- Synthesis and characterization of (Z)-[N3NFO]+ and (E)-[N3NFO]+
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(Figure Presented) A new stable polynitrogen ion: The second known example of a stable nitrogen fluoride oxide ion, [N3NFO]+, was prepared as its [SbF6]- salt and characterized by multinuclear NMR and vibrational spectroscopy and electronic-structure calculations. The cation is planar and exists as two stereoisomers (see picture; N blue, O red, F dark blue).
- Wilson, William W.,Haiges, Ralf,Boatz, Jerry A.,Christe, Karl O.
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- Mechanism of the reaction NO + H2 on the Pt(100)-hex surface under conditions of the spatially nonuniform distribution of reacting species
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The interaction of hydrogen with NOads/1 × 1 islands produced by NO adsorption on the reconstructed surface Pt(100)-hex was studied by high-resolution electron energy loss spectroscopy (HREELS) and the temperature-programmed reaction (TPR) method. The islands are areas of the unreconstructed surface Pt(100)-1 × 1 saturated with NOads molecules. The hexagonal phase around these islands adsorbs much more hydrogen near room temperature than does the clean Pt(100)-hex surface. It is assumed that hydrogen is adsorbed on the hexagonal surface areas that are adjacent to, and are modified by, the NOads/1 × 1 islands. The reaction of adsorbed hydrogen atoms with NOads takes place upon heating and has the character of so-called surface explosion. The TPR peaks of the products of this reaction-nitrogen and water-occur at T des ~ 365-370 K, their full width at half-maximum being ~5-10 K. In the case of the NO ads/1 × 1 islands preactivated by heating in vacuo above the NO desorption onset temperature (375-425 K), after the admission of hydrogen at 300 K, the reaction proceeds in an autocatalytic regime and the product formation rate increases monotonically at its initial stage. In the case of activation at 375 K, during the initial, slow stage of the reaction (induction period), hydrogen reacts with nitric oxide molecules bound to structure defects (NOdef). After activation at 425 K, the induction period is characterized by the formation and consumption of imido species (NH ads). It is assumed that NHads formation involves N ads atoms that have resulted from NOads dissociation on defects upon thermal activation. The induction period is followed by a rapid stage of the reaction, during which hydrogen reacts with NO 1 × 1 molecules adsorbed on 1 × 1 areas, irrespective of the activation temperature. After the completion of the reaction, the areas of the unreconstructed phase 1 × 1 are saturated with adsorbed hydrogen. The formation of Hads is accompanied by the formation of a small amount of amino species (NH2ads).
- Smirnov,Zemlyanov,Vovk
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- Diversion of Catalytic C-N Bond Formation to Catalytic Oxidation of NH3 through Modification of the Hydrogen Atom Abstractor
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We report that (TMP)Ru(NH3)2 (TMP = tetramesitylporphryin) is a molecular catalyst for oxidation of ammonia to dinitrogen. An aryloxy radical, tri-tert-butylphenoxyl (ArO·), abstracts H atoms from a bound ammonia ligand of (TMP)Ru(NH3)2, leading to the discovery of a new catalytic C-N coupling to the para position of ArO· to form 4-amino-2,4,6-tri-tert-butylcyclohexa-2,5-dien-1-one. Modification of the aryloxy radical to 2,6-di-tert-butyl-4-tritylphenoxyl radical, which contains a trityl group at the para position, prevents C-N coupling and diverts the reaction to catalytic oxidation of NH3 to give N2. We achieved 125 ± 5 turnovers at 22 °C for oxidation of NH3, the highest turnover number (TON) reported to date for a molecular catalyst.
