The effect of the duration of n-butane/air pretreatment on the morphology and reactivity of (VO)2P2O7 catalysts

Three vanadium pyrophosphate catalysts have been prepared by calcining vanadium hydrogen phosphate hemihydrate (VOHPO₄0.5H₂O, prepared in an organic medium) for different lengths of time (40, 100 and 132 h) in a n-butane (0.75%)/air mixture at 473 K. The catalysts were designated VPO40, VPO100 and VPO132. Increasing the duration of reaction with n-butane/air mixture led to an increase in the total surface area from 21.3 m²g^–1 (VPO40) to 24.9 m²g^–1(VPO100) and to 27.0 m²g^–1(VPO132). It also led to the complete removal of the VOPO₄ phase from catalysts VPO100 and VPO132, this VOPO₄ phase having seen as a minor component of catalyst VPO40. Scanning electron microscopy showed that longer periods of pretreatment in the n-butane/air mixture produced catalysts with increasing amounts of a characteristic rosette-type of agglomerate. Temperature-programmed reduction with H₂ resulted in the removal of 11 monolayers equivalent of oxygen from all three of these catalysts at a peak maximum temperature of 1000 K with the development of a second reduction peak at 1100 K which increases with increasing time of n-butane/air pretreatment. The morphology produced by extended pretreatment in the n-butane/air mixture at 673 K is therefore predisposed to reaction with H₂ (and probably with n-butane). Apparently paradoxically, increasing the duration of n-butane/air pretreatment results in catalysts which on temperature-programmed desorption desorb less oxygen.     

Spectroscopic Study of the Vanadium-Phosphate Catalyst Used in the Selective Oxidation of n-Butane to Maleic Anhydride

UV—VIS and electron spin resonance spectra were used to investigate the electronic structure of the vanadium—phosphate catalyst used in the selective oxidation of n-butane to maleic anhydride during its preparation as well as in the course of its interaction with oxygen and n-butane or with a mixture of these two substances. V³⁺ and V⁴⁺ were identified in the catalyst. It has been shown that V³⁺ ions can act as electron donor (via the transition V³⁺ → V⁴⁺) during the adsorption of oxygen and thus participate in the catalytic oxidation of n-butane.     

A comparative study of electrocoagulation and electro-Fenton for food industry wastewater treatment: Multiple response optimization and cost analysis

ABSTRACT

In this study, response surface methodology was applied for food wastewater by electrocoagulation (EC) and electro-Fenton (EF) processes. The optimum conditions for the chemical oxygen demand (COD) removal were found to be 21.36 min, pH 10 and 86 mA/cm² in EC, whereas 27.11 min, pH 2.38, 86 mA/cm² and H₂O₂/COD:2 in EF process. COD removal efficiencies were determined to be 29.4% for EC and 59.1% for EF processes and higher than 99% total suspended solids removal efficiencies were achieved. It can be concluded that high COD removal was obtained (4998 mg/L COD removal by EC and 10,047 mg/L COD removal by EF).     

Hydroconversion of n-heptane on platinum/H-Mordenite catalysts prepared via different routes

Two Pt/H-mordenite catalysts were prepared via different routes: (a) by impregnating H₂PtCl₆ in H-mordenite (HM) (catalyst 1) and (b) in NH₄HM (catalyst II), followed by drying, calcination and reduction. Catalyst I was found (i) to be more active for n-heptane hydroconversion, (ii) to be more selective for its isomerisation, (iii) to encounter more diffusion limitation as it yields a larger Thiele modulus, (iv) to give a lower effectiveness factor and (v) to give lower activation energy, E_a, values than catalyst II. A study of the pressure effect between 1·5 and 5·5 MNm^?2 showed an increase of the catalytic activities to a maximum at 3·0 MNm^?2, followed by a decrease. A compensation effect plot gave a linear relationship between In A (pre-exponential factor in the Arrhenius equation) and E_a at various pressures for n-heptane hydroconversion and its hydrocracking. High selectivities for central hydrocracking of heptane components and high iso-butane to n-butane ratios were obtained on both catalysts.     

