Nonaqueous synthesis of ZSM-35 and ZSM-5

ZSM-35 and ZSM-5 were prepared from nonaqueous systems for the first time. The kinetics of crystallization was studied. The apparent activation energy of nucleation (En) and the growth of crystal (Ec) were measured. En = 7.2 Kcal/mol; Ec = 6.2 Kcal/mol. The trinary phase diagram of ZSM-35 and ZSM-5 is illustrated. During the synthesis, the molar ratio of SiO₂/Al₂O₃ does not change in the solid phase and the aluminosilicate polyanions do not exist in the liquid phase. This is evidence of a solid-phase transformation mechanism in the synthesis of the zeolites. It can be seen from i.r. spectra that the band at about 550 cm⁻¹ increases with the increase of crystallization time, which further confirms that the procedure of crystallization of zeolite in the nonaqueous system takes place in the solid phase.     

High-temperature and short-time hydrothermal fabrication of nanostructured ZSM-5 catalyst with suitable pore geometry and strong intrinsic acidity used in methanol to light olefins conversion

High temperature hydrothermal synthesis method was developed to preparation of nanostructured ZSM-5 molecular sieves at short crystallization time. A series of catalysts were synthesized at various temperatures and crystallization times for achievement of pure ZSM-5 phase with MFI structure. The synthesized catalysts were investigated with XRD, FESEM, EDX, BET-BJH, FTIR and TPD-NH₃ techniques. The results revealed that hydrothermal synthesis conditions generally affected the nucleation rate, particle size, textural properties and acidic nature of ZSM-5 catalysts. It was found that pure ZSM-5 materials with high crystallinity could be obtained at specific crystallization conditions of about 300?°C for 1.5?h and also 350?°C for 0.5?h. Increasing the hydrothermal temperature to 350?°C and decreasing the crystallization time to 0.5?h led to the formation of small particles with high specific surface area of 392?m²/g. Furthermore, ammonia TPD spectra showed that ZSM-5(300-1.5) catalyst contained higher amount of acid sites and less acid strength compared to ZSM-5(350-0.5) catalyst. The catalytic performance of samples was studied for conversion of methanol to light olefins under different reaction conditions. Interestingly, the proper pore geometry along with the strong intrinsic acidity resulted in a tendency for excessive production of light olefins for ZSM-5(350-0.5) catalyst. The selectivity of light olefins over this catalyst was increased about 94% in the long time on stream (2100?min). Also, the possible reaction pathway for ZSM-5 synthesis at high temperatures was discussed in details.     

The synthesis of nano-sized ZSM-5 zeolite by dry gel conversion method and investigating the effects of experimental parameters by Taguchi experimental design

In this study ZSM-5 Nano particles with high crystallinity were synthesized using a dry gel conversion technique. An L9 orthogonal array of the Taguchi method was applied to investigate the effect of synthesis parameters, such as crystallization time, gel drying temperature, molar composition of template (TPAOH) and water content in the crystallization stage on crystallinity and particle size of the ZSM-5 catalyst. The products were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Beside short crystallization time, the particle sizes were considerably smaller in comparison with those prepared using the hydrothermal method. The results showed that the particle size and crystallinity increased with increasing water content and crystallization time. The effects of gel drying temperature and molar composition of template were found to be more complex, however. Comparing to hydrothermal method, ZSM-5 samples synthesized with the dry gel conversion exhibited higher selectivity to gasoline than other hydrocarbons.     

Synthesis of b-axis oriented ZSM-5 zeolite by mechanochemical-assisted quasi-solvent-free method and its MTO catalytic performance

In this paper, b-axis oriented ZSM-5 zeolite was synthesized by solvent-free method with ammonia as growth regulator. Zeolites were characterized by modern detection techniques such as XRD, SEM, BET and NH₃-TPD. The results showed that ammonia could not only promote the crystallization of ZSM-5 zeolite, but also direct the synthesis of ZSM-5 zeolite with b-axis oriented morphology, which was beneficial to enhance the selectivity of light olefins. B-axis oriented ZSM-5 zeolite did not need to be mixed and aged in aqueous solution, which could reduce the discharge of sewage, and avoided the generation of autogenic pressure in the crystallization process. Furthermore, it is consistent with the concept of environmental friendliness, which could guide the green preparation of industrial ZSM-5 zeolites.     

