Formation of mixed oxide powders in flames: Part II. SiO2−GeO2 and Al2O3−TiO2

1992 ◽  
Vol 7 (7) ◽  
pp. 1870-1875 ◽  
Author(s):  
Cheng-Hung Hung ◽  
Philippe F. Miquel ◽  
Joseph L. Katz
Keyword(s):  
Light Scattering ◽  
Mixed Oxide ◽  
Mixed Oxides ◽  
Electrophoretic Method ◽  
X Ray ◽  
Oxide Powders ◽  
Flame Burner ◽  
Carbon Coated ◽  
Oxide Particles ◽  
Counterflow Diffusion Flame

SiO2−GeO2 and Al2O3−TiO2 mixed oxide powders were synthesized using a counterflow diffusion flame burner. SiCl4, GeCl4, Al(CH3)3, and TiCl4 were used as source materials for the formation of oxide particles in hydrogen-oxygen flames. In situ particle sizes were determined using dynamic light-scattering. Powders were collected using two different methods, a thermophoretic method (particles are collected onto carbon coated TEM grids) and an electrophoretic method (particles are collected onto stainless steel strips). Their size, morphology, and crystalline form were examined using a transmission electron microscope and an x-ray diffractometer. A photomultiplier at 90° to the argon ion laser beam was used to measure the light-scattering intensity. The formation of the mixed oxides was investigated using Si to Ge and Al to Ti ratios of 3:5 and 1:1, respectively. Heterogeneous nucleation of the SiO2 on the surface of the GeO2 was observed. In Al2O3−TiO2 mixtures, both oxide particles form at the same temperature. X-ray diffraction analysis of particles sampled at temperatures higher than 1553 K showed the presence of rutile, γ–Al2O3, and aluminum titanate. Although the particle formation process for SiO2−GeO2 is very different from that for Al2O3−TiO2, both mixed oxides result in very uniform mixtures.

Formation and characterization of nanostructured V—P—O particles in flames: A new route for the formation of catalysts

1994 ◽  
Vol 9 (3) ◽  
pp. 746-754 ◽  
Author(s):  
Philippe F. Miquel ◽  
Joseph L. Katz
Keyword(s):  
Spherical Particles ◽  
Crystalline Phases ◽  
Oxide Powders ◽  
Liquid Precursors ◽  
Bet Analysis ◽  
Flame Burner ◽  
Carbon Coated ◽  
Higher Temperature ◽  
Counterflow Diffusion Flame ◽  
Lower Temperature

A counterflow diffusion flame burner was used to produce nanophase vanadium-phosphorus oxide powders in a hydrogen-oxygen flame. Liquid precursors, i.e., VOCl3 and PCl3, were used as source materials in a 1:1 ratio. In situ formation processes were investigated at two temperatures by laser light scattering, by emission and absorption spectroscopy, and by collecting particles directly onto carbon-coated TEM grids. At the higher temperature, the collected powders are spherical particles about 30 to 50 nm in diameter. At the lower temperature, the powders collected are chain-like structures composed of particles 5 to 10 nm in diameter. Particles formed in the burner were collected also from the burner's flanges and from two auxiliary strips. Their crystalline phases and surface area were determined by x-ray diffractometry, FT-IR spectroscopy, and BET analysis by nitrogen desorption. These results indicate a strong influence of temperature on the crystalline phases of the powders. At the higher temperature, the powder collected is a mixture of VOPO4 · 2H2O and δ-VOPO4. This mixture forms Λ-VOPO4 upon subsequent reheating at 750 °C. At the lower temperature, the powders collected are a VOHxPO4 · yH2O phase and VO(H2PO4)2, and form β-VOPO4 and V(PO3)3, respectively, upon subsequent reheating at 750 °C.

scholarly journals Effect of Mg/Al molar ratio on the basicity of Mg-Al mixed oxide derived from Mg-Al hydrotalcite

2020 ◽  
Vol 10 (6) ◽  
pp. 625
Author(s):  
Said Arhzaf ◽  
Mohammed Naciri Bennani ◽  
Sadik Abouarnadasse ◽  
Hamid Ziyat ◽  
Omar Qabaqous
Keyword(s):  
Thermal Analysis ◽  
Mixed Oxide ◽  
Mixed Oxides ◽  
Molar Ratio ◽  
Acid Molecule ◽  
X Ray Diffraction ◽  
Phenol Adsorption ◽  
X Ray ◽  
Maximum Quantity ◽  
Uv Visible

