Eco-friendly synthesis of high silica zeolite Y with choline as green and innocent structure-directing agent

Zeolite synthesis in contemporary chemical industries is predominantly conducted using organic structure‐directing agents(OSDAs),which are chronically hazardous to humans and the environment.It is a growing trend to develop an eco‐friendly and nuisanceless OSDA for zeolite synthesis.Herein,choline is employed as a non‐toxic and green OSDA to synthesize high silica Y zeolite with SiO2/Al2O3 ratios of 6.5–6.8.The prepared Y zeolite samples exhibited outstanding(hydro)thermal stability at ultrahigh temperature owing to the higher SiO2/Al2O3 ratio.The XRF,SEM,29Si‐NMR and 13Na+results suggested that choline plays a structure‐directing role in the synthesis of Y zeolite,while the feed molar fraction of Na+is a crucial determinant for the framework SiO2/Al2O3 ratio and the crystal morphology.

Organotemplate-free Hydrothermal Synthesis of SUZ-4 Zeolite: Influence of Synthesis Conditions

Various conditions were investigated in detail for the novel organic template-free static hydrothermal synthesis of SUZ-4 zeolite in the presence of seeds. The obtained samples were characterized by XRD （X-ray diffraction）, SEM （scanning electron microscope）, TG （thermal gravimetric analysis）, ICP （inductively coupling plasma） elemental analysis, nitrogen sorption isotherm and surface area. The results show that pure SUZ-4 zeolites with high crystallinity are obtained in a broad window of synthesis conditions： seed mass concentration 0.2%-2%, SIO2/A1203 molar ratio 21 25, KOH/SiO2 molar ratio 0.33 0.43, H20/SiO2 molar ratio 7.14-38.1, aging time 24 h, crystallization temperature 160℃, and crystallization time 6-10 d. Also, crystallinity and size of the rod-like SUZ-4 zeolite crystals are found to alter with the conditions.

Studies on the Synthesis, Properties and Preparation Methods of Zeolite ZK-4

A zeolite designated as ZK-4 was synthesized hydrothermally in the system (TMA)2ONa2O-Al2O3- SiO2- H2O at 80 - 100℃ with tetramethylammonium hydroxide as an organic templating agent. The pure zeolite ZK-4 could be prepared by using the mother liquor obtained after filtration as the source of templating agent. The effect of some synthetic conditions such as the amount of tetramethylammonium hydroxide used, n [ (TMA)2O + Na2O] /n (Al2O3) ratio, n (SiO2)/n(Al2O3) ratio and crystallization time, etc. on the crystalline phase of the product was investigated. When the following molar ratios of the reaction mixture, n (SiO2)/n (Al2O3) 4-10, n[(TMA)2O+Na2O]/ n (Al2O3 ) > 7, n (Na2O)/n (Al2O3)=0. 5-2. 0, n (H2O)/ n(A12O3)=80-450, were used, pure zeolite ZK-4 could be obtained. The synthetic products were characterized by X-ray powder diffraction, atomic absorption spectrophotometry (AAS), adsorption measurement, thermogravimetric analysis(TGA), and 29Si magic angle spinning nuclear magnetic resonance technique. Zeolite ZK-4 has a higher thermal stability than sodium zeolite A due to higher n(Si)/n(Al) ratio of zeolite ZK-4.

Insights into the Organotemplate-Free Synthesis of Zeolite Catalysts

As the most important nanoporous material, zeolites, which have intricate micropores, are essential heterogeneous catalysts in industrial processes. Zeolites are generally synthesized with organic templates under hydrothermal conditions; however, this method is environmentally unfriendly and costly due to the formation of harmful gases and polluted water. This article briefly summarizes the role of organic templates and describes designed routes for the organotemplate-free synthesis of zeolites, aided by zeolite seeds and zeolite seeds solution. Furthermore, this review explicates that the micmpore volume decreases with an increase of the Si/Al ratios in the organotemplate-free synthesis of zeolite products, where Na^＋ exists as an alkali cation. This feature is very important in directing the synthesis of zeolite catalysts with controllable Si/AI ratios under organotemplate-free conditions, and is thus important for the efficient design of zeolites.

