Different Types Of Zeolites Research Articles

Biodiesel production from waste oils by using lipase immobilized on hydrotalcite and zeolites

In this work, hydrotalcite and four different types of zeolites were used as immobilization metarial. The size and type of the zeolite particles did not effect the amount of protein adsorbed. It was found that hydrotalcite is more efficient than zeolites studied. The amount of protein adsorbed (Pg) on hydrotalcite 13 mg/g was higher than that of zeolite as 9 mg/g. The amount of protein adsorbed on hydrotalcite was the highest at pH 8.5 and 4 °C. The immobilization of enzyme on hydrotalcite reached steady state after 5 h. Immobilized lipase retained 36% of the initial activity at 45 °C and 14% of initial activity at 55 °C, after the seventh cycle. Immobilized lipase on hydrotalcite was found to able to catalyse the transesterification of waste cooking oil with methanol to produce methyl esters. Lipase immobilized on zeolites did not show significant yields at the same reaction conditions.

An XRD study of the effect of the SiO 2/Na 2O ratio on the alkali activation of fly ash

Soluble silica has a very significant effect on the microstructural and mechanical development of the cementitious materials produced as a result of the alkali activation of fly ash. In this study, four different alkaline solutions with different soluble silica contents were used to activate fly ash. The primary reaction product was a sodium aluminosilicate gel, while different types of zeolites appeared as minority phases. The percentage and composition of these reaction products were found to depend on both the soluble silica content present in the activating solutions and the thermal curing time. In addition, the amount of gel was observed to have a decisive effect on the mechanical strength developing in the material.

Physisorption of Hydrogen in A, X and ZSM-5 Types of Zeolites at Moderately High Pressures

The hydrogen adsorption properties and uptake capacities of the A, X and ZSM-5 types of zeolites were investigated at temperatures of 77, 195 and 293 K and pressures up to 7 MPa, using a conventional volumetric adsorption apparatus. All hydrogen adsorption isotherms were basically type I, but the maximum in isotherm, a unique feature of supercritical adsorption, was observed at high pressures of 2-5 MPa at 77 K. The isosteric heats of adsorption were determined from the isotherms and the factors that influence their variations were discussed. Different types of zeolites exhibited remarkably different hydrogen uptake, based on both the framework structure and the nature of the cations present. The highest gravimetric storage capacity of 2.55wt% was obtained for NaX-type zeolite at 4 MPa and 77 K. In CaA, NaX and ZSM-5 types of zeolites, hydrogen uptakes were proportional to the specific surface areas, which were associated with the available void volumes of the zeolites. A threshold in hydrogen adsorption observed in NaA and KA was attributed to a pore blocking effect by large cations in KA. A ratio of the kinetic diameter of adsorbate to the effective opening diameter of zeolite was used to judge the blocking effect for physisorption.

Microscopic single particle characterization of zeolites synthesized in a soil polluted by copper or cadmium and treated with coal fly ash

In the perspective of the development of new soil remediation technologies, zeolites can be directly synthesized in soil from fused coal fly ash to reduce heavy metal mobility and availability. Such a process promotes the formation of metal hydroxide/oxide precipitates which can be also occluded inside the structure of the forming minerals. In this study, different types of zeolites (zeolite X, P, and A) were synthesized by treating soil samples, artificially contaminated by high concentrations of Cu or Cd ions, with fused coal fly ash at 30 and 60 °C. The formed zeolites were characterized for their amount, structure, chemical composition and size. To accomplish this survey, besides quantitative X-ray diffraction analyses (XRD), an automated single particle analysis (ASPA) method using electron probe X-ray microanalysis (EPXMA) was employed for the first time for direct zeolite characterization in soil samples. The obtained results provide new information for assessing the role of heavy metals in zeolite crystallization in coal fly ash-treated soils. Heavy metal contamination, while not significantly hindering the zeolite formation process, can influence crystal size and preferentially drive zeolite synthesis toward the formation of sodalite unit-based zeolite X and zeolite A, even at 60 °C. The presence and nature of metal precipitate occlusions inside the forming zeolite minerals might have also favored the preferential synthesis of certain zeolitic structures.

