L-type Zeolites Research Articles

Orientation of Co2+ and Cu2+ ions introduced L-type zeolite observed with a magnetic field

L-type zeolite with Co2+ and Cu2+ ions in 3d-transition-metal ions were prepared via ion exchange. The suspension containing these zeolite was used for slip-casting under a 12 T magnetic field applied perpendicular to the substrate surface, resulting in an orientation parallel to the c-axis for Co-L and an orientation vertical to the c-axis for Cu-L. The orientation behavior was strongly affected by the magnetocrystalline anisotropy of the L-type zeolite introduced by Co2+ and Cu2+ ions. X-ray absorption fine structure and diffuse-reflectance measurements indicated that the introduced Co2+ and Cu2+ ions formed six-coordinated hydration complexes in the zeolite structure. These hydrated complexes have a distorted octahedral structure. The results suggest that the stable direction of the magnetic moment of the hydration complex at site B of L-type zeolite depends on the strain direction. The Co2+ and Cu2+ hydration complexes have different strain directions, and the difference in orientation is speculated to be due to the different stable directions of the magnetic moment within the zeolite.

Magnetic orientation behavior of L-type zeolite with rare-earth elements under low magnetic field.

The magnetic orientation of L-type zeolite ion-exchanged with various rare-earth elements was observed under a low magnetic field of 0.9 T. The orientation along the applied magnetic field was classified into three types: c-axis orientation for Ce3+, Pr3+, Nd3+, Tb3+, Dy3+ and Ho3+, ab-plane orientation for Er3+, Tm3+ and Yb3+, and random orientation for Eu3+ and Gd3+. The different orientation behavior was considered to originate from the electronic structures of the rare-earth ions introduced into the zeolite structure.

Ammonia adsorption by L-type zeolite and Prussian blue from aqueous and culture solutions

Modern regenerative medicine and pharmaceutical manufacturing require a large-scale culture of cells. Consequently, cells must be suspension-cultured at high densities, which is challenging because more metabolites, especially ammonia, are produced that inhibit cell proliferation. To address this problem, we tested four zeolites (L-type zeolite, ferrierite, mordenite, and Y-type zeolite) and Prussian blue for their ability to adsorb NH4+ (the predominant form of ammonia in a culture-solution pH) from an aqueous solution and a culture solution. The L-type zeolite and Prussian blue effectively adsorbed NH4+ from aqueous solutions, while the other absorbents were ineffective. Notably, neither adsorbent removed glucose, a representative nutrient, from the aqueous solution. Kinetics and equilibrium studies revealed that both adsorbents (L-type zeolite and Prussian blue) obey pseudo-second-order kinetics and are well fitted by the Langmuir isotherm model. The L-type zeolite also exhibited a high NH4+-adsorption in the culture solution. Further, while the L-type zeolite exhibited minimal cytotoxicity, Prussian blue was cytotoxic. Using the L-type zeolite for adsorption is simple and cost-effective, thus making it a suitable NH4+ adsorbent for culture solutions. Furthermore, reusing an expensive culture solution on a large scale can effectively lower costs of producing cell cultures intended for pharmaceutical manufacturing and regenerative medicine purposes. Thus, it is expected that this method will be used to regenerate culture solutions on a large-scale.

Selective Conversion of Glucose to 5-Hydroxymethylfurfural by Using L-Type Zeolites with Different Morphologies

In the present work, the morphology of L-type zeolite (LTL topology) has been modified in order to evaluate the influence of several protonated-form LTL-zeolites with different morphologies on their stability and catalytic performance in the conversion of glucose into 5-hydroxymethylfurfural (5-HMF). Physico-chemical characterization of the LTL-based catalysts has revealed that the three types of morphologies (needle, short rod and cylinder) are active, providing complete glucose conversion and high 5-HMF yield values. The addition of CaCl2 had a positive influence on the catalytic performance. It was found that morphology influences the textural and acid properties of LTL-zeolites, and hence their catalytic performance. The best catalytic results have been obtained with the NEEDLE-LTL, showing nanoparticles with a length of 4.46 μm and a width of 0.63 μm, which attains a 5-HMF yield of 63%, at 175 °C after 90 min of reaction, and a glucose conversion of 88%. The reusability study has revealed a progressive decrease in 5-HMF yield after each catalytic cycle. Different regeneration methods have been essayed without recovering the initial catalytic activity. The presence of organic molecules in micropores has been demonstrated by TG analysis, which are difficult to remove even after a regeneration process at 550 °C.

