Effect of the addition of triphenylphosphine oxide,hexabromocyclododecane, and ethyl bromide on a CH<Subscript>4</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame at atmospheric pressure

The chemical and thermal structure of a Mache-Hebra burner stabilized premixed rich CH₄/O₂/N₂ flame with additives of vapors of triphenylphosphine oxide [(C₆H₅)₃PO], hexabromocyclododecane (C₁₂H₁₈Br₆), and ethyl bromide (C₂H₅Br) was studied experimentally using molecular beam mass spectrometry (MBMS) and a microthermocouple method. The concentration profiles of stable and active species, including atoms and free radicals, and flame temperature pro.les were determined at a pressure of 1 atm. A comparison of the experimental and modeling results on the flame structure shows that MBMS is a suitable method for studying the structure of flames stabilized on a Mache-Hebra burner under near-adiabatic conditions. The relative flame inhibition effectiveness of the added compounds is estimated from changes in the peak concentrations of H and OH radicals in the flame and from changes in the flame propagation velocity. The results of the investigation suggest that place of action of the examined flame retardants is the gas phase. __________ Translated from Fizika Goreniya i Vzryva, Vol. 43, No. 5, pp. 12–20, September–October, 2007.     

Experimental study of the structure of a rich premixed 1,3-butadiene/CH4/O2/Ar flame

The structure of a laminar rich premixed 1,3-butadiene/CH₄/O₂/Ar flame has been investigated, 1,3-butadiene, methane, oxygen, and argon mole fractions being 0.033, 0.2073, 0.3315, and 0.4280, respectively, for an equivalence ratio of 1.80. The flame has been stabilized on a burner at a pressure of 6.7 kPa. The concentration profiles of stable species have been measured by gas chromatography after sampling with a quartz probe. The quantified species include carbon monoxide and dioxide, methane, oxygen, hydrogen, ethane, ethylene, acetylene, propyne, allene, propene, cyclopropane, 1,3-butadiene, butenes, 1-butyne, vinylacetylene, diacetylene, C₅ compounds, benzene, and toluene. The temperature distribution in the flame has also been measured. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 89–95, November–December, 2006.     

Sorption studies of CO<Subscript>2</Subscript>, CH<Subscript>4</Subscript>, N<Subscript>2</Subscript>, CO,O<Subscript>2</Subscript> and Ar on nanoporous aluminum terephthalate [MIL-53(Al)]

Aluminum terephthalate, MIL-53(Al), metal–organic framework synthesized hydrothermally and purified by solvent extraction method was used as an adsorbent for gas adsorption studies. The synthesized MIL-53(Al) was characterized by powder X-Ray diffraction analysis, surface area measurement using N₂ adsorption–desorption at 77 K, FTIR spectroscopy and thermo gravimetric analysis. Adsorption isotherms of CO₂, CH₄, CO, N₂, O₂ and Ar were measured at 288 and 303 K. The absolute adsorption capacity was found in the order CO₂>CH₄>CO>N₂>Ar>O₂. Henry’s constants, heat of adsorption in the low pressure region and adsorption selectivities for the adsorbate gases were calculated from their adsorption isotherms. The high selectivity and low heat of adsorption for CO₂ suggests that MIL-53(Al) is a potential adsorbent material for the separation of CO₂ from gas mixtures. The high selectivity for CH₄ over O₂ and its low heat of adsorption suggests that MIL-53(Al) could also be a compatible adsorbent for the separation of methane from methane–oxygen gas mixtures.     

Effects of La<Subscript>2</Subscript>O<Subscript>3</Subscript> on ZrO<Subscript>2</Subscript> supported Ni catalysts for autothermal reforming of CH<Subscript>4</Subscript>

The effect of La₂O₃ content in Ni-La-Zr catalyst was investigated for the autothermal reforming (ATR) of CH₄. The catalysts were prepared by the coprecipitation method and had a mesoporous structure. Temperature programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) indicated that a strong interaction developed between Ni species and the support with the addition of La₂O₃. Thermogravimetric analysis (TGA) and H₂-pulse chemisorption showed that the addition of La₂O₃ led to well dispersed NiO molecules on the support. Ni-La-Zr catalysts gave much higher CH₄ conversion than Ni-Zr catalyst. The Ni-La-Zr containing 3.2 wt% La₂O₃ showed the highest activity. The optimum conditions for maximal CH₄ conversion and H₂ yield were H₂O/CH₄=1.00, O₂/CH₄=0.75. Under these conditions, CH₄ conversion of 83% was achieved at 700 °C. In excess O₂ (O₂/CH₄>0.88), the catalytic activity was decreased due to sintering of the catalyst.     