Electro-oxidation of phenol on zeolite/graphite composite electrodes: Part 2. Influence of zeolite type and composition

In this work, the electro-oxidation of phenol was investigated by cyclic voltammetry using composite electrodes built with graphite and different types of zeolites; porous and non-porous silica were also used for comparison purposes. In part 1 of this series it was shown that a NaY/graphite composite electrode has a very good response for phenol oxidation. In this work the influence of the nature and structure of the zeolite component by using different zeolites, such as Y, Beta, ZSM5, X and A, both in their sodium and protonic forms was analysed. Among all the zeolites that were used in this study, NaY with a Si/Al ratio of 2.5 seems to produce the best results for the electrochemical oxidation of phenol, by producing a larger current and a lower oxidation potential. It was also concluded that sodium zeolites consistently show better results than acidic ones and that the increase in hydrophobicity is not advantageous either.

Hydroisomerization of n-decane over Pt/SAPO-41 catalyst

A series of SAPO-41A zeolites with different silicon contents was hydrothermally synthesized from a new route by using phosphorous acid (H 3PO 3) as a phosphorus source. They were characterized by XRD, SEM, ICP, IR and NH 3-TPD. The silicon content which was incorporated into the framework affected not only the acid sites but also the acid strength of SAPO-41A. The excellent performance of the hydroisomerization of n-decane can be obtained over SAPO-41A with proper silicon content in the framework. Bifunctional catalysts consisting of platinum supported on different types of zeolite (SAPO-41A, SAPO-41B, SAPO-11, MCM-22, Hβ) were investigated for the hydroisomerization of n-decane. Pt/Hβ and Pt/MCM-22 catalysts exhibited a higher hydrocracking activity due to their strong acid sites. The SAPO-based catalysts showed better catalytic performance for the hydroisomerization of n-decane, which can be primarily ascribed to their weaker and more suitable acid strength. Especially the SAPO-41A catalysts showed the highest hydroisomerization activity and selectivity among the SAPO-based catalysts. This is because their pore dimensions are larger than those of SAPO-11 and their grain sizes are smaller than those of SAPO-41B. Furthermore, some important variables affecting the activity and selectivity of a Pt/SAPO-41A catalyst, such as reaction parameters and metal content, were investigated. The conversion of n-decane was 84.04–92.29%, and the selectivity to isomers reached 90.50–85.30% over a 0.5 wt.% Pt/SAPO-41A3 catalyst when the reaction was performed at 310–330 °C. This can be attributed to the catalyst's suitable acid strength, distinct channel dimension, small crystal size and the proper ratio of the acid sites to the metallic sites.

Preparation of nano-gold in zeolites for CO oxidation: Effects of structures and number of ion exchange sites of zeolites

Nano-gold was prepared in different types of zeolite (Y, β and mordenite) in pH-adjusted chloroauric acid solution. The effects of the pore structures and the aluminum content on the loading of gold and on the reaction activity for CO oxidation at 0 °C were investigated. The gold loading in each zeolite was strongly related to the aluminum content; it was also affected by the structure of the zeolite. HRTEM results revealed that a few particles of gold around 1 nm in diameter were formed in the cage of Y-type zeolite with less aluminum loading (1.8 wt.%), and there was aggregation of gold species on the exterior surface of the zeolite; in contrast, more particles of gold around 1 nm were formed in Y-type zeolite with more aluminum loading (12.4 wt.%), no aggregation was observed. The results from the temperature-programmed reduction in hydrogen indicated that the gold species were reduced in the smaller pores (in β and mordenite) only at lower temperatures. Nevertheless, gold was easily sintered in the channels of β and mordenite during CO oxidation, causing severely reducing the activity. The cage-like pore in Y-type zeolite with 12.4 wt.% aluminum loading prevented the sintering of gold, and its hydrophilic surface favored the activation of gold species; therefore, this Au/Y catalyst exhibited high catalytic activity and stability for CO oxidation.

