Low temperature decomposition of nitrous oxide over Fe/ZSM-5: Modelling of the dynamic behaviour

The kinetics of N₂O decomposition to gaseous nitrogen and oxygen over HZSM-5 catalysts with low content of iron (<400 ppm) under transient and steady-state conditions was investigated in the temperature range of 250–380 °C. The catalysts were prepared from the HZSM-5 with Fe in the framework upon steaming at 550 °C followed by thermal activation in He at 1050 °C. The N₂O decomposition began at 280 °C. The reaction kinetics was first order towards N₂O during the transient period, and of zero order under steady-state conditions. The increase of the reaction rate with time (autocatalytic behaviour) was observed up to the steady state. This increase was assigned to the catalysis by adsorbed NO formed slowly on the zeolite surface from N₂O. The formation of NO was confirmed by temperature-programmed desorption at temperatures >360 °C. The amount of surface NO during the transient increases with the reaction temperature, the reaction time, and the N₂O concentration in the gas phase up to a maximum value. The maximum amount of surface NO was found to be independent on the temperature and N₂O concentration in the gas phase. This leads to a first-order N₂O decomposition during the transient period, and to a zero-order under steady state. A kinetic model is proposed for the autocatalytic reaction. The simulated concentration–time profiles were consistent with the experimental data under transient as well as under steady-state conditions giving a proof for the kinetic model suggested in this study.     

Experimental Investigations On Production Of Excited Ozone Species From A Silent Discharge Ozone Generator

Ozone decomposition kinetics are investigated together with the influence of energy input to an ozone generator. Decomposition is considered in a solid bed reactor, a gas phase reactor and a bubbling reactor. Ozone is produced at the same concentration and gas flow rate using two methods: 1) from the generator at a higher power giving higher ozone concentration, then ozone is diluted by oxygen before entering the decomposition reactor, and 2) at a lower power without dilution.     

氯丙烯环氧化反应器气相安全控制条件

在相转移法氯丙烯环氧化反应过程中,由于少量双氧水发生无效分解生成氧气,导致反应器气相存在燃爆危险性。测试了工况条件下氯丙烯-氧-氮三元体系的燃爆特性,得出该体系的极限氧浓度值(LOC)为10.9%;考察了主要因素对气相氧浓度的影响。研究发现,要降低气相氧浓度,应尽可能降低催化剂用量,适当提高搅拌速度,严格控制H_2O_2用量;应在液相沸腾后开始H_2O_2进料,并控制反应初始阶段的H_2O_2进料量,以避免瞬间H_2O_2进料过快。     

Catalytic destruction of methyl tertiary butyl ether (MTBE) using oxidized carbon

Decomposition of methyl tert-butyl ether (MTBE) in the gas phase was studied using carbon catalysts with chemically modified surface. Carbon samples with different surface chemical properties were obtained from commercial activated carbon D43/1 (CarboTech, Essen, Germany) by oxidation in liquid phase with various oxidants as well as in air. The catalytic tests were performed in a flow reactor at a temperature range of 353–473 K. Isobutene and methanol are the only products of the MTBE decomposition. The generation of surface acidic oxides considerably enhances the catalytic activity of the carbons. However, the activity is controlled not only by the number and strength of acidic groups, but also by their accessibility. The most active carbon is that oxidized with air at 673 K, which contains pores wider than the pores of other oxidized carbons.     

NO在Ag-Pt双金属表面上的吸附和分解

本文在超高真空条件下，对NO在Pt(110)单晶面和Ag-Pt双金属模型催化剂表面上的吸附和分解进行了研究。结果表明，NO在Ag-Pt双金属表面的Pt活性中心分解，生成的强吸附氧物种可迁移到Ag原子表面，在低温630K下脱附，并提出了氧物种迁移模型。     

CF4 decomposition by thermal plasma processing

Decomposition of CF₄ was investigated by thermal plasma method. Thermal plasma processes applied to environmental problems have the features of high temperature, high activity and rapid decomposition rate, so it can perfectly decompose non-decomposed materials like CF₄ to a high degree. Before the experiment, thermodynamic equilibrium calculations were performed from 300 K to 5,000 K at atmospheric pressure. Based on the thermodynamic equilibrium calculations, the trends in decomposition and recombination of CF₄ were studied. Decomposition was carried out by injecting mixtures of CF₄ bubbled by Ar, with some addition gases, such as H₂ and O₂, at atmospheric pressure. Experiments were performed to determine the effects of additive gas identity, additive gas dilution, input power, etc. on the decomposition of CF₄. Plasma input power has a slight effect on CF₄ decomposition, and the injection of reacting gas through a torch increased CF₄ decomposition. Supply of H₂ and O₂ as addition gases increased the CF₄ decomposition to 99% for experimental conditions tested.     

