系列硅铝比纳米薄层ZSM-5分子筛的合成和表征

以自制不对称双子季铵盐表面活性剂为模板, 在水热合成体系中控制合成系列硅铝比纳米薄层ZSM-5分子筛.采用X射线衍射(XRD)、N₂吸附-脱附、X射线荧光光谱(XRF)、扫描电镜(SEM)和²⁷Al魔角旋转核磁共振(²⁷Al MAS-NMR)对合成的样品进行了表征. 详细研究了晶化温度、晶化时间、结构导向剂(SDA)用量、碱度等对合成的影响和纳米薄层ZSM-5分子筛的形成过程. 结果表明: 分子筛硅铝比越高, 结构导向剂用量越大, 所需的晶化时间越短; 晶化温度越高, 晶化时间越短; 且不同硅铝比纳米薄层ZSM-5分子筛的形貌规整度、比表面积和介孔/微孔孔容比例随着硅铝比而变化.     

晶种导向下干胶法合成ZSM-5分子筛

以廉价水玻璃为硅源,在晶种替代有机模板剂的条件下采用干胶法合成了ZSM-5分子筛。利用XRD、SEM、TEM、FTIR、N₂吸附-脱附和NH₃-TPD等分析方法对合成样品进行了表征和测试,考察了合成条件对ZSM-5分子筛晶化过程的影响。结果表明,在硅铝比（n/n）为30~70,钠硅比（n/n）为0.12~0.20时都可以得到结晶度良好的ZSM-5分子筛。研究发现,干胶法合成ZSM-5,在不引入外加水的情况下也可以得到ZSM-5样品,外加水的引入能够有效地提高晶化速率;与水热法合成ZSM-5分子筛相比,干胶法可以显著地缩短晶化时间,同时,合成样品的晶体尺寸也有所减小。     

四丙基氢氧化铵改性纳米HZSM-5分子筛及其在甲醇制汽油中的催化性能

采用四丙基氢氧化铵(TPAOH)溶液对纳米ZSM-5分子筛进行改性, 运用X射线衍射、扫描电镜、²⁷Al和²⁹Si固体核磁、X射线光电子能谱、N₂物理吸附脱附法和NH₃程序升温脱附等手段对所制样品进行了表征, 并评价了其催化甲醇制汽油反应性能. 结果表明, 改性后的HZSM-5相对结晶度增加, 晶体形貌更加规整, 表面硅铝比增加, 比表面积和微孔表面积增大, 强酸位酸量增多. 同时, TPAOH改性不仅可以使分子筛脱硅脱铝, 而且伴有二次晶化补硅补铝, 改变了分子筛的硅铝分布. 改性的HZSM-5在甲醇制汽油反应中的稳定性大幅度提高, 其寿命由70h增至170h以上, 随着TPAOH处理时间的增加, 催化剂寿命增加, 氢转移反应加快, 导致油相产品中异构烷烃增多, 烯烃减少.     

柠檬酸溶液中NaY分子筛的脱铝行为

硅铝分子筛有机酸配合脱铝是提高其稳定性、引入介孔的一种重要方法.采用X射线衍射、N₂物理吸附、高分辨透射电镜、傅里叶变换红外光谱、²⁷Al和²⁹Si固体魔角自旋核磁共振光谱等方法研究了NaY分子筛柠檬酸脱铝行为.结果表明,柠檬酸浓度对NaY分子筛骨架Al原子的脱出影响尤为显著.反应起始阶段,分子筛骨架铝原子快速脱出,其晶体结构遭到严重破坏.随着反应的进行,分子筛硅铝比和结晶度皆有所增加,表明其骨架结构可能进行了重新排列.75℃下,0.10 mol/L柠檬酸处理2 h的脱铝分子筛样品,与NaY分子筛样品相比,其骨架硅铝比增加了0.6、外表面增加了17 m²·g^-1,脱铝同时产生了大量无定形硅.     

