Structural and magnetic features of La0.7Sr0.3Mn1−xCoxO3 nano-catalysts for ethane combustion and CO oxidation

Structural, magnetic and catalytic properties of La_0.7Sr_0.3Mn_1−xCo_xO₃ (x=0.00, 0.25, 0.50, 0.75, 1.00) nano-perovskites prepared by the citrate method are investigated. The structural characterization of the compounds by X-ray powder diffraction and using X׳Pert package and Fullprof program is an evidence for a monoclinic structure (P21/n space group) with x=0.50 and a rhombohedral structure (R-3c space group) for other samples. These results have been confirmed by the FT-IR measurements. Crystallite size of the powders obtained from Halder–Wagner method has been compared with the Scherrer method. The structural and magnetic results suggest the presence of different concentrations of various cations of Co⁺², Co⁺³, Co⁺⁴, Mn⁺⁴ and Mn⁺³ in the samples. Activation energy, band gap energy, and electrical conductivity measurements have been employed to explain catalytic performance of the samples. The results of performance tests show that the sample with x=0.25 has the highest catalytic activity for CO oxidation, whereas, the sample with x=0.75 has the highest catalytic activity for C₂H₆ combustion.     

Surfactant (in situ)–Surfactant (Synthetic) Interaction in Na2CO3/Surfactant/Acidic Oil Systems for Enhanced Oil Recovery: Its Contribution to Dynamic Interfacial Tension Behavior

The effect of synthetic surfactant molecular structure on the dynamic interfacial tension (DIFT) behavior in Na₂CO₃/surfactant/crude oil was investigated. Three surfactants, a nonionic (iC₁₇(EO)₁₃), an alcohol propoxy sulfate (C_14–15(PO)₈SO₄), and sodium dodecyl sulfate (SDS) were considered in this study. Sodium tripolyphosphate (STPP) was added to ensure complete compatibility between brine and Na₂CO₃. In Na₂CO₃/iC₁₇(EO)₁₃/oil and Na₂CO₃/C_14–15(PO)₈SO₄/oil systems, a strong synergistic effect for lowering the dynamic interfacial tension was observed, in which the dynamic IFT are initially reduced to ultralow transient minima in the range 1.1 × 10^?3–6.6 × 10^?3 mNm^?1 followed by an increment to a practically similar equilibrium value of 0.22 mNm^?1 independent of Na₂CO₃ concentration (for iC₁₇(EO)₁₃) and to decreasing equilibrium values with increasing alkali concentrations (for C_14–15(PO)₈SO₄). The observed difference in the equilibrium IFT for the two systems suggest that in both systems, the mixed interfacial film is efficient in reducing the dynamic interfacial tension to ultralow transient minima (～10^?3 mNm^?1) but the mixed film soap‐iC₁₇(EO)₁₃ is much less efficient than the mixed film soap‐C_14–15(PO)₈SO₄ in resisting soap diffusion from the interface to the bulk phases. In both systems, the synergism was attributed, in part, to the intermolecular and intramolecular ion–dipole interactions between the soap molecules and the synthetic surfactant as well as to some shielding effect of the electrostatic repulsion between the carboxylate groups by the nearby ethylene oxide (13 EO) and propylene oxide (8 PO) groups in the mixed interfacial monolayer. SDS surfactant showed a much lower synergism relative to iC₁₇(EO)₁₃ and C_14–15(PO)₈SO₄, probably due to the absence of ion–dipole interactions and shielding effect in the mixed interfacial layer at the oil–water interface.     

