Framework Effects on Activation and Functionalisation of Methane in Zinc-Exchanged Zeolites

The first selective oxidation of methane to methanol is reported herein for zinc-exchanged MOR (Zn/MOR). Under identical conditions, Zn/FER and Zn/ZSM-5 both form zinc formate and methanol. Selective methane activation to form [Zn-CH₃]⁺ species was confirmed by ¹³C MAS NMR spectroscopy for all three frameworks. The percentage of active zinc sites, measured through quantitative NMR spectroscopy studies, varied with the zeolite framework and was found to be ZSM-5 (5.7 %), MOR (1.2 %) and FER (0.5 %). For Zn/MOR, two signals were observed in the ¹³C MAS NMR spectrum, resulting from two distinct [Zn-CH₃]⁺ species present in the 12 MR and 8 MR side pockets, as supported by additional NMR experiments. The observed products of oxidation of the [Zn-CH₃]⁺ species are shown to depend on the zeolite framework type and the oxidative conditions used. These results lay the foundation for developing structure–function correlations for methane conversion over zinc-exchanged zeolites.     

Investigation and Modeling of the Hydrothermal Stability of Technically Relevant Zeolites

The dense-structured zeolites of types ZSM-5 (MFI) and mordenite (MOR) of different SiO₂/Al₂O₃ moduli are relatively stable under treatment by liquid water for 72 hours up to 513 K. The open-structured zeolites of types Y in dealuminated modification (FAU) and beta (BEA) undergo strong decomposition in the same range. For these two sample types a mathematical model for the decomposition of the zeolite framework is established that takes into account the influence of modulus as well as temperature. Here the kinetic of the solid phase reaction is a superposition of two different mechanisms described by the Monod equation. Dedicated to the late of Wolfgang Schirmer.     

Ethanol conversion to aromatic hydrocarbons over several zeolite catalysts

Summary H-ZSM-5 (Si/Al₂ = 29) zeolite showed especially high activity in the conversion of ethanol to BTX (benzene, toluene, xylenes), while other zeolites exclusively formed ethylene. Noble metal catalysts supported on H-ZSM-5 (29) zeolite have high activity for the formation of BTX. Of these, Au/H-ZSM-5 catalyst can partially inhibit carbon deposition during the reaction, thus maintaining constant catalytic activity for BTX formation.     

ZSM-5／MOR复合分子筛催化剂对混合C4烃转化反应的催化性能

以ZSM-5/丝光沸石(MOR)复合分子筛为催化剂,对混合C4烃的催化转化反应进行了评价,并采用程序升温脱附和原位红外光谱技术对ZSM-5/MOR的酸性进行了表征. 结果表明,与ZSM-5相比, MOR具有很低的催化活性,但ZSM-5/MOR复合分子筛具有较高的催化活性,随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加, C4烃转化率稍有升高;在C4烃转化率大致相同的情况下,乙烯和丙烯的总选择性比较接近,但苯和甲苯的总收率却快速升高. 随着ZSM-5/MOR复合分子筛中ZSM-5含量的增加,弱酸和中强酸的酸量逐渐减少,强酸的酸量有所增加. 由于ZSM-5/MOR复合分子筛中MOR对ZSM-5起到分散作用而产生更多的L酸中心,且此L酸中心处于分子筛的外表面而具有较高的能量,导致苯和甲苯的总收率升高.     

Catalytic Oxidation of CO and Benzene over Metal Nanoparticles Loaded on Hierarchical MFI Zeolite

In order to obtain highly active catalytic materials for oxidation of carbon monoxide and volatile organic compounds (VOCs), monometallic platinum, copper, and palladium catalysts were prepared by using of two types of ZSM-5 zeolite as supports—parent ZSM-5 and the same one treated by HF and NH₄F buffer solution. The catalyst samples, obtained by loading of platinum, palladium, and copper on ZSM-5 zeolite treated using HF and NH₄F buffer solution, were more active in the reaction of CO and benzene oxidation compared with catalyst samples containing untreated zeolite. The presence of secondary mesoporosity played a positive role in increasing the catalytic activity due to improved reactant diffusion. The only exception was the copper catalysts in the reaction of CO oxidation, in which case the catalyst, based on untreated ZSM-5 zeolite, was more active. In this specific case, the key role is played by the oxidative state of copper species loaded on the ZSM-5 zeolites.     

