Experimental and modeling study of a lean premixed iso-butene/hydrogen/oxygen/argon flame

The experimental structure of a lean iso-butene/hydrogen/oxygen/argon flame (2.7% iC₄H₈, 4.5% H₂, 83.0% O₂, 9.8% Ar, ? = 0.225) has been determined by molecular beam mass spectrometry at low pressure (40 mbar). The detected species throughout the flame thickness were: H₂, CH₃, O, OH, H₂O, C₂H₂, CO, C₂H₄, CH₂O, O₂, HO₂, Ar, C₃H₄, C₃H₆, CO₂, C₂H₄O, C₄H₆, iC₄H₈, C₃H₆O, C₄H₆O and C₄H₈O. An original model, validated against premixed rich C₂H₄, has been extended by building a sub-mechanism taking into account the formation and the consumption of species involved in iso-butene combustion. This mechanism contains 520 reactions and 99 chemical species. A good agreement appears between calculated mole fraction profiles predicted by this mechanism, compared to experimental results.     

Hydrothermal synthesis,crystal structure and fluorescent properties of a novel 1D polymer: VO2(C7H3O4N)Ag(C10H8N2)·H2O

The hydrothermal synthesis of V₂O₅, AgNO₃, pyridine-2,6-dicarboxylic acid (H₂pdc) and 2,2′-bipyridine (bpy) in water at 160 °C for 4 days yields a novel 1D coordination polymer VO₂(C₇H₃O₄N)Ag(C₁₀H₈N₂)·H₂O (1). Each V center chelates to a tridentate ligand pdc^2? and coordinates to two O atoms, while the square based pyramid conformation of Ag center consists of three O atoms and a bpy molecular. V and Ag polyhedra alternate by either carboxyl or oxo bridges to further form a unique 3d–4d heterometal-based 1D double-chain ribbon.     

Concerning the Radical Character of Superoxide. The H—O Bond Energy of HO−2

The strength of the H-O bond in H⁻O₂ should be a good indicator of the chemical reactivity of superoxide, O⁻₂, as a hydrogen atom abstractor. This quantity can be calculated if the electron affinity of HO₂ is known. A recent experimental determination of the electron affinity of HO₂ [V. M. Bierbaum, R. J. Schmitt and C. H. DePuy, J. Am. Chem. Soc., 103 , 6262–6263 (1981)] gave that value as 27.4 ± 0.2 kcal mol⁻¹. The H-O bond energy of HO⁻⁻₂ can then be calculated from that value to be approximately 66 kcal mol⁻¹. Various theoretical methods may also be used to approximate the value of the electron affinity of HO₂. These methods generally give values in accord with the experimental result. Based on the low H—O bond energy of 66 kcal mol⁻¹ for HO⁻₂, superoxide is expected to be relatively unreactive, comparable to iodine atoms but less reactive than bromine atoms or HO₂ and much less reactive than chlorine atoms or hydroxyl radicals. Based on our analysis, we predict that superoxide can only react as a hydrogen atom abstractor with substrates that contain relatively weak bonds to hydrogen such as hydroxylamine or hydroquinones.     

Surface modification of tetrafluoroethylene–hexafluoropropylene (FEP) copolymer by remote H2, N2, O2, and Ar plasmas

Tetrafluoroethylene–hexafluoropropylene (FEP) copolymer sheets were modified by remote H₂, N₂, O₂, and Ar plasmas, and the effects of the modification on adhesion between FEP sheets and copper metal were investigated. The four plasmas were able to modify the FEP surfaces' hydrophilicity. Defluorination and oxidation reactions on the FEP surfaces occurred with exposure to the plasma. The hydrophilic modification by H₂ plasma was best, followed by modification by O₂, Ar, and N₂ plasmas. The surface modification of FEP by all four remote plasmas was effective in improving adhesion with copper metal. The peel strength order of the FEP/Cu adhesive joints was H₂ plasma > Ar plasma > N₂ plasma > O₂ plasma. Mild surface modification is important for the adhesion improvement of FEP with Cu metal. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1258–1267, 2002     

Direct synthesis of H2O2 from H2 and O2 over Pd/H-beta catalyst in an aqueous acidic medium: Influence of halide ions present in the catalyst or reaction medium on H2O2 formation