Removal of 1,1′-Dimethyl-4,4′bipyridyl Dichloride from Aqueous Solution by Natural and Activated Bentonite

The sorption of 1,1′-dimethyl-4,4′bipyridilium dichloride (paraquat) on bentonite desiccated at 110°C untreated, and acid-treated with H₂SO₄ solutions over a concentration range between 0·25 M and 1·00 M , from aqueous solution at 30°C has been studied by using batch experiments. In addition, column experiments were carried out with the bentonite sample treated with the 1·00 M H₂SO₄ solution [B-A(1·00)] by using two aqueous solutions of paraquat of different concentrations (C = 29·40 mg dm⁻³ and C = 65·38 mg dm⁻³). The experimental data points have been fitted to the Langmuir equation in order to calculate the sorption capacities (X_m) of the samples; X_m values range from 1·35×10⁵ mg kg⁻¹ for the sample acid-treated with 0·375 M H₂SO₄ [B-A(0·375)] up to 1·96×10⁵ mg kg⁻¹ for the untreated bentonite [B-N]. The removal efficiency (R) has also been calculated; R values ranging from 44·61% for the [B-A(0·375)] sample up to 67·23% for B-N. The batch experiments show that the natural bentonite is more effective than the acid-treated bentonite in relation to sorption of paraquat. The column experiments show that the B-A(1·00) sample might be reasonably used in removing paraquat, the column efficiency increasing from 37·55% for the C = 65·38 mg dm⁻³ aqueous solution of paraquat up to 66·58% for the C = 29·40 mg dm⁻³ one. © 1997 SCI.     

The vapour-liquid equilibrium of ternary systems with limited miscibility at atmospheric pressure

The complete study of the vapour-liquid equilibrium of ternary systems with limited miscibility requires vapour-liquid equilibrium determinations and liquid-liquid equilibrium determinations at boiling point. The vapour-liquid equilibrium was determined by means of an equilibrium still based on the principle of Giilespie but modified in such a way that an accurate boiling point measurement, even for systems with heterogeneous liquid was possible and that the vapour phase was analysed without previous condensation. Two ternary systems have been studied: the system methanol-ethylacetate-water and the system ethanol-ethylacetate-water. The ternary data have been predicted by means of the equation of Renon and Prausnitz. The parameters are determined by correlating the binary data. The ternary vapour-liquid equilibrium are predicted within 1-2. 10 ^?2 mol fraction for the vapour composition and 1°C for the boiling point. The position of the predicted tielines of the liquid-liquid equilibrium at boiling point was almost coinciding with the position of the experimental tielines. There was a slight deviation of the predicted and experimental binodal.     

Phase equilibrium of the CO2/glycerol system: Experimental data by in situ FT-IR spectroscopy and thermodynamic modeling

Phase equilibrium experimental data for the CO₂/glycerol system are reported in this paper. The measurements were performed using an in situ FT-IR method for temperatures ranging from 40 °C to 200 °C and pressures up to 35.0 MPa, allowing determination of the mutual solubility of both compounds. Concerning the CO₂ rich phase, it was observed that the glycerol solubility in CO₂ was extremely low (in the range of 10⁻⁵ in mole fraction) in the pressure and temperature domains investigated here. Conversely, the glycerol rich phase dissolved CO₂ at mole fractions up to 0.13. Negligible swelling of the glycerol rich phase has been observed. Modeling of the phase equilibrium has been performed using the Peng–Robinson equation of state (PR EoS) with classical van der Waals one fluid and EoS/G^E based mixing rules (PSRK and MHV2). Satisfactory agreement was observed between modeling results and experimental measurements when PSRK mixing rules are used in combination with UNIQUAC model, although UNIFAC predictive approach gives unsatisfactory representation of experimental behavior.     

Pressure dependent mechanical properties of calcium carbides

The mechanical properties of newly synthesized Ca₂C₃ and Ca₂C under pressure have been studied by using the first-principles calculations with generalized gradient approximation. The equilibrium geometry, elastic stiffness constants, various moduli, and Pugh's ratio of the C2/m phase of Ca₂C₃ and the C2/m and Pnma phases of CaC₂ are systematically studied. The elastic stiffness constants of C2/m-Ca₂C₃ under 0–30GPa, C2/m-Ca₂C under 0–7.5 GPa, and Pnma-Ca₂C under 7.5–30 GPa satisfy the Born?Huang mechanical criteria. The three phases of calcium carbides exhibit ductile characteristics. The surface constructions of bulk and Young's moduli illustrate the mechanical anisotropy of Ca₂C₃ and Ca₂C. Our results are consistent with previously obtained experimental and theoretical data and have significant implications for the application of calcium carbides.     