Influence of the nature and porosity of different supports on the acidic and catalytic properties of H3PW12O40

In order to obtain highly dispersed heteropolyacid (HPA) species, H₃PW₁₂O₄₀ was supported on various supports exhibiting different porosities and surface chemical properties. Amorphous and monoclinic amphoteric zirconias, activated montmorillonite (AC) and hexagonal silica (HMS) were chosen as supports. It was observed that the zirconia support partly decomposed HPA at low coverage, giving the lacunary anion PW₁₁O₃₉ ^7–, due to the reaction with basic hydroxyl groups, whereas montmorillonite and HMS did not. Catalytic properties for n-butane to isobutane isomerisation at 473 K and propan-2-ol decomposition at 353 K were compared for all samples as a function of HPA loadings and compared to data already published on bulk H₃PW₁₂O₄₀ and Cs_1.9H_1.1PW₁₂O₄₀ samples. It was found for HPA/AC samples that, although their activity for propan-2-ol decomposition varied linearly with HPA loading, their activity for n-butane isomerisation was very weak, which indicates a weaker acid strength by supporting the HPA. This is probably due to the exchange of protons from the HPA by the exchangeable cations of the montmorillonite, the new protons associated with the clay being much less acidic. It also appeared, when comparing with catalytic data already published on for HPA/HMS, that HMS was the best support for HPA without modifying appreciably its catalytic and thus their acid properties, the HPA being certainly bonded to the HMS walls by hydrogen bonding. Assuming a diameter of 1.2 nm for each Keggin anion, the turnover frequency (TOF) values for n-butane isomerisation at 473 K were calculated per surface Keggin species for HPA/HMS, bulk H₃PW₁₂O₄₀ and Cs_1.9H_1.1PW₁₂O₄₀, and were found to be equal to 155, 113 and 100×10^–5 s^–1, respectively, and thus to be very close, showing that the acid strength of the three samples was comparable. It was found to equal only 3.4×10^–5 s^–1 for the HPA/AC sample, in agreement with a weaker acid strength. At last, mesoporosity of the support was found to favour n-butane isomerisation reaction.     

Profiling of arachidonic acid metabolites in rabbit platelets by radio gas chromatography

A method for profiling arachidonic acid metabolites by radio gas chromatography (GC) is described. The incubation mixture of rabbit platelets with [¹⁴C]arachidonic acid was purified on a Sep-Pak C₁₈ cartridge and derivatized with diazomethane,O-methylhydroxylamine and dimethylisopropylsilylimidazole. The recovery of total¹⁴C-radioactivity was 93.1±7.2%. Loss of radioactivity during derivatization was negligible. Baseline separations for [¹⁴C]arachidonic acid and its metabolites were obtained in a single run within 45 min by GC using a synchronized accumulating radioisotope detector (GC/SARD). The recovery of radioactivity from the GC column was virtually 100%. The chemical structures of the metabolites were confirmed by GC/mass spectrometry; peaks of arachidonic acid metabolites were assigned by comparison of the methylene unit values with those of radioactive peaks in GC/SARD analyses. The intra-assay coefficients of variation in GC/SARD analyses were less than 10%. The method was used to map the profile of arachidonic acid metabolites formed by rabbit platelets in the presence of indomethacin, baicalein or glutathione.     

Characterization of palladium supported on sulfated zirconia catalysts by DRIFTS, XAS and n-butane isomerization reaction in the presence of hydrogen

Palladium supported on sulfated zirconia (PdSZ) has been characterized by the n-butane isomerization reaction in the presence of hydrogen, X-ray absorption spectroscopy (XAS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) of adsorbed carbon monoxide. Catalyst calcination at 873 K followed by hydrogen reduction at 513 K results in the formation of 30–40 Å Pd metal clusters, but the surface can only weakly adsorb CO, though stronger than Pd-free, sulfated zirconia catalysts. In the presence of hydrogen, PdSZ has a lower n-butane isomerization activity than SZ, and the Pd function cannot stabilize the reaction at low H₂/n-butane ratios.     

