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1.
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.  相似文献   

2.
The adsorption of NO, NO/O2 mixtures and NO2 on pure ZrO2 and on two series of catalysts supported on ZrO2, one containing vanadia and the other molybdena (ZV and ZMo, respectively), has been investigated. The V and Mo surface contents of the latter were ≤3 atoms nm−2 and ≤5 atoms nm−2, respectively. All samples had been previously submitted to a standard oxidation treatment. On all samples, only extremely minor amounts of NOx surface species are formed by NO interaction at room temperature (RT). NOx surface species are formed in greater amounts on pure ZrO2 when NO and O2 are coadsorbed at RT; they are mainly nitrites, small amounts of nitrates, and small amounts of (O2NO−H)δ− species; when ZrO2 is warmed to 623 K in the NO/O2 mixture, nitrites decrease, nitrates and (O2NO−H)δ− species increase. The same NOx species as on the ZrO2 surface free from V (or Mo) are formed on ZV (or ZMo) samples with surface V (or Mo) density <1.5 atoms nm−2; however, they occur in decreased amount with increasing V (or Mo) coverage. On ZV samples with a surface V density of 1.5–3 atoms nm−2 (or ZMo samples with a surface Mo density of 1.5–5 atoms nm−2) when NO and O2 are coadsorbed at RT, there is formation of small amounts of nitrites, nitrates (both on ZrO2 surface free from V (or Mo) and at the edges of V- or Mo-polyoxoanions) and NO2 δ+ species, associated with V5+ (or Mo6+) of very strong Lewis acidity; when samples are warmed up 623 K in the NO/O2 mixture, nitrites disappear, nitrates increase, NO2 δ+ species remain constant or slightly decrease. When NO2 is allowed into contact at RT with oxidized samples, surface situations almost identical to those obtained for each sample warmed to 623 K in NO/O2 mixture is reached. The NOx surface species stable at 623 K, the temperature at which catalysts show the best performance in the selective catalytic reduction (SCR) of NO by NH3, are nitrates, both on ZrO2 and on polyvanadates or polymolybdates at high nuclearity. On the contrary, nitrites and NO2 δ+ species are unstable at 623 K.  相似文献   

3.
The aim of this work is to study the effect of Sr substitution on the redox properties and catalytic activity of La2−x Sr x NiO4 (x = 0.0–1.2) for NO decomposition. Results suggest that the x = 0.6 sample shows the highest activity. The characterization (TPD, TPR, etc.) of samples indicates that the x = 0.6 sample possesses suitable abilities in both oxidation and reduction, which facilitates the proceeding of oxygen desorption and NO adsorption. At temperature below 700°C, the oxygen desorption is difficult, and is the rate-determining step of NO decomposition. With the increase of reaction temperature (T > 700°C), the oxygen desorption is favorable and, the active adsorption of NO on the active site (NO + V o + Ni2+ → NO-Ni3+) turns out to be the rate-determining step. The existence of oxygen vacancy is the prerequisite condition for NO decomposition, but its quantity does not relate much to the activity. Supported by the National Hi-Tech Research and Development Program of China (863 Program)(Grant No. 2004CB 719502) and the National Natural Science Foundation of China (Grant No. 20177022)  相似文献   

4.
A pilot-scale pulse corona induced plasma chemical process (PPCP) reactor for controlling gas-phase dioxins and NO x simultaneously is installed in a garbage incineration plant. The flow rate of the sampled flue gas is 5,000 Nm3/h (N: standard state) in maximum at the PPCP reactor, which consists of 22 wire-cylinder electrodes and is energized by a 50 kW nanosecond pulse high voltage generator. With an applied plasma energy density of 2.9–6.1 Wh/Nm3, the decomposition efficiency for dioxins is 75–84% based on TEQ (toxic equivalents); the conversion efficiency of NO to NO2 is ~93% at maximum. The flue gas treated by the PPCP reactor is introduced at a rate of 50 Nm3/h to a wet-type chemical reactor, which uses an aqueous solution of sodium sulfite (Na2SO3). More than 90% of NO x is reduced to nitrogen, with negligible byproducts such as NO2 or NO3 ions left in the solution.  相似文献   