Phase equilibria in the Ho<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> system

The phase formation is investigated and the phase diagram of the Ho₂O₃-SrAl₂O₄ system is constructed. A ternary compound, namely, Ho₂SrAl₂O₇, is revealed. It is established that this compound undergoes incongruent melting.     

Highly ordered mesoporous CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript> and CuFe<Subscript>2</Subscript>O<Subscript>4</Subscript> with crystalline walls

The highly ordered mesoporous CoFe₂O₄ and CuFe₂O₄ with crystalline walls can be synthesized by hard template with using mesoporous silica SBA-15 as hard template and using ferric nitrate, cobalt nitrate, and copper nitrate as metal precursors. These new mesoporous materials above have high surface areas, narrow pore size distribution, and large pore volumes, which are believed to be valuable for the potential application in the field of sensors, catalysis, message recording, magnetics, and biology. This work provides a method to fabricate the highly ordered mesoporous materials composed of multi-metal oxides with crystalline walls. The development of such versatile approach is of great significance in practical application. It can be envisaged that this established method is significantly expandable to the controlled synthesis of the mesoporous functional materials with diverse compositions.     

Phase Equilibria in the Gd<Subscript>2</Subscript>O<Subscript>3</Subscript>-SrAl<Subscript>2</Subscript>O<Subscript>4</Subscript> System

The phase equilibria are investigated and the phase diagram is constructed for the Gd₂O₃-SrAl₂O₄ pseudobinary join of the Gd₂O₃-SrO-Al₂O₃ ternary oxide system. One ternary compound, namely, Gd₂SrAl₂O₇, is revealed in the Gd₂O₃-SrAl₂O₄ join. It is found that this compound undergoes congruent melting.     

Effect of carbon deposition over carbonaceous catalysts on CH<Subscript>4</Subscript> decomposition and CH<Subscript>4</Subscript>-CO<Subscript>2</Subscript> reforming

An investigation was made using a continuous fixed bed reactor to understand the influence of carbon deposition obtained under different conditions on CH₄-CO₂ reforming. Thermogravimetry (TG) and X-ray diffraction (XRD) were employed to study the characteristics of carbon deposition. It was found that the carbonaceous catalyst is an efficient catalyst in methane decomposition and CH₄-CO₂ reforming. The trend of methane decomposition at lower temperatures is similar to that at higher temperatures. The methane conversion is high during the initial of stage of the reaction, and then decays to a relatively fixed value after about 30 min. With temperature increase, the methane decomposition rate increases quickly. The reaction temperature has significant influence on methane decomposition, whereas the carbon deposition does not affect methane decomposition significantly. Different types of carbon deposition were formed at different methane decomposition reaction temperatures. The carbon deposition Type I generated at 900°C has a minor effect on CH₄-CO₂ reforming and it easily reacts with carbon dioxide, but the carbon deposition Type II generated at 1000°C and 1100°C clearly inhibits CH₄-CO₂ reforming and it is difficult to react with carbon dioxide. The results of XRD showed that some graphite structures were found in carbon deposition Type II.     

Initiation of combustion of a CH<Subscript>4</Subscript>-O<Subscript>2</Subscript> mixture in a supersonic flow with excitation of O<Subscript>2</Subscript> molecules by an electric discharge

The possibility of intensification of ignition of a methane-oxygen mixture in a supersonic flow behind the front of an oblique shock wave by means of excitation of O₂ molecules to the states a ¹Δ_g and b ¹Σ_g⁺ in an electric discharge is discussed. Through numerical simulations, activation of O₂ molecules by an electric discharge is demonstrated to speed up chain reactions in the CH₄-O₂ mixture and to reduce the induction-zone length. Even a small amount of energy input to O₂ molecules in the discharge (≈3·0⁻² J/cm³) can reduce the ignition-delay length by a factor of hundreds and initiate combustion at distances of ≈1 m from the discharge zone at comparatively low temperatures of the gas behind the front (≈1000 K) and moderate pressures (≈10⁵ Pa). Excitation of O₂ molecules by an electric discharge is much more efficient than simple heating of the mixture. __________ Translated from Fizika Goreniya i Vzryva, Vol. 44, No. 3, pp. 3–16, May–June, 2008.     

Synthetic spinels of the system MgO-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

Synthetic spinels of the system MgO-Cr₂O₃-Al₂O₃-Fe₂O₃ are considered and the desirability of organizing their production for the refractory industry is demonstrated. Translated from Novye Ogneupory, No. 6, pp. 32–35, June 2008.     

