Preparation and properties of an electrically heatable aluminium foam/zeolite composite

Aluminium (Al) foam/zeolite composite materials were prepared by supported zeolite crystallization of MFI-type zeolites on open cell aluminium foams. The foam fulfils the function as aluminium source for the zeolite crystallization and as support material for the resulting microcrystalline zeolite layer as well. The synthesis gel, which was added to the metallic foam contained water, a silica source and template. The zeolite crystallization was carried out at 150 °C in teflon-lined steel autoclaves under autogenic pressure. The obtained products were characterized by XRD, SEM, nitrogen adsorption measurement and X-ray computer microtomography (μ-CT). The introduction of Al into the zeolite framework was detected by thermal analysis (TG/DTA) and by energy dispersive X-ray element mapping (EDX). The electrical heating properties of the Al foam/zeolite composite material were demonstrated by contacting the sample to a power supply and subsequent increase of the power. The zeolite layer on the foam surface showed a good mechanical adherence to the support during several heating cycles.     

气相色谱法研究改性沸石材料的N_2/O_2分离性能

利用水溶液离子交换法对 1 3X ,4A和天然丝光沸石 (M)进行了Li 和Ca2 交换改性 ,并采用填充柱气相色谱法测定了改性材料的N2 /O2 分离性能。改性后X型和A型分子筛的分离性能有明显的改善 ,Ca2 改性材料的性能提高最为明显 ,其中CaX的分离度提高了 44 % ;Li 改性天然丝光沸石的分离性能也有所提高 ,分离度提高了 1 6 % ,而其Ca2 改性材料的分离性能则明显下降。利用TGA和XRD分析手段对材料进行了结构性能测定 ,并结合分子筛的结构特点对结果进行了讨论     

Methanol to olefins conversion over metal containing MFI-type zeolites

A series of metal containing MFI-type zeolites were synthesized by the rapid crystallization method with in two hours. Al(III), Cr(III), Cu (II), and Fe(III) metal ions were incorporated in the structure. Pure siliceous (Al free) MFI structured zeolite was also prepared by the same procedure as used for the metallosilicate synthesis. Si/M ratio of the synthesis gel was 100 for metallosilicates aiming for high-silica zeolites. The products have been characterized by elemental analysis, specific surface area determination, scanning electron microscopy with EDX analysis, electron spin resonance, and thermal analysis. Catalytic property of the zeolites was measured for methanol to olefin conversion reaction. The results of XRD measurement showed the only crystalline phase present was that of MFI-type zeolite. E.s.r spectroscopy has been used to study the isomorphic substitution of the metal ions incorporated in the structure. The results show that Fe(III) and Cu (II) were mainly incorporated while, Cr(III) was observed to be present in non-framework sites. The amount of template occluded into the structure was determined by thermal analysis and found to be the same for metallosilicates and highly crystalline aluminum free zeolite. The results of catalytic activity showed that about 85% selectivity (based on gaseous hydrocarbon) for C₂⁼–C₄⁼ olefin was achieved in the case of iron containing synthesized high-silica zeolite as compared with 58% in the case of Al-containing zeolite catalyst.     

Microwave synthesis of zeolites from Egyptian kaolin: Evaluation of heavy metals removal

Zeolite A and analcime were prepared using microwave method and fully characterized. Both zeolites had high surface area and sharp peak. Both zeolite types were introduced for removal of 100 mg/L of 5 metal ions. The operating conditions were optimized. Adsorption followed pseudo-first-order kinetics and fits for Langmuir, Freundlich, Dubinin–Kaganer–Radushkevich, and Temkin models. Adsorption capacities were in the order Co > V > As > Pb > Ni. Zeolite A was more efficient in metal removal than analcime due to its higher surface area. Zeolite types can be used in efficient metals removal up to more than eight cycles.     