Koloratzaile organikoz dopaturiko L-zeolita antena material luminiszente gisa

Zientzialariek askotan naturan bertan aurkitzen dute inspirazioa aurrerakuntza zientifikoak sustatzeko. Honen adibide nabaria da fotosintesian jarritako arreta berezia, eguzki-argia eraginkortasunez xurgatu eta energia kimikoan eraldatzeko gai den prozesu konplexua. Lan honen helburua fotosintesian gertatzen den oinarrizko prozesuetako bat imitatzea da, halaber, argiaren bilketaz arduratzen dena. Horretarako, eremu espektral zabalean argia xurgatzeko gai diren material fotoaktiboak garatu dira, zeinak argi gorria igortzeko berezitasuna izango baitute. Material lumineszente hauek garatzeko, koloratzaile organiko aproposak aukeratu dira L-zeolitaren nano-kanal unidimentsionaletan barneratzeko. Konfinamendu hau ezinbestekoa da energia trukea bultzatzeko, funtsezko prozesua energiaren garraioa eta eraldaketa ahalbidetzeko. Garatutako nanomaterialak aproposak dira argia tarte espektral zabalean eraginkortasunez biltzeko (antena jarrera) eta, ondoz ondoko energia trukeari esker, bereziki argi gorria igortzeko, hainbat arlo (bio)teknologikotan aplikagarria.

Efficient visible and near-infrared photoluminescence from lanthanide and bismuth functionalized zeolite L

Herein we report the achievement of a red emission and NIR emission from a lanthanide and bismuth functionalized L-type zeolite (Ln3+/Bi3+-zeolite L, Ln = Eu, Nd) prepared by a simple ion-exchange process and subsequent annealing. Fine-grained luminescent materials have been produced via this method. The morphology and size distribution of zeolite L crystals remain almost unchanged during the synthesis process as revealed by SEM images. The morphology and particle size of the obtained luminescent materials can easily be tuned by an appropriate choice of zeolite crystals. Photoluminescence studies reveal a lifetime of 1.93 ms and a 5D0 quantum efficiency (q = 66.98%) for Eu3+ in the Eu3+/Bi3+-zeolite L. In addition, a longer lifetime of 0.196 ms for Nd3+ in the annealed Nd3+/Bi3+-zeolite L has been attained compared to values for Nd3+ in the other zeolite system.

Effects of heavy rare earth addition on properties of KL zeolite-supported platinum reforming catalyst

A series of Pt RE KL catalysts, which containing 0.8 wt% platinum and 0.2 wt% RE (RE Gd, Tb, Dy, Tm, Yb, Lu), have been prepared by impregnation of the L-type zeolite support with corresponding RE nitrate aqueous solutions. The reforming reactions of n-hexane, cyclohexane and methylcyclopentane (MCP) on Pt RE KL catalysts have been investigated with a plus microcatalytic apparatus. The surface properties and the active sites of these catalysts have also been studied with TPD, TPR and plus-CS 2 poisoning test. Our results reveal that those heavy rare earth elements added to Pt KL catalyst have effect of electronic donation to Pt particles and blocking the accumulation of active Pt particles, and thus can remarkably increase the ability of resistant sulfur poisoning and the aromatic selectivity of n-hexane or MCP conversion on the Pt KL catalyst. Studies on the relationship between the magnetic properties of catalysts and the activities as well as selectivity of catalysts show that after addition of the RE, the magnetic susceptibilities of Pt RE KL catalysts decrease dramatically compared with that of Pt KL catalyst, while catalytic properties of Pt RE KL catalysts are improved, which suggests that the unpaired electron numbers of Pt particles are decreased by RE 2O 3's giving electrons to Pt particles, therefore electronic property of catalysts is one of the most important factors affecting the activity of Pt RE KL catalysts.

Isomorphous substitution of Fe3− in zeolite LTL

Fe-modified L-type zeolites were synthesized hydrothermially, partially substituting iron atoms for the framework aluminum of L-type zeolite. Chemical analysis, XRD, SEM, IR, UV VIS DRS, EPR, XAS, TG DTA, and catalytic activity studies provided the evidence of Fe3 present in the zeolite framework. Both the lattice parameters and the unit cell volume of L-type zeolites containing Fe3 increased with increasing iron content. The change in crystal morphology was obvious from a synthesis mixture in which the molar ratio of Fe2O3Al2O3 is above 0.015. The framework IR bands were shifted to lower frequencies as Fe3 incorporation into the lattice increased, and a new Si-O-Fe bond vibration was located near 668 cm−1. The presence of a signal at g = 4.4 in the EPR spectra was assigned to Fe3 isomorphously substituted in the tetrahedral positions. EXAFS at the Fe K-edge revealed that the Fe3 ions were present in the zeolite framework in a four-fold coordination with an average Fe-O distance of 1.85 A. In the UV VIS spectra, an absorption was observed at 378.7 nm which was assigned to the presence of Fe3 in the zeolite framework. TG DTA studies indicated that Fe-modified L-type zeolite lower thermal stability than the corresponding normal L-type zeolite. A toluene alkylation study reflected the acidity strength of zeolite L being weakened due to the presence of lattice iron species.

Comparison of the acidity/site energy distribution in catalytically important zeolites

The most commonly used zeolites in various catalytic reactions are HY, rare-earth-exchanged X- and Y-type zeolites, H-mordenite (HM), L-type zeolites, and the pentasil high silica (ZSM-5, ZSM-8 and ZSM-11) zeolites. These zeolites differ very widely in their Si/Al ratios and also in their channel structures and diameters. The structural Al (i.e., tetrahedral Al) is responsible for the presence of high-strength acid sites in the zeolites. Because of their different Al contents and structures, zeolites differ widely in their acidity and consequently in their catalytic properties. In the present investigation the acidity (strong acid sites) and acid strength distributions of catalytically important zeolites HY, CeNaY, CeNaX, HKL, HM, H-ZSM-5, H-ZSM-8, and H-ZSM-11 have been compared by measuring step-wise thermal desorption of pyridine from the zeolites using the GC adsorption/desorption technique.