Synthesis, characteristics of hierarchical EU-1 zeolite for xylene isomerization probe reaction

Introduced a method of synthesizing hierarchical EU-1 zeolite with organosilanes as additive, and studied the influences of following different kinds of organosilanes on the synthesis of hierarchical EU-1 zeolite: γ-glycidoxy propyl trimethoxy silane(GPTMS), N-β-(aminoethyl)-γ-aminopropyl methyl dimethoxyl silane(APAEDMS),and N-(β-aminoethyl)-γ-aminopropyl dimethoxyl(ethyoxyl) silane(TMPED). The hierarchical EU-1 samples were characterized by XRD, SEM, N_2 adsorption, FT-IR and NH_3-TPD to analyze the crystallinity, morphology, surface area, pore size distribution and acidity. The results showed that hierarchical EU-1 zeolites were successfully synthesized; organosilanes have great influence on crystal morphology of EU-1 zeolites; the exterior surface area of hierarchical EU-1 zeolite, which synthesized with organosilanes(APAEDMS) adding into synthesis system, increased by 62.1% and mesopore volume increased by 129.1% compared with conventional EU-1 zeolites, thus can reduce the diffusional restriction markedly in catalytic reaction. The catalytic performance of hierarchical EU-1zeolites were evaluated in m-xylene isomerization on fixed bed reactor. The catalytic data showed that the isomerization activity PX/X of the hierarchical EU-1 zeolites reached around 24.09% in theoretical thermodynamic equilibrium from 23.83%, and the selectivity of C_8 aromatic hydrocarbon increased from 75.16% to 84.87%. The conversion of p-xylene increased from 16.30% to 18.41%.

HYDROTHERMAL SYNTHESIS OF ZEOLITE NaA BY MICROWAVE RADIATION

In this paper,we report a novel application of microwave radiation for the synthesis of zeolite NaA in a fraction of the time required for conventional synthetic method under very mild condition.The pure product was obtained under the condition of microwave radiation in 10-20 minutes.

Synthesis and Characterization of Zeolite Hexanediamine-Theta-1

The synthesis of zeolite HXDM-Theta-1(HXDM = hexanediamine) from the reaction mixture HXDM-Al2O3-SiO2-HF-H2O is described. The formation of HXDM-Theta-1 is favoured at 150℃, and a mixture of Theta-1 and ZSM-5 is obtained at a higher temperature. The asynthesized Theta-1 was characterized by means of scanning electron micrography, thermal analysis and 13C MAS NMR techniques. Keywords Theta-1, Hydrothermal crystallization, Hexanediamine template, Thermal analysis, 13C MAS NMR

SYNTHESIS AND PROPERTIES OF A NOVEL COMPOSITE ZSM-5 ZEOLITE/VERMICULITE CATALYST

The composite ZSM—5 zeolite/vermiculite catalyst,in which tiny ZSM—5 zeolite parti- cles embedded in the vermiculite substrate,has been synthesized by hydrothermal method with vermiculite as silicon source.The catalytic behavior of resulting catalyst for xylene isomerization,propylene aromatization and toluene disproportionation is better than that of HZSM—5 zeolite.