Highly Efficient Room Temperature Synthesis of Silver‐Doped Zinc Oxide (ZnO:Ag) Nanoparticles: Structural,Optical, and Photocatalytic Properties

Synthesis of silver‐doped zinc oxide (ZnO:Ag) nanoparticles through precipitation method has been reported. The synthesis was conducted at room temperature and no subsequent thermal treatment was applied. ZnO nanoparticles were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), fourier transmission infrared spectroscopy (FTIR), and ultraviolet‐visible (UV–Vis) spectroscopy. Detailed crystallographic investigation was accomplished through Rietveld refinement. The effect of silver content on structural and optical properties of resultant ZnO nanoparticles has been reported. It was found that silver doping results in positional shifts for the XRD peaks and the absorption band edge of ZnO. These were attributed to the substitutional incorporation of Ag⁺ ions into Zn²⁺ sites within the ZnO crystal. In addition, higher silver incorporation resulted in smaller size for ZnO nanoparticles. The photocatalytic activity of the ZnO:Ag nanoparticles was also determined by methylene orange (MO) degradation studies and compared to that of undoped ZnO. Improved photocatalytic activity was obtained for ZnO:Ag nanoparticles. It has been shown that an optimum amount of silver dopant is required to obtain maximum photocatalytic activity.     

Pervaporation separation of IPA‐water mixtures through 4A zeolite‐filled sodium alginate membranes

Incorporation of zeolites into natural polymers has been shown experimentally to enhance both the flux and selectivity in pervaporative dehydration separation of organic compounds. Pervaporation is a promising membrane technique for separation of volatile organic compounds (VOCs)/water mixtures. In this study, hydrophilic sodium alginate (SA) mixed membranes were prepared using solution casting technique by incorporating zeolites into the polymer matrix. The prepared membranes were characterized by ATR‐Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), Thermal Gravimetric Analysis (TGA), and differential scanning calorimetry (DSC) were tested in a laboratory scale pervaporation experimental set‐up. The effect of experimental parameters such as the type and composition of zeolites on permeation flux and selectivity was investigated. When tested on IPA‐water mixtures, the zeolite‐filled membrane was found to give much higher selectivity. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

A study on the thermal behavior of low silica X-type zeolite ion-exchanged with alkaline earth cations

Pure and high crystalline low silica X-type zeolite with Si/Al ratio of 1 was synthesized under specific hydrothermal conditions. After preparation and characterization of Na form of the zeolite (Na-LSX) from the synthesized zeolite, Na cations were exchanged by three alkaline earth cations. The amount of the exchanged cations per 1 g of the zeolite for each cation was determined by wet chemical method. Among the various prepared samples, those containing approximately equal amount of different cations were selected and characterized by XRD, IR, and XRF techniques. TGA/DTG/DTA and XRD techniques were employed to investigate thermal behavior of the cation exchanged zeolites.     

Bactericides of coliform microorganisms from wastewater using silver-clinoptilolite rich tuffs

Wastewater-like and municipal wastewater disinfection using Mexiacan zeolites from Oaxaca and Sonora and exchanged with silver ions was investigated. The natural zeolites previously conditioned with silver ions were characterized by X-ray diffraction and electron microscopy. The elementary compositions of the silver zeolites were determined by microanalyses (Electron Dispersive Spectroscopy, EDS). E. coli and total coliform microorganisms were chosen as indicators of microbiological contamination of water following the disinfection process with silver zeolite from Oaxaca and Sonora (Ag-OZ or Ag-SZ). According to the experimental data, the coefficient of specific lethality and the decay rate were determined using the Chick–Watson and Chick models, respectively. The amount of silver in both the wastewater-like and municipal wastewater was analyzed after treatment with the silver zeolites. The disinfection kinetics seemed to be carried out in one and two steps, depending of the nature of the water in contact with silver zeolites used as bactericide. The coefficients of specific lethality show that the Ag-OZ is more efficient as a bactericide on E. coli from wastewater-like than Ag-SZ. The kinetic constants show that the decay rate of the total coliforms using Ag-OZ is higher than Ag-SZ. The amount of silver found in water after treatment varied from 0.01 to 0.50 mg/L depending on the characteristics of the natural zeolites, the nature of the water to be disinfected and the disinfection time.     