The influence of different halide ions present in the catalyst or reaction medium on the performance of Pd/H-beta catalyst in the direct H₂O₂ synthesis in an aqueous acidic (0.03 M H₃PO₄) reaction medium at 27 °C and atmospheric pressure has been thoroughly investigated. The results showed a strong influence of both the bulk Pd oxidation state in the catalyst and the halide ions added to the reaction medium on the performance of the catalyst in the H₂ to H₂O₂ oxidation, H₂O₂ decomposition/hydrogenation reactions. The different ammonium halides impregnated reduced Pd/H-beta catalyst calcined in inert (N₂) and oxidizing (air) gaseous atmospheres also revealed that the bulk Pd oxidation state and nature of the halide ions present in the catalyst together control the overall performance of the catalyst in the H₂O₂ formation reaction. The presence of halide ions in reaction medium or in the catalyst significantly changes the selectivity for H₂O₂ formation in the direct H₂O₂ synthesis. Bromide ions are found to remarkably enhance the H₂O₂ selectivity in the direct H₂O₂ synthesis irrespective of the Pd oxidation state in the catalyst. The promoting action of Br⁻ is attributed mainly to the large decrease in the H₂O₂ decomposition and hydrogenation activities of the catalyst and also inhibition for the non-selective H₂-to-water oxidation over the catalyst.     

OES study of the plasma during CVD diamond growth using CCl4/H2/O2 mixtures

Generation of atomic hydrogen in H₂/Ar/CCl₄ microwave discharges with O₂ addition has been investigated. In situ mass spectrometry and emission hydrogen-atom actinometry have been used in the microwave-plasma-assisted chemical vapor deposition (MWPACVD) reactor. Optical emission spectroscopy (OES) was used to study the intensity of H_α, H_β and H_γ lines using argon as actinometer. The results showed different increases in the atomic hydrogen concentration for the three hydrogen lines analyzed for additions of up to 1.5% CCl₄. These results confirm a previous study on the validity of the OES technique using the H_γ line intensity. An additional increase in the atomic hydrogen generation was also observed when O₂ was added to the H₂/CCl₄ mixtures. Chemical reaction products, detected by exhaust-gas mass spectrometry, showed that CCl₄ is completely dissociated in the plasma reactor with a fast conversion into hydrocarbons. The effects of O₂ addition lead an increase in CO and H₂O formation associated with a decrease in CH₄ and C₂H₂ concentration. Oxygen decreases the hydrocarbon concentration for high concentrations of halogenated precursor. This behavior inhibits the formation of solid carbon observed in mixtures with chlorine and permits the production of good-quality CVD diamond films owing to the high generation of atomic hydrogen. The films grown in different concentrations of CCl₄ and O₂ were analyzed by scanning electron microscopy and Raman spectroscopy.     

Comparison of Low Pressure and Medium Pressure UV Lamps for UV/H2O2 Treatment of Natural Waters Containing Micro Pollutants

UV/H₂O₂ advanced oxidation is an effective barrier against organic micro pollutants. Several studies have focused on the degradation of a wide range of pollutants, but regarding the comparison of low-pressure mercury lamps (LP) with medium-pressure mercury lamps (MP) with respect to energy consumption by the UV/H₂O₂ process, little is known so far. Although the absorbance of H₂O₂ at 254 nm is low, the results of this research show that the yield of hydroxyl radical formation (OH_CT) with LP lamps is comparable or higher than with MP lamps. In a water matrix with a background absorbance due to organics and nitrate, H₂O₂ absorbs UV light very effectively at 254 nm. Generally, due to the contribution of direct photolysis, the degradation of pollutants is better with MP-UV/H₂O₂ than with LP-UV/H₂O₂ at the same UV fluence. Therefore, with LP-UV/H₂O₂ micro pollutants are predominantly degraded through reaction with OH radicals. However, due to the much higher efficiency of LP lamps in converting electrical energy to UV-C light, the energy required to achieve 90% degradation (E_EO) of pesticides and pharmaceuticals can be significantly lower with LP-UV/H₂O₂ than with MP-UV/H₂O₂. Results of bench-scale tests show E_EO data of the LP-UV/H₂O₂ process to be 30%–50% lower than for the MP-UV/H₂O₂ process. At these process conditions MS2 phage inactivation was found to be more than 8 logs for both MP-UV/H₂O₂ and LP-UV/H₂O₂.     

