偏高岭土水热合成4A沸石晶化行为的研究

以偏高岭土为原料合成4A沸石,由于其合成过程工艺简单,成本低而一直受到普遍的关注,对于该法晶化过程的行为研究,近年来陆续出现报道,Rocha等^[1]研究认为偏高岭土在碱液中缓慢溶解,形成含SiO3^2-,SiOH基团和Al(OH)4^-的溶液,逐步缩合为硅铝酸钠凝胶,再进一步形成4A沸石晶粒并通过结构重排而转变为4A沸石,王建等^[2]研究提出偏高岭土在NaOH溶液中部分溶解,且迅速转变为偏高岭土,并伴有硅铝酸钠凝胶产生,同时偏高岭土也不断在碱液的作用下凝胶化,生成的凝胶再进一步转变为4A沸石,因而合成的4A沸石产品与化学合成法存在着较大的差异。对偏高岭土合成4A沸石的晶化历程,作者曾进行过研究^[3],发现偏高岭土在碱液中溶解很小,由偏高岭土转为4A沸石晶型,主要是在偏高岭土固相的基础上进行的。本文似从合成过程的机理方面,探讨偏高岭土合成4A沸石的晶化过程行为及其与化学法合成产品差异的关键所在。     

氟离子对无胺法合成高硅丝光沸石的结构导向作用

 在含氟无胺体系中合成了高硅丝光沸石，研究了合成条件对丝光沸石产物的影响．结果表明，投料n（SiO2）／n（Al2O3）＝20～200时，控制晶化条件可得到高硅丝光沸石纯相．由含氟无胺体系中丝光沸石的热力学稳定相区可见，氟离子的引入对方沸石的生成的相区无影响，ZSM－5和镁碱沸石生成的相区消失，丝光沸石生成的相区扩大，石英生成的相区缩小，且基本上变为两相共存区．合成产物丝光沸石的硅铝比随着氟硅比的升高同步增大，证明氟离子在无胺合成高硅丝光沸石时具有结构导向作用．     

高岭土合成沸石分子筛的研究进展

高岭土的化学成分主要为硅和铝,可以作为硅铝源,用于沸石分子筛的合成过程.与以常规的凝胶法合成的沸石相比,以高岭土为原料合成的沸石分子筛以及催化剂,在沸石晶粒大小、水热稳定性、活性和抗重金属性能等方面具有独特的特点,且由于高岭土价格低廉、合成沸石成本低,因此在学术界和企业界引起人们的开发研究兴趣.本文对以高岭土为原料合成沸石分子筛的机理及其研究进展进行了综述.     

偏高岭土水热合成NaY分子筛的机理研究

采用茂名高岭土水热合成NaY分子筛,用IR,XRD,NMR,SEM,HRTEM等分析了其晶化过程。结果表明：偏高岭土水热合成Y型分子筛是固相转变机理,晶化过程是一个扩散-成胶-原位重排的过程。     

气固相取代法制备Ti-β沸石Ⅰ.母体脱铝处理的影响

钛硅分子筛TS-1在有稀双氧水(30%)参与的多种有机化合物选择氧化反应中具有优异的催化性能,因而被认为是分子筛研究领域的一个里程碑[1].但由于其拓扑结构所限,TS-1孔道尺寸只有O.55 nm左右,动力学直径大于0.6 nm的有机物分子难以扩散进入其孔道内部.相继,人们报道了水热合成的Ti-β(0.7 nm×0.7 nm)[2～4]和Ti-MCM-41(2～50 nm)[5]等大孔径含钛分子筛.这些类型的含钛分子筛在催化选择氧化某些有机大分子的反应中表现出TS-1所无法比拟的催化活性.气固相取代法是制备含钛沸石的一种新颖的方法,由于其工艺简单、操作方便而受到人们的重视[6～9].本文以经过盐酸脱铝的β沸石为母体,在一定的气固相反应温度下和TiCl4蒸气接触制备Ti-β沸石,重点考察了母体的脱铝处理条件对钛进入沸石骨架的影响.     

沸石分子筛在高岭土微球上的生长

 通过不同的合成方法,在高岭土微球上生长了沸石分子筛P与沸\r\n石分子筛KSO1的混合物、单一沸石分子筛KSO1和小晶粒沸石分子筛Y,\r\n并用多种物理手段如X射线衍射、电子显微镜和固体核磁共振波谱等对\r\n合成样品进行了表征．     

AM-6分子筛的快速合成及原子线形成机理研究

报道了一种4 h快速合成AM-6分子筛的方法,考察了凝胶中K+含量和起始凝胶碱度对AM-6分子筛纯度以及晶化度的影响.结果表明,向合成体系中引入适量K+可以抑制杂相的生成,在n(K+)/n(V4+)=3和pH=12.5条件下,制备的样品为纯相且晶化度最高.结合紫外-可见吸收光谱和紫外拉曼光谱研究了AM-6分子筛的形成过...     