Structure of an atmospheric-pressure H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/N<Subscript>2</Subscript> flame doped with iron pentacarbonyl

This paper presents the measurement and simulation data on the thermal and chemical structure of an atmospheric-pressure premixed H₂/O₂/N₂ flame doped with iron pentacarbonyl Fe(CO)₅. Soft ionization molecular beam mass spectrometry was used to measure concentration profiles of the combustion products of iron pentacarbonyl: Fe, FeO₂, FeOH, and Fe(OH)₂. A comparison of experimental and simulated concentration profiles showed that they are in satisfactory agreement for FeO₂ and Fe(OH)₂ and differ significantly for Fe and FeOH. Thus, the previously proposed kinetic model for the oxidation of iron pentacarbonyl was tested and it was shown that the mechanism needs further elaboration.     

Interaction of O<Subscript>2</Subscript>, O<Subscript>3</Subscript>, and H<Subscript>2</Subscript>O<Subscript>2</Subscript> with an activated carbon

The results of the modification of AG-OV-1 activated carbon under various conditions (by atmospheric oxygen at elevated temperatures and by hydrogen peroxide or ozone) are given. The effect of the used modifier on changes in the porosity, surface state, and adsorption capacity of activated carbon is evaluated.     

Degradation kinetics of recalcitrant organic compounds in a decontamination process with UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript> and UV/H<Subscript>2</Subscript>O<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> processes

In this study, degradation aspects and kinetics of organics in a decontamination process were considered in the degradation experiments of advanced oxidation processes (AOP),i.e., UV, UV/H₂O, and UV/H₂O,/TiO₂ systems. In the oxalic acid degradation with different H₂O₂ concentrations, it was found that oxalic acid was degraded with the first order reaction and the highest degradation rate was observed at 0.1 M of hydrogen peroxide. Degradation rate of oxalic acid was much higher than that of citric acid, irrespective of degradation methods, assuming that degradation aspects are related to chemical structures. Of methods, the TiO₂ mediated photocatalysis showed the highest rate constant for oxalic acid and citric acid degradation. It was clearly showed that advanced oxidation processes were effective means to degrade recalcitrant organic compounds existing in a decontamination process.     

Separation characteristics of tetrapropylammoniumbromide templating silica/alumina composite membrane in CO<Subscript>2</Subscript>/N<Subscript>2</Subscript>, CO<Subscript>2</Subscript>/H<Subscript>2</Subscript> and CH<Subscript>4</Subscript>/H<Subscript>2</Subscript> systems

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support ( γ-Al₂O₃/ α-Al₂O₃ composite) by dip coating and then heat-treated at 550 °C. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO₂/N₂, CO₂/H₂ and CH₄/H₂ systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al₂O₃ support and nanoporous unsupport (TPABr templating SiO₂/ γ-Al₂O₃ composite layer without α-Al₂O₃ support) were investigated at 20–40 °C conditions and 0.0–1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al₂O₃ support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO₂ and CH₄. While the adsorption rates in the unsupport showed in the order of H₂> CO₂> N₂> CH₄ at low pressure range, the permeate flux in the membrane was in the order of H₂≫N₂> CH₄> CO₂. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbable/non-adsorbable mixed gases, such as CO₂/H₂ and CH₄/H₂ systems. Although light and non-adsorbable molecules, such as H₂, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO₂ and CH₄, showed a higher separation factor (CO₂/H₂=5-7, CH₄/H₂=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Synthesis and crystal structure of a new oxohalide CdPb<Subscript>2</Subscript>O<Subscript>2</Subscript>Cl<Subscript>2</Subscript>

A new compound, CdPb₂O₂Cl₂, is synthesized by the method of solid-phase reactions. The compound has monoclinic symmetry, space group C2/m, a = 12.392(8) Å, b = 3.8040(14) Å, c = 7.658(5) Å, β = 122.64(5)°, and V = 304.0(3) ų. The structure contains one symmetrically independent position of the Pb²⁺ cation coordinated by three O^2? anions (Pb²⁺-O^2? = 2.29–2.34 Å) and five Cl^? anions (Pb²⁺-Cl^? = 3.35–3.57 Å). The Cd²⁺ cation has a symmetric coordination with the formation of two bonds Cd-O = 2.15 Å and four bonds Cd-Cl = 2.73 Å. The oxygen atom is tetrahedrally coordinated by three Pb²⁺ cations and one Cd²⁺ cation, which leads to the formation of oxo-centered heterometallic OPb₃Cd tetrahedra. The tetrahedra are linked together into chains through common Pb atoms and into layered complexes due to sharing of the equatorial Cd atoms. The chlorine atoms are located above the cavities of the oxo-centered layer.     

