Spectrophotometric Determination of Ammonia and Nitrogen Oxides in the Reaction Products of Ammonia Oxidation

A spectrophotometric procedure is developed for the simultaneous determination of ammonia, NO, and NO₂ in the reaction products of the catalytic oxidation of ammonia under industrial conditions. Samples are taken from the reactor, and the analysis is made at 250°C. A multiple linear regression is used for the calibration. The relative standard deviation of the determination of ammonia and nitrogen oxides is no higher than 6%.     

Enhanced ammonia oxidation on BDD induced by inhibition of oxygen evolution reaction

Electrochemical oxidation of ammonia (NH₃ and NH₄ ⁺ ) on boron-doped diamond (BDD) electrode was studied using differential electrochemical mass-spectrometry (DEMS) and chronoamperometry. Electro-oxidation of ammonia induces inhibition of the oxygen evolution reaction (OER) due to adsorption of the ammonia oxidation products on the BDD surface. The inhibition of the OER enhances ammonia electro-oxidation, which becomes the main reaction. The amino radicals, formed during ammonia oxidation, trigger a reaction chain in which molecular oxygen dissolved in solution is involved in the ammonia electro-oxidation. Nitrogen, nitrous oxide, and nitrogen dioxide were detected as the ammonia oxidation products, with nitrogen being the main gaseous product of the oxidation.     

Treatment of off-gas evolved from thermal decomposition of sludge waste

Korea Atomic Energy Research Institute (KAERI) started a decommissioning program of a uranium conversion plant. The treatment of the sludge waste, which was generated during the operation of the plant, is one of the most important tasks in the decommissioning program of the plant. The major compounds of sludge waste are nitrate salts and uranium. The sludge waste is denitrated by thermal decomposition. The treatment of off-gas evolved from the thermal decomposition of nitrate salts in the sludge waste is investigated. The nitrate salts in the sludge were decomposed in two steps: the first decomposition is due to the ammonium nitrate, and the second is due to the sodium and calcium nitrate and calcium carbonate. The components of off-gas from the decomposition of ammonium nitrate at low temperature are NH₃, N₂O, NO₂, and NO. In addition, the components from the decomposition of sodium and calcium nitrate at high temperature are NO₂ and NO. Off-gas from the thermal decomposition is treated by the catalytic oxidation of ammonia and selective catalytic reduction (SCR). Ammonia is converted into nitrogen oxides through the oxidation catalyst and all nitrogen oxides are removed by SCR treatment besides nitrous oxide, which is greenhouse gas. An additional process is needed to remove nitrous oxide, and the feeding rate of ammonia in SCR should be controlled properly for evolved nitrogen oxides.     

Catalytic Performance of Spherical MCM-41 Modified with Copper and Iron as Catalysts of NH3-SCR Process

Spherical MCM-41 with various copper and iron loadings was prepared by surfactant directed co-condensation method. The obtained samples were characterized with respect to their structure (X-ray diffraction, XRD), texture (N₂ sorption), morphology (scanning electron microscopy, SEM), chemical composition (inductively coupled plasma optical emission spectrometry, ICP-OES), surface acidity (temperature programmed desorption of ammonia, NH₃-TPD), form, and aggregation of iron and copper species (diffuse reflectance UV-Vis spectroscopy, UV-Vis DRS) as well as their reducibility (temperature programmed reduction with hydrogen, H₂-TPR). The spherical MCM-41 samples modified with transition metals were tested as catalysts of selective catalytic reduction of NO with ammonia (NH₃-SCR). Copper containing catalysts presented high catalytic activity at low-temperature NH₃-SCR with a very high selectivity to nitrogen, which is desired reaction products. Similar results were obtained for iron containing catalysts, however in this case the loadings and forms of iron incorporated into silica samples very strongly influenced catalytic performance of the studied samples. The efficiency of the NH₃-SCR process at higher temperatures was significantly limited by the side reaction of direct ammonia oxidation. The reactivity of ammonia molecules chemisorbed on the catalysts surface in NO reduction (NH₃-SCR) and their selective oxidation (NH₃-SCO) was verified by temperature-programmed surface reactions.     

