Reactions of nitrogen oxides (NO,N2O) with the surface of a copper-chromium oxide catalyst

Weight-space and IR spectroscopic methods have been used to investigate the reaction of NO and N₂O with the surface of a copper-chromium oxide catalyst in the form of copper chromite with a 20% excess of Cr₂O₃. Comparisons have been made between the relative reactivities of the different oxides (NO, N₂O, O₂) in oxidation of the Cu⁺ and Cu^o surface centers. The role of these centers in oxidation of CO by oxygen and by nitrogen oxides is discussed.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 338–343, May–June, 1985.     

Effect of the composition and method of preparation of iron-containing and cobalt-containing catalysts on the combined reduction of NO and N<Subscript>2</Subscript>O by hydrocarbons

Binary iron-containing and cobalt-containing catalysts derived from the hydrogen form of Pentasil, zirconium dioxide, and binary supports (ZrO₂ + zeolite) display significant activity in the combined reduction of nitrous oxide and nitric oxide by C₁ and C₃-C₄ alkanes, including conditions for the selective catalytic reduction of NO + N₂O. The activity of the catalyst in the conversion of NO and N₂O depends on the method of preparation of the binary composites and the amount of the cobalt and iron components.     

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.     

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.     

Concentration limits for flame propagation in mixtures of hydrogen and oxides of nitrogen

Summary The concentration limits were determined for flame propagation in mixtures of hydrogen with nitrogen oxides (N₂O, NO₂, NO) and an inert diluent (nitrogen), the components being taken in various proportions.     

Reduction of NO by C1-C4 hydrocarbons at cobalt-containing zeolites

Data are given on the activity of high-silicon zeolites in the reduction of nitrogen oxides by methane and C₂-C₄ hydrocarbons (paraffins and olefins). It was shown that the highest degree of conversion of NO during selective catalytic reduction is obtained at the mixed forms of Co-containing zeolites at temperatures 100°C lower than at the usual Co-containing zeolites of the ZSM-5 type.L. V. Pisarzhevskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, Kiev. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 32, No. 1, pp. 47–50, January–February, 1996. Original article submitted April 3, 1995.     

Spin trapping reactions with nitric oxides. III. Alkoxyalkylnitroxides and new nitrogen centered radicals

Subsequent trapping of photochemically generated alkyl and alkoxy radicals by nitric oxide yields alkoxyalkylnitroxide radicals. New types of nitrogen centered radicals have been detected and tentatively explained by reactions of nitrogen oxides N₂O, NO, NO₂, N₂O₃, N₂O₄ with alkyl and peroxide radicals.     

Organische Phosphorverbindungen XXXVIII. Darstellung und Eigenschaften von Tris-(dialkoxyphosphonyl-methyl)-, Tris-(alkoxyphosphinyl-methyl)-und Tris-(oxophosphoranyl-methyl)-phosphinsäureestern sowie der entsprechenden Säuren [1]

Tris-chloromethyl-phosphine oxide, (ClCH₂₎₃ P?O(I), is obtained by chlorination of (HOCH₂₎₃P?O with PCl₅ or (C₆H₅₎₃PCl₂, and also by oxidation of (CICH₂₎₃P?O and (ClCh₂₎₂(CH₃)P?O. High yields of tris-(dialkyloxyphosphonly-methyl)-phosphine oxides, [RO₂(O)PCH_2]2P?O (II) (R?CH₃, C₂H₅, iso-C₃H₇, n-C₄H₉, 2- ethyl-hexyl), tris (alkyloxyphosphinyl-methyl)-phosphine oxides, [R₂(O)PCH_2]3P?O(R = C₆H₅, CH₃) are obtained by heating tris-chloromethyl-phosphine oxides, [(RO) (R′) (O)PCH_2]3P?O (R = C₄H₉, R′? C₆H₅) and tris-(oxophosphoranyl-phosphine oxides with phosphites, phosphonites and phosphinites, respectively, at 170–180°C for several hours. Compounds II possess an extraordinarily high absorption capacity. Thus a warm. 2% solution of II (R = C₂H₅) in benzene solidifies completely on cooling so that no benzene can be poured off. Tris-dihydroxyphosphonyl-methyl)-phosphine oxide, [(HO)₂(O)PCH_2]3P?O, obtained by hydrolysis of II (R ? C₂H₅) with refluxing conc. HCl or by thermal decomposition of II (R ? iso-C₃H₇) at 190°, titrates in aqueous solution as a hexabasic acid with breaks at pH = 4,4 (three equivalents) and pH = 10,7 (three equivalents). It forms crystalline salts with amines, alkali and alkaline earth metals, and is an excellent chelating agent. The ¹H- and ^31?P-NMR. spectra of all the compounds prepared are discussed.     

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.     

