CXN天然沸石的研究Ⅶ.骨架高硅超稳化改性

以高硅超稳化辉沸石(STI)为基底沸石,分别经盐酸脱铝或氟硅酸铵脱铝补硅处理后制备的改性H-STI沸石,其非骨架铝含量明显减少,而后者骨架硅铝比进一步提高.X射线荧光散射光谱(XRF),27Al高分辨率魔角旋转固体核磁共振(MAS NMR),红外(FT-IR)光谱等表征证明改性后的沸石骨架硅铝原子比分别为6.8和11.4.低温氮吸附表明,经盐酸处理的高硅STI沸石孔道开放完美,但经氟硅酸铵处理的样品孔道被部分堵塞.分段程序升温焙烧表明前者骨架热稳定性略差,1000℃焙烧后结构基本被破坏,而后者热稳定性较好,经相同温度段焙烧后仍保持较高的结晶度和热稳定性,其结构基本实现超稳化.     

CXN天然沸石的研究VII. 骨架高硅超稳化改性

以高硅超稳化辉沸石(STI)为基底沸石,分别经盐酸脱铝或氟硅酸铵脱铝补硅处理后制备的改性H-STI沸石,其非骨架铝含量明显减少,而后者骨架硅铝比进一步提高.X射线荧光散射光谱(XRF),27Al高分辨率魔角旋转固体核磁共振(MASNMR),红外(FT-IR)光谱等表征证明改性后的沸石骨架硅铝原子比分别为6.8和11.4.低温氮吸附表明,经盐酸处理的高硅STI沸石孔道开放完美,但经氟硅酸铵处理的样品孔道被部分堵塞.分段程序升温焙烧表明前者骨架热稳定性略差,1000℃焙烧后结构基本被破坏,而后者热稳定性较好,经相同温度段焙烧后仍保持较高的结晶度和热稳定性,其结构基本实现超稳化.     

CXN天然沸石的研究 VI. 耐酸性及不同阳离子型沸石结构的热稳定性

以X射线粉末衍射(XRD)结晶度测定法观测CXN (STI型)天然沸石在不同浓度盐酸(HCl)热溶液中的结构耐酸性, 以及比较和研究用不同方法制备的结构超稳化高硅H-STI-I和H-STI-II沸石及其不同阳离子交换型M-STI (M＝Li, Na, K, Ca, Ag) 系列沸石在程序阶梯升温过程中的结构热稳定性. 用X射线荧光散射(XRF), ²⁹Si与²⁷Al固体核磁共振(MAS NMR)表征超稳化高硅H型沸石的组成与结构性质. 结果表明该天然沸石在浓度低于2 mol/L盐酸中可较长时间保持结构完美. 视阳离子类型不同, 经1173 K焙烧后M-STI-I系列沸石与M-STI-II系列沸石相对结晶度降低百分数分别为2.5%～18% 与0～35%. 在M-STI-I系列沸石中, 焙烧前后相对结晶度下降幅度的次序为K型＜(H, Li, Na)型＜(Ca, Ag)型, 而M-STI-II系列沸石, (Na, K)型＜(Li, H, Ca)型＜Ag型. 从沸石骨架硅铝比、结构缺陷、阳离子种类及其氧化物形成热等方面讨论影响沸石结构热稳定性的因素.     

CXN天然沸石的研究 V. 结构超稳化

以离子交换结合控制焙烧的方法分别制得结构超稳化高硅H-STI-I和H-STI-II沸石. EDX, ²⁹Si MAS NMR, ²⁷Al MAS NMR, FT-IR等表征证明, 其骨架硅铝原子比分别为4.43和10.62. 分段程序升温焙烧后的沸石样品经粉末XRD表征表明, 其结构热稳定性达到1000 ℃以上. 结构稳定化沸石呈现反映微孔特性的I型吸附等温线, 吸附孔道完美、开放. 经历过酸处理的H-STI-II沸石, 结构缺陷增多, 其热稳定性、比表面积及孔容积略低于H-STI-I.     