5.
There is a strong interest in finding highly soluble redox compounds to improve the energy density of redox flow batteries (RFBs). However, the performance of electrolytes is often negatively influenced by high solute concentration. Herein, we designed a high-potential (0.5 V vs. Ag/Ag+) catholyte for RFBs, where the charged and discharged species are both gaseous nitrogen oxides (NOx). These species can be liberated from the liquid electrolyte and stored in a separate gas container, allowing scale-up of storage capacity without increasing the concentration and volume of the electrolyte. The oxidation of NO in the presence of NO3 affords N2O3, and the reduction of N2O3 regenerates NO and NO3, together affording the electrochemical reaction: NO3+3 NO⇌2 N2O3+e with a low mass/charge ratio of 152 grams per mole of stored electron. A proof-of-concept NOx symmetric H-cell shows 200 stable cycles over 400 hours with >97 % Coulombic efficiency and negligible capacity decay.  相似文献   

6.
A novel nanocrystalline TiO2 (nano-TiO2) and Nafion composite film modified glassy carbon electrode has been developed for the determination of nitric oxide (NO) radical in an aqueous solution. This modified electrode can be employed as a NO sensor with a low detection limit, fast response, high sensitivity and selectivity. Two apparent anodic peaks were observed at 0.67 and 0.95 V at the nano-TiO2 modified glassy carbon electrode by differential pulse voltammetry (DPV). After further modification with a thin film of Nafion, which was capable of preventing some anionic interference such as nitrite and ascorbic acid, only one peak appeared and the peak current enhanced greatly. The chronocoulometric experimental results showed NO was oxidized by one-electron transfer reaction at the composite film modified electrode. The amperometric responses increased linearly with the concentrations of NO ranging from 3.6×10−7 mol/L to 5.4×10−5 mol/L. The detection limit was estimated to be 5.4×10−8 mol/L. In this sensor system, the modification film provides complete selectivity for NO over nitrite anions (NO2).  相似文献   

7.
A simple, sensitive, selective, and low-cost method is proposed for rapidly determining nitric oxide (NO) in some rat tissues. Polymer monolith microextraction (PMME) using a poly(methacrylic acid–ethylene glycol dimethacrylate) (MAA-EGDMA) monolithic column was combined with derivatization of NO using 1,3,5,7-tetramethyl-8-(3′,4′-diaminophenyl)-difluoroboradiaza-s-indacene (TMDABODIPY), and this was used to analyze the derivatives of NO by high-performance liquid chromatography (HPLC) with fluorescence detection at λ ex/λ em = 498/507 nm. The baseline separation of TMDABODIPY and its NO derivative is performed under simple conditions in which a C18 column is used and eluted with 50 mmol L−1 ethanolamine and methanol. The conditions for the extraction of NO derivatives were optimized. The limit of detection of NO was 2 × 10−12 mol L−1 (S/N = 3). The linearity range of the method was 9 × 10−11−4.5 × 10−8 mol L−1. The interday and intraday relative standard deviations were less than 5%. The proposed method was successfully applied to the determination of NO levels in some rat tissue samples including heart, kidney, and liver with recoveries varying from 87.1 to 95.2%.  相似文献   

8.
The efficiency of TiO2 (Degussa P-25) modified with an alkaline admixture (urea, BaO), sulfuric acid, or platinum in the photocatalytic oxidation of NO (50 ppm) with a flowing 7% O2 + N2 mixture under UV irradiation in a flow reactor at room temperature and atmospheric pressure is reported. Because of the progressive blocking of active sites of the photocatalyst by the reaction products (NO2, NO3), it is impossible to realize prolonged continuous removal of NO x (NO + NO2) from air without catalyst regeneration at elevated temperatures. The efficiency of the photocatalysts is characterized by specific photoadsorption capacity (SPC) calculated from the total amount of NO x adsorbed during 2-h-long irradiation. Modification of TiO2 with 5% BaO or 5% urea raises the SPC of the catalyst by a factor of 2–3. Presumably, this promoting effect is due to the basic properties of these dopants, which readily sorb NO2 and NO3. A considerable favorable effect on SPC is also attained by adding 0.5% Pt to (5% BaO)/TiO2. The SPC of the (0.5% Pt)/TiO2 catalyst depends on the state of the platinum. The samples calcined in air at 500°C, which contain Pt+ and Pt2+, have an approximately 2 times higher SPC than unpromoted TiO2 and ensure a much larger NO2/NO ratio at the reactor outlet. Conversely, the samples reduced in an H2 atmosphere at 200°C, whose platinum is in the Pt0 state, show a lower SPC than the initial TiO2 and cause no significant change in the NO2/NO ratio.  相似文献   

