Preparation of ZSM-12 Zeolite from RHS and Its Application for Synthesis of n-type ZnO Semiconductor Nanoparticles: A Green Chemistry Approach

White rice husk silica (RHS), an agriculture waste, was used as a silica source for ZSM-12 (MTW) zeolite synthesis. The ZSM-12 zeolite derived from RHS was prepared by hydrothermal method at 150 °C in the presence of tetraethylammonium hydroxide. Zinc oxide nanoparticles (NPs) were grown in zeolite substrates using a solid state reaction. The crystallization of ZSM-12 zeolite and ZnO/ZSM-12 nanocomposite (NC) was monitored by XRD, FTIR and SEM, TEM, and BET techniques. It was found that complete crystallization of ZSM-12 zeolite phase was achieved after 6 days. The XRD patterns declared the presence of both ZnO NPs and ZSM-12 zeolite in NC. The SEM image of ZSM-12 and NC demonstrated large spherical aggregates with size diameter of 2.5 µm. The TEM image of ZSM-12 showed formation of ZnO NPs with particle size ~?35 nm on ZSM-12 zeolite. The BET results indicated that pore volume and surface area of ZnO/ZSM-12 NC was bigger than ZSM-12 zeolite. On the basis of the obtained experimental results, it was founded that ZnO NPs were encapsulated into channels of ZSM-12 zeolite.

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Synthesis of a new molecular sieve using DABCO-based structure-directing agent

A new 1,4-diazabicyclo[2.2.2]octane (DABCO)-based quaternary ammonium compound is designed, synthesized, and used as structure-directing agent (SDA) for molecular sieve synthesis. Several 1,1′-alkylenedi(4-aza-1-azonia-2,5-dimethylbicyclo[2.2.2]octane) type SDAs are used in all-silica synthesis mixtures. Among the SDAs tested, the use of 1,1′-butylenedi(4-aza-1-azonia-2,5-dimethylbicyclo[2.2.2]octane) gives a new phase (GUS-1), whereas the use of other SDAs gives zeolite beta (^*BEA), ZSM-12 (MTW), and ZSM-5 (MFI). The GUS-1 is indexed in the orthorhombic crystal class with refined lattice constants a=16.4206(4) Å, b=20.0540(4) Å and c=5.0464(1) Å. The crystalline architecture of GUS-1 shows the same [0 0 1] projection of the framework as that of mordenite (MOR), and is characterized by a one-dimensional 12-membered ring channel system that is closely related to the channels of ZSM-12. The GUS-1 is stable to heat upon calcination at 700 °C in air. The calcined material exhibits adsorption capacity that is comparable to typical large-pore one-dimensional microporous silicates. The behavior of the SDA during synthesis is also discussed.     

Estimation of crystalline phase in ZSM-5 zeolites by infrared spectroscopy

A fast and accurate method for identification and determination of purity of Zeolite Socony Mobil 5 (ZSM-5) zeolite was developed using the IR optical density ratio of the bands at 550 and 450 cm^?1 in the mid-IR region of the structure spectra. The optical density values obtained from the proposed method, for ZSM-5 zeolite synthesized, are compared with those of the Bayer ZSM-5 zeolite used as reference material. For well-crystallized calcined ZSM-5 zeolite, this ratio is circa 0.8. This ratio is found to be less, if amorphous silicate is present in zeolite. The presence of a band at 550 cmSUP>?1 in addition to the one at 450 cm^?1 shows that ZSM-5 zeolite has been formed even if the material is X-ray amorphous. The absence of the structure-sensitive band at 550 cm^?1 unambiguously indicates that such a zeolite has not been formed.     