Sputtered nano-cobalt on H-USY zeolite for selectively converting syngas to gasoline

Selectively converting CO and H2 to gasoline product （isoparaffin and olefin） in one step still remains a great challenge. We demonstrate effective H-USY zeolite supported nano-cobalt bifunctional catalysts for this catalytic reaction, which are prepared by the novel physical sputtering process. Particles of the sputtered cobalt exist in nano-level and are well-dispersed on acid USY zeolite. Easy activation of the loaded nano-cobalt is also achieved in a low-temperature hydrogen reduction atmosphere. In the tandem catalytic reaction, the sputtered bifunctional Co/USY catalyst exhibits a much higher CO conversion and higher isoparaffin selectiv- ity than the conventional impregnated one. Compared with H-Mor, H-Beta and other zeolites supported catalysts, H-USY zeolite supported cobalt catalyst shows the clearest promotional effect on the activity of FischerTropsch synthesis. The described synthesis herein provides a new pathway to solve the problem caused by the strong metal-support interaction （MSI） in heterogeneous catalysis.

Synthesis of ZSM-5 with the silica source from industrial hexafluorosilicic acid as transalkylation catalyst

A new effective process to improve the utilization of industrial fluorosilicic acid of phosphate fertilizer by-product has been investigated to comprehensive application of the silicon and fluorine source. Two-step ammoniation was applied to recover high-quality silica. The recovered silica can be used to hydrothermal synthesize ZSM-5 zeolite without impurity phase contamination, which was confirmed by XRD, TG, SEM, BET and EDS characteristic techniques. It was found that with the increase of SiO_2/Al_2O_3 ratio and the extension of reaction time, the crystal type transform from the orthorhombic to the monoclinic phase. The impurity fluorine content of the recovered SiO_2 from H_2SiF_6 has great influence on the hydrothermal process for ZSM-5 crystal structure formation.Moreover, the increase of fluorine ions content in the hydrothermal process can control the crystal morphology and size of synthesized ZSM-5. Catalytic properties of synthesized HZSM-5 with different SiO_2/Al_2O_3 ratio in transalkylation of toluene and 1,2,4-trimethylbenzene show good and stable catalytic performance. The ZSM-5 synthesized with recovered silica source exhibits similar catalyst life as the performance of small particle size HZSM-5, because the ZSM-5 synthesized with the silica source from industrial hexafluorosilicic acid prefers a thin disk crystal along the b axis direction, which shortens the diffusion distance of generated products.

Templates for the synthesis of zeolites

Though zeolites have been successfully synthesized for several decades,the roles of templates for zeolite synthesis are still not fully understood yet.Currently,many types of templates have been employed such as inorganic alkali metal ions,organic quaternary ammonium cations,organic amines,organic quaternary phosphonium cations,metal complexes and zeolite seeds,and the roles are mainly summarized into three aspects:structure-directing,space-filling and charge-balancing.In order to synthesize zeolites efficiently,the proposed principles to guide zeolite synthesis are the stabilization of energy between templates and zeolite framework,charge density mis-matching(CDM)and structure matching between zeolite frameworks and templates.The purpose of this review is to briefly summarize the progresses in recent years,clearly showing the roles of the templates for zeolite synthesis.

Surface-gel-conversion synthesis of submicron-thick MFI zeolite membranes to expedite shape-selective separation of hexane isomers

Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,we develop an advanced approach of surface gel conversion for synthesis of submicron-thick pure silica MFI(silicalite-1)zeolite membranes.Viscous gel is prepared by finely adjusting the precursor composition,enabling its reduced wettability.The unfavorable wetting of the support surface can effectively prevent gel penetration into alumina support voids.Aided by the seeds,the surface gel is directly and fully crystallized into an MFI zeolite membrane with minimal water steam.A membrane with a thickness of 500 nm is successfully acquired and it is free of visible cracks.Additionally,the as-synthesized membranes exhibit rapid and selective separation of hexane isomers by virtue of unprecedentedly high n-hexane permeance of 24.5×10^−7 mol m^−2 s^−1 Pa^−1 and impressive separation factors of 13.3-22.6 for n-hexane over its isomers.This developed approach is of practical interest for sustainable synthesis of high-quality zeolite membranes.

