Localized orbitals for the oxygen and nitric oxide molecules

Localized orbitals are derived for the ground states of the oxygen and nitric oxide molecules by applying localization methods separately to the orbitals containing electrons of alpha- and betaspin. Both the intrinsic energy localization and the uniform localization methods are used. The resulting localized orbitals are in good agreement with the formulae suggested by Linnett.

---

Zusammenfassung Für die Grundzustände der Moleküle O₂ und NO werden lokalisierte Orbitale abgeleitet, indem die Lokalisierungsmethoden getrennt für die Orbitale mit- und-Spin angewendet werden. Dabei werden sowohl die eigentlichen Energielokalisierungsmethoden als auch die gleichförmigen Lokalisierungsmethoden benutzt. Die erhaltenen lokalisierten Orbitale stimmen gut mit den von Linnett vorgeschlagenen Formeln überein.

---

Résumé Obtention d'orbitales localisées pour l'état fondamental des molécules d'oxygène et d'oxyde nitreux par localisation indépendante des orbitales de spin et des orbitales de spin. Emploi simultané de la localisation selon l'énergie intrinsèque et de la localisation uniforme. Les orbitales localisées résultantes sont en bon accord avec les formules suggérées par Linnett.

     

Nitrogen isotope exchange between nitric oxide and nitric acid

The rate of nitrogen isotope exchange between NO and HNO₃ has been measured as a function of nitric acid concentration of 1.5–4M·1^–1. The exchange rate law is shown to beR=k[HNO₃]²[N₂O₃] and the measured activation energy isE=67.78kJ ·M^–1 (16.2 kcal·M^–1). It is concluded that N₂O₃ participates in¹⁵N/¹⁴N exchange between NO and HNO₃ at nitric acid concentrations higher than 1.5M·1^–1.     

On the hydrogen bonding between water and ammonia molecules

The hydrogen bond N·HO between the water and ammonia molecules has been investigated ab initio using the SCF LCAO MO method. The minimal and extended basis sets of Slater type orbitals were used. It was found that the energy of the hydrogen bond is equal to 6.44 kcal/mole and the equilibrium separation of the oxygen and nitrogen atoms in the dimer is 5.72 au. At this intermolecular distance there is only one minimum in the potential energy curve for the motion of proton.     

Modelling reduction of nitric oxide by hydrogen over supported catalysts

A mean field model for NO oxidation with H₂ over supported catalysts is proposed and solved numerically. The model is composed of a system of PDEs subject to nonclassical conjugate conditions at the catalyst–support interface and includes the bulk diffusion of reactants and reaction products and surface diffusion of all intermediate products. The influence of the particle jumping rate constants via the catalyst–support interface and reaction rate constants on the evolution of the reactivity of the catalyst surface is investigated. It is shown that the conversion rates (turnover frequencies) of NO and H₂ into products, N₂, H₂O, NH₃, and N₂O, are nonmonotonous functions of time. The conversion rates of NO and H₂ into N₂ and N₂O can have one or two local maxima, while their conversion rates into H₂O and NH₃ can possess one, two, or three local maxima. The mechanism and conditions for arising of the second maximum are discussed and reaction steps that essentially increase the surface reactivity are indicated.

     

Quantum-chemical studies of the interaction between furan and pyridine molecules and surface fragments of vanadium oxide catalysts

CNDO/2 studies of the interaction between furan and pyridine molecules and coordinatively unsaturated surface centers of vanadium oxide catalysts indicate that these molecules are more tightly bound and undergo more substantial changes in their electronic structure upon coordination to centers, containing reduced vanadium ions.

---

/2 - - , , .

     

Associative vs. dissociative mechanism: Electrocatalysis of nitric oxide to ammonia

Nitric oxide reduction to ammonia by electrocatalysis is the potential application in the elimination of smog and energy conversion. In this work, the feasibility of the application of two-dimensional metal borides(MBenes) in nitric oxide electroreduction reaction(NOER) was investigated through density functional theory calculations. Including the geometry and electronic structure of five kinds of MBenes, the adsorption of NO on the surface of these substrates, the selective adsorption of hydrog...     