Morphology,order, light transmittance,and water vapor permeability of aluminum‐coated polypropylene zeolite composite films

In this study, the polypropylene–zeolite composite films having 2–6 wt % natural zeolite were coated with a thin film of aluminum (Al) by magnetron sputtering, and the contribution of the Al coating on film properties was investigated. The samples were characterized by EDX, X‐ray diffraction, SEM, AFM, UV–visible spectroscopy, and water vapor permeation analyses. The surface of the films coated with a smooth Al film having 98–131 nm thickness. EDX revealed that Al percentage on the surface appeared to be as 8–10 wt % indicating contribution of polymer surface under Al film to analysis. XRD analysis showed that the grain size of Al at the surface was 22–29 nm. The surface roughness increased after Al‐coating process. The transmission of coated films was very low for both UV and visible regions of the light spectrum. Permeation analysis indicated that water vapor permeation was lower for Al‐coated material. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Solid-state NMR studies of methanol-to-aromatics reaction over silver exchanged HZSM-5 zeolite

Solid-state NMR spectroscopy was used to study the conversion of methanol to aromatics (MTA) over silver exchanged HZSM-5 zeolites. It is the silver oxide rather than silver cation that plays a crucial role for the MTA reaction. The aromatic products (mainly toluene and benzene) are formed at the expense of the small alkanes (mainly propane and isobutane). AgZSM-5 zeolite calcined in air shows much higher activity and selectivity for the MTA conversion compared with AgZSM-5 zeolite calcined in vacuum or HZSM-5 zeolite. A possible reaction mechanism is proposed for the MTA conversion on the AgZSM-5 zeolite.     

降低氨氮污染的分子筛离子交换研究

采用化学分析、X射线衍射方法以及小型固定流化床反应评价,研究了分子筛剪切以及M、铵根离子对NaY分子筛的交换行为,提出了降低氨氮污染的分子筛交换技术。结果表明,M离子比铵根离子更容易交换分子筛中的钠;M在高温水热条件下对分子筛的结晶度破坏程度低于钠;分子筛粒径大小对其交换反应后氧化钠含量影响不大;在不增加分子筛的制备成本和铵盐投料量降低约50%的情况下,引进M盐交换制备的低钠含量分子筛,其结晶度和晶胞参数与传统工艺基本相当;以该技术制备的分子筛为活性组分制备的催化剂,其裂化反应性能与采用传统工艺制备的催化剂相当。     

不同晶系方沸石合成及其甲醇转化催化性能

以硅酸钠为硅源,硫酸铝为铝源,在极浓体系中合成方沸石。考察氢氧化钠用量、乙二胺用量、硅铝比和晶种对合成方沸石结构的影响,研究对甲醇转化制烯烃的催化性能。XRD结果表明,合成方沸石结构主要以立方晶系为主,还有四方晶系和正交晶系。方沸石对甲醇转化制烯烃的活性较低,甲醇最大转化率为68.2%,主要产物的收率分别为甲烷15.64%、乙烯2.81%、丙烯5.60%、C_4 11.29%、C_5 16.65%和C_6~+ 14.18%,其催化性能明显低于ZSM-5分子筛。     

Preparation of novel ZSM‐5 zeolite‐filled chitosan membranes for pervaporation separation of dimethyl carbonate/methanol mixtures

Novel mixed matrix membranes were prepared by incorporating ZSM‐5 zeolite into chitosan polymer for the pervaporative separation of dimethyl carbonate (DMC) from methanol. These membranes were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X‐ray diffraction (XRD) to assess their morphology, intermolecular interactions, and crystallinity. Sorption studies indicated that the degree of swelling for zeolite‐filled membranes increased with zeolite content in the membrane increasing and the separation selectivity of DMC/methanol was dominated by solubility selectivity rather than diffusivity selectivity. The characteristics of these membranes for separating DMC/methanol mixtures were investigated by varying zeolite content, feed composition, and operating temperature. The pervaporation separation index (PSI) showed that 5 wt % of ZSM‐5 zeolite‐filled membrane gave the optimum performance in the PV process. From the temperature‐dependent permeation values, the Arrhenius activation parameters were estimated. The resulting lower activation energy values obtained for zeolite‐filled membranes contribute to the framework of the zeolite. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Catalytic combustion of hexane over transition metal modified zeolites NaX and CaA