水热条件下Y型沸石的转晶行为

系统研究了以KOH为结构导向剂,Y型沸石（HY和NaY）在水热条件下转晶为MER型沸石的行为.MER型沸石是硅铝比（Si/Al）在2~3之间且具有四种尺寸8元环孔道（3.1Å×3.5Å,2.7Å×3.6Å,3.4Å×5.1Å,3.3Å×3.3Å）的硅铝沸石分子筛,在小分子催化以及分离方面具有重要的潜在应用.传统水热法合成高结晶度MER型沸石需要7~10 d,将Y型沸石置于KOH的溶液中,经水热处理可在2 d内生成高结晶度的MER型沸石,而水热处理具有等价摩尔组成的无定形硅铝凝胶则得不到高结晶度MER型沸石的纯相.HY沸石可在100和150℃发生转晶,而NaY则只能在150℃发生转晶.KOH/SiO₂比和H₂O/SiO₂比对Y型沸石的转晶行为有重大的影响,只有在最优KOH/SiO₂比和H₂O/SiO₂比条件下才能生成高结晶度的MER型沸石.该转晶合成法显著缩短了MER型沸石的合成周期,对缩短其它有重大工业应用价值的沸石分子筛的合成周期有重要的借鉴意义.     

一种用于合成ZSM－48沸石分子筛的新体系

一种用于合成ＺＳＭ－４８沸石分子筛的新体系李建权，刘光焕，董晋湘（太原工业大学精细化工研究所，太原０３００２４）关键词捏合法，极浓体系，ＺＳＭ－４８沸石，合成，表征长期以来，沸石合成一直是在模拟天然沸石形成的条件下进行的．通常的反应体系是一过饱和状态...     

微波法煅烧高岭土及合成洗涤助剂4A沸石

本文用微波法煅烧高岭土并合成4A沸石.与传统高温热处理法相比,微波法煅烧的高岭土其活化深度好,增白程度高,粒度细,能耗大为降低,显示了明显的优越性.本文还采用煅烧后的活性高岭土为原料,在微波辐射下进行4A沸石的合成,并用XRD、DTA、SEM、白度计、钙离子交换度等进行表征.与传统水热处理法相比,微波法所得样品在结晶度、白度和钙离子交换能力方面均显优势,且大大地加快了沸石晶化反应速率.经动力学处理,发现微波法合成4A沸石的晶核形成及晶体成长的表观活化能均有所下降,说明微波辐射能促进新相的形成,加快整个晶化反应速率.     

2H NMR spectroscopy of liquid crystals: structure and orientational order of a chiral smectogen in its A, C* and J* phases

²H NMR spectroscopy is employed to investigate the orientational order, molecular structure and phase transitions of the chiral smectic liquid crystal 1-methylheptyl 4'-(4-n-decyloxybenzoyloxy)biphenyl-4-carboxylate (10B1M7), showing smectic A, C* and J phases, as well as several sub-smectic C* phases. Two optically pure, differently deuteriated isotopomers have been purposely synthesized and studied.     

2H NMR spectroscopy of liquid crystals: structure and orientational order of a chiral smectogen in its A,C* and J* phases

²H NMR spectroscopy is employed to investigate the orientational order, molecular structure and phase transitions of the chiral smectic liquid crystal 1-methylheptyl 4'-(4-n-decyloxybenzoyloxy)biphenyl-4-carboxylate (10B1M7), showing smectic A, C* and J phases, as well as several sub-smectic C* phases. Two optically pure, differently deuteriated isotopomers have been purposely synthesized and studied.     

The role of a liquid crystal oligomer in stabilizing blue phases

A novel liquid crystal oligomer, 4‐(4‐cyanophenyl)phenyl 4‐octyloxy‐2‐{7‐{4‐[4‐(4‐hexylphenyl)‐2,3‐difluorophenyl]phenyloxy}heptanoyloxy}benzoate, was prepared and found to exhibit a wide temperature range of a nematic phase in spite of being far from a rod‐like structure. Furthermore, the compound induced blue phases in the mixture with a chiral smectic liquid crystal. The molecular shape and its 2,3‐difluorophenyl unit play a role in stabilizing the blue phases.     

