Importance of Pd and Pt excited states in N2O capture and activation: A comparative study with Rh and Au atoms

Nitrous oxide (N₂O) is an intermediate compound formed during catalysis occurring in automobile exhaust pipes. In this work, the N₂O capture and activation by Pt and Pd atoms in the ground and excited states of many multiplicities are studied. Pt and Pd + N₂O reactions are studied at multireference second‐order perturbation level of theory using C_s symmetry. The PtN₂O (¹A′, ⁵A′, and ⁵A″) species are spontaneously created from excited states. Only the ⁵A′ and ⁵A″ states exhibit N₂O activation reaction paths when N₂O approaches Pt end‐on by the N or O atoms side or side‐on yielding NO or N₂ as products, respectively. Pt⁺ cations ground and excited states, capture N₂O, although only Pt⁺ (⁶A′ and ⁶A″) states show N₂O activation yielding O and N₂ as products. In the Pd atom case, PdN₂O (¹A′ and ⁵A″) species are also spontaneously created from excited states. The ⁵A″ state exhibits N₂O activation yielding N₂ + O as products. Pd⁺ cations in both ground and excited states capture N₂O; however, only the [PdN₂O]⁺ (⁴A′, ⁴A″, ⁶A′, and ⁶A″) states in side‐on approaches and (⁶A′) in end‐on approach activate the N₂O and yield the N₂ bounded to the metal and O as product. The results obtained in this work are discussed and compared with previous calculations of Rh and Au atoms. The reaction paths show a metal–gas dative covalent bonding character. Löwdin charge population analyses for Pt and Pd active states show a binding done through charge donation and retrodonation between the metals and N₂O. © 2013 Wiley Periodicals, Inc.     

Recent Advances in Catalytic Decomposition of N<Subscript>2</Subscript>O on Noble Metal and Metal Oxide Catalysts

Catalytic decomposition of nitrous oxide (N₂O) is one of the most efficient methods for the removal of N₂O which is of high greenhouse potential and ozone-depleting property. Recent progress in the decomposition of N₂O has been reviewed with the focus on noble meal and metal oxide catalysts. The influence factors, such as catalyst support, preparation method, alkali metal additives and the reaction conditions (including O₂, H₂O, SO₂, NO and CO₂), on the performance of deN₂O catalysts have been discussed. Finally, future research direction for the catalytic decomposition of N₂O is proposed.     

Decomposition of nitrous oxide on AlFe-PILC catalyst

Summary Two AlFe-PILC catalysts were prepared with different OH/metal ratio and applied in nitrous oxide (N₂O) decomposition reactions. The 100% conversion of N₂O with NH₃into N₂and H₂O was achieved below 500^oC with both applied catalysts. However, the activity of catalysts in direct conversion of N₂O into N₂and O₂did not exceed 40 % below 500^oC. In this reaction the activity of AlFe-PILC catalyst synthesized at higher OH/metal ratio (4) is higher compared to the activity of AlFe-PILC catalyst with OH/metal ratio (2). Free FeO·Fe₂O₃particles were registered in the AlFe-PILC catalyst with higher OH/metal ratio (4).     

Fixation of nitrous oxide (N2O) by 1, 4, 2, 5‐diazadiborinine: A DFT study

The role of nitrous oxide (N₂O) in stratospheric ozone depletion and as a greenhouse gas has inspired the scientific community across the globe in understanding the capture, activation, and decomposition of it. Very recently people have started fixing N₂O using frustrated Lewis pairs. In this study, we have tried to analyze the fixation of N₂O by 1,4,2,5‐diazadiborinine by applying various computational tools and techniques associated with density functional theory. 1,4,2,5‐Diazadiborinine is taken as the fixing agent because of the ambiphilic nature of the two boron centers within it as reported by Wang et al. There are three possible ways of binding of N₂O within it as observed in this study. A free energy surface is also generated for the three possible paths representing their thermochemical as well as kinetic stability. The fixation of N₂O may become possible using this species as demonstrated by the current results. The nature of bonding between them is also explored through NBO, EDA, and electron density analyses.     