- Bullock, R. Morris,Dunn, Peter L.,Johnson, Samantha I.,Kaminsky, Werner
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supporting information
p. 3361 - 3365
(2020/03/06)
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- MXene-Derived Nanocomposites as Earth-Abundant Efficient Electrocatalyst for Nitrogen Reduction Reaction under Ambient Conditions
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NH3, as one of the most massively used chemical products in the world, not only serves as the main nitrogen source of chemical fertilizers but also is considered as a promising renewable energy source. Most ammonia in industry is produced by the Haber-Bosch process under extremely high temperature and pressure conditions, which is intensively energy consuming and environmentally unfriendly. Electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising way to produce NH3 under ambient conditions in recent years, but the research for efficient earth-abundant electrocatalysts is still highly limited. In this work, different TiO2 phases (anatase and rutile)/carbon nanocomposites with a sandwich architecture are produced by annealing MXene at different temperatures, which shows excellent electrocatalytic NRR performance. In 0.1 M Na2SO4, anatase TiO2/C composites show better NRR performance than the rutile ones, which achieve a large NH3 yield of 14.0 μg h-1 cm-2, a high Faradaic efficiency of 13.3% at-0.2 V vs a reversible hydrogen electrode, and a high electrochemical stability. The sandwich architecture of anatase TiO2 nanoparticles well-dispersed on the surface of carbon layers could increase the conductivity of TiO2 and the exposure of active sites, which could explain the improved NRR activity of anatase TiO2/C composites compared with previous work. Density functional theory calculations suggest that the energy barrier of most steps for the surface of anatase TiO2 is relatively lower than that of rutile TiO2, which could explain the better electrocatalytic NRR performance for anatase TiO2/C composites compared with the rutile ones.
- Zhao, Guoliang,Wang, Xin,Xu, Chen
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supporting information
p. 16672 - 16678
(2020/11/13)
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- Promoting effect of CeO2 on the catalytic activity of Ba-Y2O3for direct decomposition of NO
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The effect of CeO2 additive on the catalytic performance of Ba-Y2O3 prepared by coprecipitaion for the direct decomposition of NO was investigated. Although Ba-Y2O3 effectively catalyzed NO decomposition, its activity was clearly increased by addition of CeO2. The optimum CeO2 content was 10 mol%. CO2-TPD measurement revealed that the addition of CeO2 into Ba-Y2O3 caused an increase in the CO2 desorption peak in the temperature range of 473 and 723K derived from highly dispersed Ba species. The predominant role of CeO2 additive was suspected to effectively create the highly dispersed Ba species as catalytically active sites. Kinetic studies of NO decomposition on Ba-CeO2(10)-Y2O3 suggested that coexisting O2 suppresses the NO decomposition reaction by competitive adsorption. Isotopic transient kinetic analysis suggested a reaction pathway in which the surface NOx adspecies act as reaction intermediates for the formation of N2 in NO decomposition over Ba-CeO2-Y2O3. We concluded that CeO2 additive does not directly participate in the NO decomposition reaction as catalytically active species.
- Doi, Yasuyuki,Haneda, Masaaki,Ozawa, Masakuni
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p. 117 - 123
(2015/01/30)
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- A multi-iron system capable of rapid N2 formation and N 2 cleavage
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The six-electron oxidation of two nitrides to N2 is a key step of ammonia synthesis and decomposition reactions on surfaces. In molecular complexes, nitride coupling has been observed with terminal nitrides, but not with bridging nitride complexes that more closely resemble catalytically important surface species. Further, nitride coupling has not been reported in systems where the nitrides are derived from N2. Here, we show that a molecular diiron(II) diiron(III) bis(nitride) complex reacts with Lewis bases, leading to the rapid six-electron oxidation of two bridging nitrides to form N2. Surprisingly, these mild reagents generate high yields of iron(I) products from the iron(II/III) starting material. This is the first molecular system that both breaks and forms the triple bond of N2 at room temperature. These results highlight the ability of multi-iron species to decrease the energy barriers associated with the activation of strong bonds.
- MacLeod, K. Cory,Vinyard, David J.,Holland, Patrick L.
