1173020-41-1Relevant articles and documents
The mechanism of reduction of NO with H2 in strongly oxidizing conditions (H2-SCR) on a novel Pt/MgO-CeO2 catalyst: Effects of reaction temperature
Savva,Costa,Efstathiou
, p. 743 - 747 (2008)
Steady State Isotopic Transient Kinetic Analysis (SSITKA) experiments using on-line Mass Spectrometry (MS) and in situ Diffuse Reflectance Infrared Fourier-Transform Spectroscopy (DRIFTS) have been performed to study essential mechanistic aspects of the Selective Catalytic Reduction of NO by H2 under strongly oxidizing conditions (H2-SCR) in the 120-300°C range over a novel 0.1 wt % Pt/MgO-CeO2 catalyst. The N-path of reaction from NO to the N2 gas product was probed by following the 14NO/H2O2 → 15NO/H 2/O2 switch (SSITKA-MS and SSITKA-DRIFTS) at 1 bar total pressure. It was found that the N-pathway of reaction involves the formation of two active NO x species different in structure, one present on MgO and the other one on the CeO2 support surface. Inactive adsorbed NO x species were also found on both the MgO-CeO2 support and the Pt metal surfaces. The concentration (mol/g cat) of active NO x leading to N2 was found to change only slightly with reaction temperature in the 120-300°C range. This leads to the conclusion that other intrinsic kinetic reasons are responsible for the volcano-type conversion of NO versus the reaction temperature profile observed.
Kinetics and mechanism of the N2O reduction by NH3 on a Fe-zeolite-beta catalyst
Coq, Bernard,Mauvezin, Mathias,Delahay, Gerard,Kieger, Stephane
, p. 298 - 303 (2000)
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.
Promoter Action of Alkali Nitrate in Raney Ruthenium Catalyst for Activation of Dinitrogen
Hikita, Tokihisa,Kadowaki, Yasushi,Aika, Ken-ichi
, p. 9396 - 9402 (1991)
Alkali nitrate promoted Raney Ru catalysts were prepared by decomposition of alkali nitrates (CsNO3, RbNO3, KNO3, and NaNO3) with hydrogen over Raney Ru.These catalysts were as active as Raney Ru promoted with metallic potassium at 573 K in N2 activation (ammonia synthesis and especially isotopic equilibration reaction (IERR) of N2).The promotional behavior of alkali nitrates on Raney Ru was different from that on the supported Ru catalysts.The alkali was estimated to work as a metallic on Raney Ru, whereas it was estimated to be hydroxide on supported Ru.The more reduced form on Raney Ru-CsNO3 was considered to give a higher turnover frequency of IER of N2 than that over alumina-supported Ru-CsNO3.Since the rate of IER of N2 is a rate of tracer atom moving from N2 to adsorbed N under the condition of adsorption equilibrium, it should be slower than the rate of ammonia synthesis whose adsorption step is rate-determing in a dynamic condition.To the contrary, the rates of ammonia synthesis were slower than IER rates of N2 over Raney Ru-CsNO3, suggesting hydrogen inhibition in the N2 activation process.Indeed, the IER of N2 over Raney Ru-CsNO3 was proved to be retarded by the presence of hydrogen.A kinetic analysis disclosed that N(a) and H(a) compete with each other on the Ru surface where H(a) adsorption is stronger than N(a) adsorption at 473-523 K.The heats of adsorption of N2 and H2 were estimated from the kinetics.