Development of the bifunctional catalyst Mn-Fe-Beta for selective catalytic reduction of nitrogen oxides

The catalytic properties of the Mn-Fe-Beta system with Mn contents in the range 0.1–16 wt.% were studied in the selective catalytic reduction (SCR) of NO _x with ammonia. The catalyst structure was investigated using IR spectra of adsorbed NO, temperature-programmed reduction with hydrogen (H₂-TPR), X-ray diffraction analysis, and ESR. The use of manganese as a promoter substantially increases the activity of iron-containing catalysts in the SCR of NO _x with ammonia. At low contents (<2 wt.%), Mn exists in the cation form and the catalytic activity of the Mn-Fe-Beta system does not increase. At a higher content of Mn, clusters MnO _x begin to form, which are highly active in the oxidation of NO to NO₂ and the low-temperature catalytic activity of the Mn-Fe-Beta system increases. The observed increase in the low-temperature catalytic activity in the process of SCR of NO _x with ammonia is related to a change in the reaction route. The MnO _x clusters favor the oxidation of NO and the iron cations facilitate the reaction of “fast” SCR.     

Effects of NO2, CO,O2, and SO2 on oxidation kinetics of NO over Pt‐WO3/TiO2 catalyst for fast selective catalytic reduction process

The selective catalytic reduction rate of NO with N‐containing reducing agents can be enhanced considerably by converting a part of NO into NO₂. The enhanced reaction rate is more pronounced at lower temperatures by using an equimolar mixture of NO and NO₂. The kinetics of NO oxidation over Pt‐WO₃/TiO₂ catalyst has been determined in a fixed‐bed reactor with different concentrations of oxygen, nitric oxide, and nitrogen dioxide in the presence of 8% water. It has been found that the reaction is second order with respect to nitric oxide, first order for oxygen with a third‐order rate constant. Also, it is found that there is no effect on the reaction order with an addition of NO₂, CO, or SO₂. It follows the same second order but the reaction rate is found to be changed. It is observed that in the case of NO₂ and SO₂, the reaction rate tends to decrease, but it increases with the addition of CO into the feed. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 613–620, 2006     

Study on Oxidation Mechanism of Nitrogen Monoxide in Indoor Environment

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｒｅｃｅｎｔｙｅａｒｓ ,ｔｈｅｓｔｕｄｙｏｎｔｈｅｅｆｆｅｃｔｏｆｉｎｄｏｏｒｌｉｇｈｔ ｃｏｎｃｅｎｔｒａｔｉｏｎｇａｓｅｏｕｓｐｏｌｌｕｔｉｏｎｔｏｈｕｍａｎｈｅａｌｔｈｉｓｄｅｅｐｌｙｃｏｎｃｅｒｎｅｄ .Ｔｈｅｍａｉｎｒｅａｓｏｎｉｓｔｈａｔ,ｗｉｔｈｔｈｅｐｅｒ ｆｅｃｔｉｎｇｏｆｔｈｅｉｎｄｏｏｒｇａｓｔｉｇｈｔｎｅｓｓａｎｄｈｅａｔ ｓｈｉｅｌｄｉｎｇｐｅｒ ｆｏｒｍａｎｃｅ ,ｔｈｅａｐｐｅａｒａｎｃｅｏｆｎｅｗａｒｃｈｉｔｅｃｔｕｒａｌａｎｄｄｅｃｏ ｒａｔｉ…     