9.
NO Reduction Over Noble Metal Ionic Catalysts   总被引:1,自引:0,他引:1  
In last 40 years, catalysis for NO x removal from exhaust gas has received much attention to achieve pollution free environment. CeO2 has been found to play a major role in the area of exhaust catalysis due to its unique redox properties. In last several years, we have been exploring an entirely new approach of dispersing noble metal ions in CeO2 and TiO2 for redox catalysis. We have extensively studied Ce1−x M x O2−δ (M = Pd, Pt, Rh), Ce1−xy A x M y O2−δ (A = Ti, Zr, Sn, Fe; M = Pd, Pt) and Ti1−x M x O2−δ (M = Pd, Pt, Rh, Ru) catalysts for exhaust catalysis especially NO reduction and CO oxidation, structure–property relation and mechanism of catalytic reactions. In these catalysts, lower valent noble metal ion substitution in CeO2 and TiO2 creates noble metal ionic sites and oxide ion vacancy. NO gets molecularly adsorbed on noble metal ion site and dissociatively adsorbed on oxide ion vacancy site. Dissociative chemisorption of NO on oxide ion vacancy leads to preferential conversion of NO to N2 instead of N2O over these catalysts. It has been demonstrated that these new generation noble metal ionic catalysts (NMIC) are much more catalytically active than conventional nano crystalline noble metal catalysts especially for NO reduction.  相似文献   

10.
Using the polyglycol gel method, a series of Pr2 − x SrxCoO4 ± y (0.2 ≤ x ≤ 1.0) mixed oxides were prepared, and their catalytic activities were studied in the test reaction of NO reduction by CO. The solid-state physicochemical properties, including crystal structure, defect structure, IR spectrum, valence state of B-site ions, nonstoichiometry oxygen (y), oxygen species, and redox properties, were characterized by means of XRD, IR, TPD, TPR, XPS, and chemical analysis. The results show that all mixed oxides display a K2NiF4 structure. When x = 0.2 and 1.0, the obtained samples still have little uncertain mixed oxides; however, the mixed oxides (x = 0.4, 0.6, 0.8) all represent a single A2BO4 phase. With the increase of x, lattice parameters, unit-cell volume, and average crystalline size decrease gradually, whereas microstrain density, the concentration of Co3+, the amounts of lattice oxygen released and the concentration of oxygen vacancy increase. The catalytic activities of Pr2 − x SrxCoO4 ± y catalysts for NO reduction by CO are closely correlated with oxygen vacancy and the concentration of Co3+. Published in Russian in Kinetika i Kataliz, 2006, Vol. 47, No. 3, pp. 431–437. The text was submitted by the authors in English.  相似文献   

11.
CeO2-based solid solutions with a fluorite structure are promising materials as electrolytes of medium-temperature electrochemical devices. This work presents the results of systematic studies of structural and electric properties and oxygen nonstoichiometry of the Ce0.8(Sm1 − x Ca x )0.2O2 − δ system in a wide range of concentrations of 0 < x < 1 performed in order to establish the causes affecting the system conductivity and its behavior in a reducing medium. It is found that a single-phase solid solution of the fluorite type is formed in the whole concentration range. Parameters of its lattice cells decrease linearly at an increase in the concentration of Ca2+. Conductivity in air grows when calcium is added due to a decrease in the grain boundary resistance. The maximum conductivity in air was obtained for the composition of Ce0.8(Sm0.8Ca0.2)0.2O2 − δ and is 13.71 × 10−3 S/cm at 873 K. Studies of the dependence of conductivity of the partial pressure of oxygen showed that electron conductivity is observed at a higher oxygen partial pressure at an increase in the temperature and calcium concentration. The critical partial pressure of oxygen ( pO2 * )\left( {p_{O_2 }^* } \right) for the compositions of Ce0.8(Sm1 − x Ca x )0.2O2 − δ with x = 0; 0.2, and 0.5 is 1.83 × 10−16, 1.73 × 10−13, and 3.63 × 10−13 atm at 1173 K, respectively, and 2.76 × 10−21, 5.05 × 10−18, and 1.31 × 10−18 atm at 1023 K.  相似文献   

12.
Solid solutions of spinel-type oxides with the composition NiCr x Fe2-x O4 (x = 0.0, 0.5, 1.0, 1.5, 2.0) were prepared with the glycine–nitrate combustion synthesis. Four-point DC resistivity measurements show an increase in the conductivity as more Cr is introduced into the structure, whereas dilatometer measurements show that the linear thermal expansion decreases with increasing Cr content. The oxides were used as electrode materials in a pseudo-three-electrode setup in the temperature range of 300–600 °C. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the electrochemical behavior in 1% NO, 1% NO2, and 10% O2. NiCr2O4 shows high activity in NO and NO2 relative to O2 and can therefore be considered as a possible electrode material. Peaks were detected in the voltammograms recorded on NiCr2O4 in 1% NO. The origin of the peaks seems to be related to the oxidation of Cr or the formation of nitrogen-containing species formed on the surface of the electrode.  相似文献   