Removal of 3—(3,4—dichlorophenyl)—1, 1 dimethylurea from aqueous solution by natural and activated bentonite

The adsorption of 3-(3,4-dichlorophenyl)-1,1 dimethylurea (diuron) on bentonite desiccated at 110°C untreated, and acid treated with H₂SO₄ solutions over a concentration range between 0.25 M and 5.00 M, from aqueous solution at 30°C has been studied. In addition, adsorption of diuron on combined acid/heat treated samples (0.50 M and 2.50 M H₂SO₄/200°C and 400°C) has also been studied. The experimental data points have been fitted to the Freundlich equation in order to calculate the adsorption capacities (K) of the samples; K values range from 0.92 μg g^?1 for the untreated bentonite up to 974.42 μg g^?1 for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The removal efficiency (R) has also been calculated; R values ranging from 2.02% for the untreated bentonite up to 97.17% for the 0.50 M H₂SO₄/400°C acid/heat treated bentonite. The adsorption experiments show that bentonite heat treatment is more effective than bentonite acid treatment in relation to adsorption of diuron.     

The applicability of a nitrate melt as a cell electrolyte in a flue gas desulphurization cell

This paper presents equilibrium and kinetic studies of the O₂ and O₂/SO₂ electrodes in molten NaNO₃-KNO₃ eutectic at 380°C. For the O₂ electrode the overall reaction is given by the equation: $\text{1}\text{2}$O₂ + 2e^? = O^2?.The exchange currents for this reaction are higher with platinum than with gold and are 1–2 orders of magnitude higher than those previously measured in molten sulphates.The overall reaction of the O₂/SO₂ electrode is: SO₂ + O₂ + 2e^? = SO^2?₄.Gold is a better catalyst than platinum for this reaction, quite similar to the case in molten sulphates. Molten NaNO₃-KNO₃ seems to be an appropriate electrolyte for use in a new electrochemical flue gas desulphurization process in the temperature range of 350–450°C.     

Mechanism of inhibition of electrode reactions at high surface coverages—II

The inhibition of Cu²⁺, Cd²⁺ and Zn²⁺ discharge reactions was studied in the presence of C₄–C₆ alcohols, phenol, benzyl alcohol and cyclohexanol (SAS) in 0.5 M Na₂SO₄ + 1 mM H₂SO₄ supporting electrolyte. It is found from the results that at high surface coverages by SAS, the inhibition is due to “sieve effect” which is different from that at low coverages. The true standard rate constant is proportional to exp[(? N ΔγA_i)/(RT)] where ΔγA_i is the extra energy (in the form of work) that must be done in order to create a free area required for a discharge reaction.     

Polarization and dc capacitance of passive aluminium electrodes

The title subject has been studied by stationary and transient polarization measurements on high-purity aluminium electrodes in acetate solutions of pH 3.5–7.2 at 25°C. The potential range covered is from −1.1 to 1.0 V (sce). Potentiostatic transients accord with the Cabrera-Mott equation. Galvanostatic transients yield dc capacitance data fitting C⁻¹/E′ lines with slopes inversely equal to the surface charge density on the metal at the metal/oxide interface. The extrapolated potential of zero inverse capacitance coincides with the extrapolated potential of zero oxide film thickness. This suggests C = C_ox (invalidating C⁻¹ = C⁻¹_ox + C⁻¹_H) for the passive aluminium electrode. The data give about 20/r (r being the roughness factor) for the static dielectric contant of the passivating oxide film.     

Enhanced catalytic performance over Fe2O3-doped Pt/SO42 −/ZrO2 in n-heptane hydroisomerization

A series of Fe₂O₃-doped (1–5%) Pt/SO₄^2 −/ZrO₂ were prepared by a co-precipitation method. The incorporation of small amounts of Fe₂O₃ into Pt/SO₄^2 −/ZrO₂ results in an enhanced Brønsted acidity in the presence of H₂, which makes the Fe₂O₃-doped catalysts much more active than the undoped one for n-heptane hydroisomerization. A maximal yield of C₇ isomers appears at 3.5% Fe₂O₃.     

