Mechanism of the anion exchange reactions of the layered double hydroxides (LDHs) of Ca and Mg with Al

Radha, A. V.; Kamath, P. Vishnu; Shivakumara, C.

doi:10.1016/j.solidstatesciences.2005.05.004

Cited by 132 publications

(68 citation statements)

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“…According to the literature, materials that are of interest for the adsorption of CO 2 are mostly calcium oxides, [3][4][5] lithium oxides, [6][7][8] and hydrotalcites. [9][10][11] However, most of the commonly studied adsorbents (e.g., zeolites and activated carbon) suffer from low capacity at elevated temperatures because the CO 2 adsorption capacity of these materials decreases drastically with increasing temperature. The key improvement for such a process is to develop adsorbent materials that are capable of capturing CO 2 at high temperatures.…”

Section: Introductionmentioning

confidence: 99%

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity

Chang

Chen

et al. 2011

ChemSusChem

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We present the design and synthesis of Ca-rich Ca-Al-O oxides, with Ca(2+)/Al(3+) ratios of 1:1, 3:1, 5:1, and 7:1, which were prepared by hydrothermal decomposition of coprecipitated hydrotalcite-like Ca-Al-CO(3) precursors, for high-temperature CO(2) adsorption at 500-700 °C. In situ X-ray diffraction measurements indicate that the coprecipitated, Ca-rich, hydrotalcite-like powders with Ca(2+)/Al(3+) ratios of 5:1 and 7:1 contained Ca(OH)(2) and layered double hydroxide (LDH) phases. Upon annealing, LDH was first destroyed at approximately 200 °C to form an amorphous matrix, and then at 450-550 °C, the Ca(OH)(2) phase was converted into a CaO matrix with incorporated Al(3+) to form a homogeneous solid solution without a disrupted lattice structure. CaO nanocrystals were grown by thermal treatment of the weakly crystalline Ca-Al-O oxide matrix. Thermogravimetric analysis indicates that a CO(2) adsorption capacity of approximately 51 wt. % can be obtained from Ca-rich Ca-Al-O oxides prepared by calcination of 7:1 Ca-Al-CO(3) LDH phases at 600-700 °C. Furthermore, a relatively high CO(2) capture capability can be achieved, even with gas flows containing very low CO(2) concentrations (CO(2)/N(2) = 10 %). Approximately 95.6 % of the initial CO(2) adsorption capacity of the adsorbent is retained after 30 cycles of carbonation-calcination. TEM analysis indicates that carbonation-promoted CaCO(3) formation in the Ca-Al-O oxide matrix at 600 °C, but a subsequent desorption in N(2) at 700 °C, caused the formation CaO nanocrystals of approximately 10 nm. The CaO nanocrystals are widely distributed in the weakly crystalline Ca-Al-O oxide matrix and are present during the carbonation-calcination cycles. This demonstrates that Ca-Al-O sorbents that developed through the synthesis and calcination of Ca-rich Ca-Al LDH phases are suitable for long-term cyclic operation in severe temperature environments.

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Section: Introductionmentioning

confidence: 99%

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity

Chang

Chen

et al. 2011

ChemSusChem

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“…The LDHs have a solution chemistry in that their solubilities are higher than those of the silica-based cationic clays. There is evidence to show that anion exchange takes place by dissolution and reprecipitation [9]. Anion exchange does not take place unless the LDH of the incoming anion is less soluble than that of the outgoing anion.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

Prasanna

Kamath

2009

Journal of Colloid and Interface Science

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The arsenate-intercalated layered double hydroxide (LDH) of Mg and Al is synthesized by coprecipitation. The higher thermodynamic stability and the consequent lower solubility of the unitary arsenates preclude the formation of arsenate-intercalated LDHs of other metals directly from solution. However other M/AlAsO 4 (M = Co, Ni, Zn) LDHs could be prepared by anion exchange, showing that arsenate intercalation proceeds topotactically. The intercalation of various species of As(V) into the interlayer of LDHs and the subsequent arsenate carrying capacity are dependent upon the pH of the solution. Upon thermal decomposition, the intercalated arsenate ion undergoes reductive deintercalation to give a mixture of As(III) and As(V) oxides. The product oxides revert back to the LDH upon soaking in water on account of the compositional and morphological metastability of the former. This is in contrast with the phosphateintercalated LDHs, in which the reversibility is suppressed, consequent to the formation of stable metal phosphates.

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“…There is an equal likelihood for the formation of unitary (comprising a single metal ion) salts of the incoming anion. Thus phosphates tend to combine with the metal ions to yield metal phosphates, rather than phosphate intercalated LDHs [10,11].…”

Section: Introductionmentioning

confidence: 99%

Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al

Prasanna

Kamath

2008

Solid State Sciences

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The layered double hydroxides (LDHs) of Mg with Al readily scavenge dissolved chromate ions under a wide range of conditions. While the chromate uptake is quantitative in the LDH containing 33 mol% Al, the uptake is only 58% of the stoichiometric value in the LDH containing 25 mol% Al. This indicates that the lower symmetry of the NO 3 À ions in the LDH with 33 mol% Al facilitates the intercalation of chromate ions even under conditions of equilibration with excess dissolved nitrate ions. The chromate uptake obeys the Langmuir adsorption isotherm suggesting that the entire interlayer region of the LDH behaves like a surface. This surface is structural rather than morphological as the chromate uptake correlates negatively with the BET surface area of the LDHs.

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Mechanism of the anion exchange reactions of the layered double hydroxides (LDHs) of Ca and Mg with Al

Cited by 132 publications

References 30 publications

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al

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Mechanism of the anion exchange reactions of the layered double hydroxides (LDHs) of Ca and Mg with Al

Cited by 132 publications

References 30 publications

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO2 Capture Capacity

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO2 Capture Capacity

Synthesis and characterization of arsenate-intercalated layered double hydroxides (LDHs): Prospects for arsenic mineralization

Chromate uptake characteristics of the pristine layered double hydroxides of Mg with Al

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Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity

Ca‐Rich Ca–Al‐Oxide, High‐Temperature‐Stable Sorbents Prepared from Hydrotalcite Precursors: Synthesis, Characterization, and CO₂ Capture Capacity