Novel oxidation reaction at ambient temperature and atmospheric pressure with electric discharge and oxide surface

We investigated a novel oxidation reaction with surface-oxygen and lattice-oxygen induced using a non-equilibrium electric discharge at ambient temperature. We employed MgO, ZrO₂, and TiO₂ for this novel reaction. Methane was oxidized easily and converted into H₂, CO, and CO₂ by the surface-oxygen and lattice-oxygen of oxide with activation of discharge at ambient temperature without gas-phase oxygen. The oxide itself was stable after the reaction. Among these oxides, the tetragonal phase and amorphous phase of ZrO₂ showed remarkably high activity for methane oxidation. Consequently, up to 8% of surface and lattice oxygen of the oxide was consumed by methane oxidation induced by electric discharge. The non-equilibrium electric discharge activated both the surface-oxygen and the lattice-oxygen of the oxides and methane molecules in the gas phase. After these reactions, the oxide surface vacant sites were recovered partially through steam post-treatment. Hydrogen formed simultaneously with steam decomposition. Other reactions were also studied by changing the reaction gas: methane into carbon monoxide, carbon monoxide with oxygen, and carbon monoxide with steam. Furthermore, the correlation of reactivity between the feed gas and surface oxygen was studied. Emission spectra under a CH₄ atmosphere with electric discharge showed complex peaks caused by carbon monoxide formation at 280-500 nm at 0-4 min, suggesting that surface oxygen on oxides was probably consumed within 4 min from the start of the reaction.     

Metallorganische Peroxide,VII. Zum Mechanismus der Zersetzung von Bis-organoantimonyl-peroxiden. Teil I

Organometallic Peroxides. VII. Mechanism of the Decomposition of Bis-organoantimonyl Peroxides. Part I The decomposition of bis-organoantimonyl peroxides 1 a, b was studied regarding decomposition products, kinetics and the influence of varying conditions. We found that besides heterolytic O-O-cleavage with 1,2-rearrangement, the bromo-substituted peroxide 1 a easily splits off singlet oxygen during decomposition. The mechanism of this reaction has been elucidated.     

基于铁基载氧体的煤化学链气化还原过程中氮元素迁移行为

采用热重-质谱-红外联用技术（TG-MS-FTIR），Ar气氛下对煤进行化学链气化实验，实时分析还原过程热解阶段和水蒸气气化反应阶段的过程中固体质量变化和生成气体成分。使用X射线光电子能谱对固相产物进行表面元素分析，探究化学链气化还原过程不同阶段固相产物中氮赋存形态的变化。研究结果表明：载氧体对化学链气化还原过程不同阶段含氮气体释放均有影响。热解阶段载氧体促进自由基的生成，加速了一次热解阶段含氮气体的释放，高温下，载氧体促使NH₃转化为HCN；气化阶段载氧体的加入使半焦的石墨化程度降低，含氮气体释放速率增加。对固相产物中氮的赋存形态而言，载氧体会抑制热解阶段吡咯型氮的分解与转化，高温下，半焦的石墨化和有序化程度降低的同时，镶嵌在煤大分子里面的质子化吡啶裸露出来，质子化吡啶含量降低，吡啶型氮和吡咯型氮的含量大大提升。     

Fracture Behavior of Woven Silicon Carbide Fibers Exposed to High‐Temperature Nitrogen and Oxygen Plasmas

High‐temperature aero‐thermal heating in a 30 kW inductively coupled plasma torch was used to replicate the effects of harsh oxidizing environments during hypersonic atmospheric entry on fracture behavior and microstructure of two‐dimensional woven SiC fibers. Hi‐Nicalon SiC woven cloths were exposed to surface temperatures over 1400°C with different high‐enthalpy dissociated oxygen and nitrogen plasma flows, and were subsequently deformed in pure tension at room temperature. Changes in fiber microstructure and surface chemistry after thermal exposure were examined by scanning electron microscopy. Pure nitrogen plasmas resulted in a 50% decrease of strength in woven SiC fibers with minimal effects on the fiber structure, except for highly localized surface pitting caused by partial decomposition of silicon oxycarbonitride phase at high temperature. In contrast, exposure to dissociated oxygen and air plasmas led to severe strength reduction and embrittlement over significantly short time scales, corresponding to degradation rates up to 200 times higher than those reported with static heating at equivalent temperatures. The origin of accelerated embrittlement at microscopic scale was found related to complex gas‐surface interactions and high‐temperature oxidizing processes involving the formation of SiO₂ bubbles and microcracks on the surface. These findings are important for the development of outer fabric materials for new flexible thermal protection systems in space applications.     