Ni-Co bimetallic catalyst for CH<Subscript>4</Subscript> reforming with CO<Subscript>2</Subscript>

A co-precipitation method was employed to prepare Ni/Al₂O₃-ZrO₂, Co/Al₂ O₃-ZrO₂ and Ni-Co/Al₂O₃-ZrO₂ catalysts. Their properties were characterized by N₂ adsorption (BET), thermogravimetric analysis (TGA), temperature-programmed reduction (TPR), temperature-programmed desorption (CO₂-TPD), and temperature-programmed surface reaction (CH₄-TPSR and CO₂-TPSR). Ni-Co/Al₂O₃-ZrO₂ bimetallic catalyst has good performance in the reduction of active components Ni, Co and CO₂ adsorption. Compared with mono-metallic catalyst, bimetallic catalyst could provide more active sites and CO₂ adsorption sites (C + CO₂ = 2CO) for the methane-reforming reaction, and a more appropriate force formed between active components and composite support (SMSI) for the catalytic reaction. According to the CH₄-CO₂-TPSR, there were 80.9% and 81.5% higher CH₄ and CO₂ conversion over Ni-Co/Al₂O₃-ZrO₂ catalyst, and its better resistance to carbon deposition, less than 0.5% of coke after 4 h reaction, was found by TGA. The high activity and excellent anti-coking of the Ni-Co/Al₂O₃-ZrO₂ catalyst were closely related to the synergy between Ni and Co active metal, the strong metal-support interaction and the use of composite support.     

Crystal structure of the K<Subscript>2</Subscript>(Zn<Subscript>3</Subscript>P<Subscript>4</Subscript>O<Subscript>14</Subscript>) compound

Single crystals of potassium zinc phosphate, namely, K₂(Zn₃P₄O₁₄), are grown by crystallization of a glass of the related compound. The crystal structure of the compound is determined using single-crystal X-ray diffraction.     

Synthesis and characterization of rubbery/glassy blend membranes for CO<Subscript>2</Subscript>/CH<Subscript>4</Subscript> gas separation

A series of blend membranes made from the rubbery polyether block amide (Pebax®1657) and a glassy polymer, polyethersulfone (PES) or Matrimid 5218, were fabricated by solution casting with different ratios (10–40 %), in order to combine high permeability of the former with high selectivity of the latter polymer for CO₂/CH₄ gas separation. The membranes were characterized by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FTIR), and stress–strain tests. These blend membranes showed two distinct T _g s, indicating their immiscible nature as confirmed by SEM images. However, weak intermolecular interaction between polymers, as illustrated by the FTIR results, corresponds to some degree to their compatibility and improved mechanical strength, compared to the pure Pebax®. TGA analysis revealed that addition of glassy polymer improved membranes’ thermal stability. Effect of feed pressure on membrane separation, investigated by three different pressures (4, 8, and 12 bar), indicated increased permeability for higher pressures for both CO₂ and CH₄. Gas separation tests also pointed to improved separation properties of the blend membranes compared to those of the neat polymers, prepared the same way.     

Synthesis of nickel catalysts supported on Zr-doped ordered mesoporous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and their catalytic performance for low-temperature CO<Subscript>2</Subscript> reforming of CH<Subscript>4</Subscript>

A series of Zr-doped ordered mesoporous Al₂O₃ with various Zr contents were synthesized by evaporation-induced self-assembly strategy and the Ni-based catalysts supported on these Al₂O₃ materials were prepared by impregnation method. These catalysts with large specific surface area, big pore volume, uniform pore size possess excellent catalytic performance for the low-temperature carbon dioxide reforming of methane. The activities of these catalysts were tested in carbon dioxide reforming of methane reaction with temperature increasing from 500 to 650?°C and the stabilities of these catalysts were evaluated for long time reaction at 650?°C. It was found that when Zr/(Zr?+?Al) molar ratio?=?0.5%, the Ni/0.5ZrO₂–Al₂O₃ catalyst showed the highest activity, and exhibited superior stabilization compared to the Ni-based catalyst supported on traditional ordered mesoporous Al₂O₃. The “confinement effect” from mesoporous channels of alumina matrix is helpful to stabilize the Ni nanoparticles. As a promoter, Zr could stabilize the ordered mesoporous framework by reacting with Al₂O₃ to form ZrO₂–Al₂O₃ solid solution. Since ZrO₂ enhances the dissociation of carbon dioxide, more oxygen intermediates are given to remove the carbon formed during the reaction.