Plasma chemical preparation and characterization of perovskite-type mixed oxides

ABSTRACTThe microstructure of Ni-Mg-Al mixed oxides obtained by thermal decomposition of hydrotalcite-like compounds synthesized by a co-precipitation method has been studied by using X-ray diffraction (XRD) and atomic resolution transmission electron microscopy (TEM). XRD patterns revealed the formation of NixMg1-xO (x=0÷1), α-Al2O3 and traces of MgAl2O4 and NiAl2O4 phases. The peaks profile analysis indicated a small grain size, microdeformations and partial overlapping of peaks due to phases with different, but similar interplanar spacings. The microdeformations point out the presence of dislocations and the peaks shift associated with the presence of excess vacancies. The use of atomic resolution TEM made it possible to identify the phases, directly observe dislocations and demonstrate the vacancies excess. Atomic resolution TEM is achieved by applying an Exit Wave Reconstruction procedure with 40 low dose images taken at different defocus. The current results suggest that vacancies of metals are predominant in MgO (NiO) crystals and that vacancies of Oxygen are predominant in Al2O3 crystals.

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Effect of Complexing Agent on Morphology and Crystal Structure of La1-xCexCoO3 (x=0, 0.2, and 0.4) Perovskite-Type Mixed Oxides Catalyst Prepared by Sol-Gel Method

Materials Science Forum ◽

10.4028/www.scientific.net/msf.658.29 ◽

2010 ◽

Vol 658 ◽

pp. 29-32 ◽

Cited By ~ 1

Author(s):

Kanit Soongprasit ◽

Duangdao Aht-Ong ◽

Viboon Sricharoenchaikul ◽

Duangduen Atong

Keyword(s):

Crystal Structure ◽

Polyvinyl Alcohol ◽

Mixed Oxides ◽

Sol Gel ◽

Value Added ◽

Molar Ratio ◽

Complexing Agent ◽

Nitrate Hexahydrate ◽

Mixed Oxide Catalysts ◽

Perovskite Type

. La1-xCexCoO3 (x=0, 0.2, and 0.4) perovskite-type mixed oxides using polyvinyl alcohol (PVA) as complexing agent at two molar ratio of metal ion to PVA (1:1 and 1:2) were successfully prepared by sol-gel process. The precursor included lanthanum (II) nitrate hexahydrate, cerium (II) nitrate hexahydrate, and cobalt (II) nitrate hexahydrate where polyvinyl alcohol was added as complexing agent. The suitable condition of Cerium (Ce) substitution and PVA molar ratio were established for further application in hydrocarbon conversion to high value added products. TGA thermogram of as-prepared precursor showed that PVA absolutely decomposed at temperature higher than 500°C. XRD patterns of calcined catalyst showed both LaCoO3 rhombohedral and CeO2 cubic structures that confirmed the formation of mixed crystal structure. Nevertheless, Co3O4 slightly appeared with low peak intensity which came from the oxidation reaction of as-prepared catalyst during calcinations. XRD showed that PVA did not effect to crystal structure of synthesized catalyst. Higher PVA content added in the precursor cause the reduction of crystal growth of catalyst in calcinations step. In contrast, morphology of catalyst is directly related with PVA content such that the spongy and sheet-like structure were formed with increasing PVA content which prevented the agglomeration of particles. The results showed that PVA content play an important role in morphology of perovskite-type mixed oxide catalysts but did not affected to their crystal structures.

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Synthesis and Characterization of K-Ta Mixed Oxides for Hydrogen Generation in Photocatalysis

International Journal of Photoenergy ◽

10.1155/2012/525727 ◽

2012 ◽

Vol 2012 ◽

pp. 1-7 ◽

Cited By ~ 5

Author(s):

Beata Zielińska ◽

Ewa Mijowska ◽

Ryszard J. Kalenczuk

Keyword(s):

Diffuse Reflectance ◽

Hydrogen Generation ◽

Mixed Oxides ◽

X Ray Diffraction ◽

X Ray ◽

Raman Spectroscopic ◽

Photocatalytic Hydrogen Generation ◽

Irregular Structure ◽

Transmission Electron

K-Ta mixed oxides photocatalysts have been prepared by impregnation followed by calcination. The influence of the reaction temperature (450°C–900°C) on the phase formation, crystal morphology, and photocatalytic activity in hydrogen generation of the produced materials was investigated. The detailed analysis has revealed that all products exhibit high crystallinity and irregular structure. Moreover, two different crystal structures of potassium tantalates such as KTaO3and K2Ta4O11were obtained. It was also found that the sample composed of KTaO3and traces of unreacted Ta2O5(annealed at 600°C) exhibits the highest activity in the reaction of photocatalytic hydrogen generation. The crystallographic phases, optical and vibronic properties were examined by X-ray diffraction (XRD) and diffuse reflectance (DR) UV-vis and resonance Raman spectroscopic methods, respectively. Morphology and chemical composition of the produced samples were studied using a high-resolution transmission electron microscope (HR-TEM) and an energy dispersive X-ray spectrometer (EDX) as its mode.

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Electron Donating, Acid-Base and Catalytic Properties of Perovskite-Type Mixed Oxides of Rare Earths

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19950977 ◽

1995 ◽

Vol 60 (6) ◽

pp. 977-982

Author(s):

S. Sugunan ◽

V. Meera

Keyword(s):

Catalytic Activity ◽

Electron Donor ◽

Rare Earths ◽

Electron Affinity ◽

Mixed Oxides ◽

Catalytic Properties ◽

Surface Acidity ◽

Electron Acceptors ◽

Acid Base ◽

Perovskite Type

The electron donor properties of perovskite-type mixed oxides (LaFeO3, PrFeO3, SmFeO3, LaCoO3, PrCoO3, SmCoO3, LaNiO3, PrNiO3 and SmNiO3) were studied based on the adsorption of electron acceptors exhibiting different electron affinity viz. 7,7,8,8-tetracyanoquinodimethane, 2,3,5,6-tetrachloro-1,4-benzoquinone, p-dinitrobenzene, and m-dinitrobenzene. The surface acidity/basicity of the oxides was determined using a set of Hammett indicators. The data were correlated with the catalytic activity of the oxides for the reduction of cyclohexanone with 2-propanol.

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