ZSM-5分子筛的合成与应用

总结分析了ZSM-5分子筛合成方面的研究进展,主要包括ZSM-5分子筛的合成,ZSM-5复合分子筛以及含有杂原子的ZSM-5分子筛的合成.在介绍各具体合成方法原理的同时,还讨论了各合成方法的优势与缺陷,这为今后ZSM-5分子筛在合成方面的研究提供了一定的借鉴.其次,还介绍了ZSM-5分子筛在炼油工业、精细化工及环境保护...     

Microstructures formed by secondary growth of fired ZSM-5 seed crystals

Oriented ZSM-5 seed crystals on an α-Al₂O₃ porous substrate were hydrothermally treated in a raw sol. The ZSM-5 membranes were fabricated via secondary growth of the seed crystals. For some samples, the seed-applied substrate was fired at 300 or 600 °C before the secondary growth in order to enhance adhesion between the substrate and the seed crystals. The influence of the firing on the subsequent secondary growth of the seed crystals was examined by XRD, SEM, and TEM. The TEM images of the sample fired at 300 °C showed that the resulting membrane was continuous, and in the membrane, large ZSM-5 particles were distributed in a porous matrix. The ZSM-5 particles were slightly smaller than the used seed crystals. HR-TEM observations showed that the porous matrix is comprised of ZSM-5 micro-crystals, and the part adjacent to the large ZSM-5 crystals has the same crystallographic orientation as the large crystals. The TEM images of the sample fired at 600 °C showed that the resulting layer is comprised of particles with a core-shell structure. The core consisted of ZSM-5 micro-crystals, whereas the shell was composed of large ZSM-5 rod-like crystals. It is inferred that the formation of these interesting microstructures is related to the degradation of the template agent, NPr₄OH, in the seed crystals by firing at 300 and 600 °C. The part including no template is dissolved by a hydrothermal treatment, and the dissolved species is re-crystallized via reaction with a template agent in the used raw sol, resulting in the formation of interesting microstructures.     

浸涂晶种法合成ZSM-5分子筛膜及气体渗透性能研究

采用操作简单,方便易行的浸涂法,在多孔α-A12O3载体表面种上晶种,再水热合成出渗透率较大的ZSM-5沸石分子筛膜.用XRD,SEM和H2,N2,CO2和CH4等气体渗透对ZSM-5沸石分子筛膜进行了表征.XRD分析表明,陶瓷基质表面的膜层是ZSM-5沸石晶相,SEM结果显示合成的沸石膜层是一层连续的多晶层,厚度约10μm.在室温,0.1MPa下对H2,N2,CO2和CH4的渗透率分别为4.76×10-6,1.36×10-6,2.07×10-6和1.80×10-6mol·m2·s-1·Pa-1,H2/N2,H2/CO2,H2/CH4的理想分离因子分别为3.50,2.30,2.64.     

改性ZSM-5分子筛上乙醇胺催化胺化合成乙撑胺

研究了改性的ZSM-5沸石分子筛：F-ZSM-5、NiO-ZSM-5以及普通的H-ZSM-5沸石分子筛,在乙醇胺(MEA)催化胺化合成乙撑胺的反应中的催化性能。重点考察了催化剂酸性以及反应温度对反应的影响。F-ZSM-5与H-ZSM-5相比,有较高的酸中心密度和强度,反应中有利于生成乙二胺(EDA)。而NiO-ZSM-5含有大量中等强度的酸中心,有利于三乙烯二胺(TEDA)生成。以F-ZSM-5和NiO-ZSM-5为催化剂,在t=340℃、重量时空速度WHSV：1．1h～、NH3：MEA：H20=4．5：1．0：1．0的反应条件下,原料MEA的转化率分别为52-31％和96．40％：产物EDA、PIP、TEDA的选择性分别为8．60％、20．49％、46．99％和2．98％、13．24％、66．10％。当温度大于340℃时,MEA的转化率略有提高,但上述所希望的三种产品的选择性由于副反应的增多而很快下降。     

