Competition between NO reduction and NO decomposition over reduced V–W–O catalysts

The SCR of NO and NO decomposition were investigated over a V–W–O/Ti(Sn)O₂ catalyst on a Cr–Al steel monolith. The conversions of NO and NH₃ over the reduced and oxidised catalysts were determined. The higher conversion of NO than of NH₃ was observed in SCR over the reduced catalyst and very close conversions of both substrates were found over the oxidised one. The increase of the pre-reduction temperature was found to cause an increase in catalyst activity and its stability in direct NO decomposition. The surface tungsten cations substituted for vanadium ones in vanadia-like active species are considered to be responsible for the direct NO decomposition. The results of DFT calculations for the 10-pyramidal clusters: V₁₀O₃₁H₁₂ (V–V) and V₉WO₃₁H₁₂ (V–W) modelling (0 0 1) surfaces of vanadia and WO₃–V₂O₅ solid solution (s.s.) active species, respectively, show that preferable conditions for NO adsorption exist on W sites of s.s. species and that reduction causes an increase in their ability for electron back donation to the adsorbed molecule. Electron back donation is believed to be responsible for the electron structure reorganisation in the adsorbed NO molecule resulting in its decomposition. The high selectivity of NO decomposition to dinitrogen was considered to be connected with the formation of the tungsten nitrosyl complexes solely via the W–N bond.     

Theoretical Study of Mechanism and Kinetics of the Reaction of NO2 with s‐Triazine

The decomposition of nitramines explosives have been of great interest for a long time. However, theoretical investigations have concentrated mainly on unimolecular decomposition whereas bimolecular reactions have received only little attention. In this paper, the bimolecular reaction between NO₂ with s‐triazine (TAZ), which is an initial product during the decomposition process of hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) is investigated. The structures and potential energy surface (PES) are explored at B3LYP/6‐31G(d,p) and B3P86/6‐31G(d,p) levels, and the energies are refined using the CCSD(T)/cc‐pVTZ methods. The mechanism of the reaction is analyzed. Quantum chemistry calculations reveal that the title reactions possess small barriers that can be similar to, or smaller than that of initial decomposition reactions of RDX, which suggests that bimolecular reactions are also of great importance, and should be further investigated. Moreover, the kinetics were investigated to verify the proposed mechanism of the reaction.     

The High‐Pressure Characterization of Energetic Materials: Diaminotetrazolium Nitrate (HDAT‐NO3)

In‐situ high‐pressure room temperature synchrotron X‐ray diffraction and optical Raman and infrared spectroscopy were used to examine the structural properties, equation of state, and vibrational dynamics of diaminotetrazolium nitrate (HDAT‐NO₃). The X‐ray measurements show that the pressure–volume relations remain smooth to 12 GPa. X‐ray diffraction measurements at pressures above 12 GPa were not possible in this study because of sample decomposition resulting from several factors. X‐ray diffraction reveals no indication of a phase transition to at least 12 GPa, but slight variations in the c/b unit cell ratio suggests modifications within the hydrogen bonding sub‐lattice. Vibrational measurements show the ambient phase of HDAT‐NO₃ to remain the dominant phase to 33 GPa.     

High activity and wide temperature window of Fe‐Cu‐SSZ‐13 in the selective catalytic reduction of NO with ammonia

Fe‐Cu‐SSZ‐13 catalysts were prepared by aqueous solution ion‐exchange method based on the one‐pot synthesized Cu‐SSZ‐13. The catalysts were applied to the selective catalytic reduction (SCR) of NO with NH₃ and characterized by the means of XRD, UV‐Vis, EPR, XPS, NH₃‐TPD, and so on. The selected Fe‐Cu‐SSZ‐13‐1 catalyst exhibited the high NO conversion (>90%) in the wide temperature range (225–625°C), which also showed good N₂ selectivity and excellent hydrothermal stability. The results of XPS showed that the Cu and Fe species were in the internal and outer parts of the SSZ‐13 crystals, respectively. The results of UV‐Vis and EPR indicated that the monomeric Cu²⁺ ions coordinated to three oxygen atoms on the six‐ring sites and Fe monomers are the real active species in the NH₃‐SCR reaction. Furthermore, the influence of intracrystalline mass‐transfer limitations on the Fe‐Cu‐SSZ‐13 catalysts is related to the location of active species in the SSZ‐13 crystals. © 2015 American Institute of Chemical Engineers AIChE J, 61: 3825–3837, 2015     

Catalytic removal of NO

The aim of this paper is to review the catalytic reactions for the removal of NO and, more particularly, to discuss the reduction of NO in the presence of NH₃, CO, H₂ or hydrocarbons as well as the decomposition of NO. The nature of the different active species, their formation due to dispersion and their interaction with different supports as well as the corresponding correlations with catalytic performance are also discussed. Another goal of this review is to explain the mechanism and kinetics of these reactions on different surfaces as well as the catalyst stability.     

