Emulsion Combustion Method Research Articles

Preparation of Biscuit-Like SO2-₄/ZrO₂ Catalyst for Alkylation of o-Xylene with Styrene.

We present here a facile synthesis of SO2-₄/ZrO₂ solid superacid by impregnating the biscuit-like mesoporous ZrO₂ nanoparticles prepared by an emulsion combustion method directly into H₂SO₄ solution. The obtained solid acid catalyst was characterized by means of X-ray powder diffraction, transmission and scanning electron microscopy, thermogravimetry, Brunner-Emmet-Teller measurement, and infrared analysis. Its catalytic performance was examined by alkylation of o-xylene with styrene. The optimal catalytic formulation, obtained from the investigation of experimental conditions, was determined to be 5 wt% of catalyst loading with initial o-xylene/styrene molar ratio of 5 under reaction temperature at 120 °C for 120 min, achieving a 100% styrene conversion and a 93.3% 1-phenyl-1-xylyl ethane selectivity. The biscuit-like SO2-₄/ZrO₂ solid acid exhibited high catalytic activity and selectivity and excellent structural stability. This synthetic strategy for preparing the mesoporous SO2-₄ promoted ZrO₂ solid superacid catalyst is generalized and expected to be applied to other metal oxides.

A Theoretical Model for the Formation of Functional Micro- and Nano-Particles from Combustion of Emulsion Droplets

In this paper a theoretical model is developed to simulate the process of vaporization and burning of emulsion droplets of a fuel and the evolution and formation of micro- and nano-particles. This process is usually known as the Emulsion Combustion Method (ECM). In the ECM, a proper salt solution is mixed with a fuel to form an emulsion of micro-solution droplets. The emulsion is then sprayed into micron-sized emulsion droplets; spray droplets burn in a spray flame to form final micro- or nano-particles. A mathematical model for the entire process from the droplet interior to the gas phase processes is proposed. Model equations are solved numerically. It is found that particle characteristics are dependent on the operating and processing conditions, such as the initial size and concentration of the suspended micro solution droplets in emulsion droplets and the fuel type and fraction of the emulsion droplets. Although a quantitative evaluation of the model performance is not yet possible due to the lack of sufficient experimental data, the developed model may be used to design an ECM process to produce particles with tailored properties. The main novelty of the model is that in an ECM process it can predict whether mono-dispersed single particles will be formed or agglomerated larger particles.

The Influence of Oleic Acid to Metal Nitrate Ratio on the Particle Size and Magnetic Properties of Lanthanum Ferrite Nanoparticles by Emulsion Method

LaFeO3 nanoparticles of different sizes are prepared by varying the molar concentration of oleic acid to metal nitrate using emulsion combustion method. X-ray diffraction analysis confirms that LaFeO3 nanoparticles are crystalline in nature with an orthorhombic structure. The average particle size and saturation magnetization decreases from 56 to 32 nm and 0.20 to 0.08 emu/g, as molar concentration of oleic acid to metal nitrate increases from 0.25 to 1. The Fourier transform infrared (FTIR) spectra show the lower frequency bands are assigned to Fe–O stretching vibration (579 cm−1) and O–Fe–O deformation vibration (475 and 400 cm−1). The experimental results suggest that molar concentration of oleic acid to metal nitrate plays an important role in the particle size and magnetic property of combustion synthesized lanthanum ferrite nanoparticles.

Synthesis and Characterization of Lithium-Doped Tin Dioxide Nanocrystalline Powders by Emulsion Combustion Method

Li doped SnO2 nanoparticles were synthesized using an emulsion precursor derived from a mixed-metal and oleic acid solution. The precursors and derived oxide powders were characterized by differential thermal analysis, thermogravimetric analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM), and Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). The XRD studies reveal that the material is assigned to be SnO2 tetragonal Cassiterite phase. The average particle size as determined from TEM varies in the range 12–181 nm. The amount of Li content in the sample determined by ICP-AES was found to 1.615 wt%.

ChemInform Abstract: Synthesis and Characterization of LaAlO3 Nanopowders by Emulsion Combustion Method.

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Powder Characteristics and Three-Way Catalytic Activity of Hollow Alumina Made by the Emulsion Combustion Method

Lanthanum-doped hollow alumina particles (A-E) were made by the emulsion combustion method (ECM). Powder characteristics and three-way catalytic performance were evaluated and compared with those of precipitation-made alumina (A-P). The A-E powder was gamma alumina and 40 m 2 /g in specific surface area (SSA). The unique hollow structure resulted in a broad peak at 130 nm in the pore size distribution and a large pore volume (3.0 cm 3 /g) with pore diameters of >20 nm. The A-E powder primarily maintained its shape, crystalline phase and SSA up to 1200°C, indicating high thermal stability. Conversion of total hydrocarbon (THC) started at higher temperatures for the Rh-loaded A-E pellets (Rh/A-E) than for Rh-loaded A-P pellets (Rh/A-P) because of the low dispersion of Rh for Rh/A-E. However, a gradient of the THC conversion-temperature curve was higher for Rh/A-E than for Rh/A-P. The large pore volume can promote good gas accessibility inside the pellets for Rh/A-E, resulting in the high gradient of the THC conversion-temperature curve and thus the high activity at high temperatures where gas diffusion is likely to determine the conversion efficiency. The conversion-temperature curves of CO and NO X showed primarily similar behavior to the THC ones.