Thermal decomposition of [Cd(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>](NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Thermal decomposition of [Cd(NH₃)₆](NO₃)₂ was studied by thermogravimetry (TG) with simultaneous differential thermal analysis (SDTA) for two samples and at two different sets of measurement parameters. The gaseous products of the decomposition were on-line identified by evolved gas analysis (EGA) with a quadruple mass spectrometer (QMS). The decomposition of the title compound proceeds, for both cases, in the three main stages. In the first stage, deammination of [Cd(NH₃)₆](NO₃)₂ to [Cd(NH₃)](NO₃)₂ undergoes by three steps and 5/6 of all NH₃ molecules are liberated. At second stage the liberation of residual 1/6NH₃ molecules and the formation of Cd(NO₃)₂ undergoes. However, during this process simultaneously a two-step oxidation of a part of ammonia molecules also takes place. In a first step as a result a mixture of ammonia, water vapour and nitrogen is formatted. At the second step, subsequent oxidation of a next part of NH₃ molecules undergoes. As a result, a mixture of nitrogen oxide, nitrogen and water vapour is formatted, what for these both steps clearly indicates the EGA analysis. The third stage of the thermal decomposition is connected with the melting and subsequent decomposition of residual Cd(NO₃)₂ to oxygen, nitrogen dioxide and solid CdO. Additionally, third sample was measured by differential scanning calorimetry (DSC) and the results are fully consistent with those obtained by TG.     

Mechanism of reduction of nitrogen oxides with propene in excess oxygen catalyzed by bifunctional catalysts

HC-SCR (selective reduction of nitrogen oxide by hydrocarbon) and our view on its reaction mechanism are briefly described, and then our attempts in the last few years to design catalysts based on the concept of bifunctional catalysis for HC-SCR are reviewed. The example chosen is the NO-C₃H₆-O₂-H₂O reaction catalyzed by mechanical mixtures of transition metal oxides (e.g., Mn₂O₃) and metal-loaded ZSM-5 zeolites. The synergistic effect of two components was explained based on a reaction mechanism comprising NO oxidation, oxidative decomposition of the products of NO₂-C₃H₆ reactions and polymerization of (or carbon deposition from) C₃H₆.     

Microcalorimetric Studies of the Surface Reactivity of Pollutant Gas Atmospheres on Supported SnO2 and Ga2O3 Catalysts

The surface properties of gallium oxide and tin dioxide supported on alumina or titania have been studied by adsorption microcalorimetry. The differential heats of adsorption of various pollutant adsorbates such as sulfur dioxide, nitrogen monoxide, nitrogen dioxide and also ammonia were measured on these catalytic surfaces. NH₃, SO₂, NO₂ are strongly adsorbed while NO is only physisorbed. The supported Ga₂O₃ samples show a slight decrease in acidity as probed by ammonia adsorption, compared to alumina or titania. The addition of SnO₂ decreases the number of strong acid sites but creates a few weak and medium strength acid sites on alumina and does not modify the acidity of titania. In all cases, the basicity, probed by SO₂ adsorption, is very strongly affected by the deposition of Ga₂O₃ or SnO₂. The differential heats of NO₂ adsorption remain nearly constant on all samples. The heats of adsorption are discussed as a function of the coverage and of the amount of guest oxide. This revised version was published online in August 2006 with corrections to the Cover Date.     

高硅 Na-ZSM-5 分子筛表面 NO 的常温吸附-氧化机理

 采用程序升温表面反应 (TPSR) 和原位漫反射红外光谱 (DRIFTS) 等手段研究了常温下 NO 和 O₂ 在高硅 Na-ZSM-5 分子筛上吸附-氧化反应机理. 结果表明, Na-ZSM-5 分子筛上 NO 的催化氧化过程中伴随着显著的 NO₂ 物理吸附, 表现为 NO 氧化和 NO₂ 吸附间的动态平衡. Na-ZSM-5 分子筛表面 NO_x 吸附物种的 TPSR 和原位 DRIFTS 表征表明, 化学吸附的 NO 和气相中的 O₂  在 Na-ZSM-5 表面反应生成吸附态的 NO₃, 并继续与 NO 作用生成弱吸附的 NO₂  和 N₂ O₄, 它们吸附饱和后释放出来; 其中, 强吸附的 NO₃ 在 NO 氧化过程中起到了反应中间体的作用, 同时也促进了 NO 的吸附.     