Light-emitting boron nitride nanoparticles encapsulated in zeolite ZSM-5

We report strong visible photoluminescence (PL) at room temperature from BN nanoparticles encapsulated in ZSM-5. The investigation of powder X-ray diffraction, X-ray photoelectron spectroscopy, adsorption of N₂, UV–Vis absorption, and PL spectra shows that BN nanoparticles have been successfully encapsulated in ZSM-5. Intense blue PL can be obtained from the BN/ZSM-5 sample. Analysis of PL spectra leads us to propose that the luminescence may originate from the bound excitons at the defects or impurities in the BN nanoparticles, a quasi-direct-gap semiconductor material transferred from indirect-gap BN by encapsulation in ZSM-5.     

Acidity and catalytic activity of mesoporous ZSM-5 in comparison with zeolite ZSM-5, Al-MCM-41 and silica–alumina

Acidity of mesoporous HZSM-5 prepared using amphiphilic organosilane template molecules was measured. Brønsted acid sites were observed in the prepared sample, and the number and the strength of Brønsted acid sites were determined quantitatively by a method of infrared-mass spectroscopy/temperature-programmed desorption (IRMS-TPD) of ammonia. ΔH for ammonia adsorption as an index of the strength was ca. 150 kJ mol⁻¹ that was almost the same as on usual HZSM-5, but the number was smaller than that of HZSM-5. From the measured acidity, it was concluded that the mesoporous materials contained a smaller concentration of Brønsted acid site notable on the structure of HZSM-5. Measurements of turnover frequency (TOF) in the catalytic cracking of octane supported the conclusion. Density functional calculations showed that the defect sites Al–OH and Si–OH attached to the Brønsted acid site changed the strength of the acid sites to show some possible structures of the weak and strong Brønsted acid sites included in the mesoporous HZSM-5. Acidities of Al-MCM-41 and silica–alumina were also measured, and the difference in the solid acidities of these materials was discussed.     

Synthesis of ZSM-5 zeolite and silicalite from rice husk ash

Local rice husk was precleaned and properly heat treated to produce high purity amorphous SiO₂ for use in the synthesis of ZSM-5 zeolite and silicalite by hydrothermal treatment (150 °C) of the precursor gels (pH 11) under autogenous pressure in a short reaction time (4–24 h). A wide range of SiO₂/Al₂O₃ molar ratios (30–2075) and a small template content were employed to fully exploit the potential of rice husk ash (RHA). The mineralogical phases, morphology, specific surface area and pore volume of the synthesized products were investigated by XRD, FT-IR, SEM and BET analyses, respectively. Under the employed conditions, it was found that the gels with a low range of SiO₂/Al₂O₃ molar ratios (<80) produced an amorphous phase to poorly crystalline ZSM-5 zeolite; those with a medium range (80–200) favored well crystalline ZSM-5 zeolite production with a large surface area; whilst those with a high range of SiO₂/Al₂O₃ molar ratios (>200) yielded silicalite. The increase in Na₂O content, which was derived from the addition of NaAlO₂ to attain the desired SiO₂/Al₂O₃ molar ratio of the gel, did not significantly enhance the crystallization rate, crystallinity, or yield of products. On the contrary, these properties were greatly affected by the increase in the SiO₂/Al₂O₃ molar ratio.     