Vapour liquid equilibrium calculations for dilute aqueous solutions of CO2, H2S,NH3 and NaOH to 300°C

Henry's law constants for aqueous CO₂, H₂S and NH₃ up to 300°C have been recalculated from literature vapour pressure, enthalpy and heat capacity data. The high vapour pressure of water above 150°C causes significant solute-water interactions in the gas phase, which were calculated using the Peng-Robinson cubic equation of state. The results were combined with selected ionization constant data to derive a vapour-liquid equilibrium model for dilute solutions. The model reproduces experimental data for binary systems at solute molalities of up to 0.5 m at 100°C, 1.0 m above 250°C and ionic strengths below about 0.1 m.     

Prediction of phase behaviour of gas-containing systems with cubic equations of state

The Soave Redlich-Kwong (S.R.K.) equation of state is used to correlate the phase behaviour of light compounds-containing systems and gas-hydrocarbon systems. Gases considered include H₂, CH₄, N₂, CO₂, CO and SH₂. An extensive literature search was conducted to obtain the binary experimental vapour-liquid equilibrium data which were used to build a predictive procedure of phase behaviour. Average error in bubble pressure predictions for 812 isothermal data sets (4399 experimental points) is 4%. Calculations with systems containing highly polar substances, water and methanol, are included. Good results are obtained when the proposed method is used to predict phase behaviour of some ternary systems typically encountered in petroleum and related industries.     

Promoting and inhibiting effect of SO2 on propane oxidation over Pt/Al2O3

SO₂ adsorption, SO₂ oxidation and oxidation of propane with oxygen in the absence and the respective presence of SO₂ in the feed gas were studied over unsulfated and sulfated 1% Pt/γ-Al₂O₃.Results showed that the promoting effect of SO₂ in the reaction flux on C₃H₈ oxidation over 1% Pt/γ-Al₂O₃ depends on the presulfating temperature. Catalytic activity measurements and FTIR absorption spectra showed that during propane oxidation, Pt/support interfacial adsorbed species were formed at temperatures 25–300 °C, inhibiting C₃H₈ oxidation. However, at higher temperatures these Pt/support interfacial adsorbed species were oxidized, leading to Pt/support interfacial sulfate species, which strongly promote propane oxidation.     

Solid-liquid equilibria in concentrated aqueous salt solutions—systems with a common ion

A thermodynamic correlation is presented for solid-liquid equilibria in concentrated aqueous salt systems containing a common ion. It is assumed that no solid solutions are formed, although the solid phase can be a pure salt, a multiple salt or a hydrate. Predictions of solid-liquid equilibria in multicomponent systems are made using parameters calculated from solid-liquid equilibrium data for the constituent binary and ternary systems.Parameters are given for the prediction of solid-liquid equilibria in the aqueous system containing Na⁺, K⁺, Mg⁺⁺, NO^?₃, Cl^?, SO^--₄ from 0–50°C. These parameters correlate the available solid-liquid equilibrium data for ternary systems with an error in liquid-phase composition of less than 2 grams salt/100 grams H₂O. Errors are similar in the estimation of solid-liquid equilibria in four-component systems such as NaNO₃-NaC1-Na₂SO₄-H₂O.     

The influence of precure dilation on the stress–strain properties of ethylene–propylene terpolymer networks

A study has been made of the influence of a dilating liquid, present during vulcanization, on the stress–strain behavior of EPT vulcanizates. Stress–strain measurements performed on the vulcanizates after extraction of the dilating liquid, taken over a range of strain rates, indicate the effective absence of time-dependent behavior and suggest that a close approach to equilibrium has been achieved. From the experimental data, values of the C₁ and C₂ constants of the empirical Mooney-Rivlin equation were derived. It was found that both C₁ and C₂ decreased with increased precure dilation, C₂ decreasing more rapidly than C₁. The observed decrease in C₁ is less than would be predicted by simple analogy with the Gaussian modulus; it is suggested that this difference might be explained by changes in network configuration and topology associated with the precure dilation.     

