Synthesis of high-silica CHA type zeolite by interzeolite conversion of FAU type zeolite in the presence of seed crystals (original) (raw)
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Synthesis of high silica CHA zeolites with controlled Si/Al ratio
Studies in surface science and catalysis
Zeolites with the CHA topology have been synthesized with Si/Al ratios ranging from 15 to 133. ICP-AES analysis shows that the Si/Al ratio in the material is close to linearly related to the Si/Al ratio in the reaction mixture, while powder XRD shows that the unit cell parameters decrease with increasing Si/Al ratio. The difference between the unit cell parameters for the as-synthesized and the calcined samples show that the structure directing agent sterically hinders the contraction in the c-axis direction for the as-synthesized samples. A relationship between the Si/Al ratio in the material and the a-axis has been established. The particle size of the material also shows a dependency on the Si/Al ratio of the material.
Hydrothermal synthesis of alkali-free chabazite zeolites
Journal of Porous Materials, 2020
Alkali-free siliceous CHA zeolites with a wide Si/Al ratio ranging from 11 to infinity have been synthesized in hydroxide and fluoride media using either N,N,N-Trimethyl-1-adamantammonium (TMAda), N,N,N-Dimethylethylcyclohexyl ammonium (DMECHA) cations, or a mixture thereof. TMAda, in combination with other low-cost organic templates, allowed the formation of pure silica CHA without any impurities in the synthesis gel with an H 2 O/SiO 2 ratio of 3. Single-phase crystalline pure silica CHA was produced by DMECHA within a very narrow range of H 2 O/SiO 2 ratio, and small deviations in the water content from this range led to the formation of a slightly less dense zeolite beta phase. Alkali-free siliceous CHA zeolites possessing a high crystallinity and a variety of particle sizes were successfully prepared for the first time using a low-cost DMECHA template, particularly by a direct interzeolite transformation of FAU zeolites having the same secondary building unit of double-6-rings (D6Rs). This makes DMECHA an attractive organic structure-directing agent (OSDA) for wide applications of CHA zeolites as catalysts and adsorbents.
1985
The synthesis, crystallization and structure o f heteroatom containing ZSM-5 type zeolite (M-ZSM-5) (Xu Ruren and Pang Wenqin (Plenary lecture) 27 Synthesis of ZSM-5 type zeolites i n the system (Na, K) 2 0-A1 2 0 3-Si0 2-H 2 0 without and with ΤPA Br (A. Nastro, C. Colella and R. Aiello) 39 Crystallization of ZSM-5 type zeolites from reaction mixtures free o f organic cations (Ü.M. Berak and R. Mostowicz) 47 Nature and structure o f high silica zeolites synthesized i n presence of (poly) alkyl mono-and diamines (Z. Gabelica, M. Cavez-Bierman, P. Bodart, A. Gourgue, and J.B. Nagy) 55 Factors influencing the crystal morphology o f ZSM-5 type zeolites (R. Mostowicz and J.M. Berak) 65 The influence of alkali metal cations on the formation o f silicalite in NH^OH-TBAOH systems (Tu Kungang and Xu Ruren) 73 Template variation i n the synthesis o f zeolite ZSM-5 (F.J. van der Gaag, J.C. Jansen and H.van Bekkum) 81 The synthesis o f high silica zeolites i n the absence of sodium ion
Chemistry - A European Journal, 2013
Dedicated to Professor Takashi Tatsumi on the occasion of his 65th birthday Introduction Zeolites have important applications in catalysis, adsorption, and ion-exchange processes as a result of their molecularsized micropores, which confer unique properties on these materials. [1] Over the past decade, various new zeolitic materials with either large (12-membered-ring, 12-R) or extralarge (> 12-R) micropores have been synthesized with the aid of bulky structure-directing agents (SDAs). [2-4] To date, over 200 different zeolite framework type codes (FTCs) [5] have been approved by the International Zeolite Association (IZA). The MCM-68 zeolite (FTC: MSE), first reported by researchers at Mobil Corporation in 2000, is a new type of three-dimensional zeolite with a 12 10 10-R channel system. [6] This zeolite has a characteristic structure in which a straight 12-R channel intersects two independent tortuous 10-R channels and, in addition, it possesses an 18-R 12-R supercage that is accessible only through 10-R channels. [7] These unique features of the MCM-68 zeolite have attracted attention because there are only a handful of acidic zeolites that contain three-dimensional channel systems with large pores. Zeolites of this type are known to exhibit unique acid-catalytic properties [8, 9] and are potentially useful as shape-selective catalysts for the alkylation of aromatics, [10-12] as well as for the production of propylene by naphtha cracking. [13] Their use as hydrocarbon traps has also been reported. [14] In addition, titanium-substituted MCM-68 has demonstrated performance superior to that of TS-1 ([Ti]-MFI) for the oxidation of phenol and olefins with H 2 O 2 as oxidant. [15] MCM-68 has been synthesized under hydrothermal conditions by using N,N,N',N'-tetraethyl-exo,exo-bicycloA C H T U N G T R E N N U N G [2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium diiodide (TEBOP 2+ (I À) 2) as the SDA. The gel composition window for the successful crystallization of pure MCM-68 is very narrow and the product is limited to a Si/Al molar ratio in the range of 9-12. We have previously overcome this limitation by employing the steam-assisted crystallization (SAC) method [16] to obtain a precursor of the pure silica version of the MSE topology (YNU-2P) or its stabilized microporous version (YNU-2). [17, 18] Even so, the current requirement for a crystallization period of 14 days or more during the synthesis of MCM-68 remains an important unresolved issue. Recently, however, researchers at the Universal Oil Products Company (UOP) [19] reported the synthesis of the UZM-35 zeolite, which has an identical topology to MSE but can be synthesized in only 5-9 days by using a processing temperature of 175 8C in conjunction with dimethyldipropylammonium hydroxide as the SDA. The synthesis of zeolites typically involves the conversion of an amorphous phase into a specific type of zeolite. In reality, though, the formation of a given zeolite proceeds through a process of gradual transformation. This sequential process begins with the amorphous phase, which undergoes a transition through a semi-stable form of the zeolite to the final stable zeolite product. [20, 21] This phenomenon suggests the possibility of an alternative synthetic strategy involving
Enhanced synthetic efficiency of CHA zeolite crystallized at higher temperatures
Catalysis Today, 2018
High-quality CHA zeolite is successfully synthesized by solvent-free route at 240 °C with high space-time yields (STYs) and high catalytic performance Raw materials 240 °C, 1.5h Highlight High silica CHA zeolite (S-CHA) is synthesized at higher temperatures. S-CHA has very high space-time yields. The key to successful high-temperature synthesis of S-CHA is solvent-free route. Organic template is stable up to 240C under solvent-free conditions.