分子筛ZSM-5的改性研究进展

介绍了ZSM-5分子筛的相关知识,阐述了对其改性的必要性。基于改性原理,从金属改性、复合改性和其他改性三方面综述了国内分子筛ZSM-5的改性研究进展,重点介绍了ZSM-5表面功能化后金属改性和复合改性的方法。评述了金属改性、预掺杂和后掺杂对改性的ZSH-5催化剂催化性能的影响。     

Catalytic dehydration of methanol to dimethyl ether over mordenite catalysts

The conversion of methanol to dimethyl ether was carried out over various commercial mordenite and ion-exchanged catalysts to evaluate the catalytic performance of mordenite catalysts with different pore structures and acidities. These catalysts were compared for their catalytic properties in a fixed-bed reactor at 1 atm, 573 K and LHSV of 2.84 h^− 1. The catalysts were characterized by BET, ICP, NH₃-TPD, XRD, TGA and FT-IR techniques. The ion-exchanged mordenite showed higher activity, selectivity and good stability in dehydration of methanol due to the addition of medium acid sites. Also, the effect of water on catalyst deactivation was investigated over two selected catalysts in order to develop a suitable catalyst for synthesis of dimethyl ether. It was found that the H-mordenite catalyst supplied by Süd-chemie Co., (MCDH-1) was more active and less deactivated than another one in a feed containing 20 wt.% water.     

ZSM-5沸石分子筛脱硫脱氮机理及改性方法

综述了近年分子筛的脱硫脱氮机理及动力学,从表面酸性和孔结构两方面评述了ZSM-5分子筛的改性。重点综述了基于ZSM-5的杂原子分子筛、分子筛膜、纳米分子筛的研究动态和发展趋势,指出了研究应用中存在的问题以及今后的研究方向。     

小晶粒ZSM-5分子筛的合成

采用水热合成法,选择合理的原料和配料比合成ZSM-5分子筛,对影响分子筛合成的主要因素如n(SiO_2)∶n(Al_2O_3)、n(H_2O)∶n(SiO_2)、晶化时间和晶化温度进行考察优化。XRD和SEM表征结果表明,合成的分子筛为典型的ZSM-5结构分子筛,晶粒均匀且呈单分散。通过不同因素的调控,可以合成一系列粒度(350~650)nm的ZSM-5分子筛。     

Synthesis and evaluation of ZSM-5 films on cordierite monoliths

Well-defined ZSM-5 films were prepared on cordierite monoliths using the seed film method. The monoliths were seeded with silicalite-1 seeds and hydrothermally treated either at 75 or at 150 °C in a single or several steps. By adding sodium hydroxide to the solution, the aluminum concentration in the zeolite increased. Consequently, films with different Si/Al ratios were prepared. The film thickness could be controlled from 110 nm to 9 μm. Multi-step synthesis was used to prevent bulk crystallization and ultrasound treatment was found to be beneficial (in order) to remove sedimented crystals on the top of the coatings. The zeolite-coated monoliths were active for p-xylene isomerization, and the test results indicated that the films became less deactivated than the films prepared on alumina beads.     

Chemistry of surface oxygen formed from N2O on ZSM-5 at moderate temperatures

Conversion of CH₄, C₂H₆, C₃H₈, benzene and their binary mixtures over H-NaZSM-5 catalyst in the presence of N₂O was studied. It was found that under experimental conditions methane alkylates benzene to give toluene and xylenes. Acidity of the catalyst had no effect on the reactivity of active oxygen formed from N₂O towards methane and benzene, but affected their secondary transformation. Acidic samples favored the reaction of aromatic ring methylation with methane whereas deep oxidation of CH₄ prevailed on NaHZSM-5. Based on the relative reactivities and ¹³C label distribution in the products of ¹³CH₄+C₆H₆+N₂O feed conversion, the scheme of hydrocarbon transformation was proposed.     

Conventional and microwave hydrothermal synthesis of zeolite ZSM-5 from the cupola slag

ZSM-5 type zeolites have been prepared from cupola slag waste using both conventional hydrothermal and microwave syntheses at 130–200 °C. The ZSM-5 was synthesized by conventional heating by taking advantage of the high silica content of cupola slags. Microwave heating increased the rate of ZSM-5 formation by 4 times at 150 °C compared with conventional heating. The Si/Al ratio of the ZSM-5 produced by the conventional heating and the microwave crystallization were similar 28 and 29, respectively. The conventional-heating produced ZSM-5 particles 3 μm in diameter, while, microwave-heating produced smaller ZSM-5 particles only 0.3 μm in size.     

