Behavior of Ag3 clusters inside a nanometer-sized space of ZSM-5 zeolite

We found from DFT calculations that Ag-Ag orbital interactions as well as Ag-O electrostatic interactions determine the structures of three silver cations inside a nanometer-sized cavity of ZSM-5 (Ag(3)-ZSM-5) in lower and higher spin states. Both interactions strongly depend on the number of Al atoms substituted for Si atoms on the ZSM-5 framework (ZSM-5(Al(n))), where n ranges from 1 to 3. In smaller n, stronger Ag-Ag orbital interactions and weaker Ag-O electrostatic interactions operate. Accordingly, there are significant dependencies of the structures of three silver cations on the number of Al atoms. In lower spin states of Ag(3)-ZSM-5(Al(1)) and Ag(3)-ZSM-5(Al(2)), D(3h)-like triangle clusters are contained inside ZSM-5 whereas their higher spin states have triangle clusters distorted significantly from the D(3h) structure. In lower spin states, the totally symmetric orbital consisting of 5s(Ag) orbitals is responsible for cluster formation, whereas in higher spin states occupation of a 5s(Ag)-based orbital with one node results in significant distortion of the triangle clusters. The distortion can be partially understood by analogies to Jahn-Teller distortion of the bare D(3h) Ag(3)(+) cluster in the triplet spin state. When n is 3, we found that three silver cations are isolated in a lower spin state and that a linear cluster consisting of two silver cations is formed in a higher spin state. Thus, we demonstrate from DFT calculations that the number of Al atoms can control the properties of three silver cations inside a ZSM-5 cavity. Since the structural and electronic features of the enclosed silver clusters can link to their catalytic properties, the DFT findings can help us to understand the catalytic activity of Ag-ZSM-5.     

Ozone-Assisted Catalysis of Toluene with Layered ZSM-5 and Ag/ZSM-5 Zeolites

This paper presents a new type of ozone-assisted catalysis for toluene decomposition. The different catalytic activities of ZSM-5 and Ag/ZSM-5 were incorporated into a layered catalyst with a tandem configuration. Instead of increasing the amount of metal catalyst, the layered catalyst was formed, which had an equal amount of bare ZSM-5 and Ag/ZSM-5 and could achieve both high toluene conversion and CO₂ selectivity concurrently. The properties of each catalyst were evaluated with respect to toluene conversion, formation of intermediates, CO₂ selectivity and ozone demand factor. The bare ZSM-5 exhibited higher toluene conversion than the Ag/ZSM-5, while its activity toward deep oxidation was limited. However, the Ag/ZSM-5 was found to be effective for the deep oxidation of reaction intermediates (HCOOH and CO). Separate oxidation tests with HCOOH and CO revealed that the ZSM-5-supported Ag nanoparticles could oxidize the HCOOH and CO in the absence of ozone, which was not possible with the bare ZSM-5. Plausible pathways for the oxidation of toluene with O₃ over ZSM-5 and Ag/ZSM-5 were proposed based on the experimental evidence.     

Pyrolysis of n-pentane on ZSM-5 zeolite

Pyrolysis of n-pentane has been studied at the temperature range 653–753 K on ZSM-5 zeolite. High catalytic activity and selectivity of H-ZSM-5 zeolite was found. The yield of propane was about 80 wt. %. A mechanism of the process is proposed.

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H-ZSM-5 n- 653–153 . . 80%. n-.