The issue of selectivity in the direct synthesis of H2O2 from H2 and O2: the role of the catalyst in relation to the kinetics of reaction

The kinetic behavior in the direct synthesis of H₂O₂ with Pd–Me (Me = Ag, Pt) catalysts prepared by depositing the noble metals by electroless plating deposition (EPD) or deposition–precipitation (DP) methods on α-Al₂O₃ asymmetric ceramic membrane with or without a further surface coating by a carbon thin layer is reported. The effect of the second metal with respect to Pd-only catalysts considerably depends on the presence of the carbon layer on the membrane support. Several factors in the preparation of these membranes as well as the reaction conditions (temperature, concentration of Br⁻, pH) determine the selectivity in H₂O₂ formation, influencing the rate of the consecutive reduction of H₂O₂ (which is faster with respect to H₂O₂ decomposition on the metal surface) and/or of direct H₂ + O₂ conversion to H₂O. Defective Pd sites are indicated to be responsible for the two unselective reactions leading to water formation (parallel and consecutive to H₂O₂ formation), but the rate constants of the two reactions are differently influenced from the catalytic membrane characteristics. Increasing the noble metal loading on the membrane not only increases the productivity to H₂O₂, but also the selectivity, due to the formation of larger, less defective, Pd particles.     

Improving the Activity of Rh/Al2O3 Catalyst for NO Reduction by Na Addition in the Presences of H2O and O2

The effect of Na addition on the performance of Rh/Al₂O₃ catalyst for NO reduction with CO in the presence of H₂O and O₂ was investigated. The reacted catalysts were analyzed by the FTIR technique to identify the products for further investigation on the possible catalytic reaction mechanisms and the reasons behind the H₂O poisoning. Experimental results show that the removal efficiency of NO by Rh/Al₂O₃ catalyst was 63% at 250 °C but that decreased as the H₂O content increased. Adding Na to modify the Rh/Al₂O₃ catalyst significantly enhanced the conversion of NO to 99% at 250–300 °C even as the H₂O content was 1.6 vol%. The FTIR analyses results reveal that the abundant H₂O in the flue gas can compete with NO to adsorb on the surfaces of Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts and further enhance the formation of NO₃ that reacts with H. The effects of H₂O on Rh/Al₂O₃ and Rh-Na/Al₂O₃ catalysts can be eliminated by increasing the reaction temperature to higher than 300 °C. Rh-Na/Al₂O₃ is a feasible catalyst for NO reduction at such condition with relative high H₂O and O₂ contents.     

Oxidation of ß-SiC at high temperature in Ar/O2, Ar/CO2, Ar/H2O gas mixtures: Active/passive transition

An experimental study of the active/passive transition in the oxidation of ß-SiC was carried out between 1650?°C and 1800?°C in Ar/O₂, Ar/H₂O and Ar/CO₂ gas mixtures or mixtures including two among these oxidant species. For that purpose an experimental device based on a Joule-heated SCS-6 fiber permitted determination of the oxidation regime from changes in electric current. The observed transitions were compared to results from other authors. Two predictive models of the active/passive transition were studied by means of a 3-D simulation of the experimental device in order to have an estimation of the volatilization rate of SiO₂. These models were compared against experimental results.     

吡啶改性Pd/SiO2催化剂用于H2和O2直接合成H2O2

引言过氧化氢(H2O2)是一种理想的绿色氧化剂,广泛应用于化学品合成、纺织、造纸、环保、食品、医药、冶金和农业等领域[1]。目前,蒽醌法[2-5]是工业上生产H2O2的主要方法。20世纪40年代,德国I.G.Farbenindustrie首先采用蒽醌法(又称Riedl-Pfleiderer法)工业化生产过氧化氢。该方法首先将2-烷基蒽醌(通常是2-乙基蒽醌)溶解于合适的有机溶剂中,溶液中的2-烷基蒽醌经催化剂催化加氢,被还原成蒽氢醌或5,6,7,8-四氢蒽氢醌,再经空气氧化得到蒽醌或四氢蒽醌和     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

Photocatalytic oxidation of ethylene to CO2 and H2O on ultrafine powdered TiO2 photocatalysts: Effect of the presence of O2 and H2O and the addition of Pt

The complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O has been achieved on ultrafine powdered TiO₂ photocatalysts and the addition of H₂O was found to enhance the reaction. The photocatalytic reaction has been studied by IR, ESR, and analysis of the reaction products. UV irradiation of the photocatalysts at 275 K led to the photocatalytic oxidation of C₂H₄ with O₂ into CO₂, CO, and H₂O. The large surface area of the photocatalyst is one of the most important factors in achieving a high efficiency in the photocatalytic oxidation of C₂H₄. The photoformed OH species as well as O ₂ ⁻ and O ₃ ⁻ anion radicals play a significant role as a key active species in the complete photocatalytic oxidation of C₂H₄ with O₂ into CO₂ and H₂O. Interestingly, small amount of Pt addition to the TiO₂ photocatalyst increased the amount of selective formation of CO₂ which was the oxidation product of C₂H₄ and O₂.     

The Effect of H2 and the Presence of hot-O(ads) During the Decomposition of N2O on Platinum

The decomposition of N₂O was studied using a silica-supported Pt catalyst. The catalyst was found to exhibit short-lived activity at low temperatures to yield N₂ and O_(ads), the latter remained adsorbed on the surface and poisoned the active sites. Creation of hot-O_(ads) atoms during N₂O decomposition is proposed to allow O₂ desorption at intermediate temperatures. Inclusion of H₂ as a reducing agent greatly enhanced the activity and suppressed low temperature deactivation. Simultaneous and sequential pulsing of N₂O and H₂ showed that H₂ inclusion with the N₂O gas stream produced the greatest activity. A mechanism involving H_(ads) addition to “hot” oxygen atoms for H₂O formation is proposed.     

Microwave absorption property of polyaniline nanocomposites containing TiO2 and Fe3O4 nanoparticles after FeCl36H2O treatment

It is important to manipulate the synthesis parameters or additives used in order to produce conducting polymer such as polyaniline (PAni) with moderate conductivity, magnetic and dielectric properties that could enhance its microwave absorbing and shielding properties. In this communication, novel PAni/HA/TiO₂/Fe₃O₄ nanomaterials with different Fe₃O₄ contents were prepared by template‐free method by using TiO₂ and Fe₃O₄ nanoparticles as dielectric filler and magnetic filler, respectively. Before addition of ammonium peroxydisulfate (APS) for polymerization, Fe₃O₄ aqueous solution was treated with FeCl₃6H₂O in order to disperse well the Fe₃O₄ in the mixture. The result shows that better dispersion of Fe₃O₄ in the mixture by FeCl₃6H₂O treatment could significantly improve the conductivity of the nanocomposites and also activate the formation of nanorods/tubes. Moreover, PAni/HA/TiO₂/Fe₃O₄ nanocomposites treated with FeCl₃6H₂O show better microwave absorption (99.950–99.999% absorption) compared with PAni/HA/TiO₂/Fe₃O₄ micro/nanocomposites (67.0− 99.4% absorption) without treatment in frequency range of 10–13 GHz. Among the prepared PAni/HA/TiO₂/Fe₃O₄ micro/nanocomposites and nanocomposites, PAni/HA/TiO₂/Fe₃O₄ nanocomposite (treated with FeCl₃6H₂O) with 40% Fe₃O₄ exhibit the best microwave absorption (99.999% absorption at 10 GHz) because of its high conductivity, high heterogeneity and moderate magnetization. POLYM. COMPOS., 2010. © 2010 Society of Plastics Engineers     

Grafting of N-methylolacrylamide onto flax/polyester fabric using ferrous cellulose thiocarbonate/H2O2 redox system

