20621-02-7Relevant articles and documents
Nickel-mediated N-N bond formation and N2O liberationvianitrogen oxyanion reduction
Beagan, Daniel M.,Cabelof, Alyssa C.,Carta, Veronica,Caulton, Kenneth G.,Gao, Xinfeng,Pink, Maren
, p. 10664 - 10672 (2021/08/20)
The syntheses of (DIM)Ni(NO3)2and (DIM)Ni(NO2)2, where DIM is a 1,4-diazadiene bidentate donor, are reported to enable testing of bis boryl reduced N-heterocycles for their ability to carry out stepwise deoxygenation of coordinated nitrate and nitrite, forming O(Bpin)2. Single deoxygenation of (DIM)Ni(NO2)2yields the tetrahedral complex (DIM)Ni(NO)(ONO), with a linear nitrosyl and κ1-ONO. Further deoxygenation of (DIM)Ni(NO)(ONO) results in the formation of dimeric [(DIM)Ni(NO)]2, where the dimer is linked through a Ni-Ni bond. The lost reduced nitrogen byproduct is shown to be N2O, indicating N-N bond formation in the course of the reaction. Isotopic labelling studies establish that the N-N bond of N2O is formed in a bimetallic Ni2intermediate and that the two nitrogen atoms of (DIM)Ni(NO)(ONO) become symmetry equivalent prior to N-N bond formation. The [(DIM)Ni(NO)]2dimer is susceptible to oxidation by AgX (X = NO3?, NO2?, and OTf?) as well as nitric oxide, the latter of which undergoes nitric oxide disproportionation to yield N2O and (DIM)Ni(NO)(ONO). We show that the first step in the deoxygenation of (DIM)Ni(NO)(ONO) to liberate N2O is outer sphere electron transfer, providing insight into the organic reductants employed for deoxygenation. Lastly, we show that at elevated temperatures, deoxygenation is accompanied by loss of DIM to form either pyrazine or bipyridine bridged polymers, with retention of a BpinO?bridging ligand.
Lewis Acid Activation of the Ferrous Heme-NO Fragment toward the N-N Coupling Reaction with NO to Generate N2O
Abucayon, Erwin G.,Khade, Rahul L.,Powell, Douglas R.,Zhang, Yong,Richter-Addo, George B.
supporting information, p. 4204 - 4207 (2018/04/05)
Bacterial NO reductase (bacNOR) enzymes utilize a heme/non-heme active site to couple two NO molecules to N2O. We show that BF3 coordination to the nitrosyl O-atom in (OEP)Fe(NO) activates it toward N-N bond formation with NO to generate N2O. 15N-isotopic labeling reveals a reversible nitrosyl exchange reaction and follow-up N-O bond cleavage in the N2O formation step. Other Lewis acids (B(C6F5)3 and K+) also promote the NO coupling reaction with (OEP)Fe(NO). These results, complemented by DFT calculations, provide experimental support for the cis:b3 pathway in bacNOR.
Tracking reactive intermediates by FTIR monitoring of reactions in low-temperature sublimed solids: Nitric oxide disproportionation mediated by ruthenium(II) carbonyl porphyrin Ru(TPP)(CO)
Azizyan, Arsen S.,Kurtikyan, Tigran S.,Martirosyan, Garik G.,Ford, Peter C.
, p. 5201 - 5205 (2013/06/05)
Interaction of NO (15NO) with amorphous layers of Ru(II) carbonyl porphyrin (Ru(TPP)(CO), TPP2- = meso-tetraphenylporphyrinato dianion) was monitored by FTIR spectroscopy from 80 K to room temperature. An intermediate spectrally char
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 (2008/10/09)
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.
Surface-nitrogen removal in a steady-state NO + H2 reaction on Pd(110)
Ma, Yunsheng,Matsushima, Tatsuo
, p. 1256 - 1261 (2007/10/03)
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.
Nitrogen removal pathways in a steady-state NO + CO reaction on Pd(110)
Ma, Yunsheng,Rzeznicka, Izabela,Matsushima, Tatsuo
, p. 201 - 207 (2008/10/09)
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.
Photoassisted NO reduction with NH3 over TiO2 photocatalyst
Tanaka, Tsunehiro,Teramura, Kentaro,Arakaki, Kyoko,Funabiki, Takuzo
, p. 2742 - 2743 (2007/10/03)
Photoassisted selective catalytic reduction of NO with ammonia (photo-SCR) at low temperature over irradiated TiO2 in a flow reactor was confirmed to proceed efficiently and the adsorbed ammonia reacted with NO under irradiation of TiO2.
An investigation of promoter effects in the reduction of NO by H2 under lean-burn conditions
Burch,Coleman
, p. 435 - 447 (2008/10/08)
The reduction of NO by H2 has been investigated under lean conditions at temperatures representative of automotive cold-start conditions (3- and Na2O-modified Pt/Al2O3 and Pt/SiO2 catalysts. It has been found that small additions of sodium significantly increase the NO conversion while larger loadings of sodium have a severe poisoning effect. However, in the presence of excess O2 no enhancement in nitrogen selectivity at low temperatures has been observed for all loadings of Na. Indeed, an adverse effect has been found at higher temperatures. Addition of molybdenum as a promoter results in increases in NO conversion and nitrogen selectivity for all loadings tested. The optimal formulation was determined to be 1% Pt/10% MoO3/0.27% Na2O/Al2O3. Steady-state isotopic-transient kinetic (SSITK) experiments were performed on this and a model Pt/MoO3/Na2O/SiO2 catalyst using labelled nitric oxide in order to estimate the surface concentrations of species leading to N2, N2O, and retained NO. The data reveal significantly greater surface concentrations of N2 precursors over the modified catalysts for both the Pt/Al2O3 and Pt/SiO2 systems and this has been used to rationalise the increased selectivity to N2. An additional significant effect of the molybdenum promoter has been proposed because when the concentrations of N2 intermediates and the amount of available platinum in the modified catalysts are calculated, the storage of N2 precursors on the MoO3 seems to occur. This effect has been further explored using the modified SiO2 catalyst in non-steady-state transient experiments where the reductant supply (i.e., the H2) is cut off. It has been found that the decay in the production of N2 is very significantly delayed in comparison with the unmodified catalysts, and it is proposed that this is consistent with the trapping on the Mo of a reduced intermediate that can form N2 even in the absence of the normal H2 reductant. The mechanistic consequences of these novel results are discussed.
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 (2007/10/02)
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.
Stoicheiometric and Nitrogen-15 Labelling Studies on the Hyponitrous Acid- Nitrous Acid Reaction
Bonner, Francis T.,Donald, Caroline E.
, p. 527 - 532 (2007/10/02)
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.