Comparative study of electrocoagulation and electrochemical Fenton treatment of aqueous solution of benzoic acid (BA): Optimization of process and sludge analysis

Benzoic acid containing synthetic solution was pretreated by acid precipitation at various pH (1-3) and temperature (15-60 °C). Pre-treated solution was further treated by electrocoagulation (EC) and electrochemical Fenton (EF) processes using iron anode and graphite cathode. Optimization of independent operating parameters, namely, initial pH: (3-11), current density (A/m²): (15.24-76.21), electrolyte concentration (mol/L): (0.03-0.07) and electrolysis time (min): (15-95) for EC process and pH: (1-5), current density (A/m²): (15.24-76.21), H₂O₂ concentration (mg/L): (100-500) and electrolysis time (min): (15-95) for EF process, was performed using central composite design (CCD) in response surface methodology (RSM). Maximum removal efficiencies of BA- 76.83%, 88.50%; chemical oxygen demand (COD) - 69.23%, 82.21% and energy consumption (kWh/kg COD removed) - 30.86, 21.15 were achieved by EC and EF processes, respectively, at optimum operating conditions. It was found that EF process is more efficient than EC process based on removal of BA and COD with lower energy consumption. The sludge obtained after EC and EF treatments was analyzed by XRD, FTIR, DTA/TGA and SEM/EDX techniques.     

Mesostructured Sulfated Zirconia with High Catalytic Activity in n-Butane Isomerization

A mesostructured sulfated zirconia with a large surface area (189 m²/g) has been successfully prepared using a triblock copolymer as a structure-directing agent. The resulting material was characterized by XRD, TEM, nitrogen adsorption, FTIR and TG/DTA, which suggested that the mesostructured sulfated zirconia was tetragonal crystalline. Catalytic testing showed that the mesostructured sulfated zirconia was much more active than conventional sulfated zirconia for n-butane isomerization.     

C4烷烃在ZSM-5分子筛和Y分子筛上的吸附和扩散研究

采用气相色谱法研究了正丁烷和异丁烷在ZSM-5分子筛和Y分子筛上的扩散性能。烃分子的吸附平衡常数随温度的升高而降低，而扩散系数随温度的升高而增大。研究发现，烃分子的有效分子直径和分子形状是决定其扩散快慢的主要因素，同时分子筛孔道的大小对烃分子的扩散也存在影响，分子筛孔道越大，烃分子的扩散越快。     

Die Bestimmung der isosteren Adsorptionswärme von n-Butan an den Zeolithen NaX und NaY

Isosteric Heat of Adsorption of n-Butane on Zeolites NaX and NaY Using the technique of measuring isosteres the equilibria of adsorption of n-butane on zeolites NaX and NaY were investigated. From the isosteres the heats of adsorption were calculated. Although the differences between the enthalpies are small the zeolithe with higher electrostatic field in the cavity always shows larger heats of adsorption. These differences are explained assuming an adsorption of the n-butane molecules at (or near) Na⁺-cations in SIII position (which are found only in NaX-zeolites).     