Novel bent-shaped liquid crystalline compounds II. Synthesis and properties of the 1,3-bis4-[4-(4-alkyloxybenzoyloxy)benzylidene]aminophenoxypropan-2-ols

A series of new symmetric dimer compounds was synthesized, constaining 2-hydroxy-1,3-dioxypropylene as the central linkage and terminal alkyl chains with different lengths. The chemical structures of the liquid crystal dimers (2ES-n) were examined by FTIR and ¹H NMR spectroscopy. Their mesomorphism, thermodynamic properties and optical textures were investigated by differential scanning calorimetry, polarizing optical microscope and X-ray diffraction. For homologues with terminal propyloxy and butyloxy chains, no liquid crystalline phase was observed. Homologues with pentyloxy and hexyloxy terminal chains showed nematic phases, while those with heptyloxy, octyloxy, nonyloxy and decyloxy terminal chains displayed nematic phases and smectic phases. The results confirmed that the liquid crystalline phase changes from nematic to smectic as the terminal chain length increases.     

Preliminary communication - The effect of a substituent in the central ring on the liquid crystalline properties of di(4-alkoxycarbonylphenyl) terephthalates

Four series of di(4-alkoxycarbonylphenyl) terephthalates with different lateral substituents in the central ring and lengths of the terminal alkyl groups were synthesized. The influence of the lateral substituent on thermodynamical parameters of the phase transitions and elastic properties of the nematic phases (ratio of bend elastic constant to diamagnetic anisotropy K3/Delta chi) were studied by polarizing optical microscopy, differential scanning calorimetry and observations of the Freedericksz transition. It was found that increasing the alkyl chain length and the substituent size in the sequence H, Cl, Br, NO2 results in reduction in stability of the crystal and (as frequently observed in other cases) the liquid crystal phases. The changes in the bend elastic constant and the melting enthalpy caused by the substituent variation are correlated with each other, a fact that is explained by the dependence of short-range lamellar packing on size and polarity of substituent.     

Dielectric Relaxation and Quasielastic Neutron Scattering Study of Molecular Reorientation in the Nematic and Solid Phases of 4,4'-Di-N-Butyloxyazoxybenzene

Dielectric relaxation measurements carried out in the nematic phae of 4,4'-di-n-butyloxyazoxybenzene (BOAOB) reveal fast reorientational motions of the whole molecule around the long axis (τ₁ ∼ 60 ps) as well as slow reorientational motions of the whole molecule around the short axis (τ₁ ∼ 10^-8 s). Incoherent quasielastic neutron scattering spectra obtained for nematic BOAOB, with normal and deuteriated alkoxy terminals, are interpreted as dominated by reorientation (around the C-N bonds) of moieties consisting of benzene rings coupled with alkoxy terminal chains (τ₁ ∼ 4ps). In addition fast conformational changes occur in these chains. Dielectric relaxation measurements reveal librations of the whole molecule in the crystal phases CI and CII accompanied by reorientation of the terminal chains in these phases. The reorientations occur on the time scale amounting to 10^-8 s. Incoherent quasielastic neutron scattering spectra obtained for the CI and CII phases of BOAOB are interpreted as being dominated by overdamped librational motions of the moieties accompanied by fast conformational changes in the alkyl chains. The CIII phase corresponds to a normal molecular crystal.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

Liquid crystal properties of some substituted pyrazines

A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

Crystal structures of Ln4Ni3O8 (Ln = La, Nd) triple layer T'-type nickelates

Single-phase Ln4Ni3O8 (Ln = La, Nd) nickelates were synthesized and their crystal structures were determined by Rietveld refinement of powder neutron diffraction data. The crystal structures of these mixed-valent Ni1+/Ni2+ phases belong to the T'-type and are built by intergrowth of LnO2 fluorite layers with triple NiO2 infinite-layer structural blocks. The major driving force of transformation of the LnO rock-salt block of the parent Ln4Ni3O10-delta Ruddlesden-Popper phases to the fluorite arrangement in the reduced Ln4Ni3O8 phases is attributed to internal structural stress. This transformation allows longer Ni-O bonds in Ln4Ni3O8 without overstretching of the Ln-O bonds, especially in the equatorial plane. The observed displacement of Ni atoms from the outer NiO2 planes toward the Ni atom of the central NiO2 plane in Ln4Ni3O8 is ascribed to large electrostatic repulsion from the fluorite part of the structure. X-ray absorption spectra near the K-edge of Ni suggest that the charge density on the nickel ion is similar for all members of the T'-type Lnn+1NinO2n+2 homologous series, which correlates with nearly constant Ni-O bond lengths observed in all the reduced nickelates. This suggests that the formal changes in the valence state of Ni affect the covalency of the Ni-O bond.