The adsorption of benzene on industrially important nanostructured catalysts (H-BEA, H-ZSM-5, and H-FAU): confinement effects

The structure of industrially important zeolitic catalysts (H-BEA, H-ZSM-5, and H-FAU) and their interactions with benzene have been investigated within the framework of our-own-N-layered integrated molecular orbital+molecular mechanics (ONIOM) approach utilizing the three-layer ONIOM scheme (B3LYP/6-31G(d,p):HF/3-21G:UFF). Inclusion of the extended zeolitic framework covering the nanocavity has an effect on adsorption properties and leads to differentiation of different types of zeolite, unlike the small cluster models which are not able to make this differentiation. The ONIOM adsorption energies of benzene on ZSM-5, BEA, and FAU zeolites are −19.23, −16.11, and −15.22 kcal/mol, respectively, which agrees well with the known adsorption trend of these three zeolites. On the other hand, the small cluster models underestimate the adsorption energies and even yield an unreasonable trend of adsorption energies (−8.09, −8.48, and −8.93 kcal/mol for ZSM-5, BEA, and FAU, respectively). With the inclusion of basis set superposition error (BSSE) and the MP2 corrections, the ONIOM3(MP2/6-31G(d,p):HF/3-21G:UFF) adsorption energies are predicted to be −18.96, −16.34, and −15.18 kcal/mol, for ZSM-5, BEA, and FAU, respectively. The last value can be compared well with the experimental data (−15.31 kcal/mol) for benzene adsorption on a FAU zeolite. The results derived in this study suggest that the ONIOM3(MP2/6-31G(d,p):HF/3-21G:UFF) scheme provides a more accurate method for investigating the adsorption of aromatic hydrocarbons on these zeolites.

Structure of adsorption complexes of water in zeolites of different types studied by infrared spectroscopy and inelastic neutron scattering

We combined the results of diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) measurements (4000–1500 cm−1) and inelastic neutron scattering (INS) (5–100 meV) to study the structure of adsorption complexes of water in zeolites of types FAU and MFI exchanged with alkali metal cations. In the case of faujasites, at relatively high water loadings we observe correlation between the position of the broad band at about 3400–3500 cm−1 arising from OH-stretching of hydrogen bonded water molecules and the basicity of framework oxygen atoms of the zeolite. This result indicates that at these water loadings a significant number of water molecules forms hydrogen bonds to framework oxygen. Temperature-programmed DRIFT studies show that depending on the type of exchanged cation (Li-LSX, NaX) the position of the band at about 3400–3500 cm−1 changes suddenly in the temperature region 400–450 K and then remains stable upon further increase of the temperature. The observed behavior is caused by the formation of smaller, more strongly bonded water-cation clusters from the large web-like structures as a significant number of water molecules is removed. Bands due to hydrogen bond stretchings (O–H⋯O) and up to three librations of water molecules are observed in the INS spectra in the regions 15–44 meV and 44–89 meV respectively. The observed shifts of the band positions for different water loadings are in agreement with the results of DRIFT studies.