氟硅酸铵改性纳米HZSM-5分子筛催化甲醇制丙烯

在静态条件下, 采用不同浓度的氟硅酸铵溶液对纳米ZSM-5分子筛进行了改性处理. 利用粉末X射线衍射(XRD)、²⁷Al 魔角旋转固体核磁共振(²⁷Al MAS NMR)、X射线荧光光谱(XRF)、X射线光电子能谱(XPS)、N₂ 吸附、透射电镜(TEM)、NH₃程序升温脱附(NH₃-TPD)、吡啶吸附红外光谱(Py-IR)等技术对改性前后纳米ZSM-5分子筛的骨架结构、织构性质、酸性质进行了表征. 并在常压、反应温度为450℃、甲醇质量空速(WHSV)为1 h^-1的条件下, 研究了改性前后纳米HZSM- 的甲醇制丙烯(MTP)催化性能. 结果表明, 合适浓度的氟硅酸铵处 理能够选择性地脱除纳米ZSM-5 分子筛的外表面铝, 从而使得HZSM-5 的酸密度降低, 比表面积和孔容增大, MTP催化性能显著提高. 氟硅酸铵改性后纳米HZSM-5 的丙烯选择性和丙烯/乙烯(P/E)质量比分别由原来的 28.8%和2.6提高到45.1%和8.0, 催化剂寿命增加了近2倍.     

硼和氟掺杂ZSM-5分子筛的制备及其甲醇制丙烯反应性能

采用两步水热晶化法,通过在合成体系中加入硼酸、氟化铵、氟硼酸铵,合成出了硼和氟改性的ZSM-5分子筛。利用X射线衍射、氮气吸附-脱附、29Si固体核磁共振波谱、傅里叶变换红外光谱、扫描电子显微镜以及NH₃程序升温脱附等测试手段对样品进行了表征。结果表明：硼和氟掺杂条件下可以合成具有较高结晶度的ZSM-5分子筛,杂原子掺杂提高了分子筛的硅铝比;硼和氟掺杂可以显著降低ZSM-5分子筛的Lewis酸量,但提高了Brønsted酸量;硼和氟共同作用可以降低ZSM-5分子筛的颗粒尺寸。甲醇制丙烯评价结果显示：较低的Lewis酸量和适宜的Brønsted酸性有利于提高丙烯选择性和催化剂寿命;NH₄BF₄改性的ZSM-5分子筛（Z5-BF2）表现出较高的丙烯选择性和较长的催化剂寿命。     

具有纳米线镶嵌结构ZSM-5/L复合分子筛的合成及表征

采用两步晶化法,以四丙基氢氧化铵预处理ZSM-5为晶种,快速合成了纳米线镶嵌结构ZSM-5/L复合分子筛.通过XRD、SEM-EDX、TEM和N₂吸附-脱附等手段对合成样品的物理化学性质进行了表征.孔道性质表明复合分子筛具有微孔和介孔的多级孔道结构,椭球的L分子筛镶嵌在纳米线的ZSM-5分子筛周围.晶种预处理影响了溶胶的电荷及分子筛的形貌,当合成样品中ZSM-5的质量分数小于2%（重量百分比）时,凝胶的负电荷较多,易形成椭球状L分子筛;当合成样品中ZSM-5的质量分数大于2%（重量百分比）时,zeta电位在-39.822~-42.352 mV之间波动,ZSM-5分子筛的形貌从长条状逐渐转变为纳米线状.阳离子比影响复合分子筛中L分子筛形成,当阳离子比R=n（K₂O）/（n（K₂O）+n（Na₂O））小于0.6时,不利于L型分子筛的形成;当阳离子比大于0.6,即K⁺较多Na⁺较少时,有利于L型分子筛中α-钙霞石笼的形成.     

晶种导向干凝胶法制备成型ZSM-5分子筛

在干凝胶法制备ZSM-5 分子筛的体系中添加晶种导向剂, 控制分子筛的生长, 制备了纳米沸石组装的无粘结剂成型多级孔ZSM-5 分子筛, 一步完成纳米分子筛的制备及组装成型, 即克服了传统纳米粒子难以过滤分离的问题, 同时组装所形成的多级孔有助于改善分子在催化剂内的扩散, 从而提高催化反应效率. 以硅胶、薄水铝石为原料, 四丙基氢氧化铵(TPAOH)和ZSM-5 晶种导向胶作为粘结剂, 通过混捏、挤条得到直径2 mm的条状前驱物, 随后通过干凝胶转换法制备成型分子筛. 所用晶种导向剂组成为0.35TPAOH:1SiO₂:20H₂O:4C₂H₅OH. 通过X射线衍射(XRD), 热重(TG)分析和傅里叶变换红外(FTIR)光谱等方法对分子筛晶化过程进行了表征, 结果表明晶种导向剂加入量对分子筛生长速度及多级孔结构均有影响. 当所加晶种导向剂中TPAOH与SiO₂的摩尔比为0.025时, 经过3 h晶化, 分子筛相对结晶度达到100%. 扫描电镜(SEM)结果表明, 合成的分子筛尺寸约为200 nm, 组装形成的多级孔分子筛的介孔体积为0.28 cm³·g^-1. 通过NH₃ 程序升温脱附(NH₃-TPD)考察了所得成型分子筛的酸性, 发现该分子筛酸性与市售的粉末H-ZSM-5分子筛类似.     

