• Applied Chemistry for Engineering
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• v.5 no.2
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• pp.361-372
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• 1994

Vanadium containing MFI type zeolites have been prepared hydrothermally or by the impregnation method with $NH_4VO_3$ solution after dealumination of HZSM-5. Incorporation of vanadium into the framework of zeolite has been demonstrated by XRD, DTA, FT-IR and ESR analyses. Upon $NH_4VO_3$ impregnation and calcination of dealuminated zeolite, vanadium substitution into the framework could be performed like a hydrothermally synthesized zeolite. Vanadium in zeolite is able to pass redox cycles at high temperatures, and it is shown that vanadium is probably fixed and atomically dispersed in the structure of zeolite. The catalytic benzene hydroxylation, hexanes and alcohols oxidation were used for evaluating the properties of vanadium incorporated MFI zeolite.

• Applied Chemistry for Engineering
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• v.18 no.5
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• pp.459-466
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• 2007

In this study, H-type beta zeolites (BEA) having various metals were used as the adsorbent for the removal of sulfur containing odorants. The different adsorbents containing single or bimetals were utilized to investigate the performance in the individual adsorption of TBM and THT odorants or in the competitive adsorption between them by using a continuous adsorptive bed system. The result shows that the pure H-type BEA zeolite exhibited the highest adsorption capacity for TBM compound, but the higher amount of THT was removed and adsorbed on a HBEA adsorbent having Fe, Pd metal and ZnO oxide. In the case of bimetal containing adsorbents, Cu-Zn/HBEA and Fe-Mo/HBEA showed a higher adsorption capacity for TBM.

• Nuclear Engineering and Technology
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• v.50 no.1
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• pp.151-158
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• 2018

The neutron powder diffractometer (NPD) is used to study a variety of technologically important and scientifically driven materials such as superconductors, multiferroics, catalysts, alloys, ceramics, cements, colossal magnetoresistance perovskites, magnets, thermoelectrics, zeolites, pharmaceuticals, etc. Monte Carlo-based codes are powerful tools to evaluate the neutronic behavior of the NPD. In the present study, MCNPX 2.6.0 and Vitess 3.3a codes were applied to simulate NPD facilities, which could be equipped with different optic devices such as pyrolytic graphite or neutron chopper. So, the Monte Carlo-based codes were used to simulate the NPD facility of the 5 MW Tehran Research Reactor. The simulation results were compared to the experimental data. The theoretical results showed good conformity to experimental data, which indicates acceptable performance of the Vitess 3.3a code in the neutron optic section of calculations. Another extracted result of this work shows that application of neutron chopper instead of monochromator could be efficient to keep neutron flux intensity higher than $10^6n/s/cm^2$ at sample position.

• Bulletin of the Korean Chemical Society
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• v.25 no.8
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• pp.1125-1129
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• 2004

This work assesses the potential of natural Analcime Zeolite as an adsorbent for preconcentration of lead (II) traces. Lead is quantitatively retained on 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol by column method with Analcime in the pH range of 5-6.5 and 2 mL $min^{?1}$ flow rate. Lead was removed from the column with 10.0 mL of 4 M hydrochloric acid and was determined by anodic stripping differential pulse voltammetry. 0.5ppb detection limit was obtained and linear dynamic range was 3 to $1.2{\times}10^5$ ppb in final solution with correlation coefficient of 0.999 and relative standard deviation of ${\pm}$ 1.2% (for eight replicate determination of 2.5 ${\mu}g\;mL^{?1}$ of lead). Various parameters such as the effect of pH, flow rate, instrumental conditions and interferences of some ions on the determination of lead have been studied in detail for optimization of conditions. The method was successfully applied for determination of lead in various samples.

• Journal of Environmental Health Sciences
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• v.45 no.6
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• pp.561-568
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• 2019

Objectives: The most commonly detected heavy metals in rocks and soils, including Pb, Cd, Cu, Fe, Mn and As, are representative pollutants discharged from abandoned mines and have been listed as potential sources of contamination in drinking water. This study focused on increasing the removal efficiency of heavy metals from drinking water resources by surface modification of natural adsorbents to reduce potential health risks. Methods: Iron oxide coating and graft polymerization with zeolites and talc was conducted for bipolar surface modification to increase the combining capacity of heavy metals for their removal from water. The removal efficiency of heavy metals was measured before and after the surface modification. Results: The removal efficiency of Pb, Cu, and Cd by surface modified zeolite showed 100, 92, and 61.5%, respectively, increases compared to 64, 64, and 38% for non-modified zeolite. This implies that bipolar surface modified natural adsorbents have a good potential use in heavy metal removal. The more interesting finding is the removal increase for As, which has both cation and anion characteristics showing 27% removal efficiency where as non-modified zeolite showed only 2% removal. Conclusions: Zeolite is one of the most widely used adsorptive materials in water treatment processes and bipolar surface modification of zeolite increases its applicability in the removal of heavy metals, especially As.