Effect of Calcination Temperature of Kaolin Microspheres on the In situ Synthesis of ZSM-5

ZSM-5 zeolite has been successfully synthesized in-situ on calcined kaolin microspheres by the hydrothermal method using n-butylamine as a template. The supported ZSM-5 was characterized by X-ray diffraction and scanning electron microscopy. The effect of calcination temperature of kaolin microspheres on the in-situ synthesis of ZSM-5 was investigated. The influence of the pretreatment temperature on the properties of kaolin microspheres including phase transformation, amounts of active SiO₂ and Al₂O₃, and pore structures, was studied using fourier transform infrared (FT-IR), nitrogen adsorption and chemical analysis. The results showed that when the calcination temperature increased from 300 to 900 °C, the amount of active SiO₂ in the kaolin microspheres increased slightly and the amount of active Al₂O₃ initially increased rapidly and then decreased steadily. The surface area and pore volume of the kaolin calcined at both low and high temperatures was less than those of kaolin calcined at a medium temperature. The property changes of kaolin caused the relative crystallinity of in situ synthesized ZSM-5 to vary.     

TEABr directed synthesis of ZSM-12 and its NMR characterization

Synthesis of ZSM-12 using tetraethylammonium bromide (TEABr) as the template was investigated. Among the various parameters that affect the crystallization of ZSM-12, aluminum content of the gel, OH⁻/SiO₂ and TEA/SiO₂ ratios were the important determinants. Systematic variations of these parameters revealed that the TEABr-assisted synthesis had many similarities to the synthesis using TEAOH template reported earlier, with the exception that the OH⁻/SiO₂ ratios had to be maintained at lower values. Furthermore, the OH⁻/SiO₂ ratios favorable for ZSM-12 formation lie in a very narrow range. The source of alkalinity also affected the rate of crystallization and the composition of the product. The crystallization was found to be faster and better incorporation of aluminum in the zeolite framework was obtained when NaOH was used to provide alkalinity rather than KOH. Successful synthesis of highly crystalline ZSM-12 samples with Si/Al ratio around 30 was achieved using a minimal amount of relatively inexpensive TEABr (TEA/SiO₂=0.125).

Aluminum-27 NMR spectroscopy unambiguously revealed that all aluminum atoms are incorporated in the zeolite framework in tetrahedral coordination. The NMR line-widths of aluminum signals of the calcined samples were significantly larger than those with template incorporated samples. Spin-lattice relaxation times, conventional and rotating frame, as well as magic angle spinning (MAS) cross-polarization data with variable contact time support that there is a significant proton reservoir in the aluminum framework. The NMR data indicate that many distorted tetrahedral sites are formed upon removal of the template and some of these sites contain Al–OH moieties.     

Sn-ZSM-12, a new,large pore MTW type tin-silicate molecular sieve: synthesis,characterization and catalytic properties in oxidation reactions

A new large pore tin-silicate analogue of zeolite ZSM-12 (MTW topology) with Si/Sn molar ratio >70 has been synthesized hydrothermally using a new template, hexamethylene bis(benzyl dimethyl ammonium hydroxide). This material exhibits an expansion in unit cell volume (XRD), an IR band at 970 cm^–1 and a charge transfer band at 205 nm in the UV-Vis region indicating the presence of Si-O-Sn units with Sn⁴⁺ centers in T_d configuration. Sn-ZSM-12 catalyzes the oxidation of phenol,m-cresol andm-xylene using dilute H₂O₂ as an oxidizing agent.     

Influence of the calcination treatment on the catalytic properties of hierarchical ZSM-5

The effect of the calcination conditions on the properties and catalytic performance of hierarchical ZSM-5 zeolite has been investigated using different reactions as catalytic tests: acylation of aromatic substrates and rearrangement of linear and cyclic epoxides. The hierarchical h-ZSM-5 material was prepared by crystallization of silanized protozeolitic units. The removal of the organics present in the as-synthesized ZSM-5 samples has been carried out using two different calcination procedures: (i) directly under air atmosphere; (ii) following a two-step (nitrogen-air) treatment.Clear differences are noticed related to the textural properties of the ZSM-5 samples, since the h-ZSM-5 presents higher BET and external surface area than standard ZSM-5 zeolite. Whereas the calcination method does not affect the properties of the reference ZSM-5 sample, noticeable changes were observed over the hierarchical zeolite. The concentration of Brønsted acid sites decreases by half for one-step air calcination, but only a quarter when using a two-step nitrogen/air calcination, showing that the aluminium present in hierarchical ZSM-5 is very sensitive to the calcination conditions as it may undergo framework extraction and dehydroxylation phenomena. For all the studied reactions, the hierarchical sample, calcined by a two-step treatment, presents higher activity than when using direct air calcination.     