金属改性P/HZSM-5分子筛催化乙醇芳构化

以P/HZSM-5分子筛为基础, 通过浸渍法制备了Cr、Co、Cu、Zn等金属改性的M-P/HZSM-5分子筛. 采用X射线衍射(XRD), 比表面积(BET)和氨气程序升温(NH₃-TPD)等方法对其进行了表征, 并考察了其催化乙醇芳构化的活性. 结果表明, 改性后的ZSM-5分子筛保持原有的骨架结构, 但比表面积降低, 酸性分布发生变化; Cu-P/HZSM-5分子筛有较高催化活性. P和Cu的负载量分别为3%和5%, 先浸渍P再浸渍Cu, 反应温度400 °C, 质量空速(WHSV)为1.0 h^-1时轻质芳烃(BTX)收率可达到57.6%.     

Cu-ETS-10催化NH3选择性还原NOx性能

采用离子交换法制备了Cu-ETS-10钛硅分子筛催化剂,该催化剂对于NH₃选择性催化还原（SCR）NO_x反应具有较高的催化活性、N₂选择性和抗SO₂性能.结果表明,Cu-ETS-10钛硅分子筛具有丰富的微孔结构和较高的比表面积（288-380m²/g）;原子发射光谱、程序升温还原技术和原位红外漫反射等表征结果表明,Cu在Cu-ETS-10钛硅分子筛中具有多种存在形态,其中Cu²⁺物种为Cu-ETS-10的活性中心,其含量随Cu含量的增加而先增后降,与催化活性的变化趋势一致.     

Microwave synthesis,characterization and catalytic properties of titanium-incorporated ZSM-5 zeolite

Titanium-incorporated ZSM-5 zeolites (Si/Al = 50–200 and Si/Ti = 70) were successfully synthesized in a one-step sol-gel process under microwave irradiation. The characteristics of Ti-ZSM-5 zeolites were investigated using X-ray power diffraction, UV/Vis-DRS, FT-IR spectroscopy and solid-state ²⁷Al-NMR to monitor the physico-chemical properties. Simultaneously, the acidic properties were characterized by the NH₃-TPD profile. The characterization results revealed that the Ti⁴⁺ and Al³⁺ ions were well incorporated into the framework of Ti-ZSM-5 zeolite. The prepared zeolite was moderately active but selective in the dehydration of methanol to dimethyl ether.     

Crystallization of ZSM-12 Zeolite with Different Si/Al Ratio

In this work the acid properties of a series of HZSM-12 zeolites with different Si/Al ratio were studied. The ZSM-12 crystals were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na₂O:x Al₂O₃:100SiO₂:2000H₂O, with x = 0.50, 0.67, 1, 1.25 and 2, respectively. The gels were crystallized at 140^∘C for 6 days, then washed, dried and calcined to remove the MTEA template. The samples were ion-exchanged with an ammonium chloride solution and calcined again to obtain the zeolites in the acid form. The materials thus obtained were characterized by XRD, SEM, BET, TG and n-butylamine adsorption. The Si/Al ratio in the reaction mixture affects the amount of zeolite produced and the size of the particles. The XRD analysis indicated that the ZSM-12 zeolite crystallizes in a pure form only with Si/Al ratio above 33. The SEM analysis showed the presence of crystallites with very well defined prismatic shapes. The removal of the MTEA of the pores of the ZSM-12 by TG indicated that there are two kinds of internal sites occupied by MTEA inside the structure. The BET area of the ZSM-12 decreases proportionally with the crystallinity of materials. The desorption of n-butylamine showed that the acid site density is proportional to aluminum content, but the Si/Al ratio shows little influence on the relative strengths of these sites.     