Hexane deep oxidation was studied over NaX and CaA zeolites modified by ion exchange with transition metals (Mn²⁺, Co²⁺, Fe³⁺), the percentage of ion exchanged, determined by ICP-MS, varying between 39 and 98%. Parent and exchanged zeolites were characterized by X-ray diffraction (XRD), N₂ physisorption, temperature-programmed reduction (TPR), oxygen and ammonia temperature-programmed desorption (TPD) and inverse gas chromatography (IGC). Catalytic activities were evaluated through the recording of light-off curves in a pulsed microreactor, catalytic activity being correlated with physicochemical properties of the solids (crystallinity, surface acidity, adsorption properties and morphological parameters). As general trend, CaA zeolites are more active than NaX zeolites. Mn-exchanged CaA zeolite was the most active catalyst for hexane oxidation, whereas the addition of Fe to the zeolites leads to strong chemical and morphological changes in the parent zeolite.     

硅源对ZSM-5分子筛合成和催化性能的影响

为了考察硅源对ZSM-5分子筛合成和催化性能的影响,分别采用白炭黑、硅胶、硅溶胶和单分散SiO₂为硅源合成ZSM-5分子筛,对合成的ZSM-5分子筛进行XRD、SEM、BET和NH₃-TPD表征,并以C₄烯烃为原料评价合成的ZSM-5分子筛的催化裂解性能。结果表明,以硅溶胶为硅源合成的ZSM-5分子筛具有较好的结晶度和催化活性。水热处理使分子筛酸量减少,孔容缩小,改善了分子筛的乙烯丙烯选择性。经600 ℃水热处理4 h的ZSM-5分子筛在常压、580 ℃和空速9 h^-1反应条件下,丁烯催化裂解为乙烯和丙烯平均转化率为90.2%,乙烯和丙烯总收率达61.1%。     

NH3-TPD and FTIR spectroscopy of pyridine adsorption studies for characterization of Ag- and Cu-exchanged X zeolites

Pure crystalline NaX zeolites with Si/Al = 1.2 is prepared by the hydrothermal method. The modification is achieved by following the conventional ion-exchange technique to obtain Ag- and Cu-exchanged forms of NaX zeolite with different metal loadings ranging from low to high exchange. Compositional and structural investigations of all samples are performed by atomic absorption spectrometry, elemental analysis, powder XRD, and nitrogen adsorption porosimetry. The acidity of all exchanged zeolites is investigated using both the ammonia temperature-programmed desorption (NH₃-TPD) carried out by microbalance, and the pyridine adsorption performed via Fourier transform infrared spectroscopy (FTIR). XRD analysis shows the global conservation of the zeolitic structure after ionic exchange. The crystallinity loss is more important for zeolites exchanged at high degree of copper. Porosity measurements indicate a decrease of the porous volumes and the specific surface areas when the Ag or Cu exchange degree is raised. Mesopores particularly appear at high exchange degree of copper. NH₃-TPD indicates that the increase of Ag and Cu-exchange degrees leads to an increase of the global acidity, which is more pronounced for Cu-exchanged zeolites. The strength of acid sites for Ag-exchanged zeolites is weaker than for Cu-exchanged zeolites. The FTIR spectroscopy analysis by pyridine adsorption confirms the formation of extra framework aluminum (EFAL) species, inducing an increase in the concentration and the strength of the Lewis acidity. The formation of EFAL is more important for Cu-exchanged zeolites.     