Isotopic transient kinetic analysis of Cs-promoted Ru/MgO during ammonia synthesis
Davis,McClaine
, p. 387 - 396 (2002)
Steady-state isotopic transient kinetic analysis was utilized to analyze a Cs-promoted Ru/MgO catalyst (1.75 wt% Ru) for NH3 synthesis. For comparison, an unpromoted Ru[SiO2 (22 wt % Ru) catalyst was also studied. Steady-state and isotopic transient measurements were carried out at 603-673 K with a stoichiometric ratio of N2 and H2 at a total pressure of 3 atm. The fractional surface coverage of nitrogen-containing intermediates based on total H2 chemisorption was 0.02-0.05 on both catalysts under the conditions used. However, the intrinsic turnover frequency of NH3 synthesis over Cs-Ru/MgO was two orders of magnitude greater than that of the unpromoted Ru/SiO2. The combination of the Cs promoter and MgO support improved the intrinsic activity of ruthenium, presumably by lowering the barrier for dinitrogen dissociation.
Stoicheiometric and Nitrogen-15 Labelling Studies on the Hyponitrous Acid- Nitrous Acid Reaction
Bonner, Francis T.,Donald, Caroline E.
, p. 527 - 532 (1989)
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.
Cleavage of the N2 triple bond by the Ti dimer: A route to molecular materials for dinitrogen activation?
Himmel, Hans-Joerg,Huebner, Olaf,Klopper, Wim,Manceron, Laurent
, p. 2799 - 2802 (2006)
The Ti dimer is fairly weakly bound, but highly reactive, and completely cleaves the strong N2 triple bond in just one step without activation energy (see scheme; Ti red, N blue). In contrast, a Ti atom in its ground electronic state does not react with N2. (Figure Presented)
A fast transient kinetic study of the effect of H2 on the selective catalytic reduction of NOx with octane using isotopically labelled 15NO
Breen,Burch,Hardacre,Hill,Rioche
, p. 1 - 9 (2007)
The H2-assisted hydrocarbon selective catalytic reduction (HC-SCR) of NOx was investigated using fast transient kinetic analysis coupled with isotopically labelled 15NO. This allowed monitoring of the evolution of products and reactants during switches of H2 in and out of the SCR reaction mix. The results obtained with a time resolution of less than 1 s showed that the effect on the reaction of the removal or addition of H2 was essentially instantaneous. This is consistent with the view that H2 has a direct chemical effect on the reaction mechanism rather than a secondary one through the formation of active Ag clusters. The effect of H2 partial pressure was investigated at 245 °C, it was found that increasing partial pressure of H2 resulted in increasing conversion of NO and octane. It was also found that the addition of H2 at 245 °C had different effects on the product distribution depending on its partial pressure. The change of the nitrogen balance over time during switches in and out of hydrogen showed that significant quantities of N-containing species were stored when hydrogen was introduced to the system. The positive nitrogen balance on removal of H2 from the gas phase showed that these stored species continued to react after removal of hydrogen to form N2.
Influence of O2 and H2 on NO reduction by NH 3 over Ag/Al2O3: A transient isotopic approach
Kondratenko, Evgenii V.,Kondratenko, Vita A.,Richter, Manfred,Fricke, Rolf
, p. 23 - 33 (2006)
Mechanistic aspects of low-temperature (423-723 K) selective catalytic reduction of NO with NH3 (NH3-SCR) over an Ag(1.7 wt%)/Al2O3 (2Ag/Al2O3) catalyst in the presence and absence of O2 and H2 were studied using a transient low-pressure (peak pressure 2O3 showed very low activity in the NH3-SCR reaction. The activity increased tremendously after ex situ reduction of 2Ag/Al2O3 in a hydrogen flow (5 vol% H 2 in Ar) at 373 K for 30 min. This observation was related to the creation of reduced Ag species, which catalyze O2 and NO dissociation, yielding adsorbed oxygen species. O2 is a better supplier of oxygen species. Oxygen species played a key role in NH3 dehydrogenation, yielding reactive NHx fragments that are important intermediates for nitrogen formation via a coupling reaction between NO and NH3. This reaction pathway predominated over direct NO decomposition to N2 in the presence of O2. In addition to generation of active oxygen species, gas-phase oxygen accelerated transformation of surface N-containing intermediates into gas-phase reaction products. The role of hydrogen in the NH3-SCR reaction is to transform oxidized Ag species into reduced species that are active sites for O2 and NO adsorption. Our findings suggest that the reduction of oxidized Ag is responsible for the boosting effect of H2 in the NH3-SCR reaction, and also that H2 helps decrease total N2O production.