Morphology of Oxide Particles Made by the Emulsion Combustion Method

Various oxide powders were prepared by the emulsion combustion method (ECM) using metal precursors, kerosene, and a surfactant. The product particles were characterized by transmission electron microscopy (TEM), nitrogen adsorption, and X‐ray diffraction. Hollow γ‐Al2O3 particles were produced from aluminum nitrate or chloride precursors dispersed in air, whereas dispersion of the precursor emulsion in oxygen resulted in solid α‐Al2O3 particles. Hollow spheres were obtained also for TiO2, ZrO2, and Y2O3 by ECM of TiCl4, zirconium oxynitrate, and yttrium nitrate in aqueous solution. A simple method was developed to predict the thickness and diameter of hollow particles using the nitrogen adsorption data and initial droplet concentration of the ECM spray. The TEM diameter and shell thickness of hollow particles were consistent with those predicted. In contrast, solid particles were formed by ECM for ZnO, Fe2O3, CeO2, and MgO from aqueous solutions of their corresponding nitrates.

Emulsion Combustion and Flame Spray Synthesis of Zinc Oxide/Silica Particles

Two flame spray methods, emulsion combustion method (ECM) and flame spray pyrolysis (FSP), were compared for synthesis of pure and mixed SiO2 and ZnO nanoparticles. The effect of silicon precursor was investigated using liquid hexamethyldisiloxane (HMDSO) or SiO2 sol, while for ZnO zinc acetate (ZA) was used. Gas phase reaction took place when using HMDSO as Si precursor, forming nanoparticles, whereas the SiO2 sol used as Si source was not evaporated in the flame, creating large aggregates of the sol particles (e.g. 1 μm). The FSP of ZA produced ZnO homogeneous nanoparticles. Lower flame temperatures in ECM than in FSP resulted in mixed gas and liquid phase reaction, forming ZnO particles with inhomogeneous sizes. The FSP of HMDSO and ZA led to intimate gas-phase mixing of Zn and Si, suppressing each other's particle growth, forming nanoparticles of 19 nm in BET-equivalent average primary particle diameter. Nucleation of ZnO and SiO2 occurred independently by ECM of HMDSO and ZA as well as by FSP of the SiO2 sol and ZA, creating a ZnO and SiO2 mixture. The reaction of ZnO with SiO2 was likely to be enhanced by ECM of the SiO2 sol and ZA where both Zn and Si species were not evaporated completely, resulting in ZnO, β-willemite and Zn1.7SiO4 mixed phase.

Characteristics and Sintering Behavior of Barium Titanate Powder Synthesized by Emulsion Combustion Method.

Barium titanate (BaTiO 3 ) powder was synthesized using the emulsion combustion method (ECM) from a water-in-oil-type emulsion, in which a barium nitrate aqueous solution, a titania sol, kerosene and a surfactant were included, at a firing temperature of 850°C. Particle characteristics and sintering behavior of the synthesized particles were evaluated. The particles of the synthesized powder were nearly spherical in shape, 200-500 nm in diameter and polycrystalline. The diameter of the particle was almost consistent with that calculated from the size of the aqueous microsphere in the emulsion, the concentration of metal ions and the density of BaTiO 3 . The X-ray diffraction (XRD) pattern showed that the main product (over 95%) was BaTiO 3 and that a small amount of Ba 2 TiO 4 was synthesized. The compact of the synthesized powder was densified up to 90% of the theoretical density at a sintering temperature of 1200°C, which was 100°C lower than that of the powder produced by the hydrothermal process. The fine polycrystalline structure of the ECM-made particles was considered to enhance the densification at a lower temperature. The sintered specimen showed a typical temperature dependence of dielectric constant in BaTiO 3 , which included two peaks at 20 and 120°C, corresponding to orthorhombic-tetragonal and tetragonal-cubic phase transitions, respectively.

Preparation and Characterization of Nano-structured Ceramic Powders Synthesized by Emulsion Combustion Method

The emulsion combustion method (ECM), a novel powder production process, was originally developed to synthesize nano-structured metal-oxide powders. Metal ions in the aqueous droplets were rapidly oxidized by the combustion of the surrounding flammable liquid. The ECM achieved a small reaction field and a short reaction period to fabricate the submicron-sized hollow ceramic particles with extremely thin wall and chemically homogeneous ceramic powder. Alumina, zirconia, zirconia–ceria solid solutions and barium titanate were synthesized by the ECM process. Alumina and zirconia powders were characterized to be metastable in crystalline phase and hollow structure. The wall thickness of alumina was about 10 nm. The zirconia–ceria powders were found to be single-phase solid solutions for a wide composition range. These powders were characterized as equiaxed-shape, submicron-sized chemically homogeneous materials. The powder formation mechanism was investigated through the synthesis of barium titanate powder with different metal sources.

Metal oxide powder synthesis by the “emulsion combustion” method

Alumina powders were synthesized by the emulsion combustion method, using w/o (water in oil) type emulsions with different aqueous microsphere sizes. The effects of microsphere size on the size and shape of the synthesized powder were evaluated. The powders were spherical and hollow in shape with a very thin shell (from 10 to 20 nm in thickness) when synthesized from large aqueous microspheres (from 200 nm to 1 μm). The sizes and specific surface areas of the powders were consistent with those calculated. Large particles, which did not correspond to the microsphere size, were obtained from small aqueous microspheres (6 nm). The short distance (7 nm) between microspheres causes the adhesion of particles during the firing process.