Effects of the zeolite framework on the adsorption of ethylene and benzene on alkali-exchanged zeolites: an ONIOM study

The density functional theory (B3LYP/6-31G(d,p)) and our-own- N-layered integrated molecular orbital + molecular mechanics (ONIOM) approach utilizing two-layer ONIOM schemes (B3LYP/6-31G(d,p): UFF) have been employed to investigate the structures of alkali-exchanged faujasite (FAU) and ZSM-5 zeolites, and their interactions with ethylene and benzene. Inclusion of the extended zeolite framework has an effect on the structure and energetics of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM-5 and FAU), which cannot be drawn from typical small quantum clusters. The ONIOM binding energies of the Li-ZSM-5 and Li-FAU zeolites that are bound to an ethylene are −16.94 and −14.27 kcal/mol, respectively, and to a benzene are −28.78 and −19.46 kcal/mol, respectively, which agrees favorably with the known adsorption trend of these two zeolites. On the other hand, the quantum cluster models yield virtually the same binding energies for both zeolites/C 2H 4 complexes (−12.25 kcal/mol versus −12.91 kcal/mol) and even yield an unreasonable trend of adsorption energies for zeolites/C 6H 6 complexes (−11.91, −15.75 kcal/mol, for Li-ZSM-5 and Li-FAU, respectively). For the larger cation-exchanged Na-ZSM-5/C 2H 4 and Na-FAU/C 2H 4 complexes, the calculated interaction energies (−15.67 kcal/mol versus −11.83 kcal/mol) are predicted to be lower than those of smaller Li-zeolites following the conventional electrostatic trend. With the inclusion of basis set correction and the effects of the extended framework included in the ONIOM model, the interaction energy for the Na-FAU/C 2H 4 complex is predicted to be −8.65 kcal/mol, which can be compared favorably with the experimental data (8.8–9.6 kcal/mol) for ethylene adsorption on a Na-Y zeolite.

Theoretical study of the adsorption of ethylene on alkali‐exchanged zeolites

AbstractThe structures of alkali‐exchanged faujasite (X–FAU, X = Li+ or Na+ ion) and ZSM‐5 (Li–ZSM‐5) zeolites and their interactions with ethylene have been investigated by means of quantum cluster and embedded cluster approaches at the B3LYP/6‐31G(d, p) level of theory. Inclusion of the Madelung potential from the zeolite framework has a significant effect on the structure and interaction energies of the adsorption complexes and leads to differentiation of different types of zeolites (ZSM‐5 and FAU) that cannot be drawn from a typical quantum cluster model, H3SiO(X)Al(OH)2OSiH3. The Li–ZSM‐5 zeolite is predicted to have a higher Lewis acidity and thus higher ethylene adsorption energy than the Li–FAU zeolites (16.4 vs. 14.4 kcal/mol), in good agreement with the known acidity trend of these two zeolites. On the other hand, the cluster models give virtually the same adsorption energies for both zeolite complexes (8.9 vs. 9.1 kcal/mol). For the larger cation‐exchanged Na–FAU complex, the adsorption energy (11.6 kcal/mol) is predicted to be lower than that of Li–FAU zeolites, which compares well with the experimental estimate of about 9.6 kcal/mol for ethylene adsorption on a less acidic Na–X zeolite. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 333–340, 2003

Characterization of Acidic OH Groups in Zeolites of Different Types: An Interpretation of NH3-TPD Results in the Light of Confinement Effects

Ammonia TPD experiments have been carried out on protonated forms of the zeolites FAU, FER, MFI, and MOR to investigate the acid strength dependence on OH group location and Al content. Effective adsorption energy distributions are derived using a regularization method and corrected to achieve a truer measure of acid strength using nonspecific interaction energies from atomistic Monte Carlo simulations. The correction energies include all interactions not associated with the OH groups and range from 18 to 37 kJ/mol, depending on the region and the zeolite structure. In the FAU structure, we find a bimodal distribution of adsorption energies in both the supercages and the sodalite cages, with the stronger acid sites being more common in the supercages. In contrast, essentially the same acid strength for different regions in MOR is seen, though the acid strength for those sites in the side pockets may be slightly lower. For FER and MFI, the TPD gives unimodal distributions and therefore prohibits distinctio...

