The orthorhombic/monoclinic transition in single crystals of zeolite ZSM-5

X-ray photographs of single crystals of zeolite H-ZSM-5 (Si_11.96Al_0.04H_0.04O₂₄) at different temperatures are presented. The reversible orthorhombic/monoclinic transition, previously observed with XRD and ²⁹Si m.a.s. n.m.r. on powder samples of H-ZSM-5, is confirmed. Upon cooling, the orthorhombic H-ZSM-5 single crystal changes into an aggregate of monoclinic twin domains. The directions of a and c in the orthorhombic single crystal and in the monoclinic twinned crystal (a ≈ 90.5°) are identical. The deviation of α from 90° can be ascribed to a mutual shift of successive (010) pentasil layers along c, induced by a distortion or rotation of the T₄ and T₆ rings interconnecting the layers. The space group of the monoclinic phase most probably is P₁²n11.     

Crystallization kinetics of zeolite ZSM-5

Zeolite ZSM-5 was synthesized from aluminosilicate gels in the presence of organic templates — tetrapropylammonium bromide (TPABr) and pyrrolidine (Py) — at temperatures of 423, 438 and 453 K. Nucleation and crystallization processes were subjected to a detailed kinetic analysis. The nucleation region is subdivided into two periods: induction and transition ones. Values of nucleation energy and crystallization energy, preexponential factor, rate of crystallization, and geometric factor have been calculated. Correlations between the estimated kinetic characteristics were found. The activation energy and the preexponential factor for the transitional and crystal-growth periods have the character of a kinetic compensation effect. The mechanism of the crystallization process is discussed on the basis of the kinetic features and correlations.     

Synthesis of ZSM-5 zeolite composite membranes for CO2 separation

ZSM-5 type zeolites were synthesized by the hydrothermal treatment of the reaction mixture of silica sol, aluminum nitrate, sodium hydroxide, and TPABr at the temperature range of 150–180 °C in the autoclave. The shape of the ZSM-5 zeolite calcined at 450 °C was spherical or polyhedral and its crystalline size was 0.5–3 m. The synthetic ZSM-5 was found to be highly hydrophobic and active for CO₂ adsorption. ZSM-5 zeolite composite membranes supported with porous -alumina tubes have been synthesized by dip coating or pressurized coating of the reaction sol-mixture followed by hydrothermal treatment. The permeation mechanism of CO₂ through ZSM-5 membranes was a surface diffusion and the membranes prepared by the pressurized-coating hydrothermal treatment showed a fairly high CO₂/N₂ separation factor of 9.0 and a permeability of 10^–8–10^–7 mol/m² ·s·Pa at room temperature.     

Steaming of ZSM-5 zeolite film

The change in morphology of the ZSM-5 zeolite films during steaming at 443 K was studied. The crystal growth of zeolite, 5–10 μm in size, from the layer of microcyrstalline ZSM-5 zeolites was first visualized by scanning electron microscopy.     

Crystallization process of zeolite ZSM-5 and zeolite ZSM-35 in a special autoclave

By use of a special autoclave, the crystallization process of the dehydrated amorphous gels was studied in the Na₂OAl₂O₃SiO₂⁻ ethylenediamine (EDA) — triethylamine (Et₃N) — H₂O system. In one run, zeolites ZSM-5 and ZSM-35 can be simultaneously synthesized at different areas of the autoclave. The data demonstrate that Gabelica's hypothesis (Gabelica, Z., Blom, N. and Derouane, E.G.Appl. Catal. 1983,5, 227) could be correct at some conditions.     

调控晶粒尺寸合成高渗透ZSM-5沸石膜

用原位水势合成法,在170℃下通过调控不同的晶粒尺寸在α-Al2O3陶瓷管上合成ZSM-5沸石膜,用XRD,SEM对膜进行表征,表明生成致密的ZSM-5沸石膜;对膜进行单气体渗透量测试,膜的H2渗透量3.69×10-6mol/(m2·s·Pa),H2/C3H8的理想分离因子为25 6.     