Progress in zeolite synthesis promotes advanced applications
Microporous and Mesoporous Materials, 2014
This article outlines the importance of zeolite synthesis and their unique physicochemical characteristics promoting advanced applications. The main strategies for preparation of zeolites including organic-template assisted, organic-template free and alternative procedures are considered for synthesis of crystallites offering control and fine-tuning of their properties. Besides, rational design of zeolites with pre-determined structure, porosity, size, morphology, and composition are more viable by studying carefully the chemical and physical parameters controlling the zeolite synthesis and understanding the crystallization mechanism. Finally, a particular attention to the preparation of zeolites with nanosized dimensions and their utilization in innovative applications including photovoltaic, medicine and holographic sensors are presented.
Journal of Crystal Growth, 2011
Hydrothermal conversion of Faujasite-type (FAU) zeolite into Levynite (LEV) zeolite without the use of an organic structure-directing agent (OSDA) was successfully achieved in the presence of non-calcined seed crystals. The interzeolite conversion depended strongly upon the alkalinity (OH À /SiO 2 ) of the starting gel, the Si/Al ratio of the starting FAU zeolite and the type of alkaline metal employed. Successful conversion of FAU zeolites into pure LEV zeolite was achieved only for FAU zeolites with Si/Al ratios in the range of 19-26, under highly alkaline conditions (OH À /SiO 2 ¼0.6) by using NaOH as an alkali source. Although the yield of LEV zeolite prepared by this method was lower (18-26%) than that of the conventional hydrothermal synthesis with the use of SDA, the obtained LEV zeolite exhibited a unique core/shell structure.
LTA and FAU zeolites were successfully synthesized from a Venezuelan sodium silicate solution, by hydrothermal crystallization under autogenous pressure at 100 °C, with 2 – 24 h crystallization times. The synthesized materials were characterized by XRD, BET specific surface area and SEM. A series of synthesis tests were performed to study the influence of the molar composition of the starting mixture over zeolites crystallization. The effect of crystallization time for a particular synthesis mixture composition was studied for both zeolites types. The reuse as alkaline medium of the mother liquor separated during filtration, and the effect of the aging before crystallization were additionally studied. The experimental results are in agreement with the crystallization mechanism proposed for zeolites synthesis in liquid phase. The use of a 2SiO 2 :Al 2 O 3 :6.Na 2 O:240H 2 O synthesis mixture composition allows obtaining LTA zeolite within 2 h of crystallization. For FAU zeolite, no aging period was needed when starting with a 4SiO 2 :Al 2 O 3 :6.6Na 2 O:264H 2 O composition. It was possible to synthesize both zeolites with high purity and crystallinity and with adequate water adsorption properties.
Microporous and Mesoporous Materials, 2009
The highly crystalline and pure LEV zeolite was obtained from the hydrothermal conversion of FAU zeolite as a crystalline aluminosilicate source in the presence of choline hydroxide. As LEV zeolite was not obtained from a conventional amorphous aluminosilicate gel, the advantage and uniqueness of the hydrothermal conversion of FAU zeolite was proven. The hydrothermal conversion of FAU zeolite into LEV zeolite depended significantly upon the Si/Al ratio of the starting FAU zeolite. Only the FAU zeolites with Si/Al ratios of 16-22 were converted into LEV zeolite. Most of all choline species as a SDA existed intact in zeolitic pores. As expected, the protonated LEV zeolite exhibited a good performance for conversion of ethanol to light olefins. The product yields were 35.8% of C 2 H 4 and 34.4% of C 3 H 6 .
Chemistry
The study on the synthesis of zeolites, including both the development of novel techniques of synthesis and the discovery of new zeolitic frameworks, has a background of several decades. In this context, the application of organic structure-directing agents (SDAs) is one of the key factors having an important role in the formation of porous zeolitic networks as well as the crystallization process of zeolites. There are various elements that are needed to be explored for elucidating the effects of organic SDAs on the final physicochemical properties of zeolites. Although SDAs were firstly used as pore generators in the synthesis of high-silica zeolites, further studies proved their multiple roles during the synthesis of zeolites, such as their influences on the crystallization evolution of zeolite, the size of the crystal and the chemical composition, which is beyond their porogen properties. The aim of this mini review is to present and briefly summarize these features as well as th...