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH₃-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.     

The influence of pore structure on reaction mechanism of propylene dimerization in zeolite: A theoretical viewpoint

Molecular sieves have been widely used in the petrochemical industry as environment-friendly catalysts. The pore structure is an important factor influencing the catalytic performance of the zeolite. In this work, a combined Our own N-layered Integrated molecular Orbital and Molecular mechanics method was used to study the mechanism of propylene dimerization in four zeolites (ZSM-5, BEA, MCM-22, and MOR) with different pore structures. Comparing the stepwise mechanism and the concerted mechanism, it is found that the two mechanisms compete with each other in the macroporous BEA, MCM-22, and MOR zeolites, and both mechanisms are possible. However, in ZSM-5 zeolite with medium pore size, the propylene dimerization reaction tends to proceed according to the stepwise mechanism. Furthermore, no matter which mechanism is adopted, the activation energy of propylene dimerization reaction in MCM-22 is the smallest in the four zeolites, indicating that its MWW-type structure (A framework type defined by the International Zeolite Association) may be the most favorable pore structure for the reaction and possesses the highest catalytic activity.     

低硅铝比ZSM-5分子筛的合成及其正庚烷裂化反应性能

以氨水为矿化剂,通过添加NH₄⁺离子水热合成了具有较低骨架硅铝比的ZSM-5分子筛。通过X射线衍射(XRD)、扫描电镜(SEM)、固体核磁共振(MAS-NMR)等表征手段,研究了硅源、铝源、矿化剂、阳离子等对ZSM-5分子筛的结晶度、形貌尺寸和骨架硅铝比等的影响,研究了ZSM-5分子筛的骨架硅铝比对正庚烷催化裂化反应的影响。研究表明,投料硅铝比越低,铝原子越难进入到分子筛骨架中;当氨水为矿化剂、正硅酸四乙酯为硅源时可以合成骨架硅铝比较低的氢型ZSM-5分子筛,添加NH₄⁺离子可以增强骨架铝的嵌入,进一步降低分子筛的骨架硅铝比(24.2)。正庚烷裂化反应结果表明,降低分子筛的骨架硅铝比可以提高正庚烷裂化反应的活性,但会降低低碳烯烃的选择性。     

Glycerol Upgrading over Zeolites by Batch-Reactor Liquid-Phase Oligomerization: Heterogeneous versus Homogeneous Reaction

Glycerol upgrading to diglycerols in the presence of basic (Na⁺ or Cs⁺) ion-exchanged (FAU or BEA) zeolite catalysts was studied in a liquid-phase batch rector at 260 °C under normal pressure. Homogeneous NaHCO₃ and CsHCO₃ catalysts were studied for comparison. All the catalysts, including NaHCO₃ and CsHCO₃, displayed the same conversion–selectivity relationship. The selectivity to linear diglycerols decreased at higher conversions/reaction times owing to the consecutive formation of higher oligomers, with preferential further conversion of α,α′-diglycerol. The maximum yield of linear diglycerols was limited to about 30 %. The activities of the zeolites followed the order X>Y>Beta, independent of the alkali ion present. Catalysis by the zeolites starts with an induction period attributed to a slow leaching of alkaline cations from the zeolite. Thereafter, the reaction is characterized by a progressive loss of the microporous structure of the zeolite and increasing overlap of heterogeneous and homogeneous catalysis, where, primarily, the activity depends on the cation content of the zeolite.     

