LTL-type Zeolite Research Articles

The Effect of Cation Exchange on the Pore Geometry of Zeolite L

Zeolites with the LTL framework topology are attractive materials for use in optoelectronics, gas adsorption and as chemical reactors. This is due to their unique, one-dimensional (1D) channel systems which are large enough to act as hosts for organic dye molecules and other guest materials. Here, we use high-resolution X-ray diffraction to show the effect of cation exchange on the pore geometry of LTL-type zeolites. The nature of the exchanging cation is shown to influence the free access diameter, volume and water content of the 12-ring (12R) channel systems. As such, cation exchange can be used to tune the molecular sieving and adsorption properties of LTL-type zeolites. This offers new possibilities for these materials in technologically relevant applications.

CHA-Type Zeolite Prepared by Interzeolite Conversion Method Using FAU and LTL-Type Zeolite: Effect of the Raw Materials on the Crystallization Mechanism, and Physicochemical and Catalytic Properties

The effect of the raw materials including parent zeolite as aluminosilicate sources and organic structure-directing agents (OSDAs) on the crystallization mechanism, and physicochemical and catalytic properties of the CHA-type aluminosilicate zeolite was investigated. For this purpose, the FAU-type and the LTL-type zeolites were used as raw material, and trymethyladamantyl ammonium hydroxide and tetraethyl ammonium hydroxide were used as OSDAs. We firstly found that the CHA-type aluminosilicate zeolite was crystallized from the combination of the LTL-type zeolite and tetraethyl ammonium hydroxide as raw materials. The crystallization behaviors were also monitored in detail. The crystallization was delayed by using the LTL-type zeolite as the starting material regardless of the type of OSDA because of the low solubility of the LTL-type zeolite compared to the FAU-type zeolite. We have found that the Al distribution in the CHA framework was dependent on the raw materials. Thus, the prepared CHA-type aluminosilicate zeolite from the LTL-type zeolite exhibited a high thermal stability and catalytic performance in the methanol to olefins reaction.

Morphological effects on catalytic performance of LTL zeolites in acylation of 2-methylfuran enhanced by non-microwave instant heating

Morphological characteristics of zeolites can have significant effects on the catalytic reactions. However, the roles of zeolite morphology on catalytic reactions, particularly Friedel-Crafts acylation of 2-methylfuran, are still not clear. Hence, LTL-type zeolites with different morphologies are prepared by using bamboo leaf bio-silica source where the zeolites are used to elucidate the morphological properties in this acylation reaction. The results show that LTL zeolites with short-rod, cylindrical, stick-like and nanosized shapes can be prepared by simply tuning the water content of the precursor hydrogels and the crystallization time. The morphological properties of LTL zeolites are also found to have pronounced influences on their surface properties (surface areas, pore volumes, number of micropore channels, textural properties) and acidity (amount, strength and type) where these properties affect their catalytic activity in acylation of 2-methylfuran under non-microwave instant heating condition. Furthermore, the influence of temperature and heating time on the kinetics of catalytic acylation of 2-methylfuran, and the catalytic comparative study between nanosized LTL zeolite and several homogeneous and heterogeneous catalysts are also discussed.

Detection of CO2 and O2 by iron loaded LTL zeolite films

Detection of oxygen and carbon dioxide is important in the field of chemical and biosensors for atmosphere and biosystem monitoring and fermentation processes. The present study reports on the preparation of zeolite films doped with iron nanoparticles for detection of CO2 and O2 in gas phase. Pure nanosized LTL type zeolite with monomodal particle size distribution loaded with iron (Fe-LTL) was prepared under hydrothermal condition from colloidal precursor suspensions. The zeolite was loaded with iron to different levels by ion exchange. The Fe-LTL suspensions were used for preparation of thin films on silicon wafers via spin coating method. The reduction of the iron in the zeolite films was carried out under H2 flow (50% H2 in Ar) at 300 °C. The presence of iron nanoparticles is proved by in situ ultra-violet-visible spectroscopy. The properties of the films including surface roughness, thickness, porosity, and mechanical stability were studied. In addition, the loading and distribution of iron in the zeolite films were investigated. The Fe-LTL zeolite films were used to detect O2 and CO2 in a concentration dependent mode, followed by IR spectroscopy. The changes in the IR bands at 855 and 642 cm–1 (Fe‒O‒H and Fe‒O bending vibrations) and at 2363 and 2333 cm–1 (CO2 asymmetric stretching) corresponding to the presence of O2 and CO2, respectively, were evaluated. The response to O2 and CO2 was instant, which was attributed to great accessibility of the iron in the nanosized zeolite crystals. The saturation of the Fe-LTL films with CO2 and O2 at each concentration was reached within less than a minute. The Fe-LTL films detected both oxygen and carbon dioxide in contrast, to the pure LTL zeolite film.