二次水热合成法制备ZSM-5分子筛膜及其渗透汽化性能

采用二次水热合成法在管状多孔莫来石支撑体上制备高耐酸性ZSM-5分子筛膜,系统地研究分子筛晶种和合成溶胶中H₂O/SiO₂摩尔比率对ZSM-5分子筛膜生长与渗透汽化性能的影响,采用X射线衍射、冷场扫描电子显微镜和电子能谱等表征技术分别对制备的ZSM-5分子筛及其ZSM-5分子筛膜的结构、形貌和Si/Al比进行表征。针对分离75℃、90% HAc/H₂O的水溶液,最优化条件下制备的ZSM-5分子筛膜表现出优良的渗透汽化性能,渗透通量和分离因子分别为0.98kg/(m²·h)和890。此外,本研究所采用制备耐酸性ZSM-5分子筛膜的方法表现出良好的重现性,重复制备的12根ZSM-5分子筛膜在75℃下分离90% HAc/H₂O的水溶液时,平均通量和分离系数分别为（0.85±0.15）kg/(m²·h)和650±290。再者,ZSM-5分子筛膜在45～75℃的温度范围内分离50%～95% HAc/H₂O水溶液时都表现出优良的渗透汽化性能。     

In-situ synthesis and catalytic activity of ZSM-5 zeolite

ZSM-5 zeolite has been hydrothermally synthesized in-situ on the external surface of calcined kaolinite in the presence of n-butylamine. This supported zeolite was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy and N₂ adsorption. Several synthesis variables were systematically investigated, including SiO₂ to Al₂O₃ ratio, pH, crystallization time, and crystallization temperature. After mixing the ZSM-5 with a Fluid Catalytic Cracking (FCC) catalyst, catalytic performance was evaluated by cracking vacuum gas oil (VGO) in a micro-fixed bed reactor. ZSM-5 addition was favorable for the production of light olefins by catalytic cracking of VGO.     

Investigation on the morphology of hierarchical mesoporous ZSM-5 zeolite prepared by the CO2-in-water microemulsion method

A series of hierarchical mesoporous ZSM-5 zeolites with different morphology were successfully synthesized by the CO₂-in-water microemulsion method, and mesoporosity was formed without organotemplate. The different synthesis conditions, including silica alumina molar ratio, stirring time and compressed CO₂ pressure, were systematically investigated to discuss the influence of these conditions on the morphology of ZSM-5 zeolite. The resulting samples were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), inductively coupled plasma (ICP) and nitrogen adsorption-desorption measurement. XRD results indicated that compressed CO₂ route for the synthesis of MFI zeolites had a fast crystallization rate and good crystallinity. SEM images showed that the ZSM-5 hierarchical mesoporous ZSM-5 zeolite had a uniform chain-like crystal morphology, whereas silicalite-1 displayed a monodisperse crystal morphology. In addition, the nitrogen adsorption-desorption measurement provided sufficient evidence for the presence of hierarchical mesopores in ZSM-5 zeolite.     

碱处理对高岭土微球上原位合成 ZSM-5分子筛的影响

以碱处理的焙烧高岭土微球（CKM）为载体,采用原位合成方法成功制备了ZSM-5分子筛。考察了碱处理条件对原位合成的影响。采用XRD、FESEM、N2吸附-脱附、NH3-TPD对合成样品进行了表征。结果表明：碱处理条件对晶化产物的化学组成、形貌结构有显著影响。7.4%（质量分数）的氢氧化钠溶液在95 ℃、1.5 h条件下处理的 CKM表面合成出纯相的ZSM-5分子筛,颗粒尺寸约为0.8~1 μm,比表面积为128 m2/g,总孔容、微孔比表面积和酸量均明显增加。     

A new <Emphasis Type="Italic">n</Emphasis>-alkane hydroisomerization catalyst modified with nanosized molybdenum carbides and its catalytic properties in diesel fraction hydroisomerization. I. Synthesis and physicochemical properties of different acidic supports for hydroisomerization catalysts

Hydroisomerization catalysts based on nanosized molybdenum carbides are developed. Such catalysts are resistant to sulfur compounds and can be used for the synthesis of waxy diesel fuels with the same characteristics as on platinum-containing catalysts. In the first part of this work, acidic supports with different types of porous structure and concentrations and strengths of Brønsted acidic sites (e.g., silicoaluminophosphate SAPO-31, zeolite ZSM-12, modified zeolite Beta, and desiliconized zeolite ZSM-5) are synthesized for a new type of catalysts. Their physicochemical properties are studied by means of adsorption, temperature- programmed desorption of ammonia (TPD-NH₃), nuclear magnetic resonance (NMR) spectroscopy, and scanning electron microscopy (SEM).     