Kinetics of nitric oxide oxidation

Nitrogen oxides are nowadays a subject of global concern. Several types of nitrogen oxides exist in the environment: N₂O, NO, NO₂, N₂O₃, N₂O₄, N₂O₅. The abbreviation NO _x usually relates to nitric oxide NO, nitrogen dioxide NO₂, and nitrous oxide N₂O. The first two are harmful pollutants for both environment and human health, whereas the third is one of the greenhouse gases. Implementation of stringent NO _x emission regulations requires the development of new NO _x removal technologies from exhaust gases. One of many proposals for NO _x emission reduction is the application of an oxidizing agent which would transform NO _x to higher nitrogen oxides with higher solubility in water. The main objective of the paper was to present the rate constant of nitric oxide oxidation, determined in our studies.     

FePO<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> Catalysts for Propylene Glycol Oxidation

FePО₄/SiO₂ supported catalysts with a different content of iron phosphate are prepared. The properties of the catalyst are changed by the introduction of alkali metal compounds (Na or Cs) on its surface. The samples obtained are characterized by X-ray diffraction, low-temperature nitrogen adsorption, temperatureprogrammed reduction by hydrogen, and temperature-programmed desorption of ammonia. The catalytic properties are investigated in the reaction of gas-phase propylene glycol oxidation. It is shown that the selectivity of methylglyoxal formation on the unmodified catalysts is determined by the state of the supported active component and by its reduction–oxidation ability under the action of a reaction mixture.     

Effectiveness of nitric oxide ozonation

Attempts to develop new technologies of NO _x (NO + NO₂) emission reduction are still carried out all around the world. One of the relatively new approaches is the application of ozone injection into the exhaust gas stream followed by the absorption process. Ozone is used to transform NO _x to higher nitrogen oxides which yield nitric acid with better effectiveness. The main objective of this paper was to study the influence of mole ratio (MR) O₃/NO used in the ozonation process of NO _x on the effectiveness of NO _x oxidation to higher oxides. The ozonation process was carried out in a flow reactor for concentrations of nitric oxide in the range of 1.5 × 10⁻⁵−7.7 × 10⁻⁵ mol dm⁻³ and varying O₃/NO mole ratios. Measurements were conducted with the use of a FTIR spectrometer. The results obtained prove that for MR higher than 1, the oxidation effectiveness of nitric oxides generally reaches 95 %, whereas for MR higher than 2, oxidation of NO _x to higher nitrogen oxides is completed.     

Simulation of radiation-chemical transformations in aqueous nitric oxide and nitrite solutions

A kinetic model of radiation-chemical transformations of nitrogen oxide and nitrites in aqueous solutions is proposed. It includes the previously developed reaction scheme for water and H₂, H₂O₂, and O₂ solutions complemented by the reactions of water radiolysis products with NO and NO₂⁻. It has been shown that the model describes well experimental data on the decomposition of the compounds and the buildup of products depending on the absorbed dose in aqueous solutions at different pH values.     

Achievements,Challenges, and Perspectives on Nitrogen Electrochemistry for Carbon-Neutral Energy Technologies

Unrestrained anthropogenic activities have severely disrupted the global natural nitrogen cycle, causing numerous energy and environmental issues. Electrocatalytic nitrogen transformation is a feasible and promising strategy for achieving a sustainable nitrogen economy. Synergistically combining multiple nitrogen reactions can realize efficient renewable energy storage and conversion, restore the global nitrogen balance, and remediate environmental crises. Here, we provide a unique aspect to discuss the intriguing nitrogen electrochemistry by linking three essential nitrogen-containing compounds (i.e., N₂, NH₃, and NO₃⁻) and integrating four essential electrochemical reactions, i.e., the nitrogen reduction reaction (N₂RR), nitrogen oxidation reaction (N₂OR), nitrate reduction reaction (NO₃RR), and ammonia oxidation reaction (NH₃OR). This minireview also summarizes the acquired knowledge of rational catalyst design and underlying reaction mechanisms for these interlinked nitrogen reactions. We further underscore the associated clean energy technologies and a sustainable nitrogen-based economy.     