Capturing the Formation of Sub-nanometer Sized CdS Clusters in LTL Zeolite

The radiolytic preparation of sub-nanometer sized CdS clusters in LTL-type zeolite crystals in suspension is reported. The growing process of CdS in the zeolite crystals using a γ-ray irradiator (low dose rate) and a pulse electron accelerator (high dose rate) is followed by UV–vis spectroscopy. The pulse electron accelerator equipped with a transient absorption setup allowed the real-time capturing of CdS formed in the zeolite suspension. Two distinct stages during the formation of sub-nanometer sized CdS clusters in the LTL-type zeolite are identified: (i) fast formation of dispersed small oligomers exhibiting a well-defined sharp absorption peak, which is shifted from 292 to 350 nm in the course of the growth process, and (ii) formation of interconnected CdS clusters along the zeolite channels by diffusion-assisted process. Additionally, the presence of sub-nanometer sized CdS clusters in the zeolite channels is confirmed by transmission electron microscopy (TEM). The sub-nanometer sized CdS clusters formed in the LTL-type zeolite suspension exhibit good stability under hydrous conditions, and no coalesce in the presence of water is observed.

Role of Structural Similarity Between Starting Zeolite and Product Zeolite in the Interzeolite Conversion Process

GIS- and LTL- (the three capital characters indicate the framework type-code) type zeolites were obtained by organic structure-directing agent free hydrothermal conversion of FAU-type zeolite at 125 degrees C in the presence of NaOH and KOH, respectively. MOR-type zeolite was found coexisting with GIS-type when the hydrothermal conversion with NaOH was carried out at 140 degrees C. There was a common building unit consisting of four-membered ring chain such as d6r, dsc, and dcc (the three characters indicate the composite building unit-code) units present in both the starting zeolite (FAU-type zeolite) and the product zeolites (GIS- and LTL-type zeolites), which was the crucial factor for crystal growth through interzeolite conversion. In the case of severe hydrothermal synthesis conditions such as high temperature, however, the crystallization behavior was similar to that observed in conventional hydrothermal synthesis using amorphous materials because the starting zeolite was excessively decomposed. The hypothesis was confirmed by successful interzeolite conversion of *BEA- to MFI-type zeolite which shared the common composite building unit mor.

Nanosized molecular sieves utilized as an environmentally friendly alternative to antioxidants for lubricant oils

Lubricants play a significant part in current environmental considerations since they are an integral and indispensable component of modern technology. The production, application and disposal of the lubricants have to follow increasingly strict requirements for protecting the environment and living organisms. In this respect, molecular sieve (LTL type zeolite) is investigated as a potential environmentally friendly alternative to traditional antioxidant additives for lubricant oils. Accelerated oxidation experiments using pure base oil and additivated base oil in the presence of the LTL molecular sieve are carried out in parallel, and the oxidation processes are monitored by FT-IR spectroscopy, spectrophotometry, chromatography, total acid number (TAN) and Karl-Fischer titrations. The LTL molecular sieve shows the potential of slowing down the oxidation rate of the oils and also resulted in a lower rate of production of solid polymeric residues. In addition, it is demonstrated that the mode of action of the LTL molecular sieve is different in nature in comparison to the organic counterparts (original antioxidants). The LTL type molecular sieve controls the water generation, while the amount of carboxylic acids is only affected in a modest amount. Apparently during the continuous oxidation of the lubricants, the zeolite adsorbs not only carboxylic acids but also other acid products such as alcohols, ketones and aldehydes. And more importantly, the LTL type molecular sieve has a greater influence in halting the steps which lead to the polymerization of the oils.

Nanoporous copper silicates with one-dimensional 12-ring channel systems.

Exploring new channels: A range of alkali-metal copper silicates that contain double layers of silicate tetrahedra have been prepared, which contain straight 12-ring channels that are analogous to those found in LTL-type zeolites. The framework that defines the 12-ring channels is neutral and, consequently, only neutral MOH and H2O species are able to fill these channels.

The compatibility of compositional and structural features of aluminous large pore zeolites with sorption characteristics

The parent NaX and KL samples were prepared by hydrothermal crystallization and their corresponding K- and Na-exchanged forms were obtained by post-synthesis modification by conventional ion-exchange technique. NaX, NaKX, KL and NaKL samples were characterized by powder XRD, IR, low temperature nitrogen adsorption and chemical analyses. Their sorption uptake behaviour has been investigated by gravimetric method. The kinetics of sorption using different sorbate probe molecules such as water, benzene and n-hexane was measured at 298 K, at P/P0 = 0.5 for 90 minutes. All the results obtained were discussed in terms of the compositional and structural variations of the adsorbents. Lack of high dimensionality of the pore system, less openness in structure, low average framework oxygen charge and less number of accessible nonframework cations are some of the prominent factors which has resulted in reduced hydro- and organo-philicity in LTL type zeolites as compared to X-type. The size and concentration of the accessible nonframework cations were also found to influence the sorptive properties of these aluminous large pore zeolites. Among all the probe molecules, n-hexane was found to be as a promising probe for differentiating the structural peculiarities especially dimensionality of the pore system.