Low‐Temperature Selective Catalytic Reduction of NO on an Iron Ore Catalyst in a Magnetically Fluidized Bed

Low‐temperature selective catalytic reduction of NO from simulated flue gas by NH₃ on admixtures of iron ore and iron catalyst in a magnetically fluidized bed was experimentally studied. It was found that iron ore exerts a prominent catalytic effect on NO removal resulting in high removal efficiency without magnetic fields. Since iron ore is insensitive to magnetic fields due to its antiferromagnetic property, NO removal efficiency with iron ore as catalyst is only slightly influenced by magnetic fields. The NO removal efficiency, however, can be greatly improved using admixtures of iron ore and iron as catalyst in a magnetically fluidized bed. At defined magnetic field intensity and the same temperature, the removal efficiency reaches higher values compared with that without magnetic fields.     

Bifurcation Analysis on Pt and Ir for the Reduction of NO by CO

Due to the importance of the NO‐CO reaction in current catalytic converters, reduction of NO by CO on Pt group catalysts is important to study. Various reaction mechanisms have been proposed for the NO‐CO reaction on Pt(100), which shows bifurcations, kinetic oscillations and multiple steady states under ultra high vacuum (UHV) conditions due to complex surface dynamics. Some experiments on supported Pt group catalysts reported in literature show oscillations and bistability under atmospheric conditions as well. Industrially relevant conditions require the modelling and detailed analysis of the system at atmospheric pressure. We have proposed a reaction mechanism for the NO‐CO system on Pt group catalysts and coupled it with an isothermal PSR model to obtain solutions at atmospheric conditions with the continuation software CONTENT 1.5, at different operating conditions. Simulation results suggest that Pt(111) shows bifurcations at certain operating conditions while Ir(111) shows stable solutions at all the operating conditions studied here.     

脉冲放电NO脱除过程模拟

建立了数学模型,把所考虑的NO/N₂/O₂/H₂O脉冲放电体系中的主要化学反应,归结为各物种浓度的刚性常微分方程组的初值问题来求解,计算方法选用Rosenbrock法,得到了物种浓度随停留时间的演化规律。结果表明：NO还原和氧化在其脱除过程中同时共存,当NO,N₂,O₂,H₂O和CO₂的体积浓度分别为200×10^-6,80%, 5％,6％和9％时,NO氧化所占的比例比NO还原的大很多;脉冲频率增大导致NO还原率和氧化率均增大;H₂O浓度增大导致HNO₃浓度增大,表明NO氧化所占的比例随H₂O浓度增大而增大。     

Well defined CuI(NO), CuI(NO)2 and CuII(NO)X (X = O− and/or NO 2 − ) complexes in CuI-ZSMS prepared by interaction of H-ZSM5 with gaseous CuCl

In this note an exchange procedure of the acidic protons of H-ZSM5 by Cu^I ions through reaction with CuCl in the gas phase is described. In the so obtained Cu^I-ZSM5 exchanged zeolite the Cu^I ions are in well defined configuration and form with NO mono and di-nitrosyl complexes of high structural and spectroscopic quality. The Cu^I(NO)₂ species are transformed at RT into Cu^II(NO)X (X=O^– and/or NO ₂ ^– ) species which could represent an intermediate in NO decomposition.     

Catalytic behavior of La–Sr–Ce–Fe–O mixed oxidic/perovskitic systems for the NO+CO and NO+CH4+O2 (lean-NOx) reactions

Mixed oxides of the general formula La_0.5Sr_xCe_yFeO_z were prepared by using the nitrate method and characterized by XRD and Mössbauer techniques. The crystal phases detected were perovskites LaFeO₃ and SrFeO_3−x and oxides -Fe₂O₃ and CeO₂ depending on x and y values. The low surface area ceramic materials have been tested for the NO+CO and NO+CH₄+O₂ (“lean-NO_x”) reactions in the temperature range 250–550°C. A noticeable enhancement in NO conversion was achieved by the substitution of La³⁺ cation at A-site with divalent Sr⁺² and tetravalent Ce⁺⁴ cations. Comparison of the activity of the present and other perovskite-type materials has pointed out that the ability of the La_0.5Sr_xCe_yFeO_z materials to reduce NO by CO or by CH₄ under “lean-NO_x” conditions is very satisfying. In particular, for the NO+CO reaction estimation of turnover frequencies (TOFs, s⁻¹) at 300°C (based on NO chemisorption) revealed values comparable to Rh/-Al₂O₃ catalyst. This is an important result considering the current tendency for replacing the very active but expensive Rh and Pt metals. It was found that there is a direct correlation between the percentage of crystal phases containing iron in La_0.5Sr_xCe_yFeO_z solids and their catalytic activity. O₂ TPD (temperature-programmed desorption) and NO TPD studies confirmed that the catalytic activity for both tested reactions is related to the defect positions in the lattice of the catalysts (e.g., oxygen vacancies, cationic defects). Additionally, a remarkable oscillatory behavior during O₂ TPD studies was observed for the La_0.5Sr_0.2Ce_0.3FeO_z and La_0.5Sr_0.5FeO_z solids.     

