Bifunctional alkyl nitrates – trace constituents of the atmosphere

Mono- and multifunctional esters of nitric acid (alkyl nitrates or organonitrates) form very complex mixtures of organic trace constituents in air. An analytical method was developed which combines selectivity in separation and detection in order to simplify this complexity in analytical terms. Mononitrates, dinitrates, keto nitrates, hydroxy nitrates of alkanes and alkenes, respecitvely, and bifunctional terpene nitrates were synthesized as reference substances. A specially developed new HPLC stationary phase (organonitrate phase) allows a group separation of mono-, di-, and hydroxy nitrates. After the HPLC preseparation the single components were finally separated by capillary HRGC-ECD and HRGC-MSD on polar and non-polar stationary phases. Mass spectrometric detection in the selected-ion-mode using the highly selective NO₂ ⁺ fragment (m/z = 46 amu) led to very good selectivities for the nitric acid ester moiety. The analysis of a 100 m³ ambient air sample using this new analytical protocol allowed the identification of seven hydroxy nitrates and 24 dinitrates ranging from C2 to C7, 22 of them for the first time ever.     

EI- and NCI-mass spectrometry of arylalkyl nitrates and their occurrence in urban air

The overall probability of the formation of arylalkyl nitrates is low in comparison to alkyl nitrates. However, measurable amounts of arylalkyl nitrates are found in traffic influenced air. It is reported here an analytical protocol based on high-volume sampling, adsorption liquid chromatography as a step in sample preparation, and high-resolution gas chromatography with electron ionization mass selective detection (HRGC/EI-MSD) as well as high-resolution gas chromatography with negative chemical ionization mass selective detection (HRGC/NCI (methane)-MSD) for the determination of arylalkyl nitrates as atmospheric constituents in urban air. The synthesis of arylalkyl nitrates as reference compounds is described. The arylalkyl nitrates can be selectively detected by the fragments M-46 (M-NO₂) and M-48 (M-NO₂-2H) in HRGC/NCI(methane)-MSD. In EI(70 EV)-MSD the dominating ions are at 46, 77, 91 and 105 u, which correspond to the NO₂ ⁺ and the phenyl, benzyl, and ethylbenzene fragments, respectively. The molecular ions are missing in (NCI-methane)-MSD and are of medium intensity in EI-MSD. Phenylethyl and phenylpropyl nitrates elute in GC in the range of n-octyl to n-dodecyl nitrate. The following arylalkyl nitrates have been identified in urban air: Benzyl nitrate (PhC1) and the three xylyl nitrates (M-PhC1), phenylethyl-1-nitrate (1Ph1C2), phenylethyl-2-nitrate (1Ph2C2), phenyl-n-propyl-1-nitrate (1Ph1C3), and phenyl-n-propyl-2-nitrate (1Ph2C3). Benzyl nitrate is the dominating compound in this group and is found at levels of 10–300 ng/m³ in urban air.     

Study by in situ FTIR of the SCR of NO by propene on Cu ion-exchanged Ti-PILC

Adsorption on Cu ion-exchanged titanium pillared clay (Cu-Ti-PILC) was investigated by in situ infrared spectroscopy to provide insight into the reaction intermediates present in the selective catalytic reduction (SCR) of NO by propene in the presence of oxygen. The NO/O₂ adsorption produced different nitrate species due to the presence of terminal and bridged Cu²⁺–OH groups. These nitrates evolved into N₂ and N₂O in small amounts once the NO catalytic cycle was finished. It can be concluded that the Cu²⁺–OH groups reacted with the nitro group, thus forming nitrates. C₃H₆ adsorption was higher and stronger than NO adsorption on the active sites of the catalyst. C₃H₆ reacted in the active site producing hydrocarbon intermediates (an organic nitro compound and acetate), which were responsible for the NO reduction.     