Characterisation of Siliceous Extra‐Framework Species in DAY Zeolites by 29Si MAS NMR and IR Spectroscopic Measurements

Dealuminated Y zeolites (DAY) were obtained by steaming of NH₄NaY at temperatures between 450 °C and 700 °C. They were characterised by means of ²⁷Al and ²⁹Si MAS NMR, IR spectroscopic and XRD measurements. The Si/Al framework ratios of samples were calculated using the ²⁹Si MAS NMR signal intensities, the wave numbers of the double‐ring vibration band w_DR and the asymmetrical TOT valence vibration w_TOT of IR spectra as well as the XRD lattice constant a₀. In contrast to actual Si/Al ratio obtained from w_DR and a₀, the NMR spectroscopic and w_TOT values were determined to be too high because of the superposition of the signals coming from dealuminated zeolite framework and silica gel which forms in the zeolite as a result of steaming. The differently determined Si/Al ratios characterise the siliceous extra‐framework species.     

Synthesis of mesoporous zeolite single crystals with cheap porogens

Mesoporous zeolite (silicalite-1, ZSM-5, TS-1) single crystals have been successfully synthesized by adding soluble starch or sodium carboxymethyl cellulose (CMC) to a conventional zeolite synthesis system. The obtained samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen sorption analysis, ²⁷Al magic angle spinning nuclear magnetic resonance (²⁷Al MAS NMR), temperature-programmed desorption of ammonia (NH₃-TPD) and ultraviolet-visible spectroscopy (UV-vis). The SEM images clearly show that all zeolite crystals possess the similar morphology with particle size of about 300 nm, the TEM images reveal that irregular intracrystal pores are randomly distributed in the whole crystal. ²⁷Al MAS NMR spectra indicate that nearly all of the Al atoms are in tetrahedral co-ordination in ZSM-5, UV-vis spectra confirm that nearly all of titanium atoms are incorporated into the framework of TS-1. The catalytic activity of meso-ZSM-5 in acetalization of cyclohexanone and meso-TS-1 in hydroxylation of phenol was also studied. The synthesis method reported in this paper is cost-effective and environmental friendly, can be easily expended to prepare other hierarchical structured zeolites.     

Surprises in the structural chemistry of zeolites

High-resolution electron microscopy, apart from strikingly confirming the correctness of the X-ray-based models for the skeletal structure of the aluminosilicate frameworks of zeolites, points to the existence of new families of ordered, crystalline microporous solids (e.g., with composition A_xB_xC_m?xO_2m · nH₂O, where A is an exchangeable monovalent cation, B is Al or Ga, C is Si or Ge, and x, m, n are integers.) It also reveals crystalline imperfections and unexpected superlattice structures in A-type and faujasitic zeolites, and the nature of the intergrowths in, for example, $\text{ZSM-5}\text{ZSM-11}$ materials. The short-range order of Si and Al within the aluminosilicate framework may be directly explored by magic-angle-spinning NMR (MASNMR) employing ²⁹Si and ²⁷Al nuclei. This technique probes the site symmetry and environment of these atoms. Al in tetrahedral as well as in octahedral sites may be readily identified and so may the populations of groups such as Si(OAl)₄, Si(OAl)₃, (OSi), etc., so that new information is obtained pertaining to Si, Al ordering in a variety of zeolitic solids.     

The appearance of adsorption ability of modified zeolites for sodium dodecylsulfate from its aqueous solution

Hydrophobic faujasite-type zeolites were prepared by the treatment of hydrophilic Na-Y_4.6 with silicon tetrachloride (SiCl₄) by way of dealumination-silicon exchange reaction. Hydrophilic-hydrophobic characters of these zeolite surfaces were evaluated by measurements of immersional heats into water orn-hexane. Adsorption rates of sodium dodecylsulfate (SDoS) on these zeolites from its aqueous solution and their adsorption characteristics were investigated, and compared with those on ZSM-5 with various Si/Al ratios.The adsorption ability of SDoS into zeolite micropores developed on the zeolite only when it was modified to some extent. The adsorption rates of SDoS were very slow and proved to be affected by molecular diffusion in zeolite pores. They depended on hydrophilic-hydrophobic character of zeolites as well as on pore structures. Adsorption isotherms of SDoS were of Langmuir type, which indicates that the adsorption occurred typically into zeolite pores. Adsorbed amount of SDoS depended on the balance of hydrophilic-hydrophobic character and number of cation site of zeolite surfaces, and had a maximum in case of ZSM-5 zeolites.     

