Oxidation of Cr(III) to Cr(VI) Species During the Thermal Decomposition Process of Zn/Cr-layered Double Hydroxide Carbonate

Fuda, Kiyoshi; Suda, Kazuhito; Matsunaga, Toshiaki

doi:10.1246/cl.1993.1479

Cited by 22 publications

(19 citation statements)

References 3 publications

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“…• C), much higher than that observed in the decomposition products of Zn-Cr-CO 3 -LDHs (30,39,40), but in agreement with previously reported data for the thermal decomposition of organic anions-containing ZnCr-LDHs (above 600…”

Section: Pxrd Analysis Of Thermally Treated Samplessupporting

confidence: 92%

“…The quantification of Cr(VI) was performed by a method described by Fuda and co-workers (30): 50 mg of the material was added to 50 cm 3 of 1 mol dm −3 HCl aqueous solution. For materials heated at temperatures above 400…”

Section: Characterizationmentioning

confidence: 99%

“…The oxidation of Cr(III) to Cr(VI) cations during the thermal decomposition of Cr(III)-containing LDHs in air is widely reported (30,39,43). It was observed that about 20-25% of the Cr(III) contained in the materials is usually oxidized to Cr(VI) at intermediate temperatures (300-400…”

Section: Variation Of Cr Oxidation Statementioning

confidence: 99%

See 2 more Smart Citations

Chemical, Structural, and Thermal Properties of Zn(II)–Cr(III) Layered Double Hydroxides Intercalated with Sulfated and Sulfonated Surfactants

Crepaldi

Pavan

Tronto

et al. 2002

Journal of Colloid and Interface Science

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Section: Pxrd Analysis Of Thermally Treated Samplessupporting

confidence: 92%

Section: Characterizationmentioning

confidence: 99%

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Chemical, Structural, and Thermal Properties of Zn(II)–Cr(III) Layered Double Hydroxides Intercalated with Sulfated and Sulfonated Surfactants

Crepaldi

Pavan

Tronto

et al. 2002

Journal of Colloid and Interface Science

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“…However, a correlation that can be made between particle size distribution in a suspension and type of coprecipitation used (constant or variable pH) is that the distribution was less affected by the hydrothermal treatment for those materials precipitated at constant pH, as indicated by the superimposition of the respective curves. the ZnCr cation combination 20 . The last decomposition, around 20%, was due to the second step of dehydroxylation and to TA decomposition 19 , occurring at different temperatures depending on the cation combination used, about 550 and 350ºC for the MgAl-and ZnCr-containing LDHs, respectively.…”

Section: Size Distribution and Average Diameter Of The Particles In Smentioning

confidence: 99%

Comparative study of the coprecipitation methods for the preparation of Layered Double Hydroxides

Crepaldi¹,

Pavan²,

Valim³

2000

J. Braz. Chem. Soc.

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A coprecipitação é o método mais frequentemente utilizado para preparar Hidróxidos Duplos Lamelares (HDLs). Duas variações deste método podem ser utilizadas, dependendo das condições adotadas quanto ao controle de pH durante a etapa de precipitação. No primeiro caso o pH não é controlado e a síntese é conduzida em pH variável, ao passo que no segundo caso o pH é mantido constante durante a precipitação. Apesar de cada grupo de pesquisa ter suas preferências, nenhum estudo sistemático e comparativo destas duas variações do método está disponível na literatura. Desta forma, o objetivo deste estudo foi comparar as propriedades de HDLs preparados através das duas variações possíveis do método de coprecipitação. Os resultados demonstraram que, embora seja mais simples a síntese realizada sem controle de pH, materiais com propriedades mais interessantes do ponto de vista tecnológico foram obtidos pelo método que utiliza pH constante. Materiais com maior cristalinidade, partículas menores, maior área superficial e maior diâmetro médio de poros foram obtidos pelo método de coprecipitação em pH constante.Coprecipitation is the method most frequently applied to prepare Layered Double Hydroxides (LDHs). Two variations of this method can be used, depending on the pH control conditions during the precipitation step. In one case the pH values are allowed to vary while in the other they are kept constant throughout coprecipitation. Although research groups have their preferences, no systematic comparison of the two variations of the coprecipitation method is available in the literature. On this basis, the objective of the present study was to compare the properties of LDHs prepared using the two forms of pH control in the coprecipitation method. The results showed that even though coprecipitation is easier to perform under conditions of variable pH values, materials with more interesting properties, from the point of view of technological applications, are obtained at constant pH. Higher crystallinity, smaller particle size, higher specific surface area and higher average pore diameter were found for materials obtained by coprecipitation at constant pH, when compared to the materials obtained at variable pH.

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“…to Cr 3? [26,27]. The temperature of main reduction maximum is gradually moved from 301 to 306°C with an increase of chromium content.…”

Section: Redox Propertiesmentioning

confidence: 99%

Chromium-modified zinc oxides

Gac

Zawadzki

Słowik

et al. 2016

J Therm Anal Calorim

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Zinc oxides modified with chromium were prepared by the co-precipitation method. Samples were calcined at 400°C. Structural and surface properties of materials were studied by means of transmission electron microscopy, X-ray diffraction and low-temperature nitrogen adsorption methods. Temperature-programmed reduction methods were used for investigation of the influence of chromium on the redox properties of zinc oxides. The nature of surface sites and the course of surface reactions occurred during methanol decomposition were determined by the temperature-programmed desorption of methanol with detection of evolved gasses by mass spectrometry and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have found that modification of ZnO with chromium led to the increase of the specific surface area of oxides and decrease of mean crystallite size of ZnO. Partial incorporation of chromium ions to the hexagonal ZnO structure, formation of strongly dispersed spinel (ZnCr 2 O 4 ) and chromium zinc oxide species (ZnOÁCrO 3 ) was observed. We have stated that methanol was adsorbed on the surface of ZnO at 100°C mainly via formation of methoxy species, and the main products of methanol desorption were carbon monoxide and hydrogen. The presence of chromium facilitated direct oxidation of methoxy groups to formate species at low temperatures (*100°C) and their transformation to hydrogen and carbon dioxide during temperature-programmed desorption. The enhanced transformation of methoxy to formate species was attributed to the labile oxygen in chromium-modified zinc oxides.

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Oxidation of Cr(III) to Cr(VI) Species During the Thermal Decomposition Process of Zn/Cr-layered Double Hydroxide Carbonate

Cited by 22 publications

References 3 publications

Chemical, Structural, and Thermal Properties of Zn(II)–Cr(III) Layered Double Hydroxides Intercalated with Sulfated and Sulfonated Surfactants

Chemical, Structural, and Thermal Properties of Zn(II)–Cr(III) Layered Double Hydroxides Intercalated with Sulfated and Sulfonated Surfactants

Comparative study of the coprecipitation methods for the preparation of Layered Double Hydroxides

Chromium-modified zinc oxides

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