Multifunctional organic nitrates as constituents in European and US urban photo-smog

Air samples of the atmospheric ground layer in the cities of Ulm in Germany, Las Vegas, Nevada, and Salt Lake City, Utah, in the US were analyzed for organic nitrates. The air samples were taken around noon in summer at sunny weather conditions. 43 (C6-C13) alkyl mononitrates, 24 (C3-C6) alkyl dinitrates, and 19 (C2-C6) hydroxy alkyl nitrates have been identified. The analytical protocol included high-volume-sampling, NP-HPLC group separation, high resolution capillary gas chromatography, and detection by the highly selective mass spectrometer detector (SIM mode, m/z = 46). The levels of the sum of 15 (C6-C10) alkyl mononitrates ranged from 2.9 to 11.0 parts per trillion (ppt(v)). The levels of the sum of 21 (C3-C6) alkyl dinitrates ranged from 2.3 to 10.5 ppt(v), and the levels of the sum of 7 (C2-C4) hydroxy alkyl nitrates ranged from 7.3 to 28 ppt(v), respectively, in the urban air samples. These results emphazise the contribution of the alkyl dinitrates and hydroxy alkyl nitrates besides the alkyl mononitrates to the budget of NO(Y) compounds. No major differences in levels and pattern of the organic nitrates are present in air of the German and the US cities.     

Separation, detection and occurrence of (C2–C8)-alkyl- and phenyl-alkyl nitrates as trace compounds in clean and polluted air

Nitric acid, HNO₃, and nitrous acid, HNO₂, are forming stable esters with alcohols, the alkyl nitrates and alkyl nitrites. Both groups of compounds are used as fuel additives, explosives and pharmaceuticals. Alkyl nitrates are also formed as complex mixtures during incomplete combustion and the abiotic transformation of alkanes, alkenes and aldehydes in air. Organic nitrates can be assigned to anthropogenic and natural sources alike. Here the synthesis of reference mixtures of alkyl nitrates is described starting with alcohols, alkyl bromides, alkyl iodides or alkanes, respectively, sampling techniques in air analysis, and the separation of alkyl nitrates and alkyl dinitrates by high resolution capillary gas chromatography using various stationary phases and electron capture (HRGC/ECD) as well as mass spectrometric detection (HRGC/MSD). A highly selective detection mode for alkyl nitrates and alkyl di- and trinitrates — in general in the presence of other organic trace compounds — is the single ion monitoring of 46 amu in GC/MS. The separation and occurrence of alkyl- and phenyl-alkyl nitrates in polluted air is reported using capillary gas chromatography with electron capture and ion trap MS detection. The reaction of alkanes with nitric acid at room temperature simulates in a good approximation the pattern of alkyl nitrates formed in air chemistry.     

氢气对Ag/Al2O3和Cu/Al2O3催化剂选择性催化C3H6还原Nox反应的影响

 添加H2对Ag/Al2O3和Cu/Al2O3催化剂选择性催化C3H6还原NOx反应具有不同的影响. 原位漫反射红外光谱分析表明,在Ag/Al2O3催化剂上, H2的存在促进了C3H6部分氧化产物烯醇式物种(RCH=CH-O-)和乙酸盐等的形成,烯醇式物种和硝酸盐为主要反应中间体,二者间的相互反应性能很强,能形成高浓度的反应关键中间体异氰酸酯(-NCO)表面吸附物种,因此NOx的去除活性提高; 而在Cu/Al2O3催化剂上, H2的存在并没有促进C3H6部分氧化产物的形成,而且抑制了硝酸盐的形成,进而抑制了C3H6部分氧化产物与硝酸盐反应形成表面-NCO 物种,导致NOx的去除活性降低.     

