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).     

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.     

Thermal behaviour of the tpa IONS in ZSM-5 zeolite: I. Effect of the Si/Al ratio and grinding

Thermal decomposition of tetrapropylammonium (TPA) ions, as a function of the Si/Al ratio and the grinding of ZSM-5 crystals, was investigated by DTA and DTG analyses. The amount and the temperature decomposition of TPA ions, such as the crystal size, increase with increasing Al/u.c. The grinding of ZSM-5 crystals lowers the temperature decomposition of TPA ions. Considerations on experimental results are reported.

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Zusammenfassung Mittels DTA und DTG wurde die thermische Zersetzung von Tetrapropylammonium- (TPA) Ionen als eine Funktion des Si/Al-Verhältnisses und der Zerkleinerung der ZSM-5 Kristalle untersucht. Grad und Temperatur der Zersetzung der TPA-Ionen wachsen mit steigendem Al-Gehalt an. Eine Zerkleinerung der ZSM-5 Kristalle senkt die Zersetzungstemperatur der TPA-Ionen.

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Work supported by Italian C.N.R. (progetto finalizzato Energetica 2).     

Control of Al distribution in ZSM-5 by conditions of zeolite synthesis

Concentration of Al-O-(Si-O)1,2-Al sequences located in one ring and forming cationic sites for divalent cations in ZSM-5 can be controlled in a wide range of their concentrations by the variation of the source of aluminium and silicon used for synthesis of this zeolite.     

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。     

红外光谱法研究不同硅铝比的ZSM-5及ZSM-11分子筛的骨架振动

红外光谱法研究分子筛的骨架振动得出了在X、Y等沸石分子筛骨架上振动频率与四面体中铝含量的线性关系^[1]。但未见到有关ZSM-5型的报道.本文用红外光谱法系壳探讨了硅铝比和ZSM-5及ZSM-11的骨架振动频率之间的线性关系,并将由IR得到的SiO₂/Al₂O₃比与化学分析值进行了比较。     

Oxidative conversion of methane over MgO/ZSM-5 catalysts with different Si/Al ratios

It is found that the lower the Si/Al ratio of ZSM-5 in the catalytic system MgO/ZSM-5, the higher is the activity and selectivity in the reaction of oxidative conversion of methane. The catalytic properties reflect quite closely the basic properties of the samples, studied by means of temperature-programmed desorption of CO₂.     

Acid properties of the HZSM-12 zeolite with different Si/Al ratio by thermo-programmed desorption

In this work was studied the acid properties of a series of HZSM-12 zeolites with different Si/Al molar ratio. The samples of ZSM-12 were synthesized by the hydrothermal method starting from a gel with the following molar composition: 20MTEA:10Na₂O:xAl₂O₃:100SiO₂:200H₂O, where: x=2, 1, 0.67 and 0.50, respectively. After the synthesis, the samples of ZSM-12 were ion-exchanged NH₄Cl solution to obtain zeolite in the acid form (HZSM-12). The acid properties were evaluated by n-butylamine thermodesorption in a TG equipment at three different heating rates. The model-free kinetic model was applied in the TG integral curves to estimate the apparent activation energy (E _a) of the n-butylamine desorption process. The results obtained showed that the HZSM-12 zeolite presents two kinds main of acid sites: one with E _a in the range of 115-125 kJ mol^-1 classified as weak and other kind with E _a varying of 230-250 kJ mol^-1 classified as strong. This revised version was published online in July 2006 with corrections to the Cover Date.     

Bread-template synthesis of hierarchical mesoporous ZSM-5 zeolite with hydrothermally stable mesoporosity

A hierarchical mesoporous ZSM-5 zeolite has been synthesized by using starch-derived bread as a meso-template. The obtained mesoporous ZSM-5 was characterized with X-ray diffraction (XRD), nitrogen sorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and thermogravimetric (TG)/differential thermal analysis (DTA) techniques. Hydrothermal treatments revealed that the mesoporosity in hierarchical mesoporous ZSM-5 exhibited excellent hydrothermal stability. Catalytic tests showed that hierarchical mesoporous ZSM-5 was more active than conventional zeolite of ZSM-5 in catalytic cracking of 1,3,5-tri-isopropylbenzene. Hydrogen adsorption measurements showed hierarchical mesoporous ZSM-5 had a higher storage capacity than the conventional ZSM-5.     

Selectivity of B, Al and Ga silicates of ZSM-5 zeolite structure in olefin synthesis from methanol

Selectivity of B, Al and Ga silicates of zeolite structures in olefin synthesis from methanol has been studied. It is determined by the concentration and strength of the centers enhancing olefin aromatization reactions.

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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.     

Effect of the Si/Al ratio of HZSM-5 zeolite on the production of dimethyl ether before and after ultrasonication

A series of as-synthesized HZSM-5 zeolites with different Si/Al ratios (25, 90, 120, 240 and 400) were post-treated by ultrasonication for an optimum time of 60 min. The morphology, acidity and textural properties of HZSM-5 were characterized with XRD, SEM, N₂ adsorption and NH₃-TPD techniques. The catalytic performance was evaluated by dehydration of methanol to dimethyl ether (DME), which is a promising gaseous automotive fuel in future. It was found that the Si/Al ratio of HZSM-5 had considerable impacts on its catalytic performance for dehydration of methanol to DME. Its activity increased with decreasing Si/Al ratio from 400 to 25. Ultrasonication of HZSM-5 could significantly improve its catalytic performance.     

