脱铝改性NaY分子筛载体对磷钨酸封装过程的影响

分别采用水热法和SiCl4气相法对NaY分子筛进行脱铝改性,作为载体应用于磷钨酸(PW)的原位封装过程。采用XRD、N2物理吸附、ICP-AES和SEM等手段对脱铝改性后NaY分子筛载体结构进行了表征。结果表明,两种脱铝方法在使NaY分子筛硅铝比接近5.5的情况下,水热法比SiCl4气相法脱铝样品的结晶度高、比表面积和孔容更大、微孔所占的比例更高,相同条件下用于磷钨酸的原位封装过程,能获得0.0569g PW/g载体的封装量,显著高于SiCl4气相法处理的样品。     

X射线衍射法测定分子筛晶胞参数与结晶度

用X射线衍射外推函数法测定饮和吸水前后NaY分子筛的晶胸参数和结果度，再与^29Si和^27Al固体魔角核磁共振谱仪所测定的NaY分子筛骨架中的硅铝比进行关联，得到了X射线衍射法测定NaY分子筛骨架中硅铝比的经验公式，达到了测定NaY分子筛骨架中硅铝比的要求。试验结果表明，测定NaY分子筛晶胞参数和结晶度的有效方法是在测定前对分子筛进行稳化处理，使其饱和吸水，比通常采用的化学方法省时，结果准确，重复性好。     

ZSM-5/Y复合结构分子筛的制备及其复合结构形成机制的探索

以工业ZSM 5分子筛作为硅源,采用水热法制备ZSM-5/Y复合结构分子筛,并对其进行了X射线衍射(XRD)、N2吸附(BET)、核磁共振(NMR)和扫描电镜(SEM)表征.结果表明,产物同时具有ZSM-5分子筛和Y型分子筛的晶相结构特征.晶种的加入能有效地提高晶化反应进程.NaOH溶液的碱性越高,对ZSM-5的溶解性越高.随着晶化时间的延长,属于ZSM-5分子筛的特征峰强度降低、Y分子筛的特征峰强度升高.在晶化时间为10、20和30h时,对体系中加入铝源和晶种进行了研究.结果发现,复合结构分子筛的合成过程伴随着分子筛上骨架硅解离、部分骨架铝解离、硅源和铝源在分子筛骨架外及骨架上晶化形成新的晶体的过程.推断ZSM-5/Y复合结构分子筛形成机制有两种:(1)铝源和溶液中溶解的硅结合;(2)铝源直接和ZSM-5分子筛骨架上的硅结合.     

电子束熔炼多晶硅对杂质铝去除机制研究

采用电子束熔炼方式,利用铝的蒸发系数较大的特点通过蒸发去除硅中的杂质铝。将实验的实测值与理论计算的蒸发量、损失量等加以比较,得到了铝在电子束下的蒸发去除速率由其在硅中扩散过程所决定的结论,并对铝的去除量与硅的损失量之间关系进行分析。     

核磁共振（NMR）法在分子筛的合成,结构及其性能研究上的应用

论述了ＮＭＲ法在分子筛研究领域的应用。通过ＮＭＲ的观测与计算可以确定分子筛骨架的硅铝比，从而分析硅，铝在骨架上的统计分布特征，以及不同结构状态，配位状态和催化机理，进一步对分子筛的合成及其性能的研究提供了重要依据。     

乙酸处理脱铝对丝光沸石结构、酸性质及其催化性能的影响

基于丝光沸石(HMOR)催化合成乙酸甲酯稳定性较差及八元环边袋结构酸性位专一性催化作用的特性, 提出了利用乙酸处理具有八元环-Na和十二元环-H的MOR以制备选择性脱铝及疏通八元环边袋结构技术。采用XRD、²⁷Al-NMR、NH₃-TPD、吡啶红外和N₂吸-脱附等手段对催化剂进行了表征, 分别考察了不同乙酸浓度处理条件对分子筛催化剂骨架结构、酸性质、微孔结构以及催化合成乙酸甲酯性能的影响。结果表明, 通过合适浓度乙酸溶液处理, HMOR分子筛的硅铝比、微孔体积、中值孔径都增大, BJH孔径分布未见明显变化, 乙酸溶液处理脱除了HMOR中十二元环的Al, 最大限度地保留了八元环边袋结构中的Al。改性后的HMOR催化剂二甲醚转化率平稳期由18 h延长至50 h, 催化剂的稳定性能得以改善, 催化剂转化率由45.6%降至43.8%, 催化剂活性略有降低。     