Selective catalytic reduction of NO by propane over CoO(x)/Al2O3: an investigation of the surface reactions using in situ infrared spectroscopy

The partial oxidation of propane and the mechanism of the selective catalytic reduction (SCR) of NO by C3H8 over CoO(x)/Al2O3 catalysts were investigated using in situ infrared spectroscopy. Emphases are placed on the formation and reactivity of surface oxygenates during the SCR reaction. The SCR reaction starts with partial oxidation of propane to adsorbed acetate and formate. Impregnation of cobalt onto alumina greatly enhanced this reaction. The as-formed acetate acts as an efficient reductant for NO reduction. Surface nitrates (nitrites) are also reactive to propane and to oxygenates generated from C3H8 + O2 reaction. Surface -NCO species are formed over CoO(x)/Al2O3 catalysts. These nitrogen containing organic species are believed to be the direct intermediates in the final formation of N2. On the basis of these investigations, a proposed reaction mechanism explains the formation and roles of all intermediates detected by IR spectroscopy in this study.     

Experimental and theoretical studies of surface nitrate species on Ag/Al2O3 using DRIFTS and DFT

Surface nitrate (NO3(-)) species on the Ag/Al2O3 play an important role in the selective catalytic reduction (SCR) of NOx. In this study, the formation and configuration of surface nitrate NO3(-)(ads) species on Ag/Al2O3 and Al2O3 in the oxidation of NO have been studied using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations. Different nitrates species (bridging, bidentate and monodentate) were observed by in situ DRIFTS and validated by DFT calculations results. Attention was especially focused on the proposal of two different bidentate nitrates species (a normal bidentate and an isolated bidentate). In addition, the thermal stability of different surface nitrate species was discussed based on the adsorption energies calculations, DRIFTS, and temperature-programmed desorption (TPD) results. It was suggested that the decomposition and desorption of the surface nitrate species could be controlled by kinetics.     

Highly effective electrodialysis for selective elimination of nitrates from drinking water

This paper considers a new and highly effective process for selective elimination of nitrates from drinking water through electrodialysis. It is based on coupled use of a modified anion exchange membrane with a nitrate-selective anion exchange resin. The latter is placed in the desalination compartment and constitutes a part of a new type of ion-conducting intermembrane spacer. A highly preferential transport of nitrate anions against chlorides and sulphates is observed to take place at low current densities. The results obtained prove that electrodialysis is a practical solution to the problem of selective elimination of nitrates from drinking water.     

Spectroscopic IR, EPR, and operando DRIFT insights into surface reaction pathways of selective reduction of NO by propene over the Co-BEA zeolite

Interaction of a Co-BEA catalyst with individual components (NO, C(3)H(6), CO, O(2)) and mixtures simulating the real feed of the selective catalytic reduction (SCR) of nitric oxide in static and pulse experiments at variable temperatures was investigated by means of IR, EPR, and operando DRIFT spectroscopy coupled with QMS/GC analysis of the products. Speciation of cobalt active sites into Co(II), mono- and polynuclear oxo-cobalt species as well as CoO clusters was quantified by IR using CO and NO as probe molecules. The key intermediates, by-products, and final products of the SCR reaction were identified and their spectroscopic signatures ascertained. Based on the spectroscopic operando results, a concise mechanistic scheme of the selective catalytic reduction of nitric oxide by propene, triggered by a two-electron Co(II)/Co(0) redox couple, was developed. It consists of a complex network of the sequential/parallel selective reduction steps that are interlocked by the rival nonselective oxidation of the intermediates and their thermal decomposition. It has been shown that the SCR process is initiated by the chemoselective capture of NO from the reaction mixture by the cobalt active sites leading to the cobalt(II) dinitrosyls, which in the excess of oxygen are partially oxidized to surface nitrates and nitrites. N(2)O is produced by semi-decomposition of the dinitrosyl intermediates on the mononuclear centers, whereas NO(2)via NO oxidation on the polynuclear oxo-cobalt sites. Cyanide and isocyanate species, formed together with propene oxygenates in the course of the C=C bond scission, are the mechanistically pivotal reaction intermediates of C(3)H(6) interaction with the dinitrosyles and NO(3)(-)/NO(2)(-) surface species. Dinitrogen is produced by three main reaction routes involving oxidation of cyanides by NO/NO(2), reduction of dinitrosyls, nitrates, and nitrites by propene oxygenates (medium temperature range) or their reduction by carbon monoxide (high temperature range).     