     

一步法合成多级孔结构ZSM-5分子筛

多级孔结构ZSM-5分子筛的合成过程复杂。利用双模板剂,通过优化晶化条件(如晶化时间与晶化温度)和Si/Al物质的量比等一步水热晶化合成了具有多级孔结构的ZSM-5分子筛,并采用XRD、N₂吸附-脱附、吡啶红外吸脱附、SEM和TEM等方法对样品的晶体结构、孔道结构、表面酸性和形貌等进行了表征。结果表明,一步法合成多级孔结构ZSM-5分子筛的适宜条件是:晶化温度160-180℃,晶化时间24-96 h,反应物组成为SiO₂/Al₂O₃/Na₂O/CTAB/TPABr/H₂O=1/x/0.4/0.05/0.12/280,(x:50-240)。其中,晶化温度160℃、晶化时间48 h和以Si/Al物质的量比50的凝胶合成的样品具有有序的介孔(平均尺寸3.60 nm)结构、较高的结晶度和较强的酸性。     

Thermal analysis of zeolite ZSM-5 precursors with different Si/Al ratios

The thermal analysis of crystalline zeolite ZSM-5 precurcors with different Si/Al ratios was carried out in a nitrogen atmosphere. Different interactions between tetrapropylammonium species and the zeolitic environment were evidenced, depending on the Al content of the crystalline precursors. The results support the mechanism of ZSM-5 formation through a condensation process from the liquid phase.

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Zusammenfassung Thermische Analysen kristalliner Zeolith- (ZSM-5) Vorprodukte mit unterschiedlichen Verhältnissen Si/Al wurden in Stickstoffatmosphäre ausgeführt. Verschiedene Wechselwirkungen zwischen den Tetrapropylammonium-Spezies und ihrer zeolithischen Umgebung wurden nachgewiesen, die vom Aluminiumgehalt der kristallinen Vorprodukte abhängen. Die Ergebnisse sprechen für einen Bildungsmechanismus des ZSM-5 über einen Kondensationsprozess aus der flüssigen Phase.

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ZSM-5 . . ZSM-5 .

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This work was carried out with the financial support of the Italian National Research Council Progetto Finalizzato Energetica 2.     

H2 adsorption on Fe/ZSM-5 zeolite: a theoretical approach

The hydrogen reduction of the red-ox Fe/ZSM-5 zeolite is an essential step for catalyst preparation. In this letter, various adsorption modes of the H(2) molecules on the Fe(III)/ZSM-5 zeolite were first explored by density functional theory, with their exact configurations provided. The adsorption energies revealed that the two configurations with Fe(III) at the sextet states are the main ones, consistent with the results of inelastic neutron scattering (INS) experiments. On such basis, the vibrational and orbital analyses were made, which will be valuable for the future studies on the Fe/ZSM-5 systems.     

甲醇芳构化反应中Ag/ZSM-5催化剂的失活特性

通过四次连续反应-再生循环实验对甲醇芳构化催化剂Ag/ZSM-5进行了失活再生研究,结果表明催化剂通过烧碳可以得到部分再生.对反应-再生后的催化剂进行了X射线衍射(XRD)、透射电子显微镜(TEM)表征,证实芳构化过程中催化剂的ZSM-5骨架结构保持完好,金属烧结也不严重.傅里叶红外光谱(FTIR)和氨-程序升温脱附(NH3-TPD)实验证实了反应生成的水使催化剂在475℃发生水热脱铝,进而导致Brφnsted酸流失及催化剂的芳构化反应能力不可逆下降.     

ZSM-5/Y复合分子筛在烃类催化裂化催化剂中的应用研究

以大庆减压蜡油为原料，考察了水热脱铝ZSM-5/Y复合分子筛的催化裂化性能，并与经同样条件水热脱铝的ZSM-5和Y型沸石的机械混合分子筛进行了对比研究。结果表明，与机械混合样品相比，复合分子筛具有较大的柴油产率和气体产率，汽油产率降低。从复合分子筛结构和ZSM-5的择形催化两方面分析了复合分子筛和机械混合分子筛裂化性能差别的原因。复合分子筛的聚集体结构不利于大分子进入分子筛结构中进行裂化，有利于汽油组分的裂化。气体数据分析支持了复合分子筛的结构特点。     