<p>The fundamental character of the Mg-Al mixed oxide (Mg<sub>n</sub>(Al)O), derived from the Mg-Al hydrotalcite (Mg<sub>n</sub>Al-CO<sub>3</sub>-HT), where n corresponds to the Mg/Al molar ratio (n: 2, 2.5, 3, 3.5 and 4), was studied by using the adsorption of phenol as a probe acid molecule. The hydrotalcite precursors were prepared by the coprecipitation method. Their derived mixed oxides were obtained by thermal treatment at 450°C in a flow of air. The resulting solids were characterized by X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermogravimetric and differential thermal analysis             (TG-DTA), nitrogen physisorption (BET) and phenol chemisorption. The phenol adsorption followed by UV-Visible spectrophotometry shows that the basicity increases with the Mg/Al molar ratio, such that maximum quantity of phenol adsorbed (Q<sub>ads</sub> = 0.54 mmol/g <sub>cat</sub>) was obtained with the mixed oxide derived from the Mg-Al hydrotalcite of Mg/Al molar ratio equal to 3.5.</p>

scholarly journals Highly Active Transition Metal-Promoted CuCeMgAlO Mixed Oxide Catalysts Obtained from Multicationic LDH Precursors for the Total Oxidation of Methane

Catalysts ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 613
Author(s):  
Hussein Mahdi S. Al-Aani ◽  
Mihaela M. Trandafir ◽  
Ioana Fechete ◽  
Lucia N. Leonat ◽  
Mihaela Badea ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transition Metal ◽  
Mixed Oxide ◽  
Mixed Oxides ◽  
Catalytic Performance ◽  
Atomic Ratio ◽  
Total Oxidation ◽  
X Ray ◽  
Oxidation Of Methane ◽  
Al2o3 Catalyst

To improve the catalytic performance of an active layered double hydroxide (LDH)-derived CuCeMgAlO mixed oxide catalyst in the total oxidation of methane, it was promoted with different transition-metal cations. Thus, two series of multicationic mixed oxides were prepared by the thermal decomposition at 750 °C of their corresponding LDH precursors synthesized by coprecipitation at constant pH of 10 under ambient atmosphere. The first series of catalysts consisted of four M(3)CuCeMgAlO mixed oxides containing 3 at.% M (M = Mn, Fe, Co, Ni), 15 at.% Cu, 10 at.% Ce (at.% with respect to cations), and with Mg/Al atomic ratio fixed to 3. The second series consisted of four Co(x)CuCeMgAlO mixed oxides with x = 1, 3, 6, and 9 at.% Co, while keeping constant the Cu and Ce contents and the Mg/Al atomic ratio. All the mixed oxides were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) coupled with X-ray energy dispersion analysis (EDX), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption at −196 °C, temperature-programmed reduction under hydrogen (H2-TPR), and diffuse reflectance UV-VIS spectroscopy (DR UV-VIS), while thermogravimetric and differential thermal analyses (TG-DTG-DTA) together with XRD were used for the LDH precursors. The catalysts were evaluated in the total oxidation of methane, a test reaction for volatile organic compounds (VOC) abatement. Their catalytic performance was explained in correlation with their physicochemical properties and was compared with that of a reference Pd/Al2O3 catalyst. Among the mixed oxides studied, Co(3)CuCeMgAlO was found to be the most active catalyst, with a temperature corresponding to 50% methane conversion (T50) of 438 °C, which was only 19 °C higher than that of a reference Pd/Al2O3 catalyst. On the other hand, this T50 value was ca. 25 °C lower than that observed for the unpromoted CuCeMgAlO system, accounting for the improved performance of the Co-promoted catalyst, which also showed a good stability on stream.

scholarly journals A barium germanium 1,2-ethanediolato complex as precursor for barium metagermanate

2018 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Thermal Decomposition ◽  
Infrared Spectroscopy ◽  
Powder Diffraction ◽  
Mixed Oxide ◽  
Phase Evolution ◽  
X Ray ◽  
Oxide Powders ◽  
Fourier Transformed Infrared Spectroscopy ◽  
Shrinkage Behaviour ◽  
Ft Ir