A simple method for determination of heats of ammonia adsorption on catalysts from thermodesorption data

The stepwise thermodesorption (TD) of NH 3 from Na and H-forms of different types of zeolites (A, Y, mordenite, erionite) was studied by the gravimetric method. The TD-experiments were carried out in the temperature range from 30 to 420°C. A correlation between the temperature of desorption and the heat of adsorption, measured calorimetrically, was discovered. It was shown that thermodesorption data can be used for a rapid estimation of heats of adsorption of NH 3 on zeolites and other acid catalysts as well as for determination of number of acid sites.

Characterizing Zeolite Acidity by Spectroscopic and Catalytic Means: A Comparison

Adsorption of H2, N2, and CO on four different protonated zeolitesH-ZSM-5, H-β, H-Y, and dealuminated H-Yat low temperatures was studied by transmission Fourier transform infrared spectroscopy. The introduction of the basic probe molecules caused a red-shift of the IR stretching bands of the zeolitic acidic OH groups. This perturbation, which is commonly interpreted as a hydrogen bonding between the acidic OH group and the adsorbate and often taken as a measure of the acidic strength, was then compared with intrinsic activities for the acid-catalyzed cracking of n-hexane previously published for the same zeolite samples. Catalytic and spectroscopic characterization of the acidity is consistent only within the same class of zeolites, e.g. comparison of differently pretreated faujasites. Spectroscopic and catalytic observations for different types of zeolites do not match perfectly, because additional effects, such as interactions of larger molecules with pore walls and the stabilization of transition state...

Adsorption of carbon monoxide on H-FAU and Li-FAU zeolites: an embedded cluster approach

The interaction of carbon monoxide with H-faujasite (H-FAU) and metal-exchange Li-FAU zeolites has been investigated by means of cluster and embedded cluster approaches at the HF/6-31G(d,p) level of theory. In the case of the protonated zeolite, the adsorption energy of the bare quantum cluster is evaluated to be −1.90 kcal/mol for the H-FAU/CO complex. Inclusion of the Madelung potential field from the zeolite framework has an effect of lengthening the OH distance, hence enhancing the binding energies of the H-FAU/CO (−3.20 kcal/mol). For adsorption of CO on the metal-exchanged zeolites, the Madelung potential was found to differentiate the different types of zeolites (ZSM-5 and FAU), that cannot be drawn from the typical 3T-quantum cluster. This finding clearly demonstrates that acidity does not depend only on the Brønsted group center, but also on the dimension of the channel where the Brønsted group is located. The adsorption energy of the embedded cluster model (−6.69 kcal/mol) lies between those of the bare quantum cluster model (−5.81 kcal/mol) and the simple naked Li(I)/CO system (−13.14 kcal/mol). Correction of the 3T cluster model to take into account the long range contribution of the electrostatic potential of the zeolite crystal is found to agree with the experimental observation.

Influence of Zeolites On The Degradation of Arabian Light Crude Oil

ABSTRACT The authors have studied the biodegradation of an Arabian Light crude oil in sterile marine water by the CUES229 marine bacteria and the BIOLEN IG30 biologic activator, both in the presence and the absence of zeolites. Two different types of zeolites, a natural one (NZ) and an artificial one (Zestek56), were used to degrade the crude in the first experiment, arising a 20% increment in the degradation in the presence of natural zeolite when compared with a similar sample without zeolites, and a 9% in the artificial zeolite. Next set of experiment were made using reactors filled with 250 g of sea water and 0.02 g of zeolite and injecting CUES 229 bacteria up to 108 cells/ml. Samples were introduced in a shaker at 110 rpm and with regulated temperature at 30-C. Time evolution of the biodegradation was deduced from gas chromatography at the time intervals 1; 7 and 15 days. Later, a similar experiment, but with BIOLEN IG30, was also made. Biodegradation of aliphatic hydrocarbons was observed –after 15 days- until the C14 fractions, using zeolites plus Biolen IG30, and until the C18 fractions, using zeolite plus CUES 229 bacteria.