含铁微孔EU-1/ZSM-5复合分子筛的合成和表征

采用预置晶种法合成了含铁的微孔EU-1/ZSM-5复合分子筛,并采用X射线粉末衍射(XRD)、扫描电子显微镜(SEM)、热重-微分热重(TG-DTG)、N₂吸附-脱附、紫外-可见吸收光谱(UV-vis DRS)、X射线吸收精细结构(XAFS)等手段进行了表征。结果表明,复合分子筛具有EU-1和ZSM-5的特征衍射峰,是两种晶相相互作用的分子分散晶相材料,微孔孔径较Fe-EU-1分子筛有所增大。随原始溶胶中铁的质量分数增加,复合分子筛具有的23.09°和23.94°处的特征衍射峰逐渐向低角度方向偏移;紫外-可见漫反射谱图中在220~245 nm出现了宽的吸收谱带;XAFS表征表明,1s→3d电子跃迁的弱吸收峰逐渐增强,同时在吸收边顶部出现的1s→4p吸收峰逐渐由宽变窄。合成工艺的最佳条件为,原始溶胶中铁的质量分数为0.075%~0.15%,晶种添加比例为15.0%~21.0%,晶种SiO₂/Al₂O₃物质的量比为50~60。     

A kinetic study on methylation of naphthalene over Fe/ZSM-5 zeolite catalysts

2,6-Dimethylnaphthalene is an important dimethylnaphthalene isomer which can be used in the production of polyethylene naphthalate. The novelty of this study is to reveal Langmuir–Hinshelwood and Eley–Rideal reaction rate equations for the methylation of naphthalene over Fe/ZSM-5 zeolite catalysts besides the proposed reaction rate equation. To investigate the kinetics and mechanisms of naphthalene methylation, the methylation experiments were carried out in a gas–solid catalytic fixed-bed reactor in the presence of Fe/ZSM-5 zeolite catalysts at two different temperatures (450 and 500 °C) and five different weight hourly space velocities (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 h^?1). A naphthalene:methanol:1,2,4-trimethyl benzene mixture having a 1:3:10 molar ratio was used as a feed stream. The methylation products were identified by using GC–MS. For the methylation kinetics of naphthalene, the reaction rates depending on the naphthalene and methanol concentration were determined. Furthermore, the effects of temperature and weight hourly space velocity on the conversion of naphthalene, the selectivity of 2,6-dimethylnaphthalene, and the ratio of 2-methylnaphthalene/1-methylnaphthalene were determined. The results of this study demonstrate that the Langmuir–Hinshelwood reaction mechanism for naphthalene methylation is more compatible at 450 °C and the Eley–Rideal reaction mechanism at 500 °C. Moreover, in addition to 2,6-dimethylnaphthalene, other dimethylnaphthalene and tri-methylnaphthalene isomers were formed in the methylation of naphthalene. The conversion of naphthalene reached approximately 70%. Moreover, the highest selectivity of 2,6-dimethylnaphthalene was almost 40%. The ratios of 2-methylnaphthalene/1-methylnaphalene demonstrate that the methylation of naphthalene to 2-methynaphthalene is much higher than to 1-methynaphthalene.     

Single-template synthesis of zeolite ZSM-5 composites with tunable mesoporosity

Hierarchically structured composites (TUD-C) with ZSM-5 crystals embedded in a well-connected mesoporous matrix were synthesized by using only one organic templating/scaffolding molecule (TPAOH).     

Formation of acetone enol on acidic zeolite ZSM-5 evidenced by H/D exchange

H/D exchange observed between bridging hydroxyl groups in acidic zeolite ZSM-5 and adsorbed acetone (acetone-d6/H-ZSM-5 and 13C-2-acetone/D-ZSM-5) indicates a concerted catalytic function of Br?nsted acid sites and neighbouring framework oxygen atoms acting as Lewis base sites.     