The thermal behaviour of [Ba(HOC2H4OH)2Ge(OC2H4O)3] (2) as a BaGeO3 precursor,and its phase evolution during thermal decomposition in different atmospheres are described herein.The precursor complex decomposes in air to a finely divided mixture of BaCO3 and GeO2, whichsubsequently reacts above 650 °C to orthorhombic BaGeO3, transforming above 800 °C tohexagonal BaGeO3. The shrinkage behaviour of BaGeO3 compacts made from the as-preparedpowders as well as from conventional mixed-oxide powders has been investigated. The sampleswere characterised by Fourier transformed infrared spectroscopy (FT-IR), X-ray powder diffraction(XRD), dilatometric measurements and thermoanalytic investigations (TG/DTA).

Formation of mixed oxide powders in flames: Part I. TiO2−SiO2

1992 ◽  
Vol 7 (7) ◽  
pp. 1861-1869 ◽  
Author(s):  
Cheng-Hung Hung ◽  
Joseph L. Katz
Keyword(s):  
Light Scattering ◽  
Optical Fibers ◽  
Mixed Oxide ◽  
Active Sites ◽  
High Surface ◽  
High Surface Area ◽  
Particle Morphology ◽  
Effect Of Temperature ◽  
Strong Temperature Dependence ◽  
Oxide Powders

Mixed oxide powders, e.g., Al2O3−TiO2, SiO2−GeO2, and TiO2−SiO2, are used in industry to produce ceramics, optical fibers, catalysts, and paint opacifiers. The properties of these products depend upon the morphology of the powders. Ceramics and optical fibers are produced using either a uniform mixture of multicomponent particles or a uniform solution. The desired morphology for catalysts is a high surface area and many active sites. TiO2 coated with a layer of SiO2 is the desired structure for use as a paint opacifier. In this paper, TiO2−SiO2 mixed oxide powders were synthesized using a counterflow diffusion flame burner. TiCl4 and SiCl4 were used as source materials for the formation of oxide particles in hydrogen-oxygen flames. In situ particle sizes were determined using dynamic light scattering. A thermophoretic sampling method also was used to collect particles directly onto carbon coated grids, and their size, morphology, and crystalline form examined using a transmission electron microscope. A photomultiplier at 90° to the argon ion laser beam was used to measure the light-scattering intensity. The effect of temperature and of Si to Ti concentration ratio on particle morphology was investigated. Strong temperature dependence was observed. At high temperatures, TiO2 particles were covered with discrete SiO2 particles. At low temperatures, the structure changes to TiO2 particles encapsulated by SiO2. TEM diffraction pattern measurements showed that the TiO2 is rutile and the SiO2 is amorphous silica. At high Si to Ti ratios, SiO2-encapsulated TiO2 particles form. At low Si to Ti ratios, one obtains TiO2 particles covered with discrete SiO2 particles.

scholarly journals Effect of Sr on the properties of Ce-Zr-La mixed oxides

2006 ◽  
Vol 71 (3) ◽  
pp. 285-291 ◽  
Author(s):  
Richuan Rao ◽  
LI Lianyong ◽  
LI Fengyi
Keyword(s):  
Mixed Oxide ◽  
Storage Capacity ◽  
Mixed Oxides ◽  
Sol Gel ◽  
Oxygen Storage Capacity ◽  
Oxygen Storage ◽  
X Ray Diffraction ◽  
Pulse Technique ◽  
X Ray ◽  
Good Thermal Stability

Ce-Zr-La-Sr mixed oxides, with different Sr contents, were prepared by the sol-gel method. In a flow-system microreactor, the reduction properties and the oxygen storage capacity (OSC) of the Ce-Zr-La-Sr mixed oxides were investigated by a temperature programmed reduction (TPR) and a pulse technique. It was shown that the properties of the Ce-Zr-La mixed oxides depend on the Sr content and that the optimum Sr content in the Ce-Zr-La-Sr mixed oxide is 3 mol%. The Ce-Zr-La-Sr mixed oxides doped with 3 mol% Sr (Ce0.52Zr0.4La0.05Sr0.03O1.945) has the largest specific surface area and better reduction properties and oxygen storage capacity in comparison to the other investigated samples. The XRD results of the Ce-Zr-La-Sr mixed oxides showed that their X-ray diffraction patterns are well in agreement with that of fluorite-type CeO2 with Sr ions incorporated into the Ce-Zr-La mixed oxide structures. With increasing calcination temperature, the intensity of the X-ray diffraction peaks increased, but no new peaks were observed. All of these indicate that the synthesized samples had good thermal stability.