Designing ABC-6 family small pore zeolites by epitaxial growth approach

Aluminosilicate small pore zeolites belonging to ABC-6 family play crucially important roles in the high methanol conversion with the high selectivity of light olefins,gas separation and storage,and selective catalytic reduction of NO_(x).In this work,we report a general method,called the epitaxial growth approach,for designing ABC-6 family small pore zeolites.It is mainly realized through the epitaxial growth on the nonporous SOD-type zeolite in the presence of inorganic cations(Na^(+)and K^(+))combined with a variety of organic structure directing agents(OSDAs).In this case,a series of ABC-6 family small pore zeolites such as ERI-,SWY-,LEV-,AFX-,and PTT-type zeolites have been successfully synthesized within a few hours.More importantly,the advanced focused ion beam(FIB)and the low-dose high-resolution transmission electron microscopy(HRTEM)imaging technique have been utilized for unraveling the zeolite heterojunction at the atomic level during the epitaxial growth process.It turns out(222)crystallographic planes of the SOD-type zeolite substrate provide unique pre-building units,which facilitate the growth of targeted ABC-6 family small pore zeolites along its c-axis.Moreover,the morphologies of ERI-type zeolite can also be tuned through the epitaxial growth approach,achieving a longer lifetime in the methanol conversion.

Methane oxidation by green oxidant to methanol over zeolite-based catalysts

To reduce greenhouse gas emission from oil and gas production,it is essential to better convert methane to useful chemicals(rather) than to flare it.Conversion of methane to liquid oxygenates(mainly methanol) has attracted extensive attention and countless efforts have been made;however,running this reaction in a green,efficient,and practical way has remained elusive.The novel catalyst and oxidants play a critical role in activating methane and converting it to oxygenates(methanol).In this review,the work of commonly used oxidants for methane partial oxidation have been summarized,in which,earth abundant oxidants,O;and H;O are promising.Moreover,H;or CO can activate O;to produce H;O;that catalyzes methane partial oxidation more efficiently and selectively than O;or H;O.Therefore,the work of using reducing agent,such as CO and H;have been reviewed,focusing on rational catalyst design that features multifunction(H;O;production and CH;activation).The novel catalyst design has advanced this reaction towards practicality with green oxidants and H;using zeolites-based catalyst.Environmentally friendly zeolite preparation methods and novel two-dimensional(2 D) zeolites that can reduce waste,improve synthesis and catalytical performance substantially are also reviewed in this work to provide insights for a more comprehensive approach to meet the environment protection needs.

Zeolitic germanosilicate analogue to pharmacosiderite crystallized in an acidic medium

Zeolites are typically synthesized in alkaline or fluoride-containing near-neutral media.Sophisticated organic structure-directing agents have been investigated for such systems with the aim of discovering materials with unprecedented structures and properties for novel technical applications.In contrast,zeolite crystallization in strongly acidic media has yet to be explored.This study demonstrates that a zeolitic silicate phase crystallizes from acidic gels using trimethylamine as an organic additive with the composition 1 SiO_(2):0.3 TMA:0.3 HCl:0.15 HF:55 H_(2)O:(0.1-0.4)GeO_(2).This phase has an interrupted four-connected framework analog to the octahedron/tetrahedron-mixed framework of the mineral family pharmacosiderite.In comparison to the pharmacosiderite-type HK_(3)(Ge_(7)O_(16))(H_(2)O)_(4),the four GeO_(6)-octahedra forming the central[HGe_(4)O_(4)O_(12)]-cluster are replaced by four SiO_(4)-tetrahedra in a[Si_(4)O_(6)(OH)2.89]-unit in the new phase.However,the structure is distorted and may contain connectivity and point defects;thus,healing by the occasional incorporation of GeO_(6)-units is necessary.The refined unit cell has a cubic symmetry,space group P-43m(#215),with a=7.7005(1)Å.Acidic-medium synthesis is a useful way to find new zeolites that move in a fundamentally different direction from sophisticated organic structure-directing agents.