ZSM-5分子筛的合成及其在丁烯催化裂解反应中的应用

采用水热合成法制备了无模板剂ZSM-5分子筛并用正硅酸甲酯(TMOS)对其进行外表面修饰改性,利用XRD、SEM、~(29)Si MAS NMR、~(27)Al MAS NMR、NH_3-TPD、BET和UV-vis DRS对合成分子筛的物相、形貌和酸性等进行了表征,并将其应用于催化丁烯裂解反应。研究表明,经水热合成的无模板剂ZSM-5结晶度较好,与添加模板剂合成的ZSM-5拥有相似的孔道结构和晶体结构以及相近的酸量,但在酸中心分布上有明显差异:孔道内酸中心数量增加且分布更加均匀,孔道交叉处酸中心数量减少;经过外表面修饰改性后,ZSM-5分子筛外表面部分不具备择形性的酸中心被钝化,使其择形选择能力增强。在催化丁烯裂解反应中,用TMOS进行外表面修饰改性的无模板剂ZSM-5分子筛作为催化剂能够有效抑制副反应的发生,丙烯和乙烯的总收率高达58%。     

Magic-Angle-Spinning NMR (MAS-NMR) Spectroscopy and the Structure of Zeolites

After outlining the chemical features and properties which make zeolites such an important group of catalysts and sorbents, the article explains how high-resolution solid-state NMR with magic-angle spinning reveals numerous new insights into their structure. ²⁹Si-MAS-NMR readily and quantitatively identifies five distinct Si(OAl)_n(OSi)_4-n structural groups in zeolitic frameworks (n = 0, 1,….4), corresponding to the first tetrahedral coordination shell of a silicon atom. Many catalytic and other chemical properties of zeolites are governed by the short-range Si, Al order, the nature of which is greatly clarified by ²⁹Si-MAS-NMR. It is shown that, as expected from Pauling's electroneutrality principle and Loewenstein's rule, both in zeolite X and in zeolite A (with Si/Al = 1.00) there are no ? Al? O? Al? linkages. In zeolite A and zeolite X with Si/Al = 1.00 there is strict alternation of Si and Al on the tetrahedral sites. Ordering models for Si/Al ratios up to 5.00 (in zeolite Y) may also be evaluated by a combination of MAS-NMR experiments and computational procedures. ²⁹Si-MAS-NMR spectra reveal the presence of numerous crystallographically distinct Si(OSi)₄ sites in silicalite/ZSM-5, suggesting that the correct space group for these related porosilicates is not Pnma. ²⁷Al-MAS-NMR clearly distinguishes tetrahedrally and octahedrally coordinated aluminum, proving that, contrary to earlier claims, Al in silicalite is tetrahedrally substituted within the framework. In combination, ²⁹Si- and ²⁷Al-MAS-NMR is a powerful tool for monitoring the course of solid-state processes (such as ultrastabilization of synthetic faujasites) and of gas-solid reactions (dealumination of zeolites with silicon tetrachloride vapor at elevated temperatures). They also permit the quantitative determination of framework Si/Al ratios in the region 1.00 < Si/Al < 10 000. Since most elements in the periodic table may be accommodated within zeolite structures, either as part of the exchangeable cations or as building units of the anionic framework, there is immense scope for investigation by MAS-NMR and its variants (cross-polarization, multiple pulse and variable-angle spinning) of bulk, surface and chemical properties. Some of the directions in which future research in zeolite science may proceed are adumbrated.     

异丁烯在不同硅铝比的NanZSM-5型分子筛中的吸附：分子模拟研究

Frameworks of NanZSM-5 type zeolites with various Si/A1 ratios have been constructed and optimized with molecular dynamic quench simulation. The results show that the structure parameters of NanZSM-5 type zeolite, including the bond length and atomic charges, are consistent with those predicted by ab initio cluster calculations. It was also observed that atomic charges of Si atoms were shifted to higher field in NanZSM-5 type zeolite with lower Si/Al ratio. Then, the adsorption of isobutene on NanZSM-5 with various Si/Al ratios has been investigated using grand canonical ensemble Monte Carlo simulation and Cvff-300-1.01 forcefield. The simulated adsorption amount was in good agreement with the experimental data. Based on these facts, the effects of Si/Al ratio on the adsorption amount and adsorption isotherms of isobutene on NanZSM-5 were predicted. The results indicated that Si/Al ratio was important for the adsorption of isobutene and the adsorption amount was decreased as the Si/Al ratio was increased, which can be explained that the atomic charge of Na^＋ cation would influence greatly the π electrons of the isobutene double bond due to the Coulomb force. In addition, the adsorption sites of isobutene and interaction energy of isobutene with NanZSM-5 were also discussed.