Nitrosation Reaction Without Nitrogen Oxide Waste Gas Emission and Its Engineering Practice

The gas-liquid phase equilibrium is used in controlling the nitrosation reaction process. Decomposition of nitrous acid and oxidation side reaction.are suppressed in a closed reaction system. The system pressure is used as the criterion of the end of reaction, avoiding excessive feeding and reducing＇the decomposition＇of nitrous acid. The head space of the reactor is used as the gas buffer, stabilizing the feeding fluctuations and inhibiting the side reaction, decomposition of nitrous acid. Nitrogen oxide concentration is controlled at the minimum level.Thus the zero release ofnitrogen ox!de waste gas can be achieved without using any absorption process.     

Decomposition of burning polytetrafluoroethylene

PTFE rods, 0.6–3.8 cm diameter, were burnt from the top downwards in a gently rising atmosphere of oxygen. The burning was only possible in concentrated oxygen, or at elevated temperature or pressure. At its surface temperature of 920 ± 25°K, the polymer evolved monomeric C₂F₄ which oxidized in a surrounding gas flame; 15–35% of all the carbon in the gas was found present as monomer just above the larger rods. Depolymerization of the solid was not its only mode of decomposition, however. The heat radiated and conducted from the flame into the condensed phase was too little to depolymerize it completely, and heterogeneous reactions with species from the gas phase must also have contributed to the decomposition. Overall, the polymer burnt in O₂, but the gaseous reactant which attacked the surface need not have been O₂ or O in all cases, for these rare species just above the larger rods. Elemental fluorine was present in the gas even when elemental oxygen was absent, and calculations indicate that F atoms would be a major flame species at equilibrium. It is possible that heterogeneous attack by flame generated F atoms consumed part of the polymer and also supplied energy to help depolymerize the rest.     

Formation and surface properties of electron-emissive coatings. IX. Thermal decomposition of the alkaline-earth formates

The thermal decomposition of alkaline-earth formates under vacuum has been studied because of the use of barium formate as a binder for cathode coatings. Techniques employed in this work include thermogravimetry, differential thermal analysis and evolved gas detection, in conjunction with gas chromatography and infrared absorption spectroscopy for identification of the gaseous decomposition products. Decomposition occurs in two stages; the first results in formation of carbonate plus a small amount of free carbon. The second stage involves initially reaction of the free carbon with carbonate to form carbon monoxide and the corresponding alkaline earth oxide. Then, at a higher temperature, thermal decomposition of the carbonate itself commences, leading to the formation of the oxide plus carbon dioxide. With calcium formate, the two carbonate decomposition processes occur concurrently; but with strontium and barium formates, reaction with free carbon commences at a significantly lower temperature than thermal decomposition of the pure carbonate.     

煤热解过程中气态产物分布的研究

利用固定床热解装置对3种不同煤种进行了热解研究,考察了温度和煤的性质对热解气态产物以及硫元素逸出规律的影响,结果表明:除了煤的性质外,温度是影响热解产物分布的重要影响因素;同时CO和CO2的逸出量与煤中氧元素的含量有关,而生成CH4和气态烃的量与H/O原子比有很大关系;热解过程中含硫物质以H2S和少量COS的方式逸出到气相,而逸出的气态硫也与煤的含硫量有直接关系.     

A Fast XPS Study of Propene Decomposition over Clean and Sulphated Pt{111}

The thermal decomposition of propene over clean and sulphate precovered Pt{111} has been followed by Fast XPS. The saturation propene coverage over the clean surface is 0.21 mL at 90 K. Propene is stable up to 200 K, above which molecular desorption and dehydrogenation result in the formation of a stable propylidyne intermediate adlayer at 300 K. Propylidyne decomposes above 400 K eventually forming graphitic carbon above 800 K. Preadsorbed surface sulphate promotes room temperature propene combustion associated with the decomposition of a thermally unstable alkyl--sulphate complex. Propylidyne also forms as on clean Pt{111}, but is less reactive, its decomposition above 450 K triggering partial oxidation with residual surface oxygen to liberate gas phase CO.     

Reaction of nitric oxide and nitric oxide + carbon monoxide with amorphous Fe-Co-B alloy powders