脱铝八面沸石的研究——Ⅲ.稳定性

以NaY沸石为原料,用SiCl_4同晶取代法制备了不同硅铝比且具有高结晶度的八面沸石,进一步将样品交换成铵型。还制备了超稳Y样品及铝交换型八面沸石。研究结果表明,随骨架硅铝比提高,八面沸石的骨架稳定性、热稳定性及水热稳定性均得到很大改善。骨架外铝会使较低硅铝比样品的水热稳定性变差。钠型及铵型样品在不同硅铝比时,对稳定性有不同影响。在骨架硅铝比相近情况下,SiC1_4脱铝沸石(DNH_4Y)较水热法脱铝沸石(USY)有好得多的热稳定性,然而二者却具有相近的水热稳定性。     

CXN天然沸石的研究 VI. 耐酸性及不同阳离子型沸石结构的热稳定性

以X射线粉末衍射(XRD)结晶度测定法观测CXN (STI型)天然沸石在不同浓度盐酸(HCl)热溶液中的结构耐酸性, 以及比较和研究用不同方法制备的结构超稳化高硅H-STI-I和H-STI-II沸石及其不同阳离子交换型M-STI (M＝Li, Na, K, Ca, Ag) 系列沸石在程序阶梯升温过程中的结构热稳定性. 用X射线荧光散射(XRF), ²⁹Si与²⁷Al固体核磁共振(MAS NMR)表征超稳化高硅H型沸石的组成与结构性质. 结果表明该天然沸石在浓度低于2 mol/L盐酸中可较长时间保持结构完美. 视阳离子类型不同, 经1173 K焙烧后M-STI-I系列沸石与M-STI-II系列沸石相对结晶度降低百分数分别为2.5%～18% 与0～35%. 在M-STI-I系列沸石中, 焙烧前后相对结晶度下降幅度的次序为K型＜(H, Li, Na)型＜(Ca, Ag)型, 而M-STI-II系列沸石, (Na, K)型＜(Li, H, Ca)型＜Ag型. 从沸石骨架硅铝比、结构缺陷、阳离子种类及其氧化物形成热等方面讨论影响沸石结构热稳定性的因素.     

天然CXN沸石分子筛水热稳定性研究 II. 水蒸汽处理温度对铵型沸石物化性质的影响

在前文研究天然Stilbite沸石(CXN沸石)水热稳定性影响因素的基础上, 以27Al与29Si MAS NMR, NH3-TPD和低温氮吸附等详细研究了铵型CXN沸石骨架铝配位状态和硅配位状态, 表面酸性与孔性质等与水蒸汽处理温度的关系. 随温度升高, 沸石骨架硅铝比逐渐提高, 并伴随硅羟基缺陷增多. 经750 ℃水蒸汽处理3 h后沸石骨架硅铝比可达到21.3. 沸石总酸量随水蒸汽处理温度的提高而降低, 沸石骨架铝脱除造成沸石孔道部分被堵塞, 但同时形成有利于分子扩散的介孔.     

β-沸石骨架铝化改性的红外光谱

β沸石是以有机胺为模板剂合成的高硅沸石．为在孔道中进行吸附和催化反应,通常是在空气中 (５５０℃ )进行焙烧,将有机胺脱除并使质子酸中心形成．但这种脱模板剂方法,会造成骨架脱铝［１ -４］,使质子酸中心显著减少．β沸石固有结构中存在着孔道位错和结构空穴,空气中焙烧脱有机胺可能会进一步损伤沸石的骨架结构［４,５］．沸石骨架改性已发展了多种铝化方法［６ -８］．有的研究工作表明,通常用红外光谱和ＭＡＳＮＭＲ表征的非骨架铝,在温和的条件下,例如回馏温度下的离子交换或者在较低温度下 (１００℃或室温 )与碱反应就可…     

超细NaY分子筛的深度脱铝

通过优化和组合不同脱铝补硅方法,依次经氟硅酸铵处理、600oC水热处理、硅溶胶+草酸处理和800oC水热处理过程,成功实现了200nm超细NaY分子筛的深度脱铝,最终产品骨架硅铝比高达27.3,比表面积为581.9m2/g,分子筛结晶度保持在65%以上.结果表明,对于超细NaY分子筛脱铝,第一步采用氟硅酸铵进行部分缺陷修补尤为重要.根据分子筛晶粒尺寸不同,需严格控制氟硅酸铵用量和处理次数.当晶粒为200nm时,氟硅酸铵与分子筛骨架铝的摩尔比为0.16,处理一次较为适宜.在连续脱铝过程中及时补修脱铝产生的缺陷是保障超细NaY分子筛成功脱铝的关键,而采用氟硅酸铵、硅溶胶、800oC高温水热处理,可有效实施这种骨架修正作用.     