Ultramicropore Engineering by Dehydration to Enable Molecular Sieving of H2 by Calcium Trimesate

The high energy footprint of commodity gas purification and increasing demand for gases require new approaches to gas separation. Kinetic separation of gas mixtures through molecular sieving can enable separation by molecular size or shape exclusion. Physisorbents must exhibit the right pore diameter to enable separation, but the 0.3–0.4 nm range relevant to small gas molecules is hard to control. Herein, dehydration of the ultramicroporous metal–organic framework Ca‐trimesate, Ca(HBTC)?H₂O (H₃BTC=trimesic acid), bnn‐1‐Ca‐H₂O, affords a narrow pore variant, Ca(HBTC), bnn‐1‐Ca. Whereas bnn‐1‐Ca‐H₂O (pore diameter 0.34 nm) exhibits ultra‐high CO₂/N₂, CO₂/CH₄, and C₂H₂/C₂H₄ binary selectivity, bnn‐1‐Ca (pore diameter 0.31 nm) offers ideal selectivity for H₂/CO₂ and H₂/N₂ under cryogenic conditions. Ca‐trimesate, the first physisorbent to exhibit H₂ sieving under cryogenic conditions, could be a prototype for a general approach to exert precise control over pore diameter in physisorbents.     

Comparison of Gas Sorption Properties of Neutral and Anionic Metal–Organic Frameworks Prepared from the Same Building Blocks but in Different Solvent Systems

Two different 3D porous metal–organic frameworks, [Zn₄O(NTN)₂]?10 DMA?7 H₂O ( SNU‐150 ) and [Zn₅(NTN)₄(DEF)₂][NH₂(C₂H₅)₂]₂?8 DEF?6 H₂O ( SNU‐151 ), are synthesized from the same metal and organic building blocks but in different solvent systems, specifically, in the absence and the presence of a small amount of acid. SNU‐150 is a doubly interpenetrated neutral framework, whereas SNU‐151 is a non‐interpenetrated anionic framework containing diethylammonium cations in the pores. Comparisons of the N₂, H₂, CO₂, and CH₄ gas adsorption capacities as well as the CO₂ adsorption selectivity over N₂ and CH₄ in desolvated SNU‐150′ (BET: 1852 m² g^?1) and SNU‐151′ (BET: 1563 m² g^?1) samples demonstrate that the charged framework is superior to the neutral framework for gas storage and gas separation, despite its smaller surface area and different framework structure.     

Study of NOx and CO2 production of cultivated soil in closed microcosm experimental system

The aim of present project was to develop a microcosm experimental method for estimation of NO_x and CO₂ emission of microbial origin from cultivated soil. The effect of different factors (such as temperature, water supply, mineral-N source and organic matter addition, role of soil organisms and heavy metal contamination) that controlling the accumulation of N₂O and CO₂ in soil atmosphere and release to air was studied in closed microcosm laboratory model experiments. The headspace gas composition of closed glass vessels of 800-1200 cm³ containing 100-200 g brown forest soil sample was analysed. The N₂O and CO₂ concentration of gas samples was analysed by gas chromatographic methods and NO-content by means of chemiluminescent detection. Concerning the results, it can be stated that the applied microcosm experimental model proved to be a suitable tool for detecting the effect of factors influencing the NO_x and CO₂ release from agricultural soil. The temporal changes of N₂O and CO₂ concentration demonstrated the impact of the coupled microbial processes resulting in these greenhouse gases. The gas production depended on the soil moisture level, temperature and C/N ratio significantly. The inhibitory effect of toxic heavy metals (e.g. Cd) could also be affected by the C/N ratio. The appearance of NO as an intermediate of microbial processes was observed as well.     

Dinitrogen Fixation: Rationalizing Strategies Utilizing Molecular Complexes

Dinitrogen (N₂) is the most abundant gas in Earth's atmosphere, but its inertness hinders its use as a nitrogen source in the biosphere and in industry. Efficient catalysts are hence required to ov. ercome the high kinetic barriers associated to N₂ transformation. In that respect, molecular complexes have demonstrated strong potential to mediate N₂ functionalization reactions under mild conditions while providing a straightforward understanding of the reaction mechanisms. This Review emphasizes the strategies for N₂ reduction and functionalization using molecular transition metal and actinide complexes according to their proposed reaction mechanisms, distinguishing complexes inducing cleavage of the N≡N bond before (dissociative mechanism) or concomitantly with functionalization (associative mechanism). We present here the main examples of stoichiometric and catalytic N₂ functionalization reactions following these strategies.     