Graft copolymerization of N-methylolacrylamide onto flax/polyester blend fabric using ferrous cellulose thiocarbonate/H₂O₂ redox system was investigated under different conditions including hydrogen peroxide concentration (1?60 mmol/l), ferrous ammonium sulphate concentration (1?50 mmol/l), N-methylolacrylamide concentration (5?200%, based on weight of sample), polymerization time (10?90 min), temperature (20?50°C), and pH of the medium (1.1?11). The nitrogen content and/or the methylol content were used for calculation of graft yields. Results obtained indicated that graft yields, derived from nitrogen analysis, are higher the greater the H₂O₂ concentration increases till 40 mmol/l, then level off. On the other hand, graft yields derived from methylol content exhibit maximum value at 10 mmol/l H₂O₂. The results indicate also that grafting was highly favoured when it was carried out using 1 mmol/l ferrous ammonium sulphate and pH 4.4 at 30°C for 60 min. The apparent activation energy of the copolymerization reaction amounts to 9.74 kJ/mol. Furthermore, the graft yield increases by increasing N-methylolacrylamide concentration within the range studied. The work was further extended to include a comparison between the polymerization efficiencies of the ferrous cellulose thiocarbonate/H₂O₂ redox system and the ferrous/H₂O₂ redox system in inducing grafting of N-methylolacrylamide onto flax/polyester blend fabric. For this reason, the two systems were studied with respect to graft yield, homopolymer proportion, total conversion, graft efficiency, and homopolymer efficiency.     

The Active Phase in the Direct Synthesis of H2O2 from H2 and O2 over Pd/SiO2 Catalyst in a H2SO4/Ethanol System

In an effort to determine the active state of supported palladium for the direct formation of H₂O₂ from H₂ and O₂, the catalytic behavior of Pd⁰/SiO₂, PdO/SiO₂ and partially reduced PdO/SiO₂ was determined. The results obtained in an ethanol slurry, with chloride ions and H₂SO₄ being present, showed that the PdO/SiO₂ catalyst was almost completely inactive for the formation of H₂O₂ at 10 °C. The Pd⁰/SiO₂ catalyst exhibited the highest activity for H₂O₂ formation, and the PdO/SiO₂ material, reduced under very mild conditions, exhibited an intermediate activity. The state of Pd on the three catalysts was characterized by XRD, TEM and XPS methods. Only Pd⁰ (the metal phase) and PdO were observed on Pd⁰/SiO₂ and PdO/SiO₂, respectively. As expected, with the partially reduced PdO/SiO₂ catalyst, both Pd⁰ and PdO phases were evident. The TEM results revealed that the Pd⁰ particles decorated the larger PdO particles. The results reported here support the role of metallic palladium, rather than the oxide, as the active phase for the direct formation of H₂O₂.     

Isotope effect of H2/D2 and H2O/D2O for the PROX reaction of CO on the FeOx/Pt/TiO2 catalyst

The oxidation reaction of CO with O₂ on the FeOx/Pt/TiO₂ catalyst is markedly enhanced by H₂ and/or H₂O, but no such enhancement occurs on the Pt/TiO₂ catalyst. Isotope effects were studied by H₂/D₂ and H₂O/D₂O on the FeOx/Pt/TiO₂ catalyst, and almost the same magnitude of isotope effect of ca. 1.4 was observed for the enhancement of the CO conversion by H₂/D₂ as well as by H₂O/D₂O at 60 °C. This result suggests that the oxidation of CO with O₂ via such intermediates as formate or bicarbonate in the presence of H₂O, in which H₂O or D₂O acts as a molecular catalyst to promote the oxidation of CO as described below.      

Comparative study of the electrical characteristics of ALD-ZnO thin films using H2O and H2O2 as the oxidants

ZnO thin films were deposited via atomic layer deposition (ALD) using H₂O and H₂O₂ as oxidants with substrate temperatures from 100°C to 200°C. The ZnO films deposited using H₂O₂ (H₂O₂-ZnO) showed lower growth rates than those deposited with H₂O (H₂O-ZnO) at these temperature range due to the lower vapor pressure of H₂O₂, which produces fewer OH⁻ functional groups; the H₂O₂-ZnO films exhibited higher electrical resistivities than the H₂O-ZnO films. The selection of H₂O₂ or H₂O as oxidants was revealed to be very important for controlling the electrical properties of ALD-ZnO thin films, as it affected the film crystallinity and number of defects. Compared to H₂O-ZnO, H₂O₂-ZnO exhibited poor crystallinity within a growth temperature range of 100-200°C, while H₂O₂-ZnO showed a strong (002) peak intensity. Photoluminescence showed that H₂O₂-ZnO had more interstitial oxygen and fewer oxygen vacancies than H₂O-ZnO. Finally, both kinds of ZnO thin films were prepared as transparent resistive oxide layers for CIGS solar cells and were evaluated.