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.     

HZSM-5型分子筛硅铝比对一步法合成二甲醚的影响

以Cu/Zn/Al(摩尔比为6∶3∶1)甲醇合成催化剂与HZSM-5型分子筛混合,制备了一步法二甲醚合成催化剂。通过改用三种不同Si/Al摩尔比（摩尔比为25、38和50）的HZSM-5型分子筛,考察了催化剂中脱水组分（HZSM-5分子筛）的酸性对二甲醚合成的影响。结果表明,随着催化剂Si/Al摩尔比的降低,分子筛的酸性增强,使得CO单程转化率提高。当催化剂Si/Al＝38时,CO对二甲醚的选择性最高,可达到68.13％,其次是催化剂Si/Al＝50,选择性最差的是Si/Al＝25的催化剂。在553 K、 3 MPa和4 000 h－1的条件下,Si/Al＝25和Si/Al＝38的催化剂CO单程转化率和DME的选择性接近一致。在此条件下,两者的时空产率达到试验的最大值,分别为0.38 gDME/(gcat·h)和0.36 gDME/(gcat·h),在试验范围内,一步法合成二甲醚催化剂最佳的Si/Al摩尔比为25。     

Redox behavior of high Si/Al ratio Cu-ZSM5 in NO decomposition

Commercial H-ZSM5 zeolites with a Si/Al ratio equal to 25 and 75 have been exchanged using copper acetate aqueous solutions with different concentrations. Copper saturation is reached at the 130 and 230% level of Cu exchange for Si/Al equal to 25 and 75, respectively, although FTIR spectra showed that a fraction of Al-OH exchange positions is still available. Catalytic activity experiments of NO decomposition have been carried out at 450°C in a fixed bed reactor. Catalysts have been characterized with H₂ TPR and NO adsorption experiments at 120°C. All samples are partially reduced upon thermal treatment under inert flow (He) leading to the formation of Cu⁺-containing sites in addition to a fraction of differently reduced copper species. The Cu⁺-containing sites, also responsible for NO adsorption and subsequent production of N₂O at 120°C, have been proposed to be the active centers. A quantitative estimation of these species, likely having multi-ionic structure, has been provided.     

Effects of ammonium exchange and Si/Al ratio on the conversion of methanol to propylene over a novel and large partical size ZSM-5

One type of ZSM-5 zeolite with large partical size was prepared and characterized by XRD, SEM, N2 adsorption-desorption, XRF, Py-IR and NH3-TPD techniques. Effects of ammonium exchange and SiO2/Al2O3 molar ratios on the reaction of methanol to propylene (MTP) over Na-ZSM-5 and H-ZSM-5 zeolites have been studied in a fixed-bed flow reactor under the operating conditions of T = 500 °C, P = 1 atm, and WHSV = 6 h-1. Ammonium exchange led to a rapid decrease in Na content for Na-ZSM-5 zeolite. The reaction results indicated that Na-ZSM-5 and H-ZSM-5 with different SiO2/Al2O3 molar ratios all exhibited high activity for methanol conversion. Ammonium exchange and the decreased SiO2/Al2O3 molar ratio of ZSM-5 zeolite led to an increase both in strong acid sites and weak acid sites. Na-ZSM-5 with high SiO2/Al2O3 molar ratio was favorable for the formation of propylene. The highest propylene selectivity (45.9%) was obtained over Na-ZSM-5 zeolite catalyst with SiO2/Al2O3 molar ratio of 220.     

Effect of ZSM-5 zeolite morphology on the catalytic performance of the alkylation of toluene with methanol

A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction(XRD),scanning electron microscope(SEM), X-ray fluorescence(XRF) and temperature-programmed desorption of ammonia(NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.     

Effect of ZSM-5 zeolite morphology on the catalytic performance of the alkylation of toluene with methanol

A series of ZSM-5 zeolites, with the morphologies of sphere, sphere with cubic particles on the surface, and cubic particles, were synthesized by hydrothermal method using n-butylamine as the template, assisted by the addition of NaCl and crystal seed. X-ray diffraction(XRD),scanning electron microscope(SEM), X-ray fluorescence(XRF) and temperature-programmed desorption of ammonia(NH3-TPD) were used to characterize these samples. The samples were tested with toluene methylation reaction. The modified sample composed of spherical particles with 3 μm crystal particles on the surface had a para-xylene selectivity of 95% and maintained 79% of the initial conversion after running the reaction for 50 h. This modified sample showed the best stability among the tested three modified samples.     

Ambient xenon sampling using an Ag/ZSM-5 zeolite

Journal of Radioanalytical and Nuclear Chemistry - An ambient xenon sampling system using Ag/ZSM-5 was designed, and its performance was tested. The xenon collection efficiency of the system was...