Contemporary Problems in the Selective Catalytic Reduction of Nitrogen Oxides (NOx)

The results from investigation of the processes involved in the catalytic reduction of nitrogen oxides are reviewed: 1) with carbon monoxide and other combustible gases (H₂, C _n H _m ) at a developed block honeycomb palladium-containing catalysts; 2) with ammonia (the SCR process) at vanadium-containing and complex oxide (Cu-Cr, Fe-Cr/-Al₂O₃) catalysts; 3) with light C₁-C₄ hydrocarbons at cation-exchange zeolites (pentasils, natural and synthetic mordenites). Mechanisms and kinetic models are proposed, and the regions of a positive and negative effect from oxygen and sulfur dioxide on the processes involved in the reduction of nitrogen oxides are established.     

Experimental and kinetic modeling of the reduction of NO by isobutane in a Jsr at 1 atm

A kinetic study of the reduction of nitric oxide (NO) by isobutane in simulated conditions of the reburning zone was carried out in a fused silica jet‐stirred reactor operating at 1 atm, at temperatures ranging from 1100 to 1450 K. In this new series of experiments, the initial mole fraction of NO was 1000 ppm, that of isobutane was 2200 ppm, and the equivalence ratio was varied from 0.75 to 2. It was demonstrated that for a given temperature, the reduction of NO is favored when the temperature is increased and a maximum NO reduction occurs slightly above stoichiometric conditions. The present results generally follow those reported in previous studies of the reduction of NO by C₁ to C₃ hydrocarbons or natural gas as reburn fuel. A detailed chemical kinetic modeling of the present experiments was performed using an updated and improved kinetic scheme (979 reversible reactions and 130 species). An overall reasonable agreement between the present data and the modeling was obtained. Furthermore, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethylene, ethane, acetylene, a natural gas blend (methane‐ethane 10:1), propene, and HCN. According to this study, the main route to NO reduction by isobutane involves ketenyl radical. The model indicates that the reduction of NO proceeds through the reaction path: iC₄H₁₀ → C₃H₆ → C₂H₄ → C₂H₃ → C₂H₂ → HCCO; HCCO + NO → HCNO + CO and HCN + CO₂; HCNO + H → HCN → NCO → NH; NH + NO → N₂ and NH + H → followed by N + NO → N₂; NH + NO → N₂O followed by N₂O + H → N₂. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 365–377, 2000     

Emission of secondary ions from osmium under oxygen and the nitrogen oxides N2O, NO and NO2

Summary Small briquettes compressed of high-purity Os powder were bombarded by primary Ar⁺ ions for moderate dynamic SIMS conditions. Secondary ion mass spectra were observed for positive ions which were produced under residual gas and under O₂, N₂O, NO, NO₂. For the different reactant gases these spectra were found rather similar, indicating that the nitrogen oxides mainly act as sources of reactive oxygen. But also some individual secondary ions containing nitrogen or NO are emitted from the target surface which, at least in the case of N₂O and NO₂, give some evidence of partial adsorptive fragmentation of the respective reactant gas molecules.     

Polar monolithic capillary columns: Analysis of light hydrocarbons

The influence of the nature of the stationary phase and carrier gas (helium, hydrogen, nitrogen, carbon dioxide, or nitrous oxide) on the efficiency and separating ability of monolithic ethyleneglycol dimethacrylate (EDMA) polymer capillary columns was studied using a model mixture of light hydrocarbons C₁-C₄. The results were compared with the properties of silica gel and divinylbenzene (DVB) monolithic columns. For EDMA polymer monolithic columns, the effect of the carrier gas on the separating ability was markedly lower than for silica gel columns. A reduction in HETP observed in the series He > H₂ > N₂ > N₂O > CO₂ is also known for hollow capillary columns with polymer stationary phases, but the change in efficiency was ～20–30% in this case. Under the optimum conditions, HETP was minimum for the columns when CO₂ or N₂O was used.     

Properties of perovskite-type oxides II: Studies in catalysis

A review is presented of some representative reactions where perovskite oxides (mostly with a rare earth element in the A sites) have been used as catalytic agents. These are mainly reactions with oxygen or hydrogen participating as one of the reactants and/or products, and they include oxygen equilibration and exchange, oxidation of CO, hydrocarbons, oxygenated compounds, H₂ and NH₃, and also the reduction of NO and SO₂, hydrogenation, hydrogenolysis and the decomposition of 2-propanol, H₂O₂ and N₂O. A study of the role of the cations in positions A and B has been attempted.     