Niobium‐Doped Titania Photocatalyst Film Prepared via a Nonaqueous Sol‐Gel Method

Niobium‐doped Titanium dioxide (Nb:TiO₂) transparent films were successfully deposited on glass substrates using a non‐aqueous sol‐gel spin coating technique. The effect of Nb concentration on the structural and photocatalytic properties of Nb:TiO₂ films was studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV visible spectroscopy. The films with 12 at.% (atomic percent) Nb doped TiO₂ showed excellent photocatalytic activity through 97.3% degradation of methylene blue (MB) after 2 h of UV irradiation.     

Enhanced Terbium Emission Due to Plasmonic Silver Nanoparticles in Bismuth Silicate

A simple way to select a suitable host material, when doped with any rare‐earth (RE) ion and incorporated with silver nanoparticles (NPs), to cause overlap between an excitation band of the RE ions and the localized surface plasmon resonance (LSPR) of the metallic NPs to study possible plasmonic enhancement is presented using Mie theory calculations. Unlike in previous studies, plasmonic enhancement was studied in a crystalline host instead of amorphous hosts. Bismuth silicate was synthesized using the sol–gel method and successfully doped with only terbium or silver, or co‐doped with terbium and silver. The formation of silver NPs was investigated using diffuse reflectance spectroscopy, transmission electron microscopy, and Auger electron spectroscopy (AES). Luminescence properties of the terbium‐doped bismuth silicate containing silver NPs were explored in detail and an enhancement of the emission from terbium ions at 545 nm when excited at 485 nm of about 2.5 times is attributed to amplification of the electric field associated with the LSPR of the silver NPs.     

Effects of steaming-made changes in physicochemical properties of Y-zeolite on cracking of bulky 1,3,5-triisopropylbenzene and coke formation

The effects of acidic properties and structural changes of Y zeolite, produced by steaming, on the zeolite cracking activity, coking tendency and distribution of various products during catalytic conversion of bulky 1,3,5-triisopropylbenzene (TIPB) are reported. NaY zeolite with framework Si/Al ratio of 2.4 was synthesized by a hydrothermal method and ammonium exchanged. The zeolite was dealuminated by a temperature-programmed steaming to form USY1 and USY2 zeolites with framework Si/Al ratio of 8.1 and 12.3 respectively. The catalysts were characterized by XRD, XRF, SEM, AAS, NH₃–TPD and N₂ adsorption–desorption techniques. The samples were in-situ activated at 748 K and evaluated by TIPB cracking at 623 K. The coke content of the catalyst beds was estimated by TPO using an FT-IR gas cell. The results of activity measurements reveal that the dealuminated zeolites lead to lower cracking activity initially; while, they exhibit higher activity at longer times. In addition, a slight modification of the window diameter of Y zeolite, as revealed by pore size distribution analyses, alters the diffusion limitation of the reactant and products through the pores of the zeolite and significantly affects the adsorbent–adsorbate interactions. TPO experiments show that compared to the precursor zeolite, lower amount of coke is formed on the dealuminated catalysts possessing lower density of acid sites. However, the coke formed on USY samples is heavier than that formed on its precursor Y zeolite. This may be attributed to the larger pores shaped in the dealuminated catalysts which in turn provide suitable places for coke formation and growth.     

The adsorption of fatty acids from vegetable oils with zeolites and bleaching clay/zeolite blends

The adsorption of model fatty acids (hepatnoic, oleic), using spiked vegetable oils, was studied using different kinds of zeolites (A-zeolite, X, Y-zeolites, mordenite), Y-zeolite exchanged with different cations (alkali, alkaline earth, transition metal ions), and with bleaching clay/zeolite blends. The adsorption process was shown to be governed by the molecular sieving properties of the zeolites involved as well as the electrostatic field strengths of the exchange cations. Facile interparticle diffusion of cations between clay and zeolite particles in the blends was verified by electron microprobe analysis and shown to cause unexpected results with respect to bleaching and fatty acid removal.