Discrimination of Cod Liver Oil According to Wild/Farmed and Geographical Origins by GC and <Superscript>13</Superscript>C NMR

The objective of this study was to test the possibility of using lipid profiles obtained by gas chromatography (GC) and ¹³C nuclear magnetic resonance (NMR) in authentication of cod liver oils according to wild/farmed and geographical origin. GC and ¹³C-NMR data of cod liver oil from wild and farmed fish from different locations in Norway and Scotland were obtained, and analyzed by principal component analysis (PCA) and linear discriminant analysis (LDA) to test if it was possible to differentiate oil from wild and cultured cod (Gadus morhua L.), and to further elucidate differences between fish from the different farms/catch area. Cod liver oils of wild and farmed origin were clearly separated in the PCA score plot both from GC and NMR data. From NMR data it was also possible to observe groupings based on geographical origin (farm/catch area) of the different samples. Using LDA with cross validation the wild/farmed classification rates were 97% for GC data and 100% for NMR data. In the classification of cod liver oils according to geographical origin (38 samples from six different farms/catch area), the correct classification rate was 63% for GC data and 95% for NMR data.     

The mechanism and application of the electro‐Fenton process for azo dye Acid Red 14 degradation using an activated carbon fibre felt cathode

BACKGROUND: The discharge of azo dyes into the environment poses concerns due to their limited biodegradability. The electro‐Fenton process (EF) is a good method to effectively degrade these dyes. The aim of this work was to study the mechanism and the feasibility of the EF reaction using an activated carbon fibre (ACF) cathode. In this study, two methods were used to measure the reactive species generated in anodic oxidation (AO), anodic oxidation with electrogenerated H₂O₂ (AO‐H₂O₂) and the EF process. Acid Red 14 (AR14) was chosen as a model pollutant. The effects of the operational parameters, pH and initial concentrations were investigated. A short‐term biodegradability test was also carried out to evaluate the EF process from a biological point of view. RESULTS: After 2 h EF reaction 118.7 µmol L^?1?OH were produced, which was much higher than that of the AO‐H₂O₂ (63.2 µmol L^?1) process. H₂O₂ is largely generated and Fe³⁺ efficiently reduced on the high surface area of the ACF cathode. The EF process provides more effective degradation of AR14 than the conventional Fenton process, and its current efficiency is significantly affected by the initial pH and the initial AR14 concentration. Following EF treatment, the biodegradability of AR14 is significantly increased. CONCLUSION: The higher formation of ^?OH in the EF process suggests it is an effective method for pollutant removal. This process also leads to increased biodegradability, which is expected to facilitate subsequent biological treatment. Copyright © 2010 Society of Chemical Industry     

Thermodynamic modeling of PVTx properties for several water/hydrocarbon systems in near-critical and supercritical conditions

Both the equation of state-excess Gibbs energy (EoS/G ^E ) model and the cubic plus association (CPA) equation of state (EoS) are compared in this study with respect to their accuracy in the correlation of PVTx for systems such as water/methanol, water/ethanol, water/benzene, water/toluene, water/methane, water/n-butane, water/n-pentane, water/n-hexane, water/heptane, and water/octane, in supercritical conditions within temperature and pressure ranges of (573–698 K) and (7.0–276.0 MPa), respectively. In the proposed EoS/G ^E model, Peng-Robinson (PR) equation of state, linear combination Vidal-Michelsen (LCVM) and Wong-Sandler (WS) mixing rules in conjunction with UNIQUAC activity coefficient model were used. Correlation of both CPA and EoS/G ^E models was evaluated by comparing the results with the experimental data. Average absolute relative deviation (AARD) for WS, LCVM, and CPA was found to be 2.99, 11.11 and 5.14%, respectively, indicating better correlation of WS model with the experimental data.     

Polymethylthiophene/Nafion-modified glassy carbon electrode for selective detection of dopamine in the presence of ascorbic acid

