therefore, it is proposed that the crystallization of zeolite A mainly occurs in the solid phase by self-assembly or rearrangement starting from the zeolite building units mainly consisting of D4R. The essential role of D4R is directly confirmed by successful conversion from a solution of D4R to zeolite A in the presence of NaCl, and the importance of solid phase is reasonably demonstrated by the successful synthesis of zeolite A from a dry aluminosilicate gel. By considering that the solid phase has a major contribution to crystallization, a novel route was designed to synthesizing zeolite A from the raw materials water glass (Na(2)SiO(3) in aqueous solution) and NaAlO(2), without additional water and NaOH; this route not only simplifies synthetic procedures, but reduces water consumption. 相似文献
19.
本文制备了不同形态的含镍Y沸石, 研究了温度, 时间和H~2S浓度对含镍Y沸石硫化的影响, 发现负载型含镍Y沸石最易硫化, 离子交换型次之, 骨架型最难硫化。考察了沸石表面硫化物物种的热稳定性和水热稳定性。指出高温下沸石脱附的水蒸汽能使硫化物发生水解, 导致催化剂失硫。用XRD, IR和化学分析等方法对硫化的含镍沸石催化剂进行表征, 硫化后沸石表面形成的NiS~x有可能是属正交晶系的Ni~7S~6化合物。对噻吩加氢脱硫反应, 硫化的含骨架镍Y沸石无催化活性, 硫化的离子交换型含镍Y沸石活性比负载型含镍Y沸石高5-6倍左右, 因其酸性较强。催化剂表面酸性位和硫化镍活性位共存, 对噻吩加氢脱硫反应是有利的。 相似文献
20.
V. V. Ordomskii Yu. V. Monakhova E. E. Knyazeva N. S. Nesterenko I. I. Ivanova 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2009,83(6):1012-1017
Micro-mesoporous materials with various ratios between micro- and mesopores were prepared by the recrystallization of zeolite
BEA in an alkaline medium in the presence of cetyltrimethylammonium bromide. The materials were characterized by X-ray diffraction,
low-temperature nitrogen adsorption, and IR spectroscopy. Recrystallization under mild conditions did not cause substantial
changes in the number of acid centers but increased the accessibility of acid centers to large-sized molecules because of
the creation of mesopores. An increase in the degree of recrystallization caused first partial and then complete zeolite transformation
into MSM-41 mesoporous aluminosilicate, which was accompanied by a decrease in the number of acid centers. The IR spectra
were used to determine the diffusion coefficients of cumene in the initial and recrystallized samples. Recrystallization increased
the diffusion coefficient by 3–4 times.
Original Russian Text ? V.V. Ordomskii, Yu.V. Monakhova, E.E. Knyazeva, N.S. Nesterenko, I.I. Ivanova, 2009, published in
Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1150–1155. 相似文献