脱铝对红辉沸石结构及结晶度的影响

以盐酸对红辉沸石进行了脱铝，用X射线衍射、红外光谱和化学分析手段对样品做了表征。探讨了酸用量与红辉沸石脱铝量、结晶度、结构变化之间的关系。结果表明，盐酸对红辉沸石脱铝速度快，脱铝量随着盐酸用量的增加而增加。随着脱铝的进行，样品的衍射峰位移呈周期性变化，面网间距总体减小，且呈现减小－增大－减小的规律性变化。随着脱铝度的提高，在3700－3200cm^-1波数范围内，出现新的吸收峰，与羟基窝的生成和变化相关。在不补硅的情况下深度脱铝，容易导致红辉沸石骨架结构崩塌。     

利用铝灰和微硅粉制备4A分子筛的研究

铝灰和微硅粉分别是铸造铝和硅铁合金冶炼过程中产生的固体废弃物,含有丰富的氧化铝和氧化硅,为了符合国家环保要求以及资源再生化利用,通过从铝灰和微硅粉中提取氧化铝、氧化硅,并以此为原料制备4A分子筛。通过水热法探究最佳工艺条件,制备出了符合国家行业标准的4A分子筛,并对其分别进行了XRD、FTIR、SEM及BET表征,测定了钙离子交换能力。结果表明：在硅铝比(n(SiO₂)/n(Al₂O₃))2.0、碱度(n(Na₂O)/n(Al₂O₃))2.5、晶化温度100℃、晶化时间10 h的条件下制备的4A分子筛具有清晰的、均匀的立方晶型结构及良好的钙离子交换能力(362 mg CaCO₃/g),可用作洗涤助剂,为固体废弃物的资源化利用提供了新思路。     

煤矸石质硅铝基材料胶凝机理的研究

系统地开展了利用低温煅烧煤矸石为主要原料制备早期强度高、水化热低且具有良好固土特性的硅铝基胶凝材料的基础研究.采用结构分析的方法,运用高分辨固体核磁共振、液体核磁共振和红外光谱等分析手段研究了煤矸石和高岭石在煅烧、碱介质中溶出和胶凝过程中硅、铝配位的变化,结合其胶凝产物的物相、形貌和水化热,从结构、配位和物相转变的角度来研究煤矸石质硅铝基胶凝材料胶凝机理.揭示了煤矸石的煅烧过程就是铝氧八面体中铝的四配位转化以及铝氧四面体和硅氧四面体解聚过程的重要规律,其中铝氧八面体中铝的四配位转化是煤矸石产生胶凝活性的本源.证明了煤矸石和高岭石在煅烧过程中铝配位的变化与地质界Thompson定律相吻合.比较研究了煤矸石和高岭石的活性与其结构之间的关系,发现低于900℃煅烧煤矸石的红外光谱中,560cm-1附近吸收峰的强度与Si、Al离子的溶出量具有正相关性;五配位铝是偏高岭石具有高活性的主要原因.证明了由于一价和二价阳离子的存在,以高岭石为主要矿物的煤矸石在煅烧过程中没有出现五配位铝.通过对硅铝质物料Si2p、Al2p和Ols结合能与其胶凝材料力学性能之间关系的研究,提出用硅、铝电子结合能评价硅铝物料胶凝活性的新方法.深入研究了不同介质条件下煅烧煤矸石的溶出特性及其胶凝机理.研究表明:煅烧煤矸石在碱性溶液中是以单聚体硅酸根离子和单聚体铝酸根离子的形式溶出;(HO)3SiO-和Al(OH)4-的溶出证明硅铝基胶凝材料反应初期是硅氧四面体和铝氧四面体的再解聚过程,体现在反应后,27Al和29Si NMR谱的共振峰向低场偏移;以硅酸钾为溶出介质,煅烧煤矸石溶出渣29Si MAS NMR谱中-97.36×10-6共振峰的出现揭示了硅铝基胶凝材料胶凝过程中原位键合的作用;随着反应的进行,27Al和29Si NMR共振峰都向高场偏移,表明胶凝过程中与中心铝原子在次级配位圈上直接连接[SiO4]四面体数量增多以及反应产物中硅氧四面体聚合度的增加.根据胶凝过程中硅、铝配位的变化,提出了硅铝基胶凝材料原位键合的反应机理,并将胶凝过程概括为解聚过程、胶结过程、原位键合过程和缩聚过程.     