Synthesis of L-type zeolites: S. Li; R. Xu Jilin University Chinese 85,103,013, Sept. 10, 1986; Appl. Apr. 1, 1985

Synthesis of L-type zeolites: S. Li; R. Xu Jilin University Chinese 85,103,013, Sept. 10, 1986; Appl. Apr. 1, 1985

Heats of adsorption of CO2 and NH3 on L-type zeolites with cations of polyvalent metals

1. The replacement of Na+ ions by Ca2+, Mg2+, and La3+ ions in L-type zeolites leads to a decrease of the heats of adsorption of CO2. 2. The heats of adsorption of NH3 on (Mg, K)L zeolite are higher than on (Na, K)L zeolite in the entire range of fillings, and they are higher on (Ca, K)L and (La, K)L zeolites than on (Na, K)L only in the range of low fillings. 3. After dehydration, almost all the Ca2+ and La3+ ions should occupy screened positions in the lattice, but Mg2+ ions are located in positions where they can be drawn into interaction with the molecules being adsorbed.

An Analysis of the Vibrational Characteristics of Zeolites Using Factor Group Methods

The complete group theoretical representations for the normal modes of twelve high-symmetry zeolite crystal structures (including sodalite, offretite, and zeolite rho, as well as A, X, Y, and L-type zeolites) have been determined by factor group analysis. Comparisons of the predicted number of Raman and infrared active vibrations were made with existing experimental data in cases where such data were available. The prospects for conducting detailed analyses of the vibrational dynamics of zeolite framework structures based on the factor-group-derived representations were also examined. Much of the accepted intuitive understanding of zeolite vibrational spectra is confirmed by the findings of this work: e.g., that the number of predicted Raman and infrared frquencies (1) is consistently far greater than the number actually observed and (2) depends more on the level of symmetry of the zeolite crystal than on the number of atoms in the Bravais unit cell. Tight overlapping of frequencies, particularly those that are primarily bond stretching in nature, is to be expected.

Influence of ammonia and pyridine adsorption on Y-, L- and M-type zeolite activity in oxidative dehydrogenation of methanol

Ammonia and pyridine have different effects upon activity and selectivity of cation forms of X, Y and L-type zeolites and mordenite in methanol oxidative transformations. Ammonia is found to suppress the activity of Y and L cobalt zeolite forms and mordenite in alcohol dehydrogenation, while it does not affect their activity in oxidative reactions. Y-type zeolites with transition metal cations are promoted by ammonia for deep oxidation reactions. Pyridine increases the activity of all studied cobalt zeolite forms in oxidative dehydrogenation of methanol to formaldehyde, but the activity of mordenite diminishes in partial and deep methanol oxidation.

Application of the thermo-gas-titrimetric technique for the estimation of ammonia content in ammonium exchanged zeolites

The application of the thermo-gas-titrimetric (TGT) technique for estimating the ammonia content in ammonium X-, Y- and L-type zeolites is described. The values of ammonia content in different zeolites determined by the TGT method are in good agreement with those obtained by other conventional methods. The use of the TGT method enables one to distinguish between the ammonium ions physically adsorbed and those exchanged by the zeolite. The details of this method and its specific advantage are described in detail.

Hydrogenation of ethylene on gadolinium X, Y and L-type zeolites

It is shown that Gd-zeolites have a catalytic activity towards ethylene hydrogenation at 1 atm. This activity decreases with an increase in the SiO2/Al2O3 ratio from 2.2 to 6.1 and 4.1, i.e. upon going from an X type zeolite to Y and L. For these types of zeolite the activity grows with an increase in Gd3+ content from 50 to 80%. Oxygen addition to the reaction mixture stabilizes the catalytic activity of zeolites.

Chemistry of soil minerals. Part XII. Transformations of metakaolinite with solutions containing barium hydroxide

Metakaolinite, with or without additions of silica, readily reacts with aqueous solutions of barium hydroxide alone, of barium plus potassium hydroxides, and of barium plus tetramethylammonium hydroxides. In the range 80 to 100° barium hydroxide produced a polymorph of celsian, two unidentified zeolitic phases, Ba-T and Ba-N, and species having a structure resembling that of Lindezeolite L. From Ba(OH)2+ KOH the zeolitic phases formed were of chabazite- and L-type, together with (Ba,K)-T and the non-zeolitic polymorph of celsian. From Ba(OH)2+ N(CH3)4OH, in addition to this non-zeolite, near-erionites, L-type zeolites, and [Ba,N(CH3)4]-T were crystallised. The properties of some of the L-type zeolites have been particularly studied. They were prepared with a wide range in Si:Al ratios and in molecule sieving properties. They possessed good thermal stability, as did the H-enriched form of one of the most aluminous preparations.