Electric discharge-induced oxidation of hydrogen cyanide

The AC high-voltage discharge-induced decomposition chemistry of trace levels of hydrogen cyanide in helium has been studied. In the absence of oxygen only low levels of molecular nitrogen were evolved. With oxygen added, the principal products were CO, CO₂, and N₂. No significant concentrations of NO or N₂O were observed. The response of a commercial NO_x analyzer to HCN and C₂N₂, in the NO_x mode, was determined to be linear through three decades in concentration. The oxidation chemistry of HCN and C₂N₂ in the stainless steel converter of the analyzer was studied as a function of the amount of added oxygen.NRL/NRC Postdoctoral Fellow (1983–1985).     

Reduction of N<Subscript>2</Subscript>O and NO over H-ZSM-5- and ZrO<Subscript>2</Subscript>-supported iron- and cobalt-containing catalysts

The combined conversion conditions were examined for the reactions of decomposition and reduction of N₂O and NO with C₁,C₃–C₄ hydrocarbons, in particular, in gas mixtures containing oxygen and sulfur dioxide, over Fe- and Co-containing catalysts supported on zeolites and zirconia, as well as on structured honeycomb monoliths.     

Photocatalytic Reduction of NO with C2H6 on a Hollandite-Type Catalyst

The photocatalytic reduction of nitrogen monoxide (NO) with ethane on the hollandite type catalyst (K₂Ga₂Sn₆O₁₆KGSO) was investigated. Using a closed-gas circulating system equipped with a Q-MASS detector and in-situ diffuse reflectance FT-IR spectroscopy. The reactant gases of NO and ¹³C₂H₆ decreased with the increasing irradiation time. In contrast, the N₂ yield increased proportionally to the conversion of ¹³C₂H₆. Nitrogen oxides such as N₂O did not reach their detectable levels. The NO adsorbed on KGSO was found to change to its activated species by UV irradiation. The oxidized products of C₂H₆ such as CH₃CHO increased in proportion to the reaction time. The present results strongly suggest that KGSO has remarkable photocatalytic activity for the reduction of NO with C₂H₆.     

Ammonia Oxidation over Conventional Combustion Catalysts

The combustion of ammonia in air over different conventional oxidation catalysts has been studied in the present work. The final oxidation product is NO, although N₂O is also formed at intermediate temperatures. The environmentally desirable product, N₂, is only appreciably yielded over iron oxides catalysts.     

Reductive and oxidative combustion of polyethylene bags: Characterization of carbonaceous and nitrogenous species

This study aims to experimentally characterize the gaseous carbonaceous and nitrogenous species from the reductive and oxidant combustion of polyethylene plastic bags. The experimental device used is the tubular furnace, coupled to two gas analyzers: a Fourier transform infrared analyzer (FTIR) and a non dispersive infrared analyzer (NDIR). The gaseous products analyzed are: CO, CO₂, CH₄, C₃H₈, C₂H₄, C₂H₂, C₆H₆, HCN, N₂O, NO, NO₂ and NH₃. The experiments were conducted at temperatures ranging from 800 to 1000 °C. The results obtained allow us to note that carbonaceous compounds are mainly emitted as carbon oxides (CO and CO₂) whether you are reductive combustion or oxidative combustion.In addition:

• -Under reductive conditions, combustion is controlled by oxygen. The hydrocarbon most active in the formation of carbon monoxide is ethylene (C₂H₄) and to a lesser extent, from 900 °C, acetylene (C₂H₂). The extents we have made show that ammonia seem to be emitted during combustion with 10% of oxygen.
• -In an oxidative environment, there is production of C₆H₆ in substantial quantities, which partly explains the presence of soot and tar in the smoke exhaust ducts. The C₂H₄, CH₄ and C₂H₂ are hydrocarbons most active in the formation of CO and CO₂. Increasing of concentration of local oxygen from 10 to 21% for the combustion of plastic bags, favors an increase in efficiency of carbon conversion about 30%. About 99% of the carbon of the fuel is found to be converted to carbon oxides or hydrocarbons. Nitrogen monoxide (NO) is the major component among the gases measured with a conversion rate of nitrogen about 20%, three times larger than that obtained during the reductive combustion of plastic bags with 10% oxygen.

     

The synthesis,electrochemistry and molecular structure of [Fe(η5-C5H4S)2Mo(NO){HB(3,5-Me2C3N2H)3}]

The new bimetallic complex [Fe(η⁵-C₅H₄S)₂Mo(NO){HB(3,5-Me₂C₃N₂H)₃)}] has been obtained from the reaction between [Fe(η⁵-C₅H₄SH)₂] and [Mo(NO){HB(3,5-Me₂C₃N₂H)₃}I₂]. Electrochemical studies reveal an anomalously cathodic oxidation potential for the metallocene redox centre. An X-ray diffraction study has revealed an FMo distance of 4.147(2) Å, with the ferrocenyl moiety oriented towards the nitrosyl ligand on the molybdenum atoms (Fe---O 3.976(6) Å), but provides no evidence for an interaction between the iron atom and the molybdenum-bound nitrosyl which might account for the electrochemical findings.