Potential of the Pb,PbSO4/H2SO4 electrode at temperatures up to 240°C

Standard lead—lead sulphate electrode potential was determined over the temperature range 20–240°C from emf measurements of the Pb, PbSO₄H₂SO₄ (0.05M)K₂SO₄KClHCl(0.1M)/AgCl, Ag and Pb, PbSO₄H₂SO₄(m)K₂SO₄H₂SO₄(0.05M)PbSO₄, Pb cells where m = 0.005, 0.01, 0.1 and 0.5 M. To this effect lead—lead sulphate electrode potential was calculated using the temperature relationship of the standard silver—silver chloride electrode potential and activity coefficients of hydrochloric acid determined by Greeley et al. at temperatures up to 260°C. Diffusion potentials occurring at the phase boundaries in the cells under investigation were calculated using the Henderson's equation. Values of the standard lead—lead sulphate electrode potential were determined by extrapolation of the E°′ function to the zero ionic strength which was calculated using the second sulphuric acid dissociation constant determined by Lietzke et al. at temperatures up to 300°C. The standard electrode potential was described in the temperature range 20–240°C by the following relationship: E°_{Pb, PbSO4/SO^2?4}(V) = 0.040-0.00126T. A change in entropy ΔS° of the electrode reaction Pb + SO^2?₄ = PbSO₄ + 2e^? is constant in this temperature range and is ?243 JK^?1 mol^?1 (?1018 cal K^?1 mol^?1).     

Performance of a UV‐assisted Hydrogen‐peroxide‐fed Spray Tower for Sulfur Dioxide Abatement

Spray towers are widely used for controlling air pollution by gases such as SO₂, CO₂, NO_x, and HCl. Results of sulfur dioxide absorption in a spray tower using solutions of 1 g L^–1 and 2 g L^–1 of hydrogen peroxide are reported. For comparison, a water and sodium hydroxide solution was also used for SO₂ abatement. The results indicate that H₂O₂ may be an important alternative for SO₂ removal in spray towers. A set of experimental removal efficiency data was obtained as a function of gas and liquid flow rates. Volumetric mass transfer coefficients (k_ga) were calculated and an experimental relationship among k_ga, gas, and liquid flow rates was proposed. As a final experiment, an oxidation process assisted by UV radiation using a 1 g L^–1 solution of H₂O₂ was carried out to speed up the SO₂ removal rate. The results obtained in this condition are similar to those achieved with a solution of 2 g L^–1 H₂O₂.     

Kinetic model of CaO/fly ash sorbent for flue gas desulphurization at moderate temperatures

Characteristics of the sulphation reaction between SO₂ and CaO/fly ash sorbent were analyzed based on TGA results to develop a kinetic model for a dry moderate temperature (400–800 °C) FGD process. It was found that SO₂ diffusion within sorbent particles involved three sub-processes: inter-particle diffusion, inter-grain diffusion and diffusion through product layers and the diffusion dominated the whole sulphation reaction process. The activation energy for product layer diffusion E_diff of 49.3 kJ mol⁻¹ being greater than the chemical reaction activation energy E_a of 13.9 kJ mol⁻¹ verified the importance of the diffusion. Predictions using the kinetic model in which k₀ varies with temperature agree well with the experimental data.     

1-Hexene Double Bond Isomerization Reaction Over SO 4 = Promoted NiO, Al2O3 and ZrO2 Acid Catalysts

Sulfated mixed oxides, SO ₄ ⁼ /Ni–Al–O and SO ₄ ⁼ /Zr–Al–O were evaluated for double bond isomerization (DBI) of 1-hexene using helium and hydrogen as carrier gases. The increase of temperature from 100 to 200 °C seems to favor the deprotonation pathway and contribute to increase the 1-hexene conversion for both catalysts and without regard of the carrier gas. The results indicate that temperature it is the main factor that contributes to improve both conversion and selectivity towards (cis + trans)-2-hexene, while the reductive atmosphere beneficiate only the SO ₄ ⁼ /Ni–Al–O catalyst performance, as hydrogen prevents this catalyst from a fast deactivation.