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p. 10226 - 10229
(2014/08/05)
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- Regeneration mechanism of a Lean NOx Trap (LNT) catalyst in the presence of NO investigated using isotope labelling techniques
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The presence of NO during the regeneration period of a Pt-Ba/Al 2O3 Lean NOx Trap (LNT) catalyst modifies significantly the evolution of products formed from the reduction of stored nitrates, particularly nitrogen and ammonia. The use of isotope labelling techniques, feeding 14NO during the storage period and 15NO during regeneration allows us to propose three different routes for nitrogen formation based on the different masses detected during regeneration, i.e. 14N2 (m/e = 28), 14N 15N (m/e = 29) and 15N2 (m/e = 30). It is proposed that the formation of nitrogen via Route 1 involves the reaction between hydrogen and 14NOx released from the storage component to form 14NH3 mainly. Then, ammonia further reacts with 14NOx located downstream to form 14N2. In Route 2, it is postulated that the incoming 15NO reacts with hydrogen to form 15NH3 in the reactor zone where the trap has been already regenerated. This isotopically labelled ammonia travels through the catalyst bed until it reaches the regeneration front where it participates in the reduction of stored nitrates (14NOx) to form 14N15N. The formation of 15N2 via Route 3 is believed to occur by the reaction between incoming 15NO and H2. The modification of the hydrogen concentration fed during regeneration affects the relative importance of H2 or 15NH3 as reductants and thus the production of 14N2 via Route 1 and 14N15N via Route 2.
- Pereda-Ayo, Benat,Gonzalez-Velasco, Juan R.,Burch, Robbie,Hardacre, Christopher,Chansai, Sarayute
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p. 177 - 186
(2012/02/06)
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- The reduction of 15N14NO by CO and by H2 over Rh/SiO2: A test of a mechanistic proposal
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A literature proposal that the reduction of nitrous oxide by carbon monoxide over rhodium catalysts proceeds by cleavage of the NN bond has been tested through the use of 15N14NO as the reactant. The results disprove the suggestion in that 14N15N is the dominant product at temperatures from 336 °C to 356 °C with nitrous oxide conversions from 26% to >99%. Little, if any, 14N 2 and 15N2 is formed, in contrast with the 25% of each expected for the model. Results for the corresponding reaction of 15N14NO with H2 are even more clear-cut in demonstrating the absence of NN bond cleavage. The activity of the Rh/SiO 2 used here for the N2O/CO system fell within the rather wide of values reported in the literature for other Rh catalysts. However, activity for the reduction of N2O by H2 was approximately five times higher than the only previous result in the literature, that for a Rh/Al2O3 catalyst.
- Cant, Noel W.,Chambers, Dean C.,Liu, Irene O.Y.
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p. 162 - 166
(2011/05/13)
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- The reaction mechanism of the high temperature ammonia oxidation to nitric oxide over LaCoO3
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Perovskites are promising catalysts for oxidation reactions. Good NO selectivity is reported for the oxidation of ammonia into nitric oxide over LaCoO3. More interestingly over this catalyst very little N 2O is produced, which makes it a potential candidate for industrial ammonia oxidation. In order to further develop perovskite catalysts, an understanding of the reaction mechanism is necessary. Steady-state, TAP and oxygen exchange experiments over LaCoO3 have been carried out. A reaction mechanism that describes the product distribution (NO, N2O and N2) as a function of the oxidation degree of the catalyst has been proposed. The reaction proceeds by a Mars and Van Krevelen mechanism. NO and N2O are formed through parallel routes from ammonia via surface nitroxyl (HNO) species. Formation of nitrogen occurs through at least three routes. Decomposition of both reaction products NO and N2O leads to N2, the latter decomposition being the fastest. The third route to N2 consists of the reaction of adsorbed ammonia with short-lived oxygen surface species, such as peroxide or superoxide species.
- Biausque, Gregory,Schuurman, Yves
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p. 306 - 313
(2011/02/27)
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- Spatial distributions of desorbing products in steady-state NO and N 2 O reductions on Pd(110)
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The angular and velocity distributions of desorbing product N2 were examined over the crystal azimuth in steady-state NO+CO and N2 O+CO reactions on Pd(110) by cross-correlation time-of-flight techniques. At surface temperatures below 600 K, N2 desorption in both reactions splits into two directional lobes collimated along 41°-45° from the surface normal toward the [001] and [00 1-] directions. Above 600 K, the normally directed N2 desorption is enhanced in the NO reduction. Each product desorption component, as well as C O2, shows a fairly asymmetric distribution about its collimation axis. Two factors, i.e., the anisotropic site structures and the reactant orientation and movements, are operative to induce such asymmetry, depending on the product emission mechanism.