天然CXN沸石分子筛水热稳定性研究Ⅰ.水热稳定性影响因素

以天然CXN沸石为基底材料,通过离子交换、焙烧和酸处理等方法研究了影响该沸石水热稳定性的因素.XRD,XRF和27Al MAS NMR等结果表明阳离子种类和位置均会影响沸石水热稳定性,其中铵型CXN沸石的水热稳定性最高.高温焙烧铵型CXN沸石虽能提高骨架硅铝比,但骨架缺陷增多导致其水热稳定性下降.还研究了水蒸汽量、处理温度和时间对沸石骨架结构变化的影响,结果表明提高温度和水蒸汽量均会降低沸石结晶度,但处理时间则对结晶度的影响较小.     

CXN天然沸石的研究1: 离子交换与结构性质表征

采用离子交换和焙烧等方法,对我国CXN天然沸石(STI型)进行改性。应用化学分析,粉末XRD,TG/DTA,^2^7AlMASNMR,^2^9SiMASNMR,低温N~2吸附等方法表征相关的结构、离子交换等性质。CXN沸石的晶胞组成Na~0~.~2Mg~0~.~1Ca~8~.~4[Al~1~7~.~2Si~5~4~.~8O~1~4~4].65H~2O,属富钙型。经离子交换脱Ca^2^+后的沸石在焙烧过程中伴随有骨架脱铝,骨架的热稳定性已由原样的500℃以下提高到700℃以上。交换改性后的沸石,呈现反映该沸石微孔特性的I型氮吸附等温线。     

Effect of thermal and acid treatment on the structure of NH4Na—Y zeolite by IR data

The structural transformations of ammonium-exchanged forms of Na-Y zeolite during thermal evacuation and acid treatment were studied using IR spectroscopy. The formation of the zeolite H-forms by shallow-bed evacuation of NH₄N-Y at 570 K is accompanied by a high-frequency shift of the bands in the IR lattice vibration spectra. In the formation of the H⁺-forms resulting from the decationization of zeolite by treatment with an aqueous HCl solution, no shifts of the bands are observed. During deep-bed calcination in air the H⁺-form, is transformed into the H-form completed by the formation of a highly-crystalline stabilized zeolite at 623 K. A rapid increase in the shallow-bed calcination temperature results in a collapse of the structure of the H- and H⁺-forms followed by the formation of amorphous SiO₂.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 236–240, February, 1995.     

An Interrupted Zeolite PKU-26 and Its Transformation to a Fully Four-Connected Zeolite PKU-27 upon Calcination

The thermal stability and structural transformation mechanism are critical for the industrial applications of zeolites and the design of new framework types. Herein, a new zeolite PKU-26 has been hydrothermally synthesized under fluoride conditions using a tetraethylammonium (TEA⁺) cation as the structure-directing agent (SDA) and its framework contains partial Q³ T atoms [Q³ for T(−O−T)₃OH]. Upon calcination, PKU-26 processed a single-crystal to single-crystal transformation to another novel zeolite PKU-27 with the elimination of terminal −OH groups and enhanced thermal stability up to 650 °C, exhibiting the first Q³→Q⁴ transformation [Q⁴ for T(−O−T)₄] in 3D zeolite frameworks. The mechanism of the structural transformation, involving proton transfer, framework dehydration, and TO₄ reconstruction, is proposed and supported by theoretical calculations.     

Structural evolution of calcium-exchanged (NH4)2SiF6-dealuminated Y zeolite after various chemical treatments

The structural evolution of Y zeolite (Si/Al 2.17) weakly dealuminated by hexafluorosilicate (Si/Al 3.13), denoted Y_D, and exchanged with calcium (CaY_D), has been studied after acid–base treatments at 80 °C close to the cation exchange conditions. The stability of the samples was followed by X-ray diffraction and solid-state NMR of ²⁹Si and ²⁷Al; Y_D zeolite was completely destroyed by treatment with acid pH 2.5 and suffered serious degradation on treatment with alkali at pH 11.8. The introduction of calcium improved the stability of the zeolite in acid and base. In acid CaY_D was not destroyed until pH 1. At pH 2, silicon and aluminium were extracted and an amorphous phase was formed. Base treatment at pH 13 did not affect the calcium-exchanged zeolite.     

