Nickel ion-exchanged zeolite-4A: reduction behaviour of nickel and structure stability

Bhat, Ramachandra; Babu, G.P.; Bhat, Adarsh

doi:10.1039/ft9959103983

Cited by 8 publications

(5 citation statements)

References 10 publications

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“…Alternately, extended thermal treatment may result in an increased migration of reduced Ag°from the cages of the zeolite framework to the surface, where the surface-supported silver nanoparticles are most accessible for effective Hg°c apture. This mechanism is consistent with a number of earlier observations by Bhatia (30) and Bhat et al (31).…”

Section: Resultssupporting

confidence: 94%

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Dong

Kuznicki

2009

Environ. Sci. Technol.

144

105

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Magnetic zeolite composites with supported silver nanoparicles are a new class of multifunctional materials with potential applications as recyclable catalysts, disinfectants, and sorbents. This study evaluated the suitability of the magnetic composites as sorbents for the removal of elemental mercury vapor from flue gases of coal-fired power plants. The sorbents were found to completely capture mercury at temperatures up to 200 degrees C, and the mercury capacity of the sorbents was found to be affected by the state, content, and size of the silver particles in the composite. Cumulative or extended thermal treatments at 400 degrees C were found to improve the mercury capture capacity, allowing the sorbent to be regenerated and recycled multiple times without performance degradation. The magnetic sorbent was readily separated from fly ash by magnetic separation, leaving the fly ash essentially free of sorbent contamination. In initial in-plant tests, the sorbents were able to capture mercury from the flue gases of an operational, full-scale, coal-fired power plant The combination of mercury capacity, ease of separation and regeneration, and recyclability makes these multifunctional magnetic composites excellent candidate sorbentsforthe control of mercury emissions from coal-fired power plants.

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Section: Resultssupporting

confidence: 94%

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Dong

Kuznicki

2009

Environ. Sci. Technol.

144

105

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“…The position of extraframework cation sites in FAU-type structure are shown in Figure . On the basis of our previous observations and some related reports, − in the hydrated zeolites, Li cations are strongly coordinated by some water molecules and easily form octahedral or tetrahedral complexes. Thus, the gradual removal of some of the complexing water molecules during dehydration processes finally causes Li cations to migrate into hexagonal prism sites and then interact with oxygen atoms from the FAU skeleton, where they are coordinated almost octahedrally by framework oxygen atoms .…”

Section: Resultssupporting

confidence: 59%

Thermal and Kinetic Performance of Water Desorption for N₂ Adsorption in Li-LSX Zeolite

et al. 2014

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The effect of small amounts of water in inhibiting the adsorption of N2 gas on different cationic forms of LSX zeolite was investigated using thermogravimetric and derivative thermogravimetry (TG-DTG) techniques at different heating rates, which is shown to be a very effective way of studying the influence of strongly adsorbed water on adsorption of less-strongly adsorbed N2 molecules. According to DTG profiles, the apparent activation energies (E) relating to the thermal desorption of water molecules existing in the skeleton of Na- and Li-LSX zeolites were estimated through both the Kissinger and Flynn–Wall–Ozawa methods. The E values calculated from these two equations were in close agreement, and the thermal dehydration mechanism was further studied on the basis of the Coats–Redfern method. Moreover, the observations for the exponential declination of N2 adsorption amount with the loading of water revealed that the adsorption capacity of cationic zeolites was significantly influenced by water through reducing heterogeneity and strength of the electric field. More specifically, the E value at high temperature was higher than that at low temperature, implying that at high temperature, decomposition of bonded water belongs to dynamic-based control, whereas the dehydration process of physisorbed water belongs to diffusion-based control at low temperature.

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“…Further destabilization is most probably caused by hydronium cations and hydroxide ions, which are formed at elevated temperatures. The presence of these ions within Co 2+ - and Ni 2+ -exchanged zeolites has been observed by several groups. ,, The hydronium ions break additional Si−O−Al bonds, causing further damage to the zeolite framework.…”

Section: Discussionmentioning

confidence: 90%

“…Therefore, we presume the presence of both silanol groups and of Ni−OH and Co−OH species. The formation of Me−OH groups due to the hydrolysis of water molecules within transition-metal-exchanged zeolites has been reported by several groups. − Silanol groups are usually formed due to structural damage of zeolites, e.g., by treatment with acidic solution. Repetition of the ion-exchange procedure clearly reduces the crystallinity of the zeolite frameworks, particularly in the case of Ni 2+ -exchanged zeolite A and of Co 2+ - and Ni 2+ -exchanged zeolite X.…”

Section: Discussionmentioning

confidence: 96%

Thermal Stability and Thermal Transformations of Co²⁺- or Ni²⁺-Exchanged Zeolites A, X, and Y

Weidenthaler

Schmidt

2000

Chem. Mater.

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The stability of Co 2+ -and Ni 2+ -exchanged zeolites strongly depends on the exchanged transition metal and the experimental conditions of the ion-exchange. An overexchange of both Co 2+ and Ni 2+ is observed with the zeolites A and X, enhanced at elevated temperatures. The interaction of the zeolite famework with acidic species formed during the exchange leads to structural damage. After the collapse of the zeolite frameworks during the calcination of the exchanged zeolites, the crystallization of CoAl 2 O 4 and NiAl 2 O 4 starts. During the calcination of Ni 2+ -exchanged zeolite A and X, NiO crystallizes prior to the formation of spinel and dissolves as the spinel crystallization starts. Depending on the zeolite precursor and the thermal conditions, SiO 2 phases such as quartz or cristobalite are formed. The amounts of crystalline and amorphous phases vary with calcination temperature and time. The phase formation processes are dependent on the ion-exchange procedures and thermal treatments. By controlling these parameters, materials with well-defined properties are accessible.

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Nickel ion-exchanged zeolite-4A: reduction behaviour of nickel and structure stability

Cited by 8 publications

References 10 publications

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Thermal and Kinetic Performance of Water Desorption for N₂ Adsorption in Li-LSX Zeolite

Thermal Stability and Thermal Transformations of Co²⁺- or Ni²⁺-Exchanged Zeolites A, X, and Y

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Nickel ion-exchanged zeolite-4A: reduction behaviour of nickel and structure stability

Cited by 8 publications

References 10 publications

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Mercury Removal from Flue Gases by Novel Regenerable Magnetic Nanocomposite Sorbents

Thermal and Kinetic Performance of Water Desorption for N2 Adsorption in Li-LSX Zeolite

Thermal Stability and Thermal Transformations of Co2+- or Ni2+-Exchanged Zeolites A, X, and Y

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Product

Resources

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Thermal and Kinetic Performance of Water Desorption for N₂ Adsorption in Li-LSX Zeolite

Thermal Stability and Thermal Transformations of Co²⁺- or Ni²⁺-Exchanged Zeolites A, X, and Y