Rapid monitoring of intermediate states and mass balance of nitrogen during denitrification by means of cavity enhanced Raman multi-gas sensing

The comprehensive investigation of changes in N cycling has been challenging so far due to difficulties with measuring gases such as N₂ and N₂O simultaneously. In this study we introduce cavity enhanced Raman gas spectroscopy as a new analytical methodology for tracing the stepwise reduction of ¹⁵N-labelled nitrate by the denitrifying bacteria Pseudomonas stutzeri. The unique capabilities of Raman multi-gas analysis enabled real-time, continuous, and non-consumptive quantification of the relevant gases (¹⁴N₂, ¹⁴N₂O, O₂, and CO₂) and to trace the fate of ¹⁵N-labeled nitrate substrate (¹⁵N₂, ¹⁵N₂O) added to a P. stutzeri culture with one single measurement. Using this new methodology, we could quantify the kinetics of the formation and degradation for all gaseous compounds (educts and products) and thus study the reaction orders. The gas quantification was complemented with the analysis of nitrate and nitrite concentrations for the online monitoring of the total nitrogen element budget. The simultaneous quantification of all gases also enabled the contactless and sterile online acquisition of the pH changes in the P. stutzeri culture by the stoichiometry of the redox reactions during denitrification and the CO₂-bicarbonate equilibrium. Continuous pH monitoring – without the need to insert an electrode into solution – elucidated e.g. an increase in the slope of the pH value coinciding with an accumulation of nitrite, which in turn led to a temporary accumulation of N₂O, due to an inhibition of nitrous oxide reductase. Cavity enhanced Raman gas spectroscopy has a high potential for the assessment of denitrification processes and can contribute substantially to our understanding of nitrogen cycling in both natural and agricultural systems.     

A fully automatic system for underway N2O measurements based on cavity ring-down spectroscopy

N₂O is one of the most important greenhouse and ozone-depleting gases and has been the source of considerable concern in recent years. The oceans account for ~ 1/4 of the global N₂O emission budget; however, the oceanic N₂O source/sink characteristics are not well understood. To enhance the study of oceanic N₂O source/sink characteristics, our laboratory developed a fully automatic underway system for surface water N₂O concentration and atmospheric N₂O mole fraction measurements consisting of a cavity ring-down spectroscopy (CRDS) instrument and an upstream device. The developed device can be programmed to switch the CRDS measurements from the equilibrator headspace to the atmospheric sample and the reference gas sample. The surface water N₂O concentration is calculated from the equilibrium headspace N₂O mole fraction in the equilibrator. The response time of this equilibrator is ~ 3.4 min, and the estimated precision of this method for surface water N₂O measurements is better than 0.5% (relative standard deviation, RSD), which is one order of magnitude better than that of traditional gas chromatographic methods and can be further optimised. Data are acquired every 20 s, and the calibration frequency requirement of this system is approximately 7–10 days. This labor-saving underway system is a powerful tool for high-precision and high-resolution measurements of atmospheric and oceanic N₂O and can significantly improve the study of the characteristics of oceanic N₂O sources/sinks and their response to climate change.     

Effects of Pressure and Electrode Length on the Abatement of N<Subscript>2</Subscript>O and CF<Subscript>4</Subscript> in a Low-Pressure Plasma Reactor

The emission of greenhouse gases, such as N₂O and fluorinated gases, has been increasingly regulated in the semiconductor industry. Pressure effects on the abatement of N₂O and CF₄ were investigated in a low-pressure plasma reactor by using Fourier transform infrared (FTIR) spectroscopy. The destruction and removal efficiency (DRE) of N₂O and CF₄ was significantly lowered below 0.2 Torr. When the pressure was increased, the DRE of CF₄ with H₂O as the reactant gas increased continuously, but that with O₂ or without any reactant gas first increased and then decreased. A larger electrode length yielded a higher DRE of N₂O and CF₄, especially at lower pressures. To understand this phenomenon, the electrical waveforms for the discharge in N₂O were analyzed in conjunction with its optical emission profiles, and the rotational temperatures for different electrode lengths were compared using the N₂ ⁺ ion band (λ = 391.4 nm). They provided insights into the mechanism involved in terms of plasma property and gas residence time.     

Metal‐Free,Room‐Temperature Oxygen‐Atom Transfer in the N2O/CO Redox Couple as Catalyzed by [Si2Ox].+ (x=2–5)

The thermal reduction of N₂O by CO mediated by the metal‐free cluster cations [Si₂O_x]^.+ (x =2–5) has been examined in the gas phase using Fourier transform ion cyclotron resonance (FT‐ICR) mass spectrometry in conjunction with quantum chemical calculations. Three successive oxidation/reduction steps occur starting from [Si₂O₂]^.+ and N₂O to form eventually [Si₂O₅]^.+; the latter as well as the intermediate oxide cluster ions react sequentially with CO molecules to regenerate [Si₂O₂]^.+. Thus, full catalytic cycles occur at ambient conditions in the gas phase. Mechanistic aspects of these sequential redox processes have been addressed to reveal the electronic origins of these unparalleled reactions.     