Influence of alkalinity on particle size distribution and crystalline structure in synthesis of zeolite beta

Influence of alkalinity (OH^-/SiO₂) on particle size distribution and crystalline structure in synthesis of zeolite beta at a short crystallization period (60 h) has been studied. The results indicate that the highest crystallinity of synthetic zeolite beta at alkalinity of 0.24, 0.35 occurs when Al₂O₃·H₂O and NaAlO₂ are respectively used as aluminium sources. At an alkalinity higher than 0.39, zeolite beta can not be obtained when Al₂O₃·H₂O is used as aluminium source. The difference of particle sizes between zeolite beta synthesized from gels of different alkalinity is 0.7–0.8 μm. The widest particle size distribution of zeolite beta synthesized occurs when the alkalinity is 0.23–0.24. Along with the increase of the alkalinity, zeolite beta synthesized changes as follows: vibration peak of 1071 cm⁻¹ by IR moves to a higher position, the framework Si/Al ratio determined by ²⁹Si MAS NMR first increases gradually and then decreases, but the change of OhAl/TdAl ratio determined by ²⁷Al MAS NMR is contrary to that of the framework of the Si/Al ratio. In addition, the Si(O⁻) site existing in the TEA-β is confirmed by NMR, and the mechanism of alkalinity influencing crystallization is discussed.     

Inactivation of external surface of mordenite and ZSM-5 by chemical vapor deposition of silicon alkoxide

The present paper describes the inactivation of the external surfaces of mordenite and ZSM-5 zeolites using chemical vapor deposition (CVD) of Si(OCH₃)₄. The external surfaces of H mordenites with different Si/Al atomic ratios, Na mordenite, and HZSM-5 were deactivated by a silica layer. The silicon concentration required for the inactivation did not depend upon the included cation and the atomic ratio of Si/Al. Si(OCH₃)₄ reacted equivalently with terminal hydroxides and acidic hydroxides.     

甲醇定向转化制二甲苯的复合分子筛ZSM-5/EU-1的合成及其应用

以硅溶胶、硫酸铝、氢氧化钠、四丙基溴化铵以及硼酸和九水硝酸铁为原料, 采用EU-1晶种, 通过水热法合成了2种含杂原子的微孔结构ZSM-5/EU-1复合分子筛。采用XRD、SEM、N2吸附–脱附和NH3-TPD对合成样品进行了表征, 并在连续流动固定床反应器上考察了该分子筛催化剂对甲醇制二甲苯反应的催化性能。结果表明: 含杂原子微孔结构的ZSM-5/EU-1复合分子筛同时具有ZSM-5和EU-1的特征衍射峰, 结晶度较好, 平均孔径明显增大, 当催化剂的酸强度和酸量增大时, 有利于甲醇芳构化趋势以及二甲苯优先扩散。B-ZSM-5/EU-1催化产物中芳烃在油相中的选择性达到84.70%; B-ZSM-5/EU-1和Fe-ZSM-5/EU-1两种分子筛催化产物的芳香烃中二甲苯的含量最高, 分别为41.32%~45.88%和33.88%~39.16%。由于B-ZSM-5/EU-1较高的酸性、酸量和相对较小的孔道内径(0.8060 nm), 较Fe-ZSM-5/EU-1更有利于产物中二甲苯的生成; 不仅如此, B-ZSM-5/EU-1复合分子筛催化产物中对二甲苯在二甲苯中选择性范围为29.75%~47.47%; 不过, Fe-ZSM-5/EU-1产物中对二甲苯在二甲苯中的含量最高可达53.75%, 这是由于Fe-ZSM-5/EU-1复合分子筛的粒径较大, 为催化反应提供了较长的孔道结构, 易使产物中邻、间二甲苯在扩散过程中异构化转化为对二甲苯的缘故。     

Seed-induced synthesis of hierarchical architectures of ZSM-5 nanocrystalline aggregates by the solid state crystallization

A seed-induced rapid synthesis of hierarchical ZSM-5 aggregates was achieved by the solid state conversion method in an inorganic system. No secondary mesoporogen was introduced to construct supplementary pore. The physical and chemical properties of the products were characterized by using XRD, SEM, TEM, XRF and N₂ adsorption–desorption techniques. The results revealed that the synthesized samples typically exhibit the uniform spherical zeolite ZSM-5 aggregates composed of loosely packed nanocrystals. It was clearly found that the morphology, mesoporosity and particle size of synthesized samples were directly affected by the type of the seed and synthesis conditions. The well-dispersed hierarchical ZSM-5 aggregates were synthesized at NaOH/SiO₂ = 0.15, 20 ≤ SiO₂/Al₂O₃ ≤ 40 with the acid of zeolite seed solution in guiding the structure. In addition, the crystal growth of zeolite samples synthesized with zeolite seed solution was studied at 433, 453, and 473 K. The results suggested that the activation energies for the induction, transition and crystallization stages were 91.44, 104.37 and 77.68 kJ?mol^?1, respectively. The method provides a cost-effective and industrially applicable route to synthesize hierarchical ZSM-5 aggregates.     