The activity of amorphous Fe---Co---B alloy powder was investigated for the decomposition and the reduction of nitrogen monoxide. The transient response technique and a fixed bed reactor were applied to study the interactions of the Fe---Co---B alloy with two gas mixtures: NO + Ar at 353 and 573 K and NO + CO + Ar at 333–573 K. Moessbauer spectroscopy and X-ray photoelectron spectroscopy (XPS) were used to study the state of the initial sample and the samples utilized in both gas mixtures. It is shown that the amorphous Fe---Co---B alloy powder has an activity for the direct decomposition of nitric oxide to nitrous oxide and nitrogen at a high gas space velocity (26 000 h⁻¹). Oxygen from the decomposed nitric oxide poisons the surface for the formation of nitrogen. In the presence of carbon monoxide (a NO + CO + Ar gas mixture) nitric oxide is reduced to nitrous oxide at 333–353 K and fully reduced to nitrogen at 373–573 K. The quantities of the carbon dioxide formed are not equal to the values expected from the stoichiometry of the NO + CO reaction. Probably, the interaction of carbon monoxide with the adsorbed oxygen (left on the surface by the decomposed nitric oxide) enhances the rate of nitric oxide decomposition to nitrous oxide and nitrogen. The rate limiting steps for both reactions of nitric oxide decomposition, as indicated by the transient response data, change with increasing temperature. The data from the Moessbauer spectroscopy and the X-ray photoelectron spectroscopy (XPS) studies have shown that the amorphous Fe---Co---B alloy powder undergoes phase changes under the conditions of both, the NO + Ar and the NO + CO + Ar gas mixtures. Boron migrates to the surface of globules and serves the accumulation of oxygen by the formation of B₂O₃ (or B(OH)₃).     

Ozone Synthesis and Decomposition in Oxygen-Fed Pulsed DBD System: Effect of Ozone Concentration,Power Density,and Residence Time

The process of ozone production in pure oxygen was studied. It was shown how the ozone concentration changes along the discharge gap, both during its generation and decomposition processes. The effect of ozone inlet concentration, power, and gas residence time on ozone concentration was analyzed. It has been shown that concentrated ozone is easily decomposed at very low discharge powers, i.e., when the increase of the average gas temperature in the gap is negligibly small. It was hypothesized that the most intense decomposition takes place in the microdischarge channels, because the process of gas heating in the gap begins inside them.     

Properties of the Solid Electrolyte Gadolinia-Doped Ceria Prepared by Thermal Decomposition of Mixed Cerium-Gadolinium Oxalate

Fine-grained powder of the mixed oxide (CeO₂)_0.9(Gd₂O₃)_0.1, which is an ionic conductor for oxygen ions, was prepared by coprecipitation of the corresponding oxalates followed by calcination. The powder was used to prepare pellets sintered at a relatively low temperature of 1000°C compared with the usual sintering temperature of 1700° to 1800°C. The size of the powder grains was determined from BET surface area (S_BET) measurements. The effect of precipitation conditions and calcination temperature on S_bet was examined. The largest surface area measured was 88 m²/g. Decomposition of the oxalate powder was followed using an optical dilatometer. The decomposition was indicated by a large shrinkage and it was completed below 300°C (for a heating rate of 3.3°C/min). The formation of the oxide was verified by X–ray diffraction analysis. It shows that the product of decomposition is the oxide and that decomposition can be carried to completion at 250°C if the heating lasts for 1 h. The pellets had a density of 83% of theoretical, small grains (0.5 μm), and a conductivity which, at 900°C, is two–thirds of the conductivity of dense samples obtained from the same raw material, but calcined and fired at much higher temperatures.     

Decomposition and Activation of Pt-Dendrimer Nanocomposites on a Silica Support

Zero valent platinum nanoparticles were stabilized in solution by the use of poly(amido)amine dendrimers and were subsequently deposited onto a porous silica support. The resulting materials were subjected to various thermal treatments in oxidizing, reducing, and inert environments, in order to remove the surrounding polymer and expose the Pt metal sites to gas phase reagents. The materials were characterized at several different stages during this process via Fourier-Transform Infrared (FTIR) spectroscopy and Transmission Electron Microscopy (TEM). The results suggest that the dendrimer decomposition occurs at its mono-substituted amide groups and begins at relatively low temperatures (～50 °C). The presence of oxygen in the gas phase and the Pt particles in the Pt-dendrimer nanocomposite accelerate this process. Oxidation at 425 °C was the most successful temperature for removing the dendrimer fragments from the Pt surface, rendering the Pt sites most accessible for carbon monoxide adsorption. Limited sintering of the Pt particles is observed under these conditions, as well as during subsequent reduction steps, necessary to yield the metallic form of Pt.     

DTA and TGA studies of flame-resistant fabrics

Preliminary thermal studies were made of cotton fabrics which had been made flame resistant by chemical modification or by blending with a flame-resistant modified acrylic fiber. DTA and TGA thermograms were made in both nitrogen and oxygen atmospheres. Differences were found in the thermograms of the untreated controls, depending upon amount of purification. Fabrics treated with the flame-retardant formulations had lower decomposition temperatures and higher percent residue. Decomposition in oxygen was more complete and proceeded at a lower temperature. Infrared spectra of selected samples, which had been partially or completely charred, were examined. These data are related to theories about the degradation of flame-resistant cotton fabrics.