Development of a certified reference material of nitrous oxide in nitrogen for emission gas measurement

A reference gas mixture of nitrous oxide (N₂O) in nitrogen, filled in a 10-L high-pressure aluminum alloy gas cylinder, has been developed as a certified reference material for emission measurement of exhaust gases from automobiles. As an example of certified values, mole fraction of N₂O is 302.36 μmol/mol. An electronic mass comparator with a home-made automatic cylinder exchanger, gas-filling equipment, and a gas chromatograph with a thermal conductivity detector have been used for the production of this CRM. The gas chromatographic analysis has of sufficient precision. The mole fraction of N₂O has good long-term stability for 10 years and is independent of inner pressure in the gas cylinder. As these results, a relative expanded uncertainty (coverage factor is 2) of the certified value has become 0.28 %. This sufficiently small uncertainty of the N₂O mole fraction will be advantageous in the calibration of analytical instruments for emission gas analysis.     

The Origin of Superhydrophobicity for Intrinsically Hydrophilic Metal Oxides: A Preferential O2 Adsorption Dominated by Oxygen Vacancies

The superhydrophobicity of intrinsically hydrophilic materials is still not well understood. Now, intrinsically hydrophilic metal oxides with different topographic structures are taken as model materials to reveal the origin of their superhydrophobicity. These metal oxides show enhanced hydrophobicity or superhydrophobicity in O₂ relative to that in air, but exhibit superhydrophilic behavior in N₂. The presence of rich oxygen vacancies greatly enhanced the adsorption of O₂ with an adsorption energy larger than N₂ and H₂O, resulting in a stable O₂ adsorption rather than air‐trapping within grooves of rough‐textured surfaces, which endows these intrinsically hydrophilic oxides with superhydrophobicity. Our results highlight a further understanding of the origin of superhydrophobicity for intrinsically hydrophilic materials, and is of great significance for designing novel devices with desired wettability.     

废水生物脱氮工艺中N2O排放数学模型研究进展

N_2O是一种重要的温室气体,而污水生物脱氮处理过程是N_2O的潜在产生源之一。随着污水处理量和处理程度的不断提高,N_2O的排放量也将不断增大。建立N_2O排放数学模型对污水生物脱氮系统中N_2O生成机制的深入研究和污水处理行业N_2O削减工艺技术的开发具有重大的理论及实践意义。本文归纳了生物脱氮工艺的原理,系统阐述了生物脱氮工艺中N_2O的生成机理和排放数学模型的类型、建立方法及应用情况。在此基础上,对生物脱氮工艺中N_2O排放数学模型的研究现状和研究方向进行了总结和展望,以期为N_2O排放数学模型的完善、N_2O排放量的削减、污水生物脱氮工艺的优化及污水处理行业的可持续发展提供理论基础和科学依据。     

A Stable Crystalline Copper(I)–N2O Complex Stabilized as the Salt of a Weakly Coordinating Anion

Nitrous oxide is considered a poor ligand, and therefore only a handful of well‐defined metal–N₂O complexes are known. Oxidation of copper powder with an extreme oxidant, [Ag₂I₂][ An ]₂ ([ An ]^?=[Al(OC(CF₃)₃)₄]^?) in perfluorinated hexane leads to Cu^I[ An ], the first auxiliary ligand‐free Cu^I salt of the perfluorinated alkoxyaluminate anion. The compound is capable of forming a stable and crystalline complex with nitrous oxide, Cu(N₂O)[ An ], where the Cu?N₂O bond is by far the strongest among all other molecular metal–N₂O complexes known. Thorough characterization of the compounds together with the crystal structure of Cu(N₂O)[ An ] complex supported with DFT calculations are presented. These give insight into the bonding in the Cu⁺–N₂O system and confirm N‐end coordination of the ligand.     

Determination of mechanism of thermal decomposition of Mg,Ca and Zn hydrazidocarbonates by evolved gas analysis

Hydrazo-carbonates are complex compounds and products of the reactions between solutions of metal ion and solutions of hydrazido-carbonic acid. The decomposition of Mg(N₂H₃COO)₂. 2H₂O, Ca(N₂H₃COO)₂·H₂O and Zn(N₂H₃COO)₂ in inert atmosphere were studied. By classical thermoanalytical methods and data on the composition of the intermediates and final products the mechanisms of the thermal decomposition could not be resolved therefore also evolved gas analysis was used (EGA). The first step of thermal decomposition of Ca and Mg hydrazidocarbonates is dehydration. With the heating the decomposition of the hydrazido-carbonates proceeds under evolution of the ammonia, carbon monoxide and/or nitrogen and carbon dioxide giving as the intermediates for calcium and magnesium compounds the corresponding carbonates oxides as the final products. The zinc compound decomposes to the oxide, ZnO but also zinc cyanamide was detected during to the thermal treatment.     