Rapid synthesis of hierarchical ZSM-5 zeolites for the reactions involving larger reactant molecules

In this study, the ZSM-5 zeolites with a high hierarchy factor were synthesized rapidly and tested for the furfural hydroxymethylation (FH) to 5-hydroxymethylfurfural (HMF). The effect of seeding techniques (STs) and templates (both soft (Cetrimonium bromide, CTAB) and hard (bio-sourced secondary template, BSST)) on the final zeolite properties were studied. A significant variation in crystallinity and morphology with the ST and type of seed was observed. The CTAB addition increased the hierarchy factor (H factor) by 3 times, and the implicit seeds decreased the hydrothermal time by 2 times. The zeolite yield, crystallinity, and pore geometry were a strong function of [CTA⁺]/[Na⁺] ratio. Slit and ink bottle-shaped pore morphologies were observed with only seed or seed + BSST and with seed + CTAB, respectively, and both exhibited the bimodal pore size distribution. The zeolites with ink bottle-shaped pores outperformed those with slit pores in the FH and showed the highest selectivity to HMF of 65%, at 34% furfural conversion. The zeolites with high H factor showed catalytic and structural stability up to 5 successive recycle runs.     

Optimization of crystal growth of hierarchical porosity ZSM-5 zeolite based on coal fly ash “waste utilization”

In this study, ZSM-5 zeolite with hierarchical porosity structure was synthesized by hydrothermal method using Al(OH)₃, SiO₂ extracted from coal fly ash as aluminum source and silicon source. The optimal synthesis parameters of ZSM-5 zeolite were determined via an orthogonal analysis table. The optimum synthesis conditions were: SiO₂/Al₂O₃/Na₂O/hexadecyltrimethylammonium bromide/tetrapropyl ammonium bromide/H₂O = 1/0.08/0.25/0.05/0.17/50, and the optimum crystallization temperature and crystallization time were 160 °C and 48 h, respectively. Scanning electron microscopy showed that the synthesized ZSM-5 zeolite exhibited a spherical shape. Nitrogen adsorption-desorption and Brunauer-Emmett-Teller measurement analysis displayed that the best sample ZSM-5 molecular sieve showed a typical type IV isotherm, and the micropores and mesopores coexisted in the sample, indicating the successful preparation of ZSM-5 zeolite with hierarchical porosity structure. The crystal growth of ZSM-5 under different hydrothermal conditions follows the “S” adjustment.     

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 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.     

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.     

海绵辅助离子液体干胶法合成ZSM-22分子筛大颗粒

采用海绵辅助的以离子液体作为结构导向剂的干凝胶转换法制备了宏观尺寸在毫米级的全硅ZSM-22沸石分子筛大颗粒, 干凝胶的制备采用了酸环境下水解含有离子液体结构导向剂的硅源的特殊方法。结果表明, 海绵辅助的离子液体干胶法对于颗粒状形貌的形成起了关键作用, 在合成过程中不加入海绵或者在传统水热合成路线中加入海绵都得不到具有这种宏观颗粒形貌的ZSM-22沸石。实验系统考察了海绵的添加量、添加时间及干胶晶化时间对合成的影响, 发现在微波老化结束后向合成体系添加适量的海绵, 有利于合成高结晶度的颗粒状全硅ZSM-22沸石。N₂O-TPD实验结果表明, 所得颗粒状ZSM-22负载氧化铜后对于N₂O的吸附能力优于后处理粘结剂成型的ZSM-22分子筛, 说明调控沸石分子筛的宏观形貌对于沸石分子筛的吸附能力具有重要作用。     

Catalytic properties and deactivation behavior of modified H-ZSM-5 in the conversion of methanol-to-aromatics

A comparative study on the effects of SiO₂ modification and mesoporous structures on catalytic performances over ZSM-5 zeolites in MTA conversion both theoretically and experimentally was done. Experimental results showed that hierarchical pores increased the production of aromatics. However, DFT calculation proved that energy barriers for producing aromatics over mesoporous ZSM-5 were larger than that of parent ZSM-5 due to decreasing acid strength after alkali treatment which significantly influenced rate-determining step. Furthermore, diffusion behaviors of toluene were studied by Molecular Dynamics. Larger pores led to the improvement of diffusion behaviors over hierarchical ZSM-5 owing to the decrease of collision frequency between molecules. Therefore, the formation of aromatics was mainly determined by diffusion limitation over hierarchical ZSM-5. The lowest BTX selectivity was obtained over SiO₂ deposited mesoporous ZSM-5 due to decreasing acid strength and blockage of pore mouth. Additionally, the deactivation of ZSM-5 serial catalysts in MTA was attributed the formation of insoluble coke. Moreover, the introduction of mesopores and silylation on external surface alleviated the deactivation of catalysts.     