氮掺杂硅铝固载TiO2多孔材料的制备及其光催化性能分析

以硅、铝和钛的无机盐为初始反应物,采用水热法制得了具有光催化活性的氮掺杂硅铝固载TiO2多孔材料(N/TiO2-SiAl).采用XRD、FESEM、FTIR、UV-Vis等现代分析技术分析表征了所得样品的物相结构及形貌;以甲基橙为探针在模拟太阳光下考察样品的光催化性能.结果表明:N/TiO2-SiAl为蜂窝状多孔材料,具有较大的比表面积;锐钛矿相TiO2以Si-O-Ti键的形式结合在无定形硅铝骨架中,并且硅铝骨架能够抑制锐钛矿相TiO2向金红石相转变;氮掺杂能够使TiO2的光响应范围向可见光区移动,在模拟太阳光照射120 min后N/TiO2-SiAl对甲基橙的降解率达到90％以上,具有较高的光催化性能,重复使用4次后降解率依然在80％以上,具有较强的光催化循环使用性能.     

Selective extraction of extraframework aluminum from USY zeolite

The extraction of extraframework aluminum from USY zeolite prepared by a hydrothermal treatment at 780°C was investigated. A series of extracted samples was prepared by the addition of concentrated hydrochloric acid to the suspension of the zeolite in a solution of NH₄NO₃. X-ray data and chemical analysis were used for the characterization of the samples. Results showed that the presence of competitive NH₄⁺ cations to the H⁺ ions in the solution increased the stability of framework aluminum toward acid. The removal of extraframework Al species was very selective at pH as low as 0.85. The discrepancy observed between the pH and the selectivity of the extraction indicated that the pH is not the decisive factor influencing the dealumination of the zeolite framework in this reaction system. It was found that the degree of framework dealumination depends on the equivalent fraction of protons S_H⁺ in the solution, and to obtain the high process selectivity, the extraction had to be carried out at as low S_H⁺ as possible. Results also showed that the supplementary dealumination of the hydrothermally treated zeolite framework during the extraframework aluminum extraction led to the decrease of the crystallinity of the USY zeolite sample.     

Effect of the nonuniform dealumination on the acidity and catalytic activity of faujasite: Part 2. Accessibility of acid sites

The implications of framework aluminum gradients in dealuminated zeolites for catalytic processes in which the reactants cannot penetrate deep inside the crystallite is discussed both theoretically and experimentally. It is shown that the Al distribution curves deduced considering uniform dealumination do not apply for cases where nonuniform dealumination occurs and therefore cannot be directly correlated with the activity shown by nonuniform dealuminated zeolites.     

Dealumination of zeolites: Part V. Influence of the hydrothermal treatment of offretite on its pore structure and acid properties

The pore distribution of a series of offretite samples dealuminated through self-steaming at various temperatures was characterized by adsorption of nitrogen, n-hexane, and 3-methylpentane, and their acidity, by ammonia adsorption followed by calorimetry and by ammonia thermodesorption. From the analysis of the nitrogen adsorption by the α_s-method, it was concluded that during dealumination at least a fraction of the microporous system, characteristic of offretite network, is converted into supermicropores (0.7−2 nm). The aluminum extraframework species resulting from the framework dealumination have practically no effect on the adsorption of nitrogen, but limit that of the n-hexane and, above all, that of 3-methylpentane. The dealuminated samples are much less acidic than is the starting offretite and the number of acid sites shown by ammonia thermodesorption is much smaller than the number of acid sites estimated from the unit cell formula. This can be related to the partial destruction of the zeolite framework owing to the formation of supermicropores, to the dehydroxylation, and maybe to the neutralization of the acid sites by cationic aluminum extraframework species created during dealumination process.     

Double rotation and variable field 27Al n.m.r. study of dealuminated Y zeolites

²⁷Al MAS n.m.r. spectroscopy has been applied to dealuminated Y zeolites at two separate fields. The spectra clearly show that the nonframework aluminum species associated with a peak observed at 30 ppm are different in samples that had different hydrothermal treatments. In samples that were treated with a single thermal dealumination, the peak at 30 ppm is caused by a tetrahedrally coordinated aluminum species with a sufficiently large quadrupole coupling to cause significant second-order shifts. The resonance at 30 ppm in a sample that was dealuminated using two thermal treatments did not exhibit large second-order shifts. These results were confirmed by double-rotation (DOR) n.m.r., which averages the anisotropy of the second-order quadrupolar interactions. The DOR spectra clearly show the existence of two tetrahedral species at 59 (framework) and 47 (nonframework) ppm in the sample treated with a single dealumination.     