Dealumination and characterization of chabazite for catalytic application

Dealumination of the small-pore zeolite chabazite (CHA) was performed with ammonium hexafluorosilicate under solid and liquid-state conditions to increase the Si-to-Al ratio from 2.0 to 6.0. In the solid state, the mesopore fraction increased with repeating hydrothermal synthesis at 423 K, which was confirmed by nitrogen adsorption?Cdesorption. In the liquid state, the formation of mesopores decreased substantially and the resulting CHA had an Si-to-Al ratio of ca. 5. The result of desorption of NO?CNO₂ from the Cu ion-exchanged dealuminated CHA in the solid state indicated that the presence of mesopores reduced NO?CNO₂ adsorption and desorption of NO₂ occurred at 383 and 683 K whereas for the high-silica analog SSZ-13 desorption of NO₂ occurred mostly at 473 and at 673 K.     

Desilication mechanism revisited: highly mesoporous all-silica zeolites enabled through pore-directing agents

The role of pore‐directing agents (PDAs) in the introduction of hierarchical porosity in silicalite‐1 in alkaline medium was investigated. By incorporation of various PDAs in aqueous NaOH, homogenously distributed mesopores were introduced in 2.5 μm silicalite‐1 crystals. It was proven for the first time that framework aluminum is not a prerequisite for the introduction of intracrystalline mesoporosity by desilication. The pore‐directing role is not directly exerted by framework trivalent cations metals, but by species on the external surface of the zeolite. The inclusion of metal complexes (Al(OH)₄^?, Ga(OH)₄^?) and tetraalkyl ammonium cations (tetramethyl ammonium (TMA⁺), tetrapropyl ammonium (TPA⁺)) in the alkaline solution led to distinct mesopore surface areas (up to 286 m² g^?1) and pore sizes centered in the range of 5–20 nm. In the case alkaline treatment was performed in the presence of Al(OH)₄^?, all aluminum partially integrated in the zeolite giving rise to both Lewis and Brønsted acidity. Apart from the concentration and location, the affinity of the PDA to the zeolite surface plays a crucial role in the pore formation process. If the PDA is attracted too strongly (e.g., TMA⁺), the dissolution is reduced dramatically. When the pore‐directing agent is not attracted to the zeolite’s external surface, excessive dissolution occurs (standard alkaline treatment). TPA⁺ proved to be the most effective PDA as its presence led to high mesopore surface areas (>200 m² g^?1) over a broad range of PDA concentrations (0.003–0.1 M ). Importantly, our results enable to extend the suitability of desilication for controlled mesopore formation to all‐silica zeolites.     

Effects of hydrochloric acid treatment on structure characteristics and C<Subscript>2</Subscript>H<Subscript>4</Subscript> adsorption capacities of Ünye bentonite from Turkey: a combined FT-IR,XRD, XRF,TG/DTA and MAS NMR study

In this study, a bentonite sample from Ünye, Turkey was treated with various HCl solutions (0.1, 1.0 and 5.0 M) at 90 °C during 3 and 6 h. X-ray diffraction (XRD), X-ray fluorescence (XRF), differential thermal analysis (DTA), thermogravimetric analysis (TG), Fourier transform infrared (FT-IR), magic angle spinning nuclear magnetic resonance (²⁹Si and ²⁷Al MAS NMR) and surface area measurement methods were employed in order to investigate the structural and thermal changes occurring as a result of the acid activation. The data for the adsorption of C₂H₄ obtained at 273 K and pressures up to 100 kPa correlated with structural properties of the acid treated bentonite samples. With the increase of both concentration of acid solution and treatment time, the specific surface area values and the retentions of C₂H₄ gas of bentonite samples increased. Bentonite treated with 5.0 M HCl for 6 h adsorbed C₂H₄ most effectively.     

无粘结剂ZSM-5沸石催化剂骨架脱铝改性的研究

对比了无粘结剂和有粘结剂ZSM-5沸石催化剂的吸附性质, 证实前者的优良品质. 以27Al固体核磁共振(MAS NMR)考察了盐酸处理、水蒸气处理及水蒸气-盐酸相结合处理后无粘结剂ZSM-5沸石催化剂的骨架脱铝行为以及非骨架铝的状态. 以X射线粉末衍射(XRD), X射线荧光光谱(XRF), 低温氮吸附, NH3-TPD和吡啶吸附原位红外光谱(in situ IR)等详细表征了骨架脱铝对其晶体、元素组成及孔结构、表面强(S)酸与弱(L)酸、Brönsted(B)酸与Lewis(L)酸酸量分布等影响. 揭示了水蒸气处理的深度骨架脱铝强烈地调变沸石的结构和表面酸性的本质, 证明了该处理方式对调变S酸和B酸起主导作用.