Mechanistic Study of Carbon Oxidation with NO2 and O2 in the Presence of a Ru/Na‐Y Catalyst

The oxidation of model soot by NO₂ and O₂ in the presence of a Ru/Na‐Y catalyst under conditions close to automotive exhaust gas after‐treatment systems is investigated. Isothermal oxidation experiments of a physical mixture of carbon black and catalyst were performed in a temperature range of 300–400 °C. A remarkable increase of the oxidation rate by NO₂ and O₂ in the presence of the Ru/Na‐Y catalyst was observed. An overall mechanism involving oxygen transfer from the Ru catalyst to the carbon surface leading to an increase of C(O) complexes is proposed. These C(O) complexes are destabilized in the presence of NO₂ increasing the carbon oxidation rate.     

NO2 inhibits the catalytic reaction of NO and O2 over Pt

The rate equation for the overall reaction of NO and O₂ over Pt/Al₂O₃ was determined to be r=k_f[NO] ^1.05±0.08[O₂]^1.03±0.08[NO₂]^0.92±0.07(1-), with k_f as the forward rate constant, =([NO₂]/K[NO][O₂]^1/2), and K as the equilibrium constant for the overall reaction. An apparent activation energy of 82 kJ mol^–1 ± 9 kJ mol^–1 was observed. The inhibition by the product NO₂ makes it imperative to include the influence of NO₂ concentration in any analysis of the kinetics of this reaction. The reaction mechanism that fits our observed orders consists of the equilibrated dissociation of NO₂ to produce a surface mostly covered by oxygen, thereby inhibiting the equilibrium adsorption of NO, and the non-dissociative adsorption of O₂, which is the proposed rate determining step.     

Conversion of volatile-nitrogen and char-nitrogen to NO during combustion

The design of low emission combustion chambers using low NO_x strategies involving staged burning or stratified combustion requires a detailed understanding of the combustion processes of the fuel volatiles and char burning. In this paper some aspects of the combustion of coal-volatiles and char are considered. The extreme cases of volatile combustion, namely premixed and diffusive burning are examined in order to consider the range of NO_x reduction options available to the combustion chamber designer. A similar set of situations is examined for char burning and the release of the fuel-nitrogen to form NO.

The implications of the processes are considered in two practical applications, those of the high temperature combustion found in pulverised coal burning and in a lower temperature regime of the conditions under fluidised bed combustion. In the case of pulverised coal flame the degree of mixedness of the volatiles played a dominant part in determining the extent of NO formation whilst the role of char-nitrogen is only to form NO and NO reduction is limited because of the short residence time and low char concentrations at the end of the reaction zone. In a circulating fluidised bed combustor it was concluded that a different situation can arise. If the bed is sufficiently large enough to give a residence time of several seconds, then the NO initially formed in the fluidised bed is reduced by the carbon in the top of the bed and the riser under steady state conditions and its concentration at the exit can be estimated by equilibrium calculations.     

Hybrids as NO Donors

Cinnamic acid and its derivatives have been studied for a variety of biological properties, including anti-inflammatory, antioxidant, anticancer, antihypertensive, and antibacterial. Many hybrids of cinnamic derivatives with other bioactive molecules have been synthesized and evaluated as nitric oxide (NO) donors. Since NO plays a significant role in various biological processes, including vasodilation, inflammation, and neurotransmission, NO donor groups are incorporated into the structures of already-known bioactive molecules to enhance their biological properties. In this review, we present cinnamic hybrids with NO-donating ability useful in the treatment of several diseases.     

Na＋／γ—Al2O3对NO的吸附特性研究

文章针对Na＋／γ-Al2O3作为吸附物质对NO的吸附性能进行了实验研究，并在实验基础上分析了Na＋／γ-Al2O3对NO吸附的性能特性，得出Na＋／γ-Al2O3对NO有很好的吸附能力，Na＋离子含量高的γ-Al2O3吸附NO的效率比Na＋离子低的效率稍高的结论。     

分解炉中NO生产模拟与优化

针对水泥行业中水泥分解炉产生NO的过程进行了机理性分析,同时推导了描述分解炉中NO生成的机理性模型,并对分解炉中的NO生成进行了全三维模拟研究.模拟结果与现场测试结果进行了比较,验证了模拟的合理性.对分解炉的生料入口位置进行了改造,在不影响生产的前提条件下,对单独分风、分料和同时分风分料时降低分解炉内NO生成的情况进行了模拟优化,分析得到了分料方法是降低分解炉中NO的最有效途径的结论,为降低水泥分解炉中NO排放提供了实用的参考依据.