The determination of ammonia in flue gas from the selective catalytic reduction of nitric oxide with ammonia

The emission of NO_x from coal-fired boilers can be limited by means of the selective catalytic reduction of NO_x with ammonia. The amounts of unreacted ammonia downstream should be low to avoid processing and environmental problems. Continuous measurement of the ammonia in the flue gas is needed. The determination of ammonia and flue gas sampling techniques are discussed. Measurements of ammonia in exhausts of a laboratory reactor and of a pilot plant for the selective catalytic reduction of NO_x with ammonia are presented. Ammonia was determined by mass spectrometry and chemiluminescence in the gas phase, and by spectrophotometric (Nessler and Berthollet reactions) or potentiometry in aqueous solution, in low (<5 μl l^?1) and high (<1000 μl l^?1) concentration ranges.     

Electrochemistry of xanthine oxidase and its interaction with nitric oxide.

With the help of nanocrystalline TiO2, the direct electrochemistry of xanthine oxidase (XOD) was achieved and two pairs of redox waves were observed. The interaction between XOD and nitric oxide (NO) was also investigated. The experimental results reveal that NO can be reduced at a XOD-nano TiO2 film modified electrode. When the NO concentration was low, the reduced product, HNO, would inactivate the protein. However, when the NO concentration was high, HNO would continue to react with NO to form N2O2- and N3O3-, which would not inhibit XOD, and thus the amount of active protein did not decrease any further.     

Promoting nitric oxide electroreduction to ammonia over electron-rich Cu modulated by Ru doping

Electrocatalytic nitric oxide (NO) reduction is a promising strategy to produce ammonia.Developing a facile approach to synthesize efficient catalysts with enhanced NO electroreduction performance is highly desirable.Here,a series of Ru-doped Cu materials are constructed through in situ electroreduction of corresponding metal hydroxides.The optimized Ru_(0.05)Cu_(0.95)exhibits superior electrocatalytic performance for ammonia synthesis by using NO/Ar (1/4,n/n) as the feedstocks (Faradaic efficiency:64.9%,yield rate:17.68μmol cm~(-2)h~(-1)),obviously outperforming Cu counterpart (Faradaic efficiency:33.0%,yield rate:5.73μmol cm~(-2)h~(-1)).Electrochemical in situ Fourier transform infrared (FTIR) spectroscopy and online differential electrochemical mass spectrometry (DEMS) are adopted to detect intermediates and unveil the possible reaction pathway.The downshift of the Cu d-band center induced by Ru doping facilitates the rate-limiting hydrogenation step and decreases the desorption energy of NH_3,leading to high Faradaic efficiency and yield of ammonia.     

Selective catalytic reduction of nitric oxide with ammonia over Fe-Cu modified highly silicated zeolites

In the present study, the solid-state ion exchange method (SSIE) was applied to introduce iron and copper into highly silicate zeolites: beta (BEA, Si/Al = 12.5), ferrierite (FER, Si/Al = 10) and mordenite (MOR, Si/Al = 10). The activity of the prepared samples in the selective catalytic reduction of NO with ammonia (NH₃-SCR) was measured. The highest performance was recorded for Cu-Fe-BEA followed by Cu-Fe-MOR while Cu-Fe-FER showed a low catalytic activity over the entire reaction temperature range. It is shown in this study that the zeolite framework is one of the parameters controlling the amount, environment and distribution of metal species formed during the ion exchange process in Cu-Fe-zeolite catalysts.     

Selective catalytic reduction of nitric oxide with ammonia: A theoretical ab initio study

Ab initio quantum chemical studies at the HF/Lanl2dz level were carried out to investigate the interaction of ammonia, NO, and a mixture of the two with vanadia/titania. It was found that the replacement of Ti_6c by V_6c is the only feasible way to form highly dispersed vanadia over the titania. The V?O species thus formed will be in octahedral symmetry with the axial distortions, and no tetrahedrally coordinated V species can be formed. Ammonia fully covers the catalyst surface either through the associative interaction with the Lewis acid site of Ti_5c or the dissociative adsorption channels. The dissociation of ammonia on the O site bridging the Ti_6c and V_6c octahedra and on the V?O group can proceed with the highest gain in energy. The formation of an adsorbed ammonium ion was found to be an energetically highly unfavorable process. The V?O group is no longer expected to play a major role in the stabilization of the surface ammonium ion. NO can be activated on the Ti_5c site of the catalyst containing predissociated ammonia on the bridging O site and V?O group. It can be expected that the SCR reaction products are formed through the reactions of both adsorbed NO and NH₂ or the desorbed NH₂ group with NO in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Infrared study of the interaction of nitric oxide with CuY zeolites

Infrared studies of the interaction of NO with CuY–A zelites have been made over the temperature range from –100°C to 400°C. Several forms of NO adsorption have been found, in particular, a stable cis-dimer at low temperatures.