Synthesis of ZSM-5 Membrane on the Anodized Alumina by Adding Promoter Ions

Adding promoter ions (e.g., NO–3 and PO3–4) can shorten hydrothermal synthesis time for continuous ZSM-5 layers on the anodized alumina from several ten hours to several hours. The anodized alumina, using as a support and a source of aluminum in the preparation of ZSM-5 crystals, was placed vertically in Teflon-lined stainless-steel autoclaves with a high H2O/SiO2 ratio aqueous solution. The results showed that a layer of well-intergrown ZSM-5 crystals was formed on anodized alumina and the adhesion between zeolite and anodized alumina was excellent. The morphology and crystallization of the ZSM-5 zeolite membrane were characterized by using SEM and XRD.     

ZSM-5 supported iron catalysts for Fischer-Tropsch production of light olefin

Fischer-Tropsch Synthesis (FTS) for olefin production from syngas was studied on Fe-Cu-K catalysts supported on ZSM-5 with three different Si/Al ratios. The catalysts were prepared by slurry-impregnation method of metallic components, and were characterized by BET surface area, XRD, hydrogen TPR and ammonia TPD. Fe-Cu-K/ZSM-5 catalyst with a low Si/Al ratio (25) is found to be superior to the other catalysts in terms of better C₂-C₄ selectivity in the FTS products and higher olefin/(olefin + paraffin) ratio in C₂-C₄ because of the facile formation of iron carbide during FTS reaction and also due to a larger number of weak acidic sites that are present in these catalysts.     

以煤系高岭土为原料合成ZSM-5分子筛

在综述有关国内外煤系高岭土的开发应用及使用高岭土合成分子筛的研究、ZSM-5分子筛的合成方法基础上,运用XRD等现代分析测试技术对以高岭土为原料合成ZSM-5分子筛的工艺条件和产品进行探究,初步确定了晶化时间为72 h,晶化温度为160℃,模板剂的加入量与硅的比为0.3︰1,是合成ZSM-5分子筛的适宜条件。     

Hydrodesulfurization over noble metals supported on ZSM-5 zeolites

Pt/HZSM-5 showed high and stable catalytic activity for the hydrodesulfurization of thiophene at 400°C and its catalytic activity was higher than that of commercial CoMo/Al₂O₃ catalyst. Pt/HZSM-5 zeolite was not poisoned by hydrogen sulfide in the hydrodesulfurization of thiophene and hydrocracking of hydrocarbons. The catalytic activity of Pt/HZSM-5 decreased with increase of SiO₂/Al₂O₃ ratio in HZSM-5. The Brønsted acid site of HZSM-5 and spillover hydrogen formed on Pt particle in Pt/HZSM-5 catalyst play an important role for the hydrodesulfurization of thiophene.     

Direct partial oxidation of methane over ZSM-5 catalyst: Zn-ZSM-5 catalyst studies

Extended studies on Zn-ZSM-5 catalyst for the production of liquid hydrocarbons in the direct partial oxidation (DPO) of CH₄ with O₂ are reported. Previously, it was reported that metal-containing ZSM-5 catalysts could produce C₅₊ hydrocarbons from pure CH₄/O₂ feeds without feed additives. Zn-ZSM-5 produced the highest C₅₊ yields of the catalysts tested. This work shows that the method of introducing Zn onto the catalyst, ion-exchange versus impregnation, does not significantly alter C₅₊ yields if low Zn content is maintained ( 0.4–0.5 wt%). Liquid hydrocarbon yields in this system doubled after 8 h on stream while overall C₂₊ yields increased by over 300%. Mechanistic implications of these findings are discussed. Finally, processing a natural gas feed over Zn-ZSM-5 gave higher C₅₊ yields over CH₄ feed but these yields were not improved over previously published results using HZSM-5.