The possible use of an electrode modified with electroactive conductive poly(3-methylthiophene) (PMeT)/Nafion as a chemical sensor was investigated for the voltammetric analysis of Dopamine (DA). The electrochemical behavior of dopamine was examined by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. By using a PMeT-modified glassy carbon (GC/PMeT) electrode, DA and Ascorbic Acid (AA) signals could be separated but the AA at high concentrations still caused significant interference by overlapping the DA peak. In comparison to the GC/PMeT electrode, the glassy carbon (GC/Nafion/PMeT) electrode modified with hybrid film Nafion/PMeT was found to permit a superior separation by shifting the oxidation of AA peak toward the less positive potential. The DPV curves for a mixture of DA and AA at an GC/Nafion/PMeT electrode in a 0.1 M H₂SO₄ solution showed peaks of DA and AA, at 0.45 and 0.21 V, respectively, indicating that the difference in the oxidation potential was 240 mV. In the 0.1 M H₂SO₄ solution, the oxidation peak current on the differential pulse voltammograms for the GC/PMeT electrode increased linearly with the concentration of DA in the range 1 × 10⁻⁶ to 1 × 10⁻³ M, and the oxidation peak current on the differential pulse voltammograms for the GC/Nafion/PMeT electrode in the range 5 × 10⁻⁷ to 2 × 10⁻⁴ M. The DA detection sensitivity of the GC/Nafion/PMeT electrode (26.7 μA μM⁻¹ cm⁻²) was 22 times higher than that of the GC/PMeT electrode (1.21 μA μM⁻¹ cm⁻²).     

Immobilization of Nafion-ordered mesoporous carbon on a glassy carbon electrode: Application to the detection of epinephrine

A stable suspension of ordered mesoporous carbon (OMC) was obtained by dispersing OMC in a solution of Nafion. By coating the suspension onto glassy carbon (GC) electrode, cyclic voltammetry was used to evaluate the electrochemical behaviors of Nafion-OMC-modified GC (Nafion-OMC/GC) electrode in 0.1 mmol L⁻¹ hexaammineruthenium(III) chloride (Ru(NH₃)₆Cl₃)/0.1 mol L⁻¹ KCl solution, where Nafion-OMC/GC electrode shows a faster electron transfer rate as compared with OMC/GC, Nafion/GC and GC electrodes. Due to the unique properties of Nafion-OMC, an obvious decrease in the overvoltage of the epinephrine (EP) oxidation (ca. 100 mV at pH 4.1 and 115 mV at pH 7.0) as well as a dramatic increase in the peak current (12 times at pH 4.1 and 6 times at pH 7.0) was observed at Nafion-OMC/GC electrode compared to that seen at GC electrode. By combining the advantages of OMC with those of Nafion, the anodic peak of EP and that of ascorbic acid (AA) were separated successfully (by ca. 144-270 mV) in the pH range of 2.0-10.0, which may make Nafion-OMC/GC electrode potential for selective determination of EP in the presence of AA at a broad pH range. As an EP sensor, the EP amperometric response at Nafion-OMC/GC electrode in pH 7.0 PBS is extremely stable, with 99% of the initial activity remaining (compared to 32% at GC surface) after 120 min stirring of 0.20 mmol L⁻¹ EP. And Nafion-OMC/GC electrode can be used to readily detect the physiological concentration of EP at pH 7.0. These make Nafion-OMC/GC electrode potential candidates for stable and efficient electrochemical sensor for the detection of EP. The solubilization of OMC by Nafion may provide a route to more precise manipulation, and functionalization for the construction of OMC-based sensors, as well as allowing OMC to be introduced to biologically relevant systems.     

A high-fat diet induces and red wine counteracts endothelial dysfunction in human volunteers

Endothelial dysfunction is associated with atherogenesis and oxidative stress in humans. In rat and rabbit blood vessels, wine polyphenol antioxidants induce vascular relaxationin vitro through the NO-cGMP pathway. To assess the effect of a regular high-fat diet (HFD) and moderate red wine consumption on endothelial function (EF), a study was performed in healthy male volunteers. EF was measured as flow-mediated dilatation of the brachial artery, employing high-resolution ultrasound after an overnight fast. Other clinical and biochemical parameters related to EF were also measured. Six volunteers received a control diet, rich in fruits and vegetables (27% calories as fat) and five volunteers received an HFD (39.5% calories as fat). Measurements were done twice on each volunteer: after a period of 30 d with diet plus 240 mL of red wine/d, and after a period of 30 d with diet, without wine. In the absence of wine, there is a reduction of EF with HFD when compared to the control diet (P=0.014). This loss of EF is not seen when both diets are supplemented with wine for 30 d (P=0.001). Plasma levels ofn−3 fatty acids (R ²=0.232,P=0.023) and lycopene (R ²=0.223,P=0.020) show a positive correlation with individual EF measurements, but they do not account for the significant differences observed among dietary groups or after wine supplementation. These results help elucidate the deleterious effect of a high-fat diet and the protective role of wine, n−3 fatty acids and dietary antioxidants in cardiovascular disease.     