Anionic emulsion-directed synthesis of zeolite ZSM-5 with tunable morphology and Si/Al ratio

Zeolite ZSM-5 was synthesized for the first time in an anionic emulsion system composed of sodium dodecylbenzene sulfonate, pentanol, cyclohexane and zeolite synthesis mixture, and subsequently characterized by XRD, SEM, FTIR, TG and N₂ adsorption techniques. It is found that altering emulsion composition and adding electrolyte can effectively change the morphologies and/or Si/Al ratios of the ZSM-5 samples. Besides the commonly seen coffin morphology, ZSM-5 particles with rare elliptic cylinder, column and ellipsoid morphologies are also obtained. Depending on the weight ratios of anionic surfactant and zeolite reaction mixture, the framework Si/Al ratios of ZSM-5 samples vary slightly. Investigations on the crystallization process further show the emulsion system can induce rapid crystallization by virtue of shortening the induction time. The ways that the emulsion system affects zeolite crystallization, framework Si/Al ratio and particle morphology are tentatively discussed.     

A method for estimation of transport properties of ZSM-5 zeolite

A method for a quick testing of transport properties of samples of a zeolite catalyst has been developed. The method is based on the application of gas-phase chromatography, where the tested sample is used as the stationary phase. Cyclopentene, cyclohexane, and 1,3,5-trimethylcyclohexane were used as the testing molecules. A retention indexes for samples comparison were introduced. The method is sensitive even to small changes in the zeolite structures caused by binding agents and/or alkali metals.     

Amine-functionalized mesoporous ZSM-5 zeolite adsorbents for carbon dioxide capture

ZSM-5 type zeolite with mesoporous structure was prepared and then amine-functionalized with tetraethylenepentamine (TEPA) by wet impregnation method to form a series of CO₂ adsorbents (ZTx). The structural properties of ZSM-5 and ZTx were characterized by XRD, FTIR, TGA/DTG, nitrogen adsorption/desorption, SEM and EDX techniques. The adsorption capacity of the adsorbents with different amine loading was measured at a temperature from 40 to 100 °C and the adsorption capacity of ZT7 was 1.80 mmol/g at 100 °C. The adsorption process and mechanism were studied by fitting the experimental data used the three adsorption kinetic models, and a complex physical and chemical mixing process was produced as the amine entered the surface and pore size of the zeolite. The high adsorption selectivity at 10% CO₂ concentration and the stability of the five adsorption desorption cycles indicated that ZT7 is a suitable and promising CO₂ adsorbent for the purification of industrial flue gas.     

Hydrodechlorination of chlorophenols over Pt- and Co-containing ZSM-5 zeolite catalysts

Summary Some of the chlorinated organic compounds are widely used commercially because of their advantageous chemical/physical properties or being toxic to pestiferous living substances. We have prepared and applied monometallic Co-, Pt- and bimetallic Co,Pt-ZSM-5 zeolite catalysts for hydrotreating 2- and 4-chlorophenols in the temperature range of 300-400 oC using a fixed-bed laboratory reactor system equipped with a gas chromatograph for analysis. In the reaction over the Pt-containing catalyst high initial conversion can be observed, the compounds transform to cyclohexanone, however, the activity of the catalyst decreases even during the 2 h reaction time. In the presence of Co-ZSM-5, the main reaction is simple hydrodechlorination resulting in phenol as the main product, and this catalyst is stable, and the activity does not change. The bimetallic catalyst combines the advantages (and disadvantages) of the monometallic samples. The hydroconversion of chlorophenols resulted in the formation of cyclohexanone with high initial selectivity. However, because of the relatively short catalyst lifetime further optimization is necessary before practical application.</o:p>     

Solid-state ion exchange of ammonium heptamolybdate tetrahydrate into ZSM-5 zeolite

Journal of Thermal Analysis and Calorimetry - Thermal decomposition (2&nbsp;K&nbsp;min?1) of ammonium heptamolybdate tetrahydrate, performed between room temperature and...     

Formation of superacid centers in the structure of zeolite ZSM-5

The structural changes and acid characteristics of the zeolite ZSM-5 modified with titanium and sulfur were studied. The modifier components were chemically bonded to the zeolite structure. The acid characteristics of zeolite changed and superacid centers appeared. A physicochemical study showed that treatment of zeolite with titanium tetrachloride and sulfuryl chloride did not change its structure and molecular-sieve properties.