Effect of zeolite pore morphology on solvent-less alkylation of benzene with 1-hexene

In an attempt to convert the carcinogenic benzene which is almost restricted for its use in gasoline, alkylation reaction with olefin 1-hexene has been conducted on various zeolites. Four zeolites having different pore topology and pore size have been applied as solid acid catalysts for effective production of alkylate in a liquid phase, solvent-less low temperature reaction. The textural properties of all the four zeolites (ZSM-5, MOR, BEA, HY) have been characterized for crystal morphology by TEM, crystal structure by XRD and FTIR, BET for surface area, N₂ sorption for porosity and TPD for acidity. Among the zeolite, BEA possessed high surface area (600.61 m²/g) and enhanced meso pores volume (0.3956 cm³/g) as compared to other zeolite samples. The performance of BEA was also observed to be superior in the liquid phase alkylation of benzene with 1-hexene in a batch reactor under autogenous pressure without using any solvent. At the optimum reaction conditions, the benzene conversion was 86.6 wt% and 3-Phenylhexane, 2-Phenylhexane yield were about 47.9 wt% and 38.7 wt% respectively on this catalyst. The BEA also exhibited longer time-on-stream and reusability performance, thus offers an attractive route for converting benzene into valuable (3-Phenylhexane, 2-Phenylhexane) alkylate product useful for the manufacturing of fine chemicals, dyestuff, detergents and scents.     

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.     

Synthesis of Pure Silica MWW Zeolite in Fluoride Medium by Using an Imidazolium-Based Long Dication

As the spacer length in 1,2-dimethylimidazolium-based dications increases beyond a specific point (six methylene units), they fail in structure-directing towards STW zeolites in any synthetic conditions. These dications can instead produce, under fluoride concentrated conditions, either *BEA [in the case of the eight-methylene-unit structure-directing agent (SDA)] or MWW (ten methylene units) zeolites. For any length of the dication, the default zeolite (MTW) is a relatively dense zeolite containing a unidimensional channel, whereas the zeolite demanding most specificity (STW, *BEA or MWW) is more porous, affording a larger concentration of the dication to be occluded. This work provides the first reported fluoride synthesis of pure silica MWW zeolites. Charge balance of the organic dications in this zeolite was achieved by combining “structural” silanolates, regular “connectivity defects” and occluded fluoride. Molecular mechanics calculations showed a perfect fit of the decamethylenebis(dimethylimidazolium) dication in the sinusoidal intralayer pore system of MWW. The calculations showed also that the dication is able to stabilize the interlayer space without disturbing the hydrogen-bonding system that holds the layers together in the as-made material. The ¹⁹F magic-angle spinning (MAS) NMR presented two distinct resonances at −71 and −83 ppm, which, on the basis of DFT calculations, we tentatively assigned to fluoride occluded in [4⁶6²] and [4¹5²6²] cages of the MWW structure, respectively. The same DFT study determines a different chemical shift of one methyl ¹³C nuclear magnetic resonance according to the imidazolium ring residing in the sinusoidal channels or in the large cup cavities, thus explaining an experimentally observed splitting of that resonance.     

Gamma-Ray Irradiation to Accelerate Crystallization of Mesoporous Zeolites

Gamma-ray (γ-ray) irradiation was introduced into zeolite synthesis. The crystallization process of zeolite NaA, NaY, Silicalite-1, and ZSM-5 were greatly accelerated. The crystallization time of NaA zeolite was significantly decreased to 18 h under γ-ray irradiation at 20 °C, while more than 102 h was needed for the conventional process. Unexpectedly, more mesopores were created during this process, and thus the adsorption capacity of CO₂ increased by 6-fold compared to the NaA prepared without γ-ray irradiation. Solid experimental evidence and density function theory (DFT) calculations demonstrated that hydroxyl free radicals (OH*) generated by γ-rays accelerated the crystallization of zeolite NaA. Besides NaA, mesoporous ZSM-5 with MFI topology was also successfully synthesized under γ-ray irradiation, which possessed excellent catalytic performance for methanol conversion, suggesting the universality of this new synthetic strategy for various zeolites.     