13.
The adsorption and activation of NO molecules on Cu-ZSM-5 catalysts with different Cu/Al and Si/Al ratios (from 0.05 to 1.4 and from 17 to 45, respectively) subjected to different pretreatment was studied by ultraviolet-visible diffuse reflectance (UV-Vis DR). It was found that the amount of chemisorbed NO and the catalyst activity in NO decomposition increased with an increase in the Cu/Al ratio to 0.35–0.40. The intensity of absorption bands at 18400 and 25600 cm−1 in the UV-Vis DR spectra increased symbatically. It was hypothesized that the adsorption of NO occurs at Cu+ ions localized in chain copper oxide structures with the formation of mono- and dinitrosyl Cu(I) complexes, and this process is accompanied by the Cu2+...Cu+ intervalence transfer band in the region of 18400 cm−1. The low-temperature activation of NO occurs through the conversion of the dinitrosyl Cu(I) complex into the π-radical anion (N2O2) stabilized at the Cu2+ ion of the chain structure, [Cu2+-cis-(N2O2)], by electron transfer from the Cu+ ion to the cis dimer (NO)2. This complex corresponds to the L → M charge transfer band in the region of 25600 cm−1. The subsequent destruction of the complex [Cu2+-cis-(N2O2)] at temperatures of 150–300°C leads to the release of N2O and the formation of the complex [Cu2+O], which further participates in the formation of the nitrite-nitrate complexes [Cu2+(NO2)], [Cu2+(NO)(NO2)], and [Cu2+(NO3)] and NO decomposition products.  相似文献   

14.
Mn–TiO2 catalysts were utilized as an ozonation catalyst for the first time to study the simultaneous catalytic ozonation of Hg0 and NO at low flue gas temperatures. BET, SEM–EDS, XRD, XPS, H2-TPR, NO x -TPD and Hg0-TPD were used to characterize the catalysts. The Mn–TiO2 catalyst, in which the molar content of metal Mn was 60%, exhibited the best catalytic activities of Hg0 and NO oxidation, compared with other Mn–TiO2 catalysts. It was found that within the range of experiment, the catalytic ozonation efficiency of Hg0 and NO was higher than that of ozonation or catalytic oxidation. The results also showed that the presence of NO gas inhibited the catalytic ozonation of elemental mercury, and the inhibition was enhanced with the NO inlet concentration, while few elemental mercury molecules did promote the catalytic ozonation of NO. The addition of H2O vapor promoted the catalytic ozonation of Hg0 and NO. In addition, 0.6Mn–TiO2 catalyst demonstrated a good TOS and cyclic stability. The catalytic ozonation of NO and Hg0 on Mn–TiO2 catalyst likely followed the Langmuir–Hinshelwood mechanism, where the hydroxyl radicals reacted with adjacently adsorbed NO molecules and elemental mercury on catalyst surface.  相似文献   

15.
Pure ceria-zirconia mixed oxides Ce x Zr1−x O2 with high specific surface area were synthesized with a new epoxyde driven sol–gel route and characterized by thermal analysis, X-ray diffraction studies and transmission electron microscopy. This sol–gel method is cheap and uses only a few steps. The Ce x Zr1−x O2 mixed oxides were obtained in the range of 0 ≤ x ≤ 1 (except for x = 0.8) and crystallised at 350 °C after decomposition of the gels. This temperature is very low in comparison with the other methods. The studies of the influence of different synthesis parameters (concentration of the sol and decomposition temperature) allowed us to determine the conditions to obtain the best homogeneity in the gel to avoid the formation of a mixture of phases instead of mixed oxides. This approach leads to the synthesis of oxide with specific surface area above 100 m2 g−1. The elaboration of an ambigel could increase this value up to 195 m2 g−1 for x = 0.5. This sol–gel synthesis offers new perspectives for these oxides in several applications. Generally, these oxides are difficult to obtain pure in large range of composition at low-temperature and with high specific surface area by other methods.  相似文献   

16.
The rates of heat release in the nitrogen dioxide—n-decane system at a molar ratio of nitrogen oxides ton-decane (β) from 2.4·10−3 to 3.1 and gaseous volumes per mole ofn-decane (V(g)) equal to 0.05–4.5 were studied in the 55.2–92.8 °C temperature range. The initial rate of the process is determined by the interaction of NO2 withn-decane. The equilibrium constants of dissociation of N2O4 inn-decane and Henry's constants of NO2 and N2O4 in ann-decane solution were determined by complex analysis of the thermodynamic equilibrium in the NO2n-decane system and dependences of the initial rates onV(g) and β. The experimentally observed self-acceleration of the process in the region of high β and lowT values was suggested to be due to the reaction of N2O4 with intermediate oxidation products. The rate constants of the reaction of NO2 withn-decane were compared with analogous values determined in its mixtures with HNO3 solutions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1789–1794, October, 1997.  相似文献   