- Ma, Yunsheng,Matsushima, Tatsuo,Shobatake, Kosuke,Kokalj, Anton
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- Synchrotron XPS and desorption study of the NO chemistry on a stepped Pt surface
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The interaction of NO with Pt(4 1 0) was studied using high-energy resolution fast XPS and temperature programmed desorption/reaction mass spectroscopy. LEED studies show that the surface in the clean state restructures, which results in the formation of some larger {1 0 0} terraces. STM measurements show, that most terraces are small, ~1 nm. Two different binding energy (BE) components were observed in the N 1s region of the core level spectra, both assigned to molecular forms of NO. NO dissociation starts between 350 and 400 K. This is a significantly higher temperature than previous literature reports suggested. This difference is thought to be caused by the restructuring of the surface used in our experiments. The reaction of NO with H2, NH3 and CO was also studied. The onset of these NO reduction reactions is determined by the NOad dissociation temperature (between 350 and 400 K) and NOad dissociation is the rate limiting step for all the reactions that were studied. Reaction with H2 yields NH3 below 600 K, but the selectivity shifts towards N2 at higher temperatures. We did not find any indication that reaction between NOad and NH3 ad proceeds via a special NO-NH3 intermediate. A new surface species was detected during the reaction between NO and CO, both in the N 1s and the C 1s spectrum. It is tentatively assigned to either CN or CNO. The reactivity of NO on Pt(4 1 0) is compared with the reactivity that was observed for Pt(1 0 0) and other noble metal surfaces, such as Pd and Rh.
- Weststrate,Bakker,Rienks,Vinod,Lizzit,Petaccia,Baraldi,Nieuwenhuys
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p. 1991 - 2001
(2008/10/09)
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- Model car-exhaust catalyst studied by TPD and TP-RAIRS: Surface reactions of NO on clean and O-covered Ir{1 0 0}
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The adsorption of NO on Ir{1 0 0} has been studied as a function of NO coverage and temperature using temperature programmed reflection absorption infrared spectroscopy (TP-RAIRS), low energy electron diffraction (LEED) and temperature programmed desorption (TPD). After saturating the clean (1 × 5)-reconstructed surface with NO at 95 K, two N2 desorption peaks are observed upon heating. The first N2 peak at 346 K results from the decomposition of bridge-bonded NO, and the second at 475 K from the decomposition of atop-bonded NO molecules. NO decomposition is proposed to be the rate limiting step for both N2 desorption states. For high NO coverages on the (1 × 5) surface, the narrow width of the first N 2 desorption peak is indicative of an autocatalytic process for which the parallel formation of N2O appears to be the crucial step. When NO is adsorbed on the metastable unreconstructed (1 × 1) phase of clean Ir{1 0 0} N2 desorption starts at lower temperatures, indicating that this surface modification is more reactive. When a high coverage of oxygen, near 0.5 ML, is pre-adsorbed on the surface, the decomposition of NO is inhibited and mainly desorption of intact NO is observed.
- Khatua, Sabyasachi,Held, Georg,King, David A.
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- Surface-nitrogen removal in a steady-state NO + H2 reaction on Pd(110)
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Surface-nitrogen removal steps were analyzed in the course of a catalyzed NO + H2 reaction on Pd(110) by angle-resolved mass spectroscopy combined with cross-correlation time-of-flight techniques. Four removal steps, i.e., (i) the associative process of nitrogen atoms, 2N(a) → N 2(g), (ii) the decomposition of the intermediate, NO(a) + N(a) → N2O(a) → N2(g) + O(a), (iii) its desorption, N 2O(a) → N2O(g), and (iv) the desorption as ammonia, N(a) + 3H(a) → NH3(g), are operative in a comparable order. Above 600 K, process (i) is predominant, whereas the others largely contribute below 600 K. Process (iv) becomes significant at H2 pressures above a critical value, about half the NO pressure. Hydrogen was a stronger reagent than CO toward NO reduction and relatively enhanced the N(a) associative process.