ZSM-22分子筛的合成及其影响因素

以1,6-己二胺(DAH)为模板剂,硫酸铝为铝源,采用动态及静态合成法,分别以正硅酸乙酯、白炭黑、硅胶为硅源,对ZSM-22分子筛的合成影响因素进行了考察,并采用X射线衍射(XRD)、扫描电镜(SEM)对合成样品进行了表征.结果表明,在晶化温度为433 K、物料比n(SiO2):n(A1203):n(DHA):n(K2...     

Computational studies on the diffusion behaviour of alkylaromatics in large pore zeolites

Alkylation of aromatics over solid acid catalysts such as zeolites, has emerged in the recent past as a viable alternative to conventional Friedel–Crafts alkylation over environmentally hostile catalysts. We studied the diffusion behaviour of ethylbenzene (EB), isobutylbenzene (IBB), o-, m- and p-isobutylethylbenzene (IBEB) in various zeolites such as offretite (OFF), cancrinite (CAN), ZSM-12 (MTW) and ZSM-18 (MEI) by computational procedures. The periodic variations of interaction energy between the molecules and zeolite framework in the calculated diffusion energy profiles are used to predict the energy barrier for diffusion. We analyzed the results to understand the product selectivity in the formation of IBEB in the transalkylation/disproportionation reaction between IBB and EB. The results indicated that the zeolites with channel-like pores are more suitable than those with cage-like pores to achieve better selectivity. The zeolites with channels whose diameters are close to the dimensions of the molecules and those which do not have intersecting channels are better selective catalysts. The efficiency of shape selective production of p-IBEB in these zeolites will be in the order MEI < OFF ∼ MTW < CAN as predicted from their diffusion energy barriers. The detailed analysis of the configurations of the molecules in the most favourable and unfavourable adsorption location, indicate that the p-IBEB has favourable interaction energy in all the four zeolites with different pore architecture, compared to o- and m-IBEB except for MEI. It could be concluded that the pore architecture plays a dominant role in controlling the adsorption and diffusion characteristics of these molecules. The actual values of interaction energy themselves are indication of their adsorption behaviour inside the pores of the zeolite. This revised version was published online in June 2006 with corrections to the Cover Date.     

Organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite

A series of ZSM-5/ZSM-11 co-crystalline zeolites with various compositions and morphologies were successfully synthesized via an organic template-free hydrothermal route and characterized by XRD, XRF, SEM, NMR and N₂ adsorption/desorption technologies. The effects of raw materials and batch composition were investigated systematically. Various silicon sources can be employed in the organic template-free synthesis of ZSM-5/ZSM-11 co-crystalline zeolite, however only a few types of aluminum sources are available. This organic template-free system is favorable to the aluminum-rich zeolite. With the increase of initial SiO₂/Al₂O₃ ratio, the ZSM-5 percentage in the ZSM-5/ZSM-11 co-crystalline zeolite increases as well as the crystal size, and especially the morphology of ZSM-5/ZSM-11 co-crystalline zeolite prepared from the colloidal silica-NaAlO₂ solution system changes gradually from nano-rod aggregation, micro-spindle to single hexagon and then to twinned hexagon crystals. Moreover, Na⁺ and OH⁻ in the initial materials can promote the nucleation of the ZSM-5/ZSM-11 co-crystalline zeolite significantly and are beneficial to the formation of crystals with relatively low length/width ratio, while K⁺ postpones the crystallization process seriously.     