Impedance study of the ion-to-electron transduction process for carbon cloth as solid-contact material in potentiometric ion sensors

Carbon cloth was studied as solid-contact material in potentiometric ion sensors by using electrochemical impedance spectroscopy and potentiometry. The ion-to-electron transduction process was studied by electrochemical impedance spectroscopy by using a two-electrode symmetrical cell where a liquid electrolyte was sandwiched between two solid electrodes, including bare glassy carbon (GC), GC/carbon cloth and GC/poly(3,4-ethylenedioxythiophene). Impedance data for different electrode/electrolyte combinations were evaluated and compared. Solid-contact K⁺-selective electrodes were fabricated by coating the carbon cloth with a conventional plasticized PVC-based K⁺-selective membrane via drop casting. These K⁺-sensors showed proper analytical performance and acceptable long-term potential stability (potential drift ≈ 1 mV/day). Solid contact reference electrodes were fabricated in an analogous manner by coating the carbon cloth with a plasticized PVC membrane containing a moderately lipophilic salt. The results indicate that carbon cloth can be used as a solid-contact material in potentiometric ion sensors and pseudo-reference electrodes.     

大气环境影响评价中挥发性有机化合物与非甲烷总烃的异同

分别从定义、监测与分析方法、执行标准等3个角度深入系统地分析了挥发性有机化合物(VOCs)和非甲烷总烃(NMHC)的异同。结果表明,NMHC的范畴在是否应包括含氧烃方面尚存在争议;目前VOCs和NMHC的实际监测分析方法与相关标准中规定的方法不完全一致;VOCs和NMHC参照执行的环境质量标准和排放标准较为混乱。对此,在大气环境影响评价中建议同时监测VOCs和NMHC,并制订统一的环境标准。     

Abnormal infrared effects and electrocatalytic properties of nanometer scale thin film of PtRu alloys for CO adsorption and oxidation

Nanometer scale thin films of PtRu alloy supported on glassy carbon (nm-PtRu/GC) were prepared using electrochemical codeposition under cyclic voltammetric conditions. The composition of the PtRu alloy was altered by varying the concentration of Pt⁴⁺ and Ru³⁺ ions in the deposition solution. STM results demonstrated that the nm-PtRu film was composed of crystallites appearing in a layered hexagonal form. The nm-PtRu/GC exhibited a high catalytic activity for CO oxidation, consisting mainly in a negative shift of potential for CO_ad oxidation. In situ FTIR spectroscopic studies revealed that the nm-PtRu/GC alloy electrodes of different surface composition exhibit abnormal infrared effects (AIREs) as observed on electrodes of nanometer scale thin films of transition metals. The AIREs observed on nm-PtRu/GC electrodes consist in the inversion of CO_ad bands, the significant enhancement of IR absorption and an increase in the FWHM. Following the increase in Ru component in the nm-PtRu thin film the FWHM was increased progressively from 20 cm^–1 on a nm-Pt/GC to 55 cm^–1 on a nm-Ru/GC electrode, and the enhancement factor of IR absorption by CO_L was between 10.5 to 13.1. The present study has provided new understanding of the structure and properties of nanometer scale thin film PtRu alloy material, and highlights its potential for fuel cell applications.