X‐ray and DFT‐calculated structures of bis[N‐(quinolin‐8‐yl)benzamidato‐κ2N,N′]copper(II)

The application of transition metal chelates as chemotherapeutic agents has the advantage that they can be used as a scaffold around which ligands with DNA recognition elements can be anchored. The facile substitution of these components allows for the DNA recognition and binding properties of the metal chelates to be tuned. Copper is a particularly interesting choice for the development of novel metallodrugs as it is an endogenous metal and is therefore less toxic than other transition metals. The title compound, [Cu(C₁₆H₁₁N₂O)₂], was synthesized by reacting N‐(quinolin‐8‐yl)benzamide and the metal in a 2:1 ratio. Ligand coordination required deprotonation of the amide N—H group and the isolated complex is therefore neutral. The metal ion adopts a flattened tetrahedral coordination geometry with the ligands in a pseudo‐trans configuration. The free rotation afforded by the formal single bond between the amide group and phenyl ring allows the phenyl rings to rotate out‐of‐plane, thus alleviating nonbonded repulsion between the phenyl rings and the quinolyl groups within the complex. Weak C—H…O interactions stabilize a dimer in the solid state. Density functional theory (DFT) simulations at the PBE/6‐311G(dp) level of theory show that the solid‐state structure (C1 symmetry) is 79.33 kJ mol⁻¹ higher in energy than the lowest energy gas‐phase structure (C2 symmetry). Natural bond orbital (NBO) analysis offers an explanation for the formation of the C—H…O interactions in electrostatic terms, but the stabilizing effect is insufficient to support the dimer in the gas phase.     

Effect of Functionalized Groups on Gas‐Adsorption Properties: Syntheses of Functionalized Microporous Metal–Organic Frameworks and Their High Gas‐Storage Capacity

The microporous metal–organic framework (MMOF) Zn₄O(L1)₂ ? 9 DMF ? 9 H₂O ( 1‐H ) and its functionalized derivatives Zn₄O(L1‐CH₃)₂ ? 9 DMF ? 9 H₂O ( 2‐CH₃ ) and Zn₄O(L1‐Cl)₂ ? 9 DMF ? 9 H₂O ( 3‐Cl ) have been synthesized and characterized (H₃L1=4‐[N,N‐bis(4‐methylbenzoic acid)amino]benzoic acid, H₃L1‐CH₃=4‐[N,N‐bis(4‐methylbenzoic acid)amino]‐2‐methylbenzoic acid, H₃L1‐Cl=4‐[N,N‐bis(4‐methylbenzoic acid)amino]‐2‐chlorobenzoic acid). Single‐crystal X‐ray diffraction analyses confirmed that the two functionalized MMOFs are isostructural to their parent MMOF, and are twofold interpenetrated three‐dimensional (3D) microporous frameworks. All of the samples possess enduring porosity with Langmuir surface areas over 1950 cm² g^?1. Their pore volumes and surface areas decrease in the order 1‐H > 2‐CH₃ > 3‐Cl . Gas‐adsorption studies show that the H₂ uptakes of these samples are among the highest of the MMOFs (2.37 wt % for 3‐Cl at 77 K and 1 bar), although their structures are interpenetrating. Furthermore, this work reveals that the adsorbate–adsorbent interaction plays a more important role in the gas‐adsorption properties of these samples at low pressure, whereas the effects of the pore volumes and surface areas dominate the gas‐adsorption properties at high pressure.     

Hydrazinium metal(II) and metal(III) ethylenediamine tetraacetate hydrates

Hydrazinium metal ethylenediaminetetraacetate complexes of molecular formula (N₂H₅)₂[Mg(edta)·H₂O], (N₂H₅)₃[Mn(edta)··H₂O](NO₃)·H₂O, N₂H₅[Fe(edta)·H₂O], N₂H₅[Cu(Hedta)·H₂O] and N₂H₅[Cd(Hedta)·H₂O]·H₂O have been synthesized and characterized by elemental and chemical analysis, conductivity and magnetic measurements and spectroscopic techniques. The thermal behaviour of these complexes has been studied by thermogravimetry and differential thermal analysis. The data set provided by the simultaneous TG-DTA curves of the complexes shows the occurrence of three or four consecutive steps such as dehydration, ligand pyrolysis and formation of metal oxides. X-ray powder diffraction patterns of copper and cadmium complexes show that they are not isomorphous. These studies suggest seven coordination for Mg,Mn, Fe complexes and six coordination for Cu and Cd derivatives.