Acidity versus metal-induced Lewis acidity in zeolites for Friedel–Crafts acylation

Acid catalysts including Ni, Ag and Fe-loaded zeolites of different structures were prepared either via cationic exchange or impregnation techniques from pristine H-zeolites (BEA, and MFI). Their catalytic activity was evaluated in the liquid-phase Friedel–Crafts acylation of anisole with propanoic acid. It turned out that, whatever the doping procedure was, the zeolite loaded with transition metals led to considerable decrease in propanoic acid conversion, regardless of the nature or the metal content. However, the extent of this detrimental effect followed the order: Ag⁺ > Ni²⁺ > Fe³⁺.Pristine acidic zeolites were not only found to be the most active, but also to be the most selective toward ortho- and para-acylation products. H-ZSM-5 zeolites yielded the highest intrinsic activity, with TOF values of 0.09 h⁻¹. The catalyst activity proved to be essentially attributed to the density and accessibility of Brønsted acid sites, playing a key role in the activation of the reactants. Brønsted sites are proposed to be the most likely catalytic species for performing this Friedel–Crafts acylation.     

Broadening the Scope for Fluoride‐Free Synthesis of Siliceous Zeolites

Siliceous zeolites are ideally suited for emerging applications in gas separations, sensors, and the next generation of low‐k dielectric materials, but the use of fluoride in the synthesis significantly hinders their commercialization. Herein, we show that the dry gel conversion (DGC) technique can overcome this problem. Fluoride‐free synthesis of two siliceous zeolites—AMH‐4 (CHA‐type) and AMH‐5 (STT‐type), has been achieved for the first time using the method. Siliceous *BEA‐, MFI‐, and *MRE‐type zeolites have also been synthesized to obtain insights into the crystallization process. Charge‐balancing interactions between the inorganic cation, organic structure‐directing agent (OSDA), and Si?O^? defects are found to be an essential aspect. We quantify this factor in terms of the “OSDA charge/silica ratio” of the as‐made zeolites and demonstrate that the DGC technique is broadly applicable and opens up new avenues for fluoride‐free siliceous zeolite synthesis.     

ZSM-5沸石结晶度对乙苯叔丁基化对位选择性的影响(英文)

Highly crystalline ZSM-5 zeolites are important for para-selective alkylation of alkyl aromatics, because they carry few external acid sites for isomerization of p-dialkyl products. Such zeolites (Si/Al = 25, 50, and 75) were synthesized in a fluoride medium between pH 4 and 6. Their crystallinities, crystal sizes, and surface areas were higher than those of a commercial ZSM-5 zeolite. Their para selectivities in alkylation were tested for vapor-phase tert-butylation of ethylbenzene between 200 and 400 °C. As expected, all the catalysts showed more than 90% para selectivity. At 300 °C, ethylbenzene conversion decreased in the order ZSM-5(25, commercial) > ZSM-5(25) > ZSM-5(50) > ZSM-5(75). The catalysts had weak, medium, and strong acid sites, but all the acid sites of ZSM-5(75) were weaker than those of ZSM-5(25) and ZSM-5(50). The high activity of commercial ZSM-5 was caused by its strong acid sites being stronger than those of the synthesized zeolites. Although the activity of the commercial catalyst was higher than those of the present catalysts, the selectivity for 4-t-butylethylbenzene (4-t-BEB) was low. The optimum feed ratio (ethylbenzene:t-butyl alcohol) was 2:1 and the feed rate was 1.65 h?1 for high ethylbenzene conversion and 4-t-BEB selectivity. Time-on-stream studies showed slow catalyst deactivation. Highly crystalline ZSM-5 zeolites are therefore better than a commercial zeolite for para-selective alkylation of alkyl aromatics. They do not require much post-modification for high para selectivity. A fluoride medium is therefore better than an alkaline medium for obtaining highly crystalline para-selective ZSM-5 zeolites.     