Change of pore-opening structure of mordenite upon dealumination by hydrochloric acid

The structure of dealuminated mordenites prepared at 340–358 K of hydrochloric acid was studied. ²⁷Al MAS n.m.r. and XPS were measured to determine the species and depth profile of alumina, and these were corroborated with adsorption experiments using adsorbates of different sizes. Adsorption capacity of nitrogen was unaltered so that the structure of mordenite was retained, while that of 2,2,4-trimethylpentane with a larger kinetic diameter increased below 358 K of dealumination temperature, but then decreased above that. The H-mordenite (HM, Norton 100-H) contained a large amount of octahedral aluminum species (ca. 28%), and the nonframework aluminum was removed preferentially by the dealumination. Aluminum depth profile showed the homogeneous distribution on the inherent HM, but the enrichment on the samples prepared above 350 K. Based upon these findings, the following conclusions were drawn: (1) On the inherent HM, a small portion of nonframework aluminum near the pore opening disturbs the adsorption of large molecules: (2) The pore-opening size of the sample dealuminated at 358 K was large enough to adsorb 2,2,4-trimethylpentane: (3) However, upon the dealumination above 358 K, the pore opening was partly destroyed or blocked by nonframework alumina again to inhibit the adsorption of large molecules. Most of the aluminum impurity species seemed to be occluded as blocks or clusters in the mordenite. These variations of structure of the pore opening can be well related to those of the catalyst activity.     

Modelling of dealumination of aluminium silicate molecular sieves

Abstract

A simplified treatment of the dealumination of aluminium silicate (zeolite like) molecular sieves has been developed that considers both the diffusion of aluminium atoms and the formation and migration of vacancy sites. The instantaneous concentration of aluminium atoms as a function of time and location has been derived according to Fick's second law. Critical parameters affecting the dealumination process are discussed. The calculated results agree with the ratios of silicon to aluminium reported in the literature from infrared and ²⁷Al NMR spectroscopy studies on the commercial aluminium silicate molecular sieves materials Mordenite and ZSM-5, following exposure to air and water vapour.     

27Al-n.m.r. characterization of natural and synthetic zeolites

Wide line and high resolution magic-angle-spinning (h.r. MAS) ²⁷Al-n.m.r. techniques are used to characterize the structure of various natural and synthetic zeolites. ²⁷Al-n.m.r. chemical shifts allow to discrimination between framework (tetrahedrally coordinated) and extra-framework (octahedrally coordinated) Al atoms. The n.m.r, intensities are used in quantitative analysis and chemical changes which occur during dealumination can be followed. From the linewidth analysis, information on interactions between aluminium atoms and neighbouring cations and/or hydration water may be obtained. The mutual influence of neighbouring Al atoms does not seem to influence the n.m.r, linewidth.     

Crystal structures of zeolites with the general formula CaAl<Subscript>2</Subscript>Si<Subscript>4</Subscript>O<Subscript>12</Subscript> · <Emphasis Type="Italic">n</Emphasis>H<Subscript>2</Subscript>O

The structures of chabazite, laumontite, and wairakite are analyzed using literature data with the aim of revealing their similar and dissimilar features. The framework of the three zeolites contain chains made up of alternating six-and four-membered rings. A distinguishing feature of chabazite is a network of oxygen-hydrogen bonds between intraframework oxygens (which link silicon (aluminum) atoms) and water molecules and between water molecules. A characteristic feature of laumontite is the ordered arrangement of the silicon and aluminum sites in the framework in the form of alternating aluminum and silicon layers. A distinguishing feature of wairakite is that there are no oxygen-hydrogen bonds between water molecules. The transition from the chabazite framework to the laumontite framework can be interpreted in terms of the ordering and displacement of aluminum and silicon atoms. In addition to the differences between the frameworks of laumontite and wairakite, which are attributable to the fact that these zeolites were formed at different temperatures and pressures, they differ in the relative arrangement of the water molecules and calcium atoms, which cannot be accounted for by different formation conditions.     

Effect of the nonuniform dealumination on the acidity and catalytic activity of faujasite

Theoretical models are used to simulate aluminum distribution in a Y zeolite crystal when an aluminum gradient along the crystal is produced by dealumination. From these models, the theoretical distribution of different types of acid sites is calculated. The effect of the aluminum gradient along the crystal on the acid site distribution is discussed, and it can be related with the differences observed in cracking activity when the Y zeolite is dealuminated by different procedures.     

Characterizations of MAPO-36 molecular sieve by solid-state n.m.r.

The structure of the MAPO-36 framework was studied by the ²⁷Al and ³¹P magic angle spinning (MAS) n.m.r. technique. The change in the ²⁷Al chemical shift from the tetrahedral aluminum position to the octahedral aluminum position upon adsorption of water indicates a secondary coordination of water molecules to aluminum atoms in the framework. The spectral change was reversible. The ³¹P MAS n.m.r. spectra also changed reversibly upon adsorption and desorption of water. A strong interaction of water molecules and phosphorus atoms was confirmed by a large enhancement of the signal by [¹H—³¹P] cross-polarization (CP) mode.