3-二茂铁基-2-丁烯酸稀土配合物的合成及抑菌活性研究

用稀土硝酸盐与3－二茂铁基－2－丁烯酸在95％乙醇中反应，合成了六种新的稀土配合物。由元素分析、红外光谱、电子光谱、失重分析和摩尔电导率对配合物进行了表征。并研究了配合物的抑菌活性，抑菌活性试验表明六种配合物具有选择性抑菌性能。     

Hydrocarbon specificity in the selective catalytic reduction of NOx over Cu-ZSM-5 and Co-ZSM-5 catalysts

Transformation of surface nitrates under CH₄ (CH₄+O₂) was found to ensure steady-state activity of Co-ZSM-5 in the selective catalytic reduction of nitrogen oxides by methane (CH₄-SCR). For Cu-ZSM-5, such species are mainly converted into NO. Relaxation of the coordination sphere due to oxygen and NO adsorption, stability of C,N-containing intermediates and activation routes of hydrocarbons (methane, propane) were analyzed as factors determining catalytic properties of Cu and Co cations.     

非均相Schiff碱配合物上苯甲醇的选择性氧化：制备条件对其结构和催化性能的影响

以常见的非均相Schiff碱配合物Cr（salten）-MCM-41（salten：N,N-双水杨醛缩二乙烯三胺）的制备过程为例,考察了均相配合物制备过程中金属盐的种类、配位体系的pH值及固载过程中的偶联剂用量对所制备的非均相配合物的结构和催化性能的影响.结果表明,由阴离子配位能力较弱的氯化物和硝酸盐提供金属中心,保持...     

Synthesis and infrared and fluorescent properties of rare earth complexes with a new aryl amide podand

Solid complexes of rare earth nitrates and picrates with a new aryl amide podand, 1,4-bis{[(2'-benzylamino-formyl)phenoxyl]methyl}-naphthaline (L) were synthesized. The complexes were characterized by elemental analysis, IR and molar conductivity measurements. At the same time, the fluorescent properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated. Under the excitation, these complexes exhibited characteristic emissions of europium and terbium ions. The counter anion factor influencing the fluorescent intensity was also discussed.     

Synthesis and infrared and luminescence spectra of rare earth complexes with a new hexapodal ligand

Solid complexes of rare earth nitrates and picrates with a new hexapodal ligand, 1,2,3,4,5,6-hexa{[(2'-benzylamino-formyl)phenoxyl]methyl}-benzene (L) have been prepared. These complexes were characterized by elemental analysis, IR and molar conductivity. At the same time, the luminescence properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated. Under the excitation of UV light, these complexes exhibited characteristic emission of europium and terbium ions. The influence of the counter anion on the luminescent intensity was also discussed.     

Reactions of NO2 with BaO/Pt(111) model catalysts: the effects of BaO film thickness and NO2 pressure on the formation of Ba(NOx)2 species

The adsorption and reaction of NO(2) on BaO (<1, ～3, and >20 monolayer equivalent (MLE))/Pt(111) model systems were studied with temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRAS) under ultra-high vacuum (UHV) as well as elevated pressure conditions. NO(2) reacts with sub-monolayer BaO (<1 MLE) to form nitrites only, whereas the reaction of NO(2) with BaO (～3 MLE)/Pt(111) produces mainly nitrites and a small amount of nitrates under UHV conditions (P(NO(2))≈ 1.0 × 10(-9) Torr) at 300 K. In contrast, a thick BaO (>20 MLE) layer on Pt(111) reacts with NO(2) to form nitrite-nitrate ion pairs under the same conditions. At elevated NO(2) pressures (≥1.0 × 10(-5) Torr), however, BaO layers at all these three coverages convert to amorphous barium nitrates at 300 K. Upon annealing to 500 K, these amorphous barium nitrate layers transform into crystalline phases. The thermal decomposition of the thus-formed Ba(NO(x))(2) species is also influenced by the coverage of BaO on the Pt(111) substrate: at low BaO coverages, these species decompose at significantly lower temperatures in comparison with those formed on thick BaO films due to the presence of a Ba(NO(x))(2)/Pt interface where the decomposition can proceed at lower temperatures. However, the thermal decomposition of the thick Ba(NO(3))(2) films follows that of bulk nitrates. Results obtained from these BaO/Pt(111) model systems under UHV and elevated pressure conditions clearly demonstrate that both the BaO film thickness and the applied NO(2) pressure are critical in the Ba(NO(x))(2) formation and subsequent thermal decomposition processes.     