Ion exchange of ammonium in natural and synthesized zeolites

In this study, zeolite Na–P and Na–Y was prepared by hydrothermal treatment of the Chinese natural clinoptilolite with NaOH. The ion exchange of NH₄⁺ into the three zeolites in the temperature range of 288–333 K was also investigated, and the thermodynamic parameters were calculated. The selectivity sequence for NH₄⁺ entering the sodium form of the three materials was Na–clinoptilolite > Na–Y > Na–P, as indicated by values of ΔG°. The results demonstrated that the Si/Al molar ratio of zeolites determined the selectivity for NH₄⁺.     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Adsorption of butyl acetate in air over silver-loaded Y and ZSM-5 zeolites: experimental and modelling studies

Adsorption behaviours of butyl acetate in air have been studied over silver-loaded Y (Si/Al=40) and ZSM-5 (Si/Al=140) zeolites. The silver metal was loaded into the zeolites by ion exchange (IE) and impregnation (IM) methods. The adsorption study was mainly conducted at a gas hourly space velocity (GHSV) of 13,000 h(-1) with the organic concentration of 1000 ppm while the desorption step was carried out at a GHSV of 5000 h(-1). The impregnated silver-loaded adsorbents showed lower uptake capacity and shorter breakthrough time by about 10 min, attributed to changes in the pore characteristics and available surface for adsorption. Silver exchanged Y (AgY(IE)) with lower hydrophobicity showed higher uptake capacity of up to 35%, longer adsorbent service time and easier desorption compared to AgZSM-5(IE). The presence of water vapour in the feed suppressed the butyl acetate adsorption of AgY(IE) by 42% due to the competitive adsorption of water on the surface and the effect was more pronounced at lower GHSV. Conversely, the adsorption capacity of AgZSM-5(IE) was minimally affected, attributed to the higher hydrophobicity of the material. A mathematical model is proposed to simulate the adsorption behaviour of butyl acetate over AgY(IE) and AgZSM-5(IE). The model parameters were successfully evaluated and used to accurately predict the breakthrough curves under various process conditions with root square mean errors of between 0.05 and 0.07.     

Study on using cellulose derivatives as pore directing agent for preparation of hierarchical ZSM-5 zeolite catalyst

Cellulose derivatives such as hydroxyethylmethylcellulose (HEMC), and hydroxypropylmethylcellulose (HPMC), which are originated from biomass, were used as mesoporous directing agent for the synthesis of hierarchical ZSM-5 zeolite. Hierarchical ZSM-5 zeolites with outstanding mesoporosity and high hierarchy factors were achieved by hydrothermal method in the presence of bio-mesoporogen. The as-synthesized hierarchical ZSM-5 zeolites were characterized by X-ray diffraction (XRD), nitrogen adsorption–desorption (BET), scanning electron microscope (SEM) to determine the structure of samples. The influences of different mesoporogens with different dosage in the synthetic process on the physicochemical and catalytic properties of hierarchical ZSM-5 zeolite were investigated. Possession of the high mesopores, high surface areas and abundant accessible acid sites, the hierarchical zeolites exhibited excellent catalytic performance in the alkylation reaction of benzene and benzyl alcohol.     

On the crystallization mechanism of zeolite ZSM-5: Part 1. Kinetic compensation effect for the synthesis with some diamines

Zeolite ZSM-5 was synthesized from the initial gel: 33 Na₂O: 44R: Al₂O₃: 100 SiO₂: 4000 H₂O: 25 H₂SO₄, where R is tetrapropylammonium bromide (TPA) and C₂, C₃, C₄, and C₆ diamines are in the temperature range 423–453 K. The kinetic analysis of the crystallization of ZSM-5 permits us to follow the role of the used templates during the consecutive steps of the process. The diminishing of the crystallization rate with the increasing of the linear dimension of the molecule is proved. A kinetic compensation effect (KCE) was established between activation energy and the preexponential factor. The obtained KCE is proof for the uniform mechanism of crystallization of zeolite with C₂, C₃, C₄, and C₆ diamines and for a different one for the synthesis with TPA.