---

- (–100+400°C) NO CuY–A . NO, ë - .

     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al=2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Cu-loaded dealuminated Y zeolites active in selective catalytic reduction of nitric oxide with ammonia

The selective catalytic reduction of NO with ammonia in the presence of oxygen has been carried out on Cu-loaded dealuminated Y zeolite catalysts. Copper was introduced by the usual ion-exchange procedure with an aqueous solution of cupric acetate. On deeply dealuminated USY zeolites, Cu²⁺ was supported in the amount larger than 2Cu/Al = 2, resulting in the formation of CuO fine particles in addition to the isolated and dimer Cu²⁺ species. The specific catalytic activity per surface copper on the CuO particles was very high compared with these Cu²⁺ species. NO adsorption measurement revealed the higher dispersion of CuO on the deeply dealuminated USY than on SiO₂, which made Cu/USY a better catalyst for the reduction of NO. The reaction intermediates were investigated through the IR spectra of adsorbed species.     

Gas chromatographic analysis of the products of catalytic reduction of nitric oxide by ammonia

The behavior of small amounts of nitric oxide in the presence of ammonia and excess oxygen on adsorbents of different textures was studied by gas chromatography. A scheme for the gas chromatographic analyses of the products of catalytic reduction of nitric oxide by ammonia and the catalytic oxidation of ammonia by oxygen was suggested. The scheme makes it possible to prevent chemical reactions between components of the gas mixture analyzed during the accumulation of the products and their analysis, to exclude the partial or complete adsorption of NO on microporous adsorbents, and to monitor the content of components at a level of 500 ppm and lower.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2508–2513, October, 1996.     

Enhancement of a Lewis acid-base interaction via solvation: ammonia molecules and the benzene radical cation

The interaction between ammonia and the benzene radical cation has been investigated by gas-phase studies of mass selected ion clusters {C(6)H(6)-(NH(3))(n=0-8)}(+) via tandem quadrupole mass spectrometry and through calculations. Experiments show a special stability for the cluster ion that contains four ammonias: {C(6)H(6)(NH(3))(4)}(+). Calculations provide evidence that the first ammonia forms a weak dative bond to the cyclohexadienyl radical cation, {C(6)H(6)-NH(3)}(+), where there is a transfer of electrons from ammonia to benzene. Additional solvating ammonia molecules form stabilizing hydrogen bonds to the ring-bound ammonia {C(6)H(6)-NH(3)}(+).(NH(3))(n), which cause cooperative changes in the structure of the cluster complex. Free ammonia is a weak hydrogen bond donor, but electron transfer from NH(3) to the benzene ring that strengthens the dative bond will increase the hydrogen acidity and the strength of the cluster hydrogen bonds to the added ammonia. A progressive "tightening" of this dative bond is observed upon addition of the first, second, and third ammonia to give a cluster stabilized by three N-(+)H x N hydrogen bonds. This shows that the energetic cost of tightening the dative bond is recovered with dividends in the formation of stable cluster hydrogen bonds.     

Quantum-mechanical simulation of the interaction of aluminum- and boron-containing zeolite clusters with molecules of water and ammonia

Quantum-mechanical computations of zeolite clusters with molecules of water and ammonia have been carried out. The clusters consisted of ten atoms of silicon and aluminum, where one atom of aluminum was also replaced with an atom of boron. Values of the bond length and bond angles have been obtained; the geometry of adsorption complexes and the bond energy for molecules of water and ammonia with atoms of aluminum and boron of a zeolite fragment have been determined. The computed values of bond energy for molecule probes yield the quantitative strength characteristic of zeolite aprotic acid centers.     

Ab initio SCF study of the interaction between L-serine phosphate and ammonia

The possible conformational changes of L -serine phosphate due to the interaction with ammonia are investigated by means of ab initio MO-LCAO-SCF calculations, using a supermolecule approach and an STO -3G basis set. The most favorable conformation of a four-hydrated L -serine phosphate anion is found to be changed by the binding of an ammonium ion. Cointeraction of ammonia and NH suggests another conformational change through the displacement of the bridging water molecule of the polyhydrated L -serine phosphate anion.