Reduction of Nitroamine (NH2NO2) by Vanadium(II) and Chromium(II) in Acid Solution
Hughes, Martin N.,Okolow-Zubkowska, Monika,Wallis, Helen L.
, p. 2009 - 2010 (1981)
Reaction of nitroamine with vanadium(II) involes a two-elctron reduction to dinitrogen, NH2(15)NO2 giving (14)N-(15)N.Reduction of nitroamine by chromium(II) gives dinitrogen and ammonia, with an overall stoicheiometry of ΔII>:Δ ca. 6:1.Hydrazine could not be detected in nitroamine-CrII reaction.A possible mechanism for this reaction is discussed, in which a hydrazido-complex of chromium is postulated to be an intermediate.
Isotopic Labeling Studies of the Effects of Temperature, Water, and Vanadia Loading on the Selective Catalytic Reduction of NO with NH3 over Vanadia-Titania Catalysts
Duffy, Bronwyn L.,Curry-Hyde, Edward H.,Cant, Noel W.,Nelson, Peter F.
, p. 7153 - 7161 (1994)
Isotopic labeling studies of the reaction between (15)NO and (14)NH3 have been performed over a range of vanadiatitania-based SCR catalysts (pure V2O5 and catalysts containing 1,4-23.2 wt percent V2O5) for the extended temperature range of 200-500 deg C.For temperatures less than 350 deg C, (14)N(15)N is always the major product.At higher temperatures, however, product distributions are very sensitive to vanadia content; ammonia oxidation to (14)NO is particularly dominant for pure V2O5 and, at 500 deg C, accounts for more than 70percent of the nitrogen-containing products.Pure V2O5 also produces significantly more (14)N(15)NO, and at much lower temperatures, than that observed for a 1.4 wt percent V2O5/TiO2 catalyst.On the basis of these results it is clear that ammonia oxidation to (14)NO is the major reason for the observed decrease in the NO conversion over vanadia-based catalysts at temperatures greater than 400 deg C.Ammonia oxidation to nitrogen and nitrous oxide is less significant; (14)N2O and (14)N2 each comprise less than 10percent of the total products for both the pure and supported vanadia catalysts.Addition of 1.6 percent water decreases the amount of nitrous oxide (largely (14)N(15)NO) produced over the supported catalyst at 450 deg C by over 90percent.A simultaneous increase in the amount of (14)N(15)N is also observed.The presence of water also suppresses the (14)NH3 oxidation to (14)N2, (14)N2O, and (14)NO, even at 500 deg C.By contrast, for pure V2O5 at 500 deg C, water has a relatively minor effect on the product distribution, and the major product remains (14)NO.In general, high temperatures, dry feed gas conditions, and high vanadia contents favor both the production of (14)N(15)NO relative to (14)N(15)N and the ammonia oxidation reaction producing (14)NO.Results from this and previous studies suggest that there is a relationship between N2O formation and NH3 oxidation capability.
ELECTROCHEMICAL REDUCTION OF NITRATE AND NITRITE IN CONCENTRATED SODIUM HYDROXIDE AT PLATINUM AND NICKEL ELECTRODES.
Li,Robertson,Chambers,Hobbs
, p. 1154 - 1158 (1988)
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.
Superbase Supported Ruthenium as a Superior Catalyst for the Isotopic Equilibration Reaction of Dinitrogen
Ohya, Asao,Aika, Ken-Ichi,Ozaki, Atsumu
, p. 321 (1984)
Turnover numbers for the isotopic equilibration reaction of dinitrogen over Ru-BeO-K, Ru-MgO-K, and Ru-CaO-K catalysts have been shown to be the highest so far reported.