A new electrochemical analyser for nitric oxide and nitrogen dioxide

Individual sensors employing Teflon-bonded diffusion electrodes have been developed to measure nitric oxide and nitrogen dioxide separately, simultaneously, and continuously at part-permillion levels. The NO sensor was biased at 1.5V and that for NO₂ at 0.8V, both relative to the hydrogen electrode. The crucial factor in the virtual elimination of response from carbon monoxide, a relatively abundant air-pollutant, was the use of gold electrodes for both detectors. At 0.8 V NO does not react on gold. Although NO₂ does oxidize at 1.5 V it was removed quantitatively from NO/NO₂ mixtures by triethanolamine on firebrick. The NO₂ reduction signal and the NO oxidation signal were stable and reproducible.     

Hydrocarbon Assisted NO Oxidation with Non-thermal Plasma in Simulated Marine Diesel Exhaust Gases

The NO oxidation performance in a non-thermal plasma (NTP) reactor under realistic synthetic exhaust gas compositions is investigated. The gas compositions differ mainly in the NO–NO₂ ratio and represent different modes of operation of a marine diesel engine. It is found that the maximum NO oxidation efficiency is independent on the NO–NO₂ ratio. Up to 55 % of the NO is mainly oxidised to NO₂ in all gas mixtures being analysed. However, the specific energy density needed to reach the highest NO oxidation varies with the gas composition between 15 and 60 J/L. The performance of the NTP-reactor was significantly improved by the addition of propene (C₃H₆) acting as an additional oxidising agent. The energy consumption for NO–NO₂ conversion was found to be between 20 and 45 eV/NO, depending on the ratio of the added propene as well as the initial concentrations of nitrogen oxides.     

Reactions of p‐Substituted Phenols with Nitrous Acid in Aqueous Solution

The reaction of phenols with nitrite (nitrous acid HONO, or its conjugated base, NO₂^?) is of importance in stomach fluids (low pH) and in atmospheric hydrometeors (mild acid and basic pH). The initial reaction associated with the oxidation/nitration of 4‐substitued phenols promoted by HONO/NO₂ depends on the pH of the solution. At low pH, the initial step involves the reaction between HONO and phenol, whereas at basic conditions this involves an electron transfer from the phenoxy anion to nitrogen dioxide (NO₂) producing the nitrite anion. The rate of both processes is determined by the donor capacity of the substituent at the 4‐position of the phenol, and the data obtained at pH 2.3 follow a linear Hammett‐type correlation with a slope equal to –1.23. The partition of the gaseous intermediates (NO and NO₂) makes the rate of HONO‐mediated oxidation dependent on their gas–liquid distribution. At low pH, the main process is phenol oxidation, even in oxygen‐free conditions, and the presence of any 4‐substituted phenol decreases the rate of HONO auto‐oxidation.     

Nitrite and Nitrate Production by NO and NO2 Dissolution in Water Utilizing Plasma Jet Resembling Gas Flow Pattern

This study investigated the reactive dissolution of nitric oxide (NO) and nitrogen dioxide (NO₂) mixtures in deionized water. The dissolution study was carried out in a flat surface type gas–liquid reaction chamber utilizing a gas flow-pattern resembling plasma jets which are often used in biomedical applications. The concentration of NO and NO₂ in the gas mixtures was varied in a broad range by oxidizing up to 800 ppm of nitric oxide in Ar carrier gas with variable amount of ozone. The production of nitrite (NO₂^?) and nitrate (NO₃^?) in the water was proportional to treatment time up to 50 min. The concentration of NO₃^? was a power function of gas phase NO₂ while the concentration of NO₂^? increased approximately linearly with gas phase NO₂. The formation of NO₂^? and NO₃^? could be described by reactions between dissolved NO₂ and NO in the water while the production rate was determined by diffusion-limited mass transport of nitrogen oxides to the bulk of the liquid. At higher NO₂ concentrations, the formation of dinitrogen tetraoxide (N₂O₄) increased the formation rate of NO₂^? and NO₃^?. The identified mass transport limitation by diffusion suggests that convection of water created by the gas jet is insufficient and dissolution of nitrogen oxides can be increased by additional mixing. In respect of practical applications, the ratio of NO₂^? /NO₃^? in water could be varied from 0.8 to 5.3 with treatment time and gas phase NO₂ and NO concentrations.