New synthesis technique of supported ZSM-5 using organo-alumino-silicic gels

This contribution deals with the synthesis of a silicon-rich ZSM-5 obtained from an amorphous organo-alumino-silicic gel. The gel was formed by reacting a mechanical mixture of RHA (rice hull ash), silica’s source, and of natural clinoptilolite, source of alumina, with glycerol during 2 h at 200 °C. After a maturation period of one day at 60 °C, the reaction product was hydrolyzed by a tetra-propyl-ammonium (TPA) solution and then aged for two days at 135 °C in a stainless steel autoclave. After washing and drying, the X-ray pattern showed a well crystallized ZSM-5. The textural analysis of the slowly calcined solid at 500 °C for 4 h, and the SEM micrographies evidence that the zeolite was supported on mesoporous silica. The proportion of both components depends on the tunable hydrolysis conditions.     

以TPABr为模板剂的ZSM-5分子筛膜的合成与表征

以四丙基溴化铵(TPABr)为模板剂,直接在多孔的α-A1_2O_3陶瓷管外表面,经过重复合成制得了渗透通量较大的ZSM-5沸石分子筛膜。以合成ZSM-5沸石的DTA/TGA分析结果为依据,确定了去除ZSM-5沸石膜中模板剂的热处理制度。用X R D和S E M对Z S M-5沸石分子筛膜进行了表征,膜的分离因子用单一的氢气和氮气的渗透通量的比值表示。X RD分析表明陶瓷基质表面的膜层是ZSM-5沸石晶相,S E M结果显示合成的沸石膜层晶体相互交连,形成一种连续的多晶层,厚度约10μm。H_2、N_2对分子筛膜的气体渗透表明,合成的ZSM-5沸石膜的H_2/N_2理想分离因子为2.87。     

ZSM-35沸石原位固相转化法合成过程控制

以乙二胺(EDA)为模板剂,采用原位固相转化法合成了ZSM-35沸石,并通过XRD对沸石晶化过程中的影响因素和晶化机理作了详细考察。结果表明,制备ZSM-35沸石适宜的硅铝摩尔比为21n(SiO2)/n(Al2O3)37;Na+与模板剂EDA协同作用,共同对ZSM-35沸石起着结构导向作用;延长晶化时间,ZSM-35沸石容易向ZSM-5沸石转晶,合成ZSM-35沸石合适的晶化时间为14～21 h。对晶化机理的考察表明ZSM-35沸石的合成过程具有固相机理的特征,并且由于ZSM-35沸石与ZSM-5沸石具有相同的次级结构单元,在晶化过程中容易发生转晶。     

Effect of Al content on the assembly of Al-MSU-S mesostructures: zeolite seed structure change from zeolite LZY to LTA with increasing Al content

Al-MSU-S mesoporous molecular sieve catalysts with Al contents ranging from 2.5 to 50 mol% have been prepared from “zeolite seed” solutions and C₁₆ TMABr templates. Hexagonal mesoporous structures are formed that exhibit significantly higher amounts of tetrahedrally coordinated Al than analogous Al-MCM-41 catalysts. The Al-MSU-S catalysts also possess smaller pores than corresponding Al-MCM-41 materials. Catalytic cumene cracking activity is very high over the low Al content materials (2.5 mol%), approaching that of zeolite ZSM-5, but the catalytic activity decreases with increasing Al. As the Al content is increased, the Al atoms remain tetrahedrally coordinated but become less accessible to the cumene reagent. This and knowledge of zeolite synthesis suggest the formation of zeolite seeds other than the large pore LZY, such as the small pore LTA structure.     

A Study on the Templating Ability of Diquaternary Cations for the Zeolite Synthesis in Terms of Energetics

Computer simulation of the interactions of diquaternary cations with zeolites ZSM-50, NU-87, ZSM-23 and ZSM-12 is carried out to determine the templating ability of diquaternary cations in the formation of these zeolites. The calculated energies are a measure of match between the geometry of diquaternary cations and the topology of the zeolite framework. The systematic synthesis results of Mioni et al., especially the dependence of the products on the chain lengths of diquaternary cations are rationalized quantitatively. We infer that it is consistent with the templating theory of zeolite synthesis that ZSM-12 and ZSM-23 both can be formed by more than one type of diquaternary cations.