17.
The structures of two salts [Co(NH3)6][Rh(NO2)6] (I) and [Co(NH3)6][(NO2)3Rh(μ-NO2)1+x (μ-OH)2−x Rh(NO2)3]·(2−x)(H2O), x = 0.17 (II) are solved. Single crystals of the salts are obtained by the counter diffusion method through the gel of aqueous solutions of [Co(NH3)6]Cl3 and Na3[Rh(NO2)6]. The structure of [Co(NH3)6][Rh(NO2)6] is consistent with the diffraction data for a polycrystalline sample of poorly soluble fine salt formed in the exchange reaction between aqueous solutions of [Co(NH3)6]Cl3 and Na3[Rh(NO2)6]. The structure of [Co(NH3)6][(NO2)3Rh(μ-NO2)1+x (μ-OH)2−x Rh(NO2)3]·(2−x)(H2O), x = 0.17 exhibits the stabilizing effect of a large cation in the formation of novel, unknown previously coordination ions: [(NO2)3Rh(μ-NO2)(μ-OH)2Rh(NO2)3]3− and [(NO2)3Rh(μ-NO2)2(μ-OH)Rh(NO2)3]3−.  相似文献   

18.
Toward achieving selective catalytic reduction of NO x by hydrocarbons at low temperatures (especially lower than 200 °C), C2H2 selective reduction of NO x was explored on H-mordenite (H-MOR) catalysts in dielectric barrier discharge (DBD) plasma. This work reported significant synergistic effects of DBD plasmas and H-MOR catalysts for C2H2 selective reduction of NO x at low temperatures (100–200 °C ) and across a wide range of O2 content (0–15%). At 100 °C, NO x conversions were 3.3, 11.6 and 66.7% for the plasma alone, catalyst alone and in-plasma catalysis (IPC) cases (with a reactant gas mixture of 500 ppm NO, 500 ppm C2H2, 10% O2 in N2, GHSV = 12,000 h−1 and input energy density of 125 J L 1), respectively. At 200 °C, NO x conversions were 3.8, 54.0 and 91.4% for the above three cases, respectively. Also, strong signals of hydrogen cyanide (HCN) byproduct were observed in the catalyst alone system by an on-line mass spectrometer. By contrast, almost no HCN was detected in the IPC system.  相似文献   

19.
The possibility of using electrochemical cells for removal of NO x from an exhaust gas with excess O2 has been examined. (La1−x Sr x ) s MnO3 (LSM) and ceria doped with Pr or Gd were selected as electrode materials and investigated in three-electrode cells. The electrodes were characterised electrochemically with electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV), and the gas composition monitored while the electrodes were polarised. The electrodes of (La0.5Sr0.5)0.99MnO3 (LSM50) and Ce0.8Pr0.2O2−δ exhibit higher current densities in 0.1% NO in Ar than in air at 300 to 400 °C during CV. This indicates some apparent selectivity towards NO compared to O2. The electrodes can remove NO, when polarised to at least −0.6 V vs. Pt/Air at 600 °C, and EIS measurements under polarisation indicate that the kinetics of the electrodes change, when the electrode potential gets below −0.6 V vs. Pt/Air.  相似文献   

20.
A new oxide-ion conductor of Aurivillius family with a general formula Bi2Al x V1 − x O5.5 − x − δ; 0 ≤ x ≤ 0.20 (BIALVOX) was synthesized by the sol-gel citrate route. Powder X-ray diffraction and simultaneous thermogravimetric and differential thermal analyses confirmed that the calcination of BIALVOX xerogels is fully completed at around 500°C after three hours of thermal treatment. It has been found that the β-orthorhombic phase is stabilized with compositions x ≤ 0.07, whereas the stabilization of the γ′-phase takes place for x ≥ 0.10. AC impedance spectroscopic investigation suggested that the charge accumulation at grain boundaries is thermally activated process. However, the maximum electrical conductivity (7.73 × 10−5 S cm−1) noticed for BIALVOX.13 at 300°C was attributed to the maximum vacancy concentration in the equatorial planes, responsible for the ion diffusion through the structure. This has been further evidenced by the temperature dependence of dielectric permittivity.  相似文献   

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