Crystallization of ZSM-5 zeolite under microgravity

Crystal growth of ZSM-5 zeolite under microgravity was carried out using a Soviet reentry system. The space-grown zeolite was composed of grains of uniform shape and size (ca. 10 μm). Most of zeolite grains were linked with each other by the edge of the grain. The electron diffraction of each grain showed a single-crystal diffraction pattern, indicating the presence of well-crystallized zeolite crystal. The relatively large difference in the surface Al concentration existed between different crystals of the space-grown zeolite, as compared with the zeolite crystals synthesized in the ground with stirring. Based on these results, the crystals growth of zeolite in the microgravity environment was discussed.     

Growth of larger crystals of ZSM-5 in the system 4(TPA)2O-38(NH4)2O-x(Li,Na,K)2 O-A12O3-59SiO2-750H2O

The synthesis of zeolite TPA-ZSM-5 with (NH₄)₂O/Al₂O₃ = 38 and different amounts of Li₂O, Na₂O or K₂O was studied. Kinetic crystallization data and the growth of the crystals as a function of time are reported. The results show an increment of the size of the crystals when alkali metal oxide is added to the system. With Li₂O, unusually uniform, large, lathshaped crystals of ZSM-5 ∼ 140 ± 10 μm in length were obtained. The time of nucleation is long when only (NH₄)₂O is used with TPA and decreases when alkali metal oxide is added to the system.     

ZSM—5沸石膜的合成与表征

叙述了沸石膜的发展与应用,综述了 Ｚ Ｓ Ｍ － ５ 沸石膜的合成、修饰与表征方法．制备膜最常用的方法为水热法在载体上直接就地合成．气相化学沉积法（ Ｃ Ｖ Ｄ） 、溶胶－ 凝胶法（ｓｏｌ － ｇｅｌ） 以及合成后积炭等方法被用来对膜的缺陷进行修饰．膜的表征手段为 Ｘ Ｒ Ｄ、 Ｓ Ｅ Ｍ、气体渗透等     

Synthesis of ZSM-5 zeolite of improved bulk and surface properties via mixed templates

Hydrothermally synthesized ZSM-5 zeolites using tetrapropyl-ammonium bromide (TPA-Br), Xylitol (Xy) and tetrapropyl-ammonium bromide + Xylitol templates; those compared with that of the parent having the same Si/Al molar ratio (64) and purchased from Mobil, were characterized with several physicochemical techniques including N₂ adsorption, XRD, TG/DSC, FTIR and pyridine-FTIR. The effect of various templates on the crystallinity, crystallites size, surface properties and thermal stabilities of the produced ZSM-5 were investigated. ZSM-5 synthesized using TPA-Br + Xy; of S _BET = 393 m² g^?1, exhibited a crystallinity percentage comprises of 142% when compared with that of the parent (taken at 100% crystallinity) and measured as well a crystallites size of 61 nm exceeding that derived from Xy (41 nm) that measured the lowest crystallinity percentages (71%), lowest S _BET (303 m² g^?1) and highest yield (65%) between all samples. The former sample showed high thermal stability (till 1,000 °C) when compared with that derived from TPA-Br, as illustrated from TG/DSC thermograms that provided a criteria on decreasing the pore radius as a result of enclosing appreciable amounts of TPA⁺ and Xy inside narrow pores of ZSM-5. This sample also indicated a hydrophobic tendency when compared with that devoted from TPA-Br. Pyridine adsorption measurements showed that addition of Xy to TPA-Br stimulate the existence of basic sites in addition to acidic ones (mainly Brönsted ones) that was in the middle between that derived from Xy and TPA-Br templates. More infomations on the textural properties, morphologies, vibrational tetrahedral co-ordination T(Si or Al)–O modes and acidity were evaluated and discussed.     

Synthesis and characterization of CeO2 supported ZSM-5 zeolite for organic dye degradation

Journal of Materials Science: Materials in Electronics - ZSM-5:CeO2 nanocomposites were prepared by two-step hydrothermal method in combination with the wet impregnation method. The synthesized...