Rod-like CuMnOx transformed from mixed oxide particles by alkaline hydrothermal treatment as a novel catalyst for catalytic combustion of toluene

2016 ◽  
Vol 18 (33) ◽  
pp. 22794-22798 ◽  
Author(s):  
W. B. Li ◽  
Z. X. Liu ◽  
R. F. Liu ◽  
J. L. Chen ◽  
B. Q. Xu
Keyword(s):  
Catalytic Activity ◽  
Hydrothermal Treatment ◽  
Mixed Oxide ◽  
Catalytic Combustion ◽  
Mixed Oxides ◽  
Copper Manganese ◽  
Oxide Particles ◽  
Novel Catalyst

Rod-like copper manganese mixed oxides by alkaline hydrothermal treatment exhibit superior catalytic activity toward toluene combustion at 210 °C.

Combinatorial synthesis of oxide powders

2001 ◽  
Vol 16 (4) ◽  
pp. 967-974 ◽  
Author(s):  
H. M. Reichenbach ◽  
P. J. McGinn
Keyword(s):  
Co Oxidation ◽  
Mixed Oxide ◽  
Oxidation Reaction ◽  
Mixed Oxides ◽  
Combinatorial Libraries ◽  
Oxide System ◽  
Synthesis Process ◽  
Powder Synthesis ◽  
Oxide Powders ◽  
Co Oxidation Reaction

Combinatorial libraries of the mixed oxide system Cu1−xCexO3 (0 ≤ x ≤ 1) have been generated using a modified Pechini powder synthesis process in conjunction with inkjet deposition. Mixed oxide crystalline powders were formed at temperatures below 500 °C. These powders have particle sizes in the range of 20.0 to 85.5 nm, and the powder surface area increases with cerium content. In addition, each of the mixed oxides (0 < x < 1) displayed catalytic activity in the CO oxidation reaction at temperatures between 150 and 350 °C. This novel protocol has also been used to generate a library of oxide powders of the perovskite-like La1−xSrxCoO3?δ system. The La–Sr–Co–O system from this protocol exhibits lower average surface areas than the Cu–Ce–O system (approximately 11.2 m2/g) due to higher decomposition temperatures but still acts as an active catalyst for the CO oxidation reaction.

scholarly journals Magnesium Effect in K/Co-Mg-Mn-Al Mixed Oxide Catalyst for Direct NO Decomposition

Catalysts ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 931
Author(s):  
Kateřina Karásková ◽  
Kateřina Pacultová ◽  
Anna Klegova ◽  
Dagmar Fridrichová ◽  
Marta Valášková ◽  
...  
Keyword(s):  
Mixed Oxide ◽  
Thermal Instability ◽  
Mixed Oxides ◽  
No Decomposition ◽  
Molar Ratio ◽  
Partial Substitution ◽  
X Ray ◽  
Mixed Oxide Catalyst ◽  
Temperature Programmed ◽  
Activity Decrease

Emission of nitric oxide represents a serious environmental problem since it contributes to the formation of acid rain and photochemical smog. Potassium-modified Co-Mn-Al mixed oxide is an effective catalyst for NO decomposition. However, there are problems related to the thermal instability of potassium species and a high content of toxic and expensive cobalt. The reported research aimed to determine whether these shortcomings can be overcome by replacing cobalt with magnesium. Therefore, a series of Co-Mg-Mn-Al mixed oxides with different Co/Mg molar ratio and promoted by various content of potassium was investigated. The catalysts were thoroughly characterized by atomic absorption spectroscopy (AAS), temperature-programmed reduction by hydrogen (TPR-H2), temperature-programmed desorption of CO2 (TPD-CO2), X-ray powder diffraction (XRD), N2 physisorption, species-resolved thermal alkali desorption (SR-TAD), and tested in direct NO decomposition with and without the addition of oxygen and water vapor. Partial substitution of magnesium for cobalt did not cause an activity decrease when the optimal molar ratio of K/Co on the normalized surface area was maintained; it means that the portion of expensive and toxic cobalt can be successfully replaced by magnesium without any decrease in catalytic activity.

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