- Ma, Yunsheng,Matsushima, Tatsuo
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p. 1256 - 1261
(2007/10/03)
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- Highly Electrophilic (Salen)ruthenium(VI) Nitrido Complexes
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A series of cationic ruthenium(VI) nitrido species containing the cyclohexyl-bridged salen ligand (L) and its derivatives, [RuVI(N)(L)]+, have been prepared by treatment of [NBun4][RuVI(N)Cl4] with H2L in methanol. The structure of [RuVI(N)(L)](ClO4) (1a) has been determined by X-ray crystallography, d(RuΞN) = 1.592 A. In solvents such as DMF or DMSO, [RuVI(N)(L)]+ undergoes a facile N...N coupling reaction at room temperature to produce N2 and [RuIII(L)(S)2]+ (S = solvent). 1a reacts rapidly with secondary amines to produce diamagnetic RuIV-hydrazido(1-) species, [RuIV(N(H)NR2)(L)(HNR2)]+. The reaction with morpholine is first order in RuVI and second order in morpholine with k(CH3CN, 25 °C) = 2.08 × 106 M-2 s-1. This rate constant is over 4 orders of magnitude larger than that of the corresponding reaction of the electrophilic osmium nitride, trans-[OsVI(N)(tpy)(Cl)2]+, with morpholine. The structure of [Ru(NHNC4H8)(L)(NHC4H8)](PF6)2 has been determined by X-ray crystallography, the Ru-N(hydrazido) distance is 1.940 A, and the Ru-N-N angle is 129.4°. Copyright
- Man, Wai-Lun,Tang, Tsz-Man,Wong, Tsz-Wing,Lau, Tai-Chu,Peng, Shie-Ming,Wong, Wing-Tak
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p. 478 - 479
(2007/10/03)
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- Nitrogen removal pathways in a steady-state NO + CO reaction on Pd(110)
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Three removal processes of surface nitrogen, i.e., (i) the decomposition of the intermediate N2O(a), (ii) its desorption without decomposition and (iii) the associative desorption of nitrogen atoms, were separately studied in a steady-state NO+CO reaction on Pd(110) through analysis of the angular and velocity distributions of desorbing products N2 and N2O. At temperatures below approximately 600 K, the processes (i) and (ii) prevailed, whereas at higher temperatures, the process (iii) contributed significantly. The branching was also sensitive to the CO/NO pressure ratio.
- Ma, Yunsheng,Rzeznicka, Izabela,Matsushima, Tatsuo
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p. 201 - 207
(2008/10/09)
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- Different CO2 collimation on stepped Pt(1 1 2): A comparison of NO(a) + CO(a) and O(a) + CO(a) reactions
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The collimation of the desorbing product CO2 is very different in the NO(a) + CO(a) and O(a) + CO(a) reactions on Pt(1 1 2) = [(S)3(1 1 1) × (0 0 1)]. In the NO(a) + CO(a) reaction, CO2 desorption collimated along the local normal of the (0 0 1) facets, whereas in the O(a) + CO(a) reaction, it sharply collimated close to the (1 1 1) terrace normal. This site switching is explained by different rate-determining steps.
- Hu, Yu-Hai,Han, Song,Horino, Hideyuki,Nieuwenhuys, Bernard Egbert,Hiratsuka, Atsuko,Ohno, Yuichi,Ivan, Kobal,Matsushima, Tatsuo
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p. 159 - 165
(2008/10/08)
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- Polar effects in nitride coupling reactions
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The nudeophilic molybdenum nitride (Et2NCS2)3MoN (1) reacts with the electrophilic osmium nitride complex TpOsNCl2 (2, Tp =hydrotris(1-pyrazolyl)borate) to produce molecular nitrogen. Reaction of 1 at the nitride is accompanied by a substantial amount of reaction at a sulfur atom of the dithiocarbamate ligand, forming the osmium thionitrosyl complex TpOs(NS)Cl2 (4). Labeling experiments establish that the N2 produced comes specifically (>96%) from mixed-metal (molybdenum-osmium) coupling. The major transition-metal-containing product of the reaction is the μ-nitrido complex TpOsCl2(μ-N)Mo(S2CNEt2)3 (3), where the bridging nitride derives primarily (82%) from the osmium nitride 2. The μ-nitrido complex 3 has been characterized crystallographically, and shows a nitride bridge that is very asymmetric (Mo-N = 1.721(3) A, Os-N = 1.906(3) A), with less multiple bonding toward osmium and more toward molybdenum. Heterometallic coupling is much faster than either homometallic coupling reaction, in particular the osmium - osmium coupling, despite the greater oxidizing power of osmium over molybdenum. The origin and implications of this kinetic effect on nitride coupling and dinitrogen cleavage are discussed.