Multifunctional organic nitrates as constituents in European and US urban photo-smog

Air samples of the atmospheric ground layer in the cities of Ulm in Germany, Las Vegas, Nevada, and Salt Lake City, Utah, in the US were analyzed for organic nitrates. The air samples were taken around noon in summer at sunny weather conditions. 43 (C₆–C₁₃) alkyl mononitrates, 24 (C₃–C₆) alkyl dinitrates, and 19 (C₂–C₆) hydroxy alkyl nitrates have been identified. The analytical protocol included high-volume-sampling, NP-HPLC group separation, high resolution capillary gas chromatography, and detection by the highly selective mass spectrometer detector (SIM mode, m/z = 46). The levels of the sum of 15 (C₆–C₁₀) alkyl mononitrates ranged from 2.9 to 11.0 parts per trillion (ppt(v)). The levels of the sum of 21 (C₃–C₆) alkyl dinitrates ranged from 2.3 to 10.5 ppt(v), and the levels of the sum of 7 (C₂–C₄) hydroxy alkyl nitrates ranged from 7.3 to 28 ppt(v), respectively, in the urban air samples. These results emphazise the contribution of the alkyl dinitrates and hydroxy alkyl nitrates besides the alkyl mononitrates to the budget of NO_Y compounds. No major differences in levels and pattern of the organic nitrates are present in air of the German and the US cities.     

Application of NO2/supercritical CO2 system for safe and selective nitration of adamantanes and tertiary alkyl bromides

A concise safe approach for selective nitration and nitroxylation of tert-alkanes, in particular adamantane, and tert-alkyl bromides utilizing NO₂ in supercritical CO₂ medium has been established. Major reaction products were tert-alkyl nitro compounds and tert-alkyl nitrates depending on the reaction conditions.     

Sustainable and High-Rate Electrosynthesis of Nitrogen Fertilizer

The conventional industrial production of nitrogen-containing fertilizers, such as urea and ammonia, relies heavily on energy-intensive processes, accounting for approximately 3 % of global annual CO₂ emissions. Herein, we report a sustainable electrocatalytic approach that realizes direct and selective synthesis of urea and ammonia from co-reduction of CO₂ and nitrates under ambient conditions. With the assistance of a copper (Cu)-based salphen organic catalyst, outstanding urea (3.64 mg h⁻¹ mg_cat⁻¹) and ammonia (9.73 mg h⁻¹ mg_cat⁻¹) yield rates are achieved, in addition to a remarkable Faradaic efficiency of 57.9±3 % for the former. This work proposes an appealing sustainable route to converting greenhouse gas and waste nitrates by renewable energies into value-added fertilizers.     

Synthesis, structure and spectroscopic properties of rare earth complexes with a new aryl amide 2,2'-bipyridine derivative

Solid complexes of rare earth nitrates and picrates with a new aryl amide ligand 3.3'-bis(benzylamido)-2,2'-bipyridine (L) were synthesized and characterized by elemental analysis, IR and molar conductivity measurements. The molecular structures of the complex [TbL(2)(NO(3))(3)H(2)O].2H(2)O have been determined by single-crystal X-ray diffraction. The fluorescent properties of the Eu(III) and Tb(III) nitrates and picrates complexes in solid state were also investigated in detail. Under the excitation, these complexes exhibited characteristic emissions of europium and terbium ions. It is worth noting that the nature of the anion has a great effect upon the composition of the complexes as well as emission properties of them.