The synthesis of zeolites from fly ash and the properties of the zeolite products

Fly ash produced during the combustion of powdered coal could be converted up to 45% into zeolite. By varying the experimental conditions different types of zeolite were produced, e.g. zeolite Na-P1, zeolite K-G and zeolite ZK19. By this zeolitization process the cation exchange capacity (CEC) was raised from 0.02 to circa 2.4 meq/g. Anionic heavy metals were largely extracted by the process water. Sorption experiments indicated that the selectivity series for zeolite Na-P1 is Ba>Cu>Cd≈Zn>Co>Ni. Besides cation exchange reactions, precipitation of hydroxides also played a role in the immobilization of heavy metals in the column experiments carried out. Column leaching experiments showed that relative to the original fly ash, the zeolitized fly ash has a better environmental quality. The results of the sorption experiments suggest that the zeolite product can be applied in environmental technology as an immobilizer of pollutants.

98/02372 Strength and corrosion behavior of SiC-based ceramics in hot coal combustion environments : Breder, K. and Parten, R. J. Oak Ridge Natl. Lab. [Rep.] ORNL/FMP, 1996, (ORNL/FMP-96/1, Proceedings of the Tenth Annual Conference on Fossil Energy Materials, 1996), 53–62

Fly ash produced during the combustion of powdered coal could be converted up to 45% into zeolite. By varying the experimental conditions different types of zeolite were produced, e.g. zeolite Na-P1, zeolite K-G and zeolite ZK19. By this zeolitization process the cation exchange capacity (CEC) was raised from 0.02 to circa 2.4 meq/g. Anionic heavy metals were largely extracted by the process water. Sorption experiments indicated that the selectivity series for zeolite Na-P1 is Ba>Cu>Cd≈Zn>Co>Ni. Besides cation exchange reactions, precipitation of hydroxides also played a role in the immobilization of heavy metals in the column experiments carried out. Column leaching experiments showed that relative to the original fly ash, the zeolitized fly ash has a better environmental quality. The results of the sorption experiments suggest that the zeolite product can be applied in environmental technology as an immobilizer of pollutants.

Aromatization of methane in the absence of oxygen over Mo-based catalysts supported on different types of zeolites

The catalytic performance of Mo-based catalysts supported on various zeolites has been studied for methane aromatization in the absence of oxygen in a fixed-bed continuous-flow quartz reactor, and their catalytic properties are correlated with features of zeolite structure. It was found that H-type silica–alumina zeolites, such as ZSM-5, ZSM-8, ZSM-11 and β possessing two-dimensional structure and pore diameter equaling the dynamic diameter of a benzene molecule (about 6 A) simultaneously, are fine supports for methane activation and aromatization catalysts. Among them, MoO3/H-ZSM-11 has the best activity and stability; for instance, a methane conversion of 8.0% and selectivity higher than 90% was obtained at 973 K. The catalytic performance of MoO3/H-ZSM-8 is somewhat lower than that of MoO3/H-ZSM-5, while activity of MoO3/H-β is lower than that of MoO3/H-ZSM-8. Catalysts supported on H-MCM-41 and H-SAPO-34 exhibit low activity for methane aromatization and those supported on H-MOR, H-X and H-Y give only a little amount of ethylene. Over MoO3/H-SAPO-5 and MoO3/H-SAPO-11 no hydrocarbons were detected.

Adsorption of methyl‐ethyl ketone vapor onto zeolites

Volatile organic compounds (VOCs) emitted from industries are often removed by carbon or zeolite adsorption. This study presents the adsorption capacity of methyl‐ethyl ketone (MEK) vapor (inlet concentration = 100 ∼ 1500 ppm) onto six different types of zeolites as a function of their properties including surface area, pore volume and Si/Al ratio. The results indicate that the MEK adsorption capacities depend on the type of zeolite, specifically on Si/Al ratio. The measured adsorption data fit reasonably well with Langmuir and Freundlich equations.