- Seymore, Sean B.,Brown, Seth N.
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p. 462 - 469
(2008/10/08)
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- Kinetics and mechanism of the N2O reduction by NH3 on a Fe-zeolite-beta catalyst
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In the context of decreasing the emissions of greenhouse gases, a Fe-exchanged zeolite-be (Fe-VEA) catalyst was shown to be very active in the reduction of N2O by NH3 in the presence of O2. NH3 accelerated the reduction of N2O to N2 on Fe-BEA. In the presence of O2, it was proposed that N2O conversion occurred through the redox cycle FeIII ? FeII with NN-O splitting mainly. N2O oxidized FeII to lead FeIII-oxocations, which were regenerated back to FeII by NH3. However, significant N-NO splitting occurred in the absence of O2. There was no inhibiting effect of O2 for the reduction of N2O by NH3, following a modified Mars and van Krevelen oxido-reduction kinetics, considering an inhibiting term of NH3.
- Coq, Bernard,Mauvezin, Mathias,Delahay, Gerard,Kieger, Stephane
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p. 298 - 303
(2008/10/08)
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- Mechanisms of the various nitric oxide reduction reactions on a platinum-rhodium (100) alloy single crystal surface
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The reduction of nitric oxide with hydrogen was studied over a Pt0.25-Rh0.75(100) alloy surface used as a model catalyst for the automotive three-way catalyst. This paper emphasizes the mechanisms of the different reactions leading to the products dinitrogen, ammonia and nitrous oxide. For this purpose the reaction was studied under various experimental conditions including reactivity measurements both in the 10-7 mbar range under steady-state conditions and in the 10 mbar range with varying NO/H2 ratio. In addition, the thermal decomposition of NO and the reactions of NO + NH3 were investigated. 15NO and 15NH3 were used in order to gather additional information concerning the mechanisms of the formation of the various N-containing products. The surface was characterized by using low-energy electron diffraction, Auger electron spectroscopy and thermal desorption spectroscopy. The main conclusions emerging from these studies are: (a) N2 can be formed by combination of 2 N adatoms in the whole temperature range used (350-1300 K), provided that sufficient N adatoms are available; (b) below 600 K the main contribution to N2 formation is via NOads + Nads → N2 + Oads; at higher temperatures the dominant mechanisms is 2Nads → N2; (c) N2O and NH3 are formed via Nads + NOads → N2O, and Nads + 3Hads → NH3, the contributions of which respectively decrease and increase with increasing temperature; (d) the selectivities to N2, NH3 and N2O are determined by the relative concentrations of NOads, Nads and Hads, which vary with the experimental conditions such as the temperature.
- Hirano, H.,Yamada, T.,Tanaka, K. I.,Siera, J.,Cobden, P.,Nieuwenhuys, B. E.
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- Stoicheiometric and Nitrogen-15 Labelling Studies on the Hyponitrous Acid- Nitrous Acid Reaction
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The stoicheiometry of the hyponitrous acid - nitrous acid reaction has been determined over a wide acidity range, up to 8.5 mol dm-3 HClO4.For approximately 1:1 reaction conditions, the major reaction pathway gives N2 and HNO3 as products, together with the production of N2O (by self decomposition of hyponitrous acid) and NO (by self decomposition of nitrous acid).In addition, (15)NO produced by self decomposition of H(15)NO2 reacts with H2(14)N2O2 to give some (14)NO and N2O of mixed isotopic composition.Reactions under other conditions gave products that may be accounted for by varying contributions from these reactions.
- Bonner, Francis T.,Donald, Caroline E.
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p. 527 - 532
(2007/10/02)
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- ELECTROCHEMICAL REDUCTION OF NITRATE AND NITRITE IN CONCENTRATED SODIUM HYDROXIDE AT PLATINUM AND NICKEL ELECTRODES.