Synthesis and characterization of cobalt modified LTL-type zeolite

Cobalt modified LTL-type zeolite (K-CoL) was hydrothermally synthesized, partially substituting framework aluminum for cobalt atoms. The isomorphous substitution of cobalt into the zeolite structure was confirmed by XRD, TGA, UV–VIS, XPS and chemical analyses. Cobalt ions were removed together with K + following NH 4Cl exchange, indicating Co 2+ also to be present as balancing or occluded cations into the channels of K-CoL. The epoxidation of R-(+)-limonene in the presence of a sacrificial aldehyde over K-CoL yields 70.7% cis-1,2-epoxide. Besides, the activity of reused K-CoL was more stable after three consecutive runs than a Co impregnated sample containing the same amount of cobalt as in K-CoL.

Estimation by a Sorption Technique of the Amorphous Contribution in the Phases Obtained during the Hydrothermal Crystallization of LTL-Type Zeolite

Sorption techniques have been employed to estimate the amorphous contribution obtained during the progressive hydrothermal crystallization of the LTL phase from the K2O–Al2O3–SiO2–H2O system at 423 K. The curve showing the progressive depletion of the amorphous content as a function of the crystallization time exhibited an inverted sigmoidal-type shape indicative of distinct induction and crystallization stages. Samples with varying amorphous contributions were characterized by sorption uptake, XRD and chemical composition. The sorption uptake changes observed were found to be helpful in estimating the progress of the crystallization process. The influence of the amorphous contribution on the BET and Langmuir surface areas, and on the micropore void volume was examined using low-temperature nitrogen sorption methods. Estimation of the amorphous contribution by XRD has been compared with that estimated via sorption uptake using different probe molecules such as water, n-hexane, cyclohexane and benzene. The sorption uptake was found to be sensitive to the extent of amorphous content in the sample and to the characteristics of the probe sorbates. The sample with a 100% amorphous contribution as estimated by XRD methods exhibited lower values for this contribution when estimated by sorption techniques. The estimation of the amorphous contribution using benzene sorption data was found to be in excellent agreement with the amorphous contribution as estimated by XRD methods. A lower agreement was exhibited by the other sorbate probes studied.

Synthesis of OFF-type zeolite in a quasi non aqueous medium: structure directing role of p-dioxane and alkaline cations

Syntheses were performed at 150°C with the starting composition 10 SiO 2:1 Al 2O 3: a Na 2O: b A 2O: c p-dioxane: d H 2O where A represents an alkaline cation (K, Rb, Cs and Li). In the presence of potassium a pure OFF-type zeolite is obtained for a Na/K molar ratio equal to 2, independently of the p-dioxane content. The OFF-type solids were characterized by XRD, SEM 29Si and 27Al MAS NMR spectroscopy. Using 13C CP MAS NMR spectroscopy, thermal and chemical analysis, one molecule of p-dioxane was found per unit cell; it is probably trapped in the gmelinite cage (1 cage per unit cell) as a complex with sodium. Indeed, in the absence of sodium, an LTL-type zeolite free of p-dioxane crystallizes. Concerning the other alkaline cations (Rb, Cs and Li), an OFF-type material was obtained with rubidium, cesium directs the synthesis toward analcime, whereas no real structure-directing effect was observed for lithium. Indeed, in the latter case, a mixture of GIS-, MAZ-, MOR- or SOD-type zeolites was obtained.

ゼオライト合成における結晶化調整剤の影響

To get more information concerning zeolite synthesis in the presence of 1-butanol (n-BuOH), influences of the alkali metal cation and the synthesis conditions on the zeolite synthesis were investigated. It was found that highly crystalline TON (Theta-1), MER (Merlinoite) and LTL (L) type zeolites were synthesized when KOH was employed as an alkali source, whereas MFI (ZSM-5) and MOR (Mordenite)type zeolites for NaOH. Characterization of zeolites obtained was conducted using X-ray diffraction, scanning electron microscopy, FT-IR, thermal analysis, 13C and 27Al MAS NMR. From the results of FT-IR and 13C CP MAS NMR measurements of as-made zeolites, it was concluded that n-BuOH molecules were occluded in the zeolitic pores of TON and MFI type zeolites, while no n-BuOH molecules for MOR, MER and LTL type zeolites.