• Journal of the Korean Society of Safety
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• v.8 no.1
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• pp.29-34
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• 1993

Two major hazardous gases. SOx and NOx. are emissioned from fossile fuels. SOx has been removed when oil is refined but NOx hasn't. So NOx is very serious problem in air pollution now There are several technologies to remove NOx. e.g. cooling method. scrubbers method. combustion method, polymer membrane method and adsorbent methods. Polymer membrane and adsorbent methods have good economic merit in removal systems of low content hazard gases. Traditional absorbents are porous silicas, aluminas. active carbon and zeolites. But these absorbents act only physisorption which has less removal performance than chemisorption. In this study. polymeric absorbent which has chemisorption as well as physisorption was analyzed about chemical structure and experimented about optimum operation conditions. The results showed that the chemical structure of the polymeric absorbent was expected as polystyrene having -N-CH$_2$COOH absorbent was revealed about 310$m^2$/g. The molar ratio of absored NO to charged NO in absorption experiments was shown 60% of the polymeric absorbent and 45% of zeolite absorbent at 3$0^{\circ}C$.

• Journal of the Korean Applied Science and Technology
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• v.19 no.2
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• pp.123-130
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• 2002

[Ga]-MFI and H-ZSM-5 catalysts were synthesized under atmospheric pressure and used in the propylene aromatization. The effect of temperature on the product distribution was also investigated. The catalytic activities of the prepared catalysts were compared with the commercialized H-ZSM-5 which was converted from $NH_{4}$-ZSM-5. In the propylene aromatization, product distribution does not depend on the ratio of Si/$Ga_{2}$ with [Ga]-MFI catalyst, but depend on the ratio of Si/$Al_{2}$ with H-ZSM-5 catalyst [Ga]-MFI catalyst shows better dehydrogenation and alkylation activities than H-ZSM-5 catalyst The addition of Ga to H-ZSM-5 catalyst increases the conversion of propylene, selectivity to aromatics, and alkylation. In the propylene aromatization, the selectivity to aromatics slightly increased with increasing temperature with [Ga]-MFI catalyst, while slightly decreased with increasing temperature with H-ZSM-5 catalyst.

• Journal of Radiation Protection and Research
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• v.3 no.1
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• pp.1-5
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• 1978

Investigation is carried out that low-level liquid radioactive wastes which is consisted of long half-life nuclides such as cesium can be treated by Korean clinoptillolite as a kind of zeolites. Column operation using a activated clinoptillolite shows good results in terms of break-through curves and comparing to clinoptillolite classified at WARD in U.S, Korean clinoptillolite shows a tailing phenomena longer than that of WARD. The fixation quantity of radioactivity in Korea clinoptillolite is to be about $75{\mu}Ci/100g$ using a $2.5{\times}10^{-3}{\mu}Ci/ml$ solution.

• Journal of Industrial and Engineering Chemistry
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• v.68
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• pp.196-208
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• 2018

The effect of channel-system of zeolite on methanol-to-DME reaction was studied. Results revealed that channels size and topology affect catalyst lifetime, type and location of coke precursors. FER and MFI showed the best resistance towards coke deposition, whilst fast deactivation was observed on MOR. Although the higher concentration and strength of acid sites, FER structure formed a lower coke amount, preferably located within the pores, while coke cluster deposited on the external surface of MOR. Analysis of acid sites distribution and strength was performed during deactivation-regeneration process. Coke location assessment was also supported by molecular simulations.

• Bulletin of the Korean Chemical Society
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• v.14 no.5
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• pp.583-588
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• 1993

Encapsulation capacities $(V_{gas})$ of, $H_2,\;N_2,\;CO,\;CH_4$ and CO, for $Cs_{2.5}Na_{9.5}-A (C_s-A)$ and $Na_{12}$-A (Na-A) zeolites have been measured in order to understand the effect of molecular properties on the $V_{gas}$. With appropriate number of large blocking cations on the main windows of cavities in zeolite A, gas molecules can be encapsulated in both the ${\alpha}$ -and ${\beta}$-cages, resulting in much large $V_{gas}.\;V_{gas}$ is proportional to the encapsulation pressure (Pe) and is also dependent on the molecular properties of encapsulated gases themselves, especially on intermolecular forces originated from the quadrupole moments of molecules in the molecular-dimensioned cavities of zeolite A. At the low range of Pe, molecules with larger $V_{gas}$ and intermolecular forces apparently have smaller increasing tendencies of $V_{gas}$ upon increases in Pe, showing a linear relationship between the tendencies and intermolecular forces rather than their sizes. Interactions between encapsulated molecules of $CH_4$ and framework of Cs-A have been estimated and they seem to depend on the number of encapsulated molecules per unit cell. On the basis of calculated density of $CO_2$, presence of liquid-like phase for the encapsulated molecules in the molecular dimensioned cavities of zeolite A is postulated.