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The electrochemical reduction of nitrite and nitrate in concentrated sodium hydroxide solution has been studied as a function of electrode material, temperature, and solution composition. Electrolysis of NaNO//3 in 3M NaOH, 0. 25M Na//2CO//3 at 80 degree C using platinized nickel cathodes resulted in high current efficiency for the overall electrode reaction, a five-electron reduction to dinitrogen. Ammonia is formed in constant current electrolyses at high current densities. The presence of oxygen in the cathode compartment was shown to increase the rate of nitrate reduction under these conditions. Nonideal cyclic voltammetric behavior was observed indicative of complex electrode processes.
- Li,Robertson,Chambers,Hobbs
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p. 1154 - 1158
(2008/10/08)
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- Reactions of NH Radicals. I. Photolysis of NH3 Vapor at 313 nm
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Photolysis of HN3 vapor was studied at 313 nm as a function of HN3 and Xe pressures, light intensity, and temperature.The photolysis of hydrazoic acid labeled with 15N was also studied.The quantum yields of N2, H2, and NH4N3 as a product were 4.85, 0.494, and 0.842 at 30 deg C and 6.7 kPa of HN3, respectively.The mechanism for the main reactions was postulated as follows: HN3+hv(313 nm) -> N2+NH(a1Δ); NH(a1Δ)+HN3 -> 2N2+2H (2); NH(a1Δ)+HN3 -> N3+NH2 (3); NH(a1Δ)+HN3 -> N2+N2H2* (4).The rate constant ratios of k3/k2=0.746 and k4/k2=1.23 were obtained at 30 deg C. (k3+k4)/k2 decrease drastically with rising temperature.Xe is effective for the collisional deactivation, NH(a1Δ)+Xe -> NH(X3Σ-)+Xe (15), and k15/(k2+k3+k4)=0.187 was obtained at 30 deg C.
- Kodama, Sukeya
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p. 2348 - 2354
(2007/10/02)
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- Mechanism of the Catalytic Reduction of Nitric Oxide by Ammonia over Cobalt-Amine Complexes in Na-Y Zeolite
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The mechanism of the NO-NH3 reaction over Co(en)2(NO2)3 complex (en=ethylenediamine), ion exchanged into Na-Y zeolite, was studied extensively and compared with that by the same complex in an aqueous solution, which has been reported previously.At room temperature, the catalytically active species are similar in both media, exhibiting similar reaction mechanisms.Ammonia treatment of the catalyst at 363 K caused the reduction of cobalt cation to CoII with the removal of NO2 groups.The catalytic behavior of this CoII(en)-Y zeolite was compared to that of CoII(NH3)-Y zeolite, prepared by a conventional cation-exchange method.During the No-NH3 reaction, mononitrosyl and dinitrosyl intermediate species were much more stable in Co(NH3) zeolite than Co(en)-Y zeolite, resulting in different reaction orders and kinetic isotope effects.It is demonstrated that a zeolite cavity can be a microreactor, where residual water acts as a solvent to assist the stabilization of the catalytically active species.
- Naito, Shuichi,Tamaru, Kenzi
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p. 315 - 319
(2007/10/02)
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- Nitrogen-tracer Experiments on the Reaction of Hydrazine with an Excess of Nitrous Acid
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Mass-spectrometric analysis of the dinitrogen and dinitrogen monoxide evolved from the reaction between (1+) and excess of HNO2 are consistent with scrambling occurring between two nitrogens of hydrazine and one nitrogen of nitrous acid.A cyclic form of hydrazoic acid is postulated as a reaction intermediate, although other explanations are possible.At low acidities, pH 3.7, substantial yields of ammonia and N2O are formed.This would be expected to disturb the pattern of tracer distribution in the evolved gases, but in fact the isotopic results were virtually the same as at higher acidities.
- Phelan, Kieran G.,Stedman, Geoffrey
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p. 1603 - 1610
(2007/10/02)
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- Nitrogen Tracer Evidence for a Cyclic Azide Species
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Tracer experiments on the reaction of 15N-enriched hydrazine with excess of nitrous acid indicate a scrambling of tracer between the nitrogens of equimolar amounts of hydrazine and nitrous acid; a cyclic azide species is suggested as an intermediate.
- Phelan, Kieran G.,Stedman, Geoffrey
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p. 299 - 300
(2007/10/02)
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