Self-Assembled Nano-Filamentous Zeolite Catalyst to Realize Efficient One-Step Ethanol Synthesis

The non-petroleum synthesis route of ethanol from syngas (H₂+CO) with methyl acetate (MA) as the core intermediate product has been confirmed as an excellent industrialization route for high purity ethanol production. However, as the central part of this tandem-catalysis path, the carbonylation of dimethyl ether (DME) to MA is limited by the undesirable catalytic activity and stability of zeolite catalysts. Herein, a facile inhibitor-assisted strategy was developed for constructing self-assembled nano-Mordenite (nano-MOR) zeolites without using any expensive or complex template. A nano-filamentous MOR zeolite with only 70 nm crystal diameter was successfully synthesized by selectively controlling the crystal growth orientation with a specific inhibitor. The catalytic performance of self-assembled nano-MOR catalysts was remarkably outstanding in DME carbonylation reaction. The highest Space-Time Yield (STY) of MA was achieved over Nanofilament MOR (NF-MOR), which was significantly improved comparing with that of the traditional Ellipsoid-MOR (ES-MOR) [3780 mmol/(kg ⋅ h) vs. 1368 mmol/(kg ⋅ h)]. One-step ethanol synthesis was realized by combining the MOR catalyst and an innovative self-reduced Cu-ZnO/SiO₂ (CZ/SiO₂) catalyst in a rationally designed dual-bed catalysis system. Adopting the tailor-made NF-MOR&CZ/SiO₂ combination, it obtained the highest STY of ethanol, about 4 times of the conventional ES-MOR&CZ combination [1800 mmol/(kg ⋅ h) vs. 476 mmol/(kg ⋅ h)]. The present self-assembled nano-MOR zeolites synthetic strategy opens a new way for the fabrication of high-performance zeolites for practical industrial applications in catalytic conversions of one-carbon (C1) small molecules to high value-added chemicals.     

Conjugate Conversion of Methanol and Lower Alkanes C3-C4 on Zeolite-Containing Catalysts

Simultaneous conversion of methanol and lower alkanes C₃-C₄ on high-silica zeolites of ZSM-5 type of various compositions (SiO₂/Al₂O₃ 30, 50, 90) was studied. The catalytic activity of zeolite catalysts and their physicochemical properties (acidity, sorption capacity, and pore structure) were evaluated.     

不同结构的分子筛在1-丁烯中催化裂解性能的研究

我们合成了不同Si含量的SAPO-18,并且利用了XRD、SEM、NH3-TPD进行了表征分析.利用微反固定床反应器评价了代表不同结构的H-ZSM-5(MFI)、H-Beta(* BEA)、SAPO-18 (AEI)系列分子筛的丁烯催化裂解性能.实验结果表明分子筛的结构和酸性对反应结果都有明显影响,分子筛酸量的增加提高了1-丁烯的转化率,但酸量过高会引发氢转移、芳构化副反应,从而降低丙烯的选择性;分子筛孔口大小、孔道结构决定了可以获得的最高丙烯选择性.具有八元环孔口、笼形结构特点的SAPO-18-0.8在线时间20 min时1-丁烯裂解中转化率为60.7％,获得的丙烯选择性达到59.1％.     

短链烷烃二元混合物在分子筛上吸附分离的分子模拟

用巨正则是系综Monte Carlo(GCMC)与构型偏倚(CBMC)相结合的方法模拟了 MFI分子筛对甲烷-丙烷、乙烷-丙烷体系(300K，345kPa)的吸附平衡，模拟结果与 文献实验结果相吻合，分别模拟了FER，ISV，MEL，MFI，MOR，TON等六种分子筛对 甲烷－丙烷、乙烷－丙烷体系（300K，345kPa）的吸附，得出甲烷－丙烷体系中分 子筛对较长链烷烃的选择性大小顺序（气相乙烷摩尔分数为0.5时）为ISV＞MEI＞ MEL＞FER＞TON＞MOR,对乙烷－丙烷体系选择性大小顺序（气相乙烷摩尔分数为0. 5时）为ISV＞MOR＞MFI＞FER＞MEL＞TON. MOR型分子筛对两个不同体系的吸附行为 表现出明显的不同，两个体中ISV的吸附量均最大，MFI，MEL，FER次之，此三